Kristensmith Taylor

Histology of Cell Structure Notes

by

The Cell Structure

The Light and Electron Microscopic Structure of Cell

A cell is a basic structural unit of any living organism and is involved in vital functions to maintain its life. Though the various cells of the body differ in their structure and function, most of them have many common structural components.

They all are surrounded by plasma membranes, possess organelles, and produce macromolecules and energy. This chapter will deal with the common structure of a cell.

The Cell

A cell is bound by the cell membrane. The cell membrane encloses the cytoplasm and nucleus. The cell varies in shape (flat, cuboidal, columnar, pyramidal, fusiform, multipolar, etc) and size (5-50 μm).

We shall study the structure of a cell under the following three headings:

  • Cell membrane
  • Cytoplasm
  • Nucleus

The Cell Remember

A cell is a structural and functional unit of any living organ¬ ism. It is the smallest and independently living part of a living organism. It varies in shape (flat, cuboidal, columnar, pyramidal, fusiform, multipolar, etc) and size (usually 5-50 μm).

Cell Membrane

The cell membrane is also known as the plasma membrane or plasmalemma. It forms the boundary of the cell and acts as a barrier between the cytoplasm and the surrounding environment of the cell.

  • The cytoplasm contains many organelles that are also made up of membranes (For example, endoplasmic reticulum, Golgi apparatus, mitochondria. etc).
  • Although the cell membrane and membranes surrounding cytoplasmic organelles differ slightly in their thickness and protein contents, they all have the same basic molecular organization and are also known as unit membranes. The cell membrane is made up of lipids, proteins, and carbohydrates.

Structure Of Cell Membrane

  • The total thickness of the cell membrane is just about 8-10 nm. Hence, it is not visible with a light microscope.
  • When viewed under an electron microscope the plasma membrane seems to be made up of three layers i.e., trilaminar.
  • The trilaminate appearance is because two dark lines are separated by a clear (unstained) intermediate zone.
  • This appearance is due to the arrangement of phospholipid molecules in two different layers.
  • A phospholipid molecule has a head and a tail end. These molecules are so arranged that their head ends face the outer and inner surface of the membrane while their tail ends face each other.

Cell Membrane Remember

The cell membrane (plasma membrane) is about 8-10 μm in thickness. It is visible only under an electron microscope and seems to be made up of three layers (trilaminate).

The trilaminate appearance of the membrane is because the heads of the phospholipid molecules form the dark-staining part of the membrane while the light-staining intermediate zone is formed by the tails of the molecules.

  • Besides the molecules of phospholipids, the membrane also contains several types of proteins in the form of globular masses. These proteins are present within the thickness of the cell membrane or may project through its outer or inner surfaces.
  • Many integral proteins pass through the entire thickness of the membrane (transmembrane proteins).
  • On the outer surface of the cell membrane, carbohydrates may attach to proteins forming glycoproteins. Although at certain places carbohydrates may also attach to lipid-forming glycolipids.
  • Thus, the carbohydrates are only present on the outer surface of the plasma membrane. The coat of glycoprotein and glycolipid, on the outer surface of the plasma membrane is called a cell coat (glycocalyx).
  • The glycocalyx is formed by carbohydrate chains and protects the cell from interaction with inappropriate proteins, chemicals, and physical injuries.

The cell membrane is composed of lipids as well as proteins. Protein molecules are about half of the total mass of the membrane, i.e., lipids and proteins are usually in 1:1 proportion by weight.

  • Besides phospholipids and glycolipids, the plasma membrane also contains cholesterol that is present among the fatty acid tails of phospholipids.
  • The lipid bilayer behaves like a fluid within which the globular proteins are free to move laterally if not attached to filaments in the underlying cytoplasm.
  • Neighboring lipid molecules may exchange places about 10 million times per second and may wander completely around a cell in a few minutes. The globular proteins of the cell membrane can float like icebergs in the sea of phospholipids.

The above description of the molecular organization of cell membrane is called as “fluid mosaic model”.

The Cell Structure Schematic Diagram Of A Cell Showing Cell Membrane

The Cell Structure Electro Micrograph Of A Plasma Cell

The Cell Structure Structure Of Cell Membrane

  1. The cell membrane of two adjacent cells
  2. Electron micrograph of two adjacent cell membrane

The Cell Structure Molecular Organization Of Plasma Membrane

  1. The cell membrane when seen under an electron microscope shows the tri-laminar appearance
  2. Structure of a phospholipid molecule.
  3. Plasma membrane

The Cell Structure Schematic Diagram Of Fluid Mosaic Model Of Plasma Membrane

There are three types of lipids in the plasma membrane i.e., phospholipids (most abundant), glycolipids, and cholesterol.

The globular proteins of the cell membrane can float like icebergs in the sea of phospholipids therefore, this model of the cell membrane is called “fluid! mosaic model.”

Cell Membrane Further Details

Lipid Raft

In the plasma membrane, there are regions containing high concentrations of cholesterol and glycosphingolipids. These regions are called “lipid rafts.”

  • Glycosphingolipids are highly saturated fatty acid chains. These along with high concentrations of cholesterol make the lipid raft area thicker than the surrounding area.
  • Because of the thickness of the raft, its fluidity is less. Raft contains a large number of integral and peripheral membrane proteins, which are involved in receiving and conveying cell-specific signals.

The Cell Structure Schematic Diagram Showing The Structure Of Lipid Raft

Proteins of the Cell Membrane and their Functions

Proteins of the cell membranes are divided into two groups, that is, integral and peripheral proteins.

  • The integral proteins are incorporated in the lipid bilayer, while peripheral proteins are present on the membrane surface.
  • Many integral proteins pass through the entire thickness of the lipid bi-layer (Transmembrane integral proteins), while other integral proteins are embedded in the outer or inner leaflets of the liquid bilayer.

Some of these transmembrane proteins are very long and many pass through the membrane many times and are thus known as multipass proteins. The peripheral proteins are present on the membrane surface.

  • Six different functional types of proteins are present in the cell membrane. These are structural, transport or carrier (pumps, channel), enzyme, receptor proteins, etc.
  • Structural proteins are part of the structure of the cell membrane. These proteins are present especially where they form junctions with neighboring cells, i.e., tight junctions.
  • Some proteins are? involved in the active transport of ions across the cell membrane and are called pumps. They transport the ions (Na+) and macromolecules such as amino acids and sugars from one surface of the membrane to another surface by their movement within the fluid lipid bilayer.
  • Some proteins form transmembrane channels that control the entry of specific ions through the cell membrane. These channels are capable of regulating the passage of ions and molecules by closing and opening their lumen. Most channels are ion channels. There are more than 100 different types of channels.

Most common ion channels are forK+ (potassium ions) orCl (chloride ions), and fewer channels are for Na+ (sodium ions) or Ca2+ (calcium ions). Most of these channels are open all the time but the opening and closing of many more channels are guarded.

  • These channels are known as “gated” channels as their opening and closing are regulated by the chemical or electrical changes occurring inside or outside the cell. When the gates are open their ions diffuse in or out of the cells.
  • Proteins of cell membranes also act as receptors for specific hormones and other signaling molecules that affect the activity of cells. For example, antidiuretic hormone is the activity of cells. For example, antidiuretic hormone permeability of cell membrane. Receptor proteins are likely to be glycoproteins in nature.
  • Some proteins of the membrane act as enzymes, e.g., certain ATPases are membrane-bound. The enzyme catalyzes the chemical reactions outside or inside the cell membrane.

Proteins of the Cell Membrane and their Functions Remember

Proteins of the cell membranes are divided into two I groups, that is, integral and peripheral proteins. Functionally they are divided into many types, i.e., structural, transport or carrier (pumps, channel), enzyme, and receptor proteins.

  • Glycoproteins and glycolipids of cell membranes may act as cell-identity markers. With the help of this marker, a cell can recognize whether other cells are of the same kind or foreign entity, For Example., ABO blood group markers, and major histocompatibility (MHC) proteins.
  • Some proteins act as linker proteins. They anchor filaments (actin) inside and (collagen) outside of the cell membrane. This helps in providing shape and stability to cells.

The Cell Structure A Portion Of Gobular Mass Of Protein May Project From Outer Or Inner Surface Of Cell Membrane

The Cell Structure The Transmembrane Serve Various Functions

  1. Some proteins act as channels for the transport of ions
  2. Transporter proteins or pumps transport specific substances across the membrane by changing their shape
  3. Receptor proteins are capable of recognizing specific ligands, which in turn may alter the cell’s function
  4. Enzyme proteins can catalyze reactions occurring on the cell surface or within the cell (a ligand is a molecule that has a high affinity for receptors).

Lipid Raft Clinical Application

Defective Receptors

The defect in the receptors may lead to various kinds of diseases. A defective receptor becomes non-functioning and does not respond to its respective hormones and other signaling molecules.

For example, when growth hormone receptors are defective they do not respond to the growth hormone resulting in a type of dwarfism (abnormal short height).

Transport across the cell membrane by formation of vesicles: Endocytosis and Exocytosis

Cells are surrounded by extracellular fluid from which they derive their nutrition and release metabolites. The cell membrane permits diffusion and active transport of ions and gases into and out of the cell but prevents passive entry of most large molecules.

  • The method by which large molecules or particulate matter (bacteria, red blood cells, and molecules of polysaccharides and proteins) can go in or out of the cell is called endocytosis and exocytosis respectively.
  • The cell membrane takes an active part in the process of endocytosis and exocytosis. The process of endocytosis involves the formation of membrane-bound vesicles.

The Cell Structure The Diagrammatic Representation Of Exoxytosis And Endocytosis Processes

Endocytosis

Endocytosis is of three types, i.e., receptor-mediated endocytosis, phagocytosis, and pinocytosis.

  • Receptor-mediated endocytosis is a highly selective type of endocytosis in which receptor protein in the plasma membrane recognizes and binds to specific ligands in the extracellular fluid. This receptor-ligand complex is pinched off and is taken in the form of a membrane-bound vesicle.
  • The process of ingestion of solid particulate matter (e.g., bacteria, pigments, or other solid particles) is called phagocytosis. It is the process of eating by the cell.
  • In the process of phagocytosis when particles come in contact with the outer surface of the cell membrane, the membrane throws pseudopodia to enclose the particles.
  • When enveloping pseudopodia meet they fuse and the particles are drawn inside the cell. The invaginated membrane is then pinched off from the rest of the cell membrane and forms a phagocytic vacuole.

The process of ingestion of fluid or other small molecules is called pinocytosis. It is the process of drinking by the cell. In the process of pinocytosis when fluid molecules come in contact with the outer surface of the cell membrane, they become indented and form a pinocytic vesicle by pinching off from the rest of the cell membrane.

The Cell Structure Receptor Mediated Endocytosis

Exocytosis

In the process of exocytosis, there occurs the discharge of substance from the cell. The membrane-bound secretory granules of vesicles come in contact with the inner surface of the cell membrane and fuse with it. Then there is a rupture of the fused portion and the contents of the vesicle are released into the extracellular space.

Exocytosis Remember

Endocytosis is the process by which a cell ingests macro¬molecules, particulate matter, liquids, and other substances. During exocytosis, substances are discharged from the cell. Endocytosis is of three types, that is, receptor-mediated endocytosis, phagocytosis, and pinocytosis.

Exocytosis Clinical application

Receptor-mediated Endocytosis and HIV Infection

  • Although receptor-mediated endocytosis is used by cells to import needed material from outside the cell, some viruses may enter the cell by this process of endocytosis.
  • The human immunodeficiency virus (HIV) usually gets attached to the CD4 receptor on the plasma membrane of helper T cells (a kind of white blood cell) and enters the cell by receptor-mediated endocytosis.
  • In this way, the cell gets infected with HIV which causes acquired immunodeficiency syndrome (AIDS).

Functions of Cell Membrane

  • It maintains the shape (structural integrity) of the cell.
  • Acts as an interface between the cytoplasm and the outside milieu (tissue fluid).
  • It controls the movements of substances in and out of the cell (i.e., only selected substances are permitted to cross).
  • It is capable of recognizing foreign bodies.
  • It transmits the chemical signals across the membrane to elicit intracellular events. Cell signaling is the communication that occurs when signaling cells release signaling molecules that bind to the cell surface receptors of target cells.
  • The cell membrane regulates the cell-to-cell interactions

Cytoplasm

In a cell, the cytoplasm extends between the plasma membrane and the nuclear envelope. The cytoplasm consists of a cytoplasmic matrix or ground substance that is also known as cytosol. The cytosol contains organelles, inclusion, and cytoskeleton.

Cytosol

The cytoplasm ground substance (cytosol) is made up of a fluid base containing ions (Na, K, Ca), various organic molecules (carbohydrates, lipids, proteins, and RNAs), and a three-dimensional network of the trabeculae.

The cytosol contains various structural elements like organelles, inclusions, and cytoskeleton.

  • The organelles are the small organs of the cell. They have their distinctive structure and are involved in various biochemical processes necessary for the metabolism of the cell (For Example., endoplasmic reticulum, Golgi complex, mitochondria, lysosomes, ribosomes, and centrioles).
  • The inclusions, on the other hand, are non-functioning elements of the cytoplasm. They are involved in the storage of nutrients such as glycogen and lipids, pigment, and secretory granules.
  • The cytoplasm also contains a cytoskeleton that is made up of microtubules and microfilaments.

Cytosol Remember

The cytoplasm consists of the cytoplasmic matrix (cytosol), which itself contains various Structural elements like organelles, inclusions, and cytoskeleton (Microtubules and microfilaments).

Cytoplasmic Organelles

Most of the organelles are membrane-bound (this membrane is similar to the plasma membrane). Examples of membranous organelles are the endoplasmic reticulum, Golgi complex, mitochondria, lysosomes peroxisomes, and endosomes. Thus their contents and functions are confined within the membrane.

On the other hand, some organelles are not bounded by a membrane and thus come in direct contact with cytosol, For Example., ribosomes and centrosomes.

Cytoplasmic Organelles Remember

Most of the cytoplasmic organelles are bound by a membrane. This membrane is similar to the plasma membrane.

Endoplasmic Reticulum

Endoplasmic reticulum (ER) is the network of membranes that may be in the form of branching and anastomosing flattened tubules and vesicles. The lumen of these tubules and vesicles is known as a cistern.

The ER is found almost throughout the cytoplasm but predominantly present near the nucleus to which it is attached.

The ER is of two different types, i.e., rough endoplasmic reticulum (RER) and smooth (SER).

The Cell Structure Inter-Relationship Of RER And Golgi Complex

  1. Secretory vesicles are transported toward the plasma membrane for exocytosis
  2. Membrane vesicles that contain membrane protein
  3. Some storage vesicles contain lysosomal enzymes
  4. Some vesicles also originate in the Cis-face of Golgi and are retrogradely transported to RER.

Endoplasmic Reticulum RER

RER is prominent in cells that are involved in protein synthesis i.e., exocrine pancreas (secretes digestive enzymes), plasma cells (secretes antibodies), and fibroblasts which synthesize collagen.

  • The RER is usually in the form of flattened sacs (cisterns) arranged one upon the other. These cisterns are connected and form a continuous system of membrane-limited cavities.
  • The membrane of RER is connected with the nuclear membrane.
  • On the outer surface of its membrane, numerous granules (25-30 nm in size) are attached. These granules are ribosomes that are responsible for the basophilic stain of RER.

The Cell Structure Electron Micrograph Showing A Small Part Of Rough Endoplamic Reticulum

Functions of RER

  • Proteins synthesized by ribosomes enter the cavity of RER for processing and storage.
  • RER is also involved in the synthesis of phospholipids.
  • In the cavity of RER, the protein may combine with the carbohydrates to form glycoprotein or it may combine with phospholipids. These reactions take place under the influence of enzymes present in RER.
  • Thus, RER is involved in the synthesis of secretory proteins and molecules used in the formation of plasma membranes (lipids and integral proteins).

Endoplasmic Reticulum SER

The SER also consists of short anastomosing tubules (Fig.1.9b). As the ribosomes are not attached on its surface

The Cell Structure Electron Micrograph Showing Tubules Of Smooth Endoplamic Reticulum

Functions of SER

Though SER is not involved in the synthesis of proteins, similar to RER it is also involved in the synthesis of phospholipids.

SER is involved in the synthesis of fat (cholesterol, triglycerides) and steroid hormones (estrogen, testosterone, etc.).

In the liver cells, it is involved in the detoxification of drugs and other chemicals (breakdown of alcohol and barbiturates, etc.).

SER is specialized in skeletal muscle fibers and is known as the sarcoplasmic reticulum, which helps in the control of muscle contraction.

Endoplasmic Reticulum Remember

  • The endoplasmic reticulum (ER) is of two different types, i.e., rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). The RER is called rough ER because of the presence of granules (ribosomes) on its surface.
  • while SER is called smooth ER because ribosomes are not attached to its surface. RER is involved in the synthesis of protein, while SER in the synthesis of fat and steroid hormones.

Golgi Complex

  • This cytoplasmic organelle is present in almost all cells but is well-developed in the secretory cells.
  • In the glandular cells, it is present between the nucleus and the apex of the cell. It is 0.5 to 2 μm in diameter.
  • It is made up of 3-20 flattened membranous sacs (cisternae) that are curved. Thus, the shape of the Golgi complex is like a shallow cup.
  • The Golgi complex has a convex and a concave surface. The convex surface faces towards the RER and nucleus, while the concave surface faces towards the cell membrane.
  • The convex surface is also called as forming face (cisface) and the concave surface is called the maturing face (trans-face).
  • The small vesicles that bud off from the RER are transported towards the cis-face of the Golgi complex where they Rise with the outermost convex cistema of forming face.
  • The secretory product then moves from the cistema of forming face to maturing face through vesicles that bud off from the periphery of one cisterna and fuse with the next.
  • While the secretory products are moving from his face to fransface of Golgi, they are modified.
  • At the trans-face or maturing face, the products are accumulated & concentrated in cisterna.
  • Membrane-bounded secretory vesicles are formed at the trans-face that leave the Golgi and move towards the apical end of the cell for secretion.

The Cell Structure Electron Micrograph Showing Glogi Apparatus, Secretory Vesicles, And Transfer Vesicles

Golgi Complex Functions

  • One of the important functions of the Golgi complex is to sort proteins for their respective pathways, that is, to the plasma membrane, secretory granules, or lysosomes.
  • Golgi is also involved in membrane synthesis (by forming the membrane vesicles).
  • It forms secretory vesicles for exocytosis.
  • It is also involved in the production of lysosomes with RER.
  • Enzymes of the Golgi modify the proteins to form glycoproteins and lipoproteins. They also modify glycolipid.

The Cell Structure Photomicrograph Of Plasma Cell Showing The Presence Of Peri-Nuclear Hallo Shown By Arrow Heads.

Golgi Complex Remember

The Golgi apparatus is made up of a series of flattened membrane-bound cisternae. It consists of a cis-face and a trans-face. Its function is in the synthesis of carbohydrates and the modification and sorting of proteins.

Lysosomes

  • Lysosomes are electron-dense, membrane-bounded bodies (vesicles), measuring 0.2-0.8 μm in diameter.
  • They are formed in the Golgi complex and are called primary lysosomes. When a primary lysosome fuses with the endocytic vesicle (the contents of which are to be digested), it is called a secondary lysosome.
  • Lysosomes contain 40 types of powerful hydrolytic (digestive) enzymes that are capable of breaking down various kinds of molecules.
  • Lysosomal enzymes work best at acid pH. Therefore, the lysosomal matrix is 100 times more acidic than cytosol. The lysosomal membrane possesses proton pumps that actively transport H+ ions into the lysosome, maintaining its lumen at pH 5.
  • Although lysosomes contain hydrolytic enzymes, their membrane is resistant to hydrolysis by their enzymes. This is because their membrane has an unusual phospholipid structure.

The membrane proteins in lysosomes are highly glycosylated. Sugar molecules cover the cytoplasmic surface proteins that protect them from digestion by lysosomal enzymes.

The Cell Structure Electron Micrograph Showing Electron Dense Lysosomes, M-Mitochondrion

Lysosomes Functions

  • Lysosomes are involved in the digestion of substances or particles (bacteria, etc), which are brought into the cell using endocytosis. This process is called heterophagy.
  • Lysosomes are also capable of digesting the old (worn out) organelles of cytosol and returning the digested components to the cytosol. This process is called autophagy.
  • In some pathological conditions, lysosomes may also destroy their cells. This process is known as autolysis.

Lysosomes Remember

Lysosomes have an acidic pH and contain 40 types of powerful hydrolytic (digestive) enzymes that are capable of breaking down various kinds of molecules. Lysosomes are involved in the digestion of substances or particles (bacteria, etc) that are brought into the cell using endocytosis.

Peroxisomes

  • Peroxisomes are small (0.2-1 μm in diameter) ovoid organelles. This structure is almost similar to lysosomes. These are also membrane-bounded bodies containing more than 40 oxidative enzymes.
  • Peroxisomes contain enzymes that oxidize amino acids and fatty acids as part of normal metabolism.
  • The enzymes of peroxisomes also oxidize toxic substances like alcohol.
  • In the process of oxidation, hydrogen peroxide (H202) is released as a by-product that is toxic to cells.
  • Peroxisomes contain an enzyme called catalase that detoxifies H202 within the cell.

Peroxisomes Clinical Application

Tay-Sachs Disease

  • This is a lysosomal storage disorder.
  • This is an inherited (genetic) disease. It is due to the absence of a single lysosomal enzyme (B-hexosaminidase).
  • In the absence of this enzyme, the glycolipid (ganglioside) cannot be broken down and thus accumulates in nerve cells.
  • This leads to inefficient working of nerve cells resulting in seizures, muscle rigidity, blindness, and death before 5 years of age.

Mitochondria

  • Mitochondria are called “powerhouses” of the cell because they generate ATP (a stable storage form of energy).
  • These are present in all types of cells, except red blood cells.
  • Their number within a cell may vary from a few to several thousand (about 2000 in each liver cell).
  • A large number of mitochondria are present in highly active cells, e.g., muscles, liver, and kidney cells.
  • This membrane-bounded organelle is elliptical in shape and measures about 0.5-3 μm in length.
  • Unlike other membrane-bound organelles, mitochondria are made up of two parallel membranes each of which is structurally similar to the plasma membrane.
  • The outer membrane is smooth while the inner membrane is arranged in a series of folds called cristae.

The inner membrane is rich in enzymes (ATP synthase) that are present in spherical bodies (elementary particles) attached to its inner surface. Intramembranous space contains specific enzymes.

  • One of them is cytochrome C, which is important in initiating apoptosis (programmed cell death).
  • The matrix is the central fluid-filled cavity of mitochondria enclosed by the inner membrane and cristae.
  • Matrix contains matrix granules, mitochondrial DNA filaments, mRNA, tRNA, and rRNA.
  • Mitochondrial DNA consists of a double helix in the form of a circle that contains 37 genes.
  • It is believed that mitochondrial genes are inherited only from the mother as the head of sperm lacks mitochondria.
  • As per the energy requirement of the cell, mitochondria may divide to increase their number. Mitochondria are present in all cells, except those lacking nuclei, i.e., RJBCs and terminal keratinocytes.
  • It shows an electron micrograph of mitochondria.

The Cell Structure The Internal Structure Of A Mitochondrion

The Cell Structure Enlarged View Of Cristae Showing Attachment Of Elementary Particles

The Cell Structure Electron Micrograph Showing Mitochondria Both Longitudinally And Transversely Cut Mitochondria

The average life span of mitochondria is about 10 days. They are self-replicating. The mitochondrion enlarges in size, replicates its DNA, and undergoes division to form two mitochondria.

Mitochondria Functions

  • As the matrix of mitochondria also contains ribosomes, some protein synthesis occurs within the mitochondria, Mitochondria are capable of synthesizing their ribosomal protein.
  • The remainder of the mitochondrial proteins is encoded by the nuclear DNA, which then comes from cytoplasm to mitochondria.
  • Mitochondria are involved in the production of a high-energy phosphate compound, adenosine triphosphate (ATP).
  • This ATP is a stable storage form of energy, which is used for many chemical reactions in the cell.
  • Granules of the matrix arc cation-binding sites. Thus, the mitochondria arc is also involved in the regulation of the concentration of certain ions in the cytosol.
  • Mitochondria sense cellular stress and decide whether the cell should live or die by initiating apoptosis (programmed cell death).

Mitochondria Remember

Mitochondria are present in all cells except those lacking nuclei, i.e., RBCs and terminal keratinocytes, A Large number of mitochondria is present in highly active cells, For Example., muscles, liver, and kidney cells. As per the energy requirement of the ceil, mitochondria may divide to increase their number. Mitochondria are involved in the Production of a high-energy phosphate compound, ATP.

Ribosomes

  • Ribosomes are small particles about 20 to 30 nm in diameter. They contain ribonucleic acid and many types of ribosomal proteins.
  • Ribosomes are made up of two subunits both of which are produced separately in nucleolus. Once produced they migrate to the cytosol and both subunits join each other.
  • Ribosomes are attached in groups on the surface of RHR. This group of ribosomes is called polyribosomes. They are present in groups because they are attached to the thread of messenger RNA.
  • Ribosomes are also scattered singly or in groups in cytoplasm (not attached to any organelle). These types of ribosomes are called free ribosomes or free polyribosomes, respectively.

Ribosomes Functions

  • Ribosomes are the site of protein synthesis.
  • Free ribosomes synthesize proteins that are used within the cell.
  • Membrane-bound ribosomes are involved in the synthesis of secretory proteins. They also synthesize proteins used in the formation of new plasma membranes.

Centrosome or Microtubule Organizing Centre

  • The centrosome is a small spherical area of cytoplasm situated near the nucleus.
  • It consists of two parts: the pericentriolar area and the centriole.
  • The pericentriolar area is made up of a dense network of smaller granular protein material.
  • In the center of the pericentriolar area, two rod-shaped structures are called centrioles. The long axis of one centriole is at a right angle to the long axis of the other.
  • Centrioles are hollow cylindrical structures each of which is made up of nine groups of three microtubules (triplets) arranged in a circular pattern.
  • Centrioles are self-replicating organelles. Just before cell division, a new centriole is synthesized near the old one.

Centrosome or Microtubule Organizing Centre Functions

  • The pericentriolar area plays an important role in the formation of mitotic spindles during cell division.
  • In a non-dividing cell, this is also involved in the synthesis of microtubules.
  • Centrioles are involved in the formation of cilia and flagella.

The Cell Structure Schematic Diagram Of Centrosome

  1. The pericentriolar area of a centrosome surrounds two centrioles. The long axes of two centrioles are perpendicular to one another.
  2. Transverse section across a centriole. Each centriole is made up of 9 bundles of microtubules, with 3 microtubules per bundle.
  3. Electron microscopic image of the centrosome, in which two centrioles (in longitudinal section) are seen arranged at a right angle to each other.
  4. Electron micrograph of a centriole as seen in the transverse section. Three microtubules are visible in each 9 bundles.

Endosomes

  • Endosomes are membrane-bounded compartments (between 100 to 500 nm in size) associated with endocytotic pathways. There are two types of endosomes, i.e., early and late endosomes.
  • Early endosomes are located near the cell membrane. The endocytotic vesicles, which originate from the cell membrane, fuse with the early endosomes.
  • The function of early endosomes is to sort the proteins received through endocytotic vesicles. Receptor proteins will go back to the plasma membrane.
  • While the remaining proteins will be transported to the late endosomes through multivesicular bodies. The multivesicular bodies are structures that transport proteins between early and late endosomes.
  • Late endosomes are located near the Golgi apparatus. The substances transported to late endosomes are degraded in the lysosomes.

Cytoplasmic Inclusions

Inclusions are non-living and non-functional components of a cell. They are simply the store of inert by-products of metabolism like lipids and glycogen. These are not membrane-bound.

  • Glycogen: Glycogen is present in the cytoplasm in the form of dense granules that are about 25-30 nm in diameter.
  • Lipid: Lipid is stored in the cytoplasm in the form of rounded droplets.
  • Pigments: Some cells may show the presence of a yellowish-brown pigment called lipofuscin. These inclusions may be membrane-bound. The lipofuscin pigments are waste products of the cell, which cannot be digested completely by the lysosomal activity.
  • Secretory granules: Sometimes, the membrane-bounded secretory vesicles are also classified as cytoplasmic inclusions.

Cytoskeleton

Different kinds of protein filaments and tubules form a network throughout the cytoplasm. This network is called a cytoskeleton. The cytoskeleton provides shape to the cell and organizes the cellular contents.

Cytoskeleton is also involved in the mobility of some cells, For Example., phagocytes. The cytoskeleton consists of the following three types of protein filaments:

  • Microfilaments
  • Intermediate filaments
  • Microtubules

The Cell Structure Schematic Diagram Of Cytoskeleton In Cytoplasm, Microfilament, Intermediate Filament And Microtubules

1. Microfilament

  • Microfilaments are the thinnest (5 nm in diameter) filaments of the cytoskeleton. These filaments are mainly present near the peripheral part of the cell and are made up of proteins called actin.
  • Microfilaments provide shape to the cell. They also provide the skeleton of microvilli, which are finger-like projections from the cell surface.
  • Microfilaments are also involved in muscle contraction, cell division, and movement of phagocytes and other cells.

2. Intermediate Filaments

  • The intermediate filaments are thicker (10 nm in diameter) than microfilaments. These filaments are found in parts of cells subjected to mechanical stress.
  • The intermediate filaments of nerve cells are called neurofilaments. The tonofibrils are filaments of epidermal cells that are composed of a protein called keratin.

Cytoskeleton Clinical Application

Alzheimer’s Disease

  • Failure to assemble the intermediate filaments leads to various diseases. The changes in neurofilaments lead to Alzheimer’s disease.
  • In this disease, there is an accumulation of tangled masses of filaments in the cytoplasm leading to the degeneration of neurons. Patients with this disease suffer from loss of memory.

Microtubules

Microtubules are hollow cylinders about 25 nm in diameter and several microns in length. They are made up of the protein tubulin. Microtubules are assembled at the centrosome, which consists of a microtubule-organizing center.

  • Microtubules are present throughout the cytoplasm where they are involved in giving shape to cells, in the intracellular transport of secretory granules, and movements of chromosomes during cell division.
  • These tubules are also present in cilia and flagella and are responsible for their movements.

Nucleus

The nucleus is a membrane-bound structure. It is either a spherical or oval-shaped structure, present usually in the center of the cell.

It contains genes, which control cellular structure and the various activities of the cell. The nucleus consists of an envelope (nuclear envelope), nuclear lamina, chromatin material, nucleolus, and nuclear matrix.

Nuclear Envelope

The nuclear envelope is made up of two parallel membranes that separate the nucleus from the cytoplasm. These membranes are similar to plasma membranes.

  • The outer nuclear membrane is continuous with rough endoplasmic reticulum.
  • In the nuclear membrane, there are several channels, which are called nuclear pores. Small molecules and ions diffuse passively through these pores.
  • However, the transport of large protein molecules from the cytosol to the nucleus and that of RNAs from the nucleus to the cytosol is regulated by nuclear pores.

The Cell Structure Schenatic Diagram Showing Part Of The Nuclear Envelope And Nuclear Lamina

The Cell Structure Electron Micrograph Of A Nuclear Envelop

Nuclear Lamina

The nuclearlamina is a thin layer adjacent to the inner nuclear membrane. It is formed by intermediate filaments, which are arranged in a square lattice.

  • The function of nuclear lamina is to provide structural stability to the interphase nucleus (nuclear envelope, nuclear pores, and chromatin).
  • The nuclear lamina disintegrates during cell division but reassembles in the daughter cells.

The Cell Structure Schematic Diagram Showing Nuclear Lamina Arranged In The Form Of Lattice

Chromatin

The nucleus plays an important role in heredity. It contains heredity units called genes. Genes are present on chromosomes, which itself is a long molecule of DNA coiled together with several proteins.

  • Innon-dividing cell (interphase cell), chromosomal material is less tightly coiled and appears as a diffuse granular mass, which is called chromatin.
  • The chromatin is stained basophilic (with hematoxylin) due to the presence of a phosphate group in DNA. In the nucleus of an interphase cell, chromatin occurs in two different arrangements, i.e., heterochromatin (condensed chromatin) and euchromatin (extended chromatin).
  • Heterochromatin stains with basic dyes and hematoxylin and thus appears as irregular dark masses. Euchromatin stains lightly with basic dyes and is seen as clear areas between heterochromatin.
  • Nuclei that are predominantly made up of euchromatin are called open-face nuclei, while nuclei that are made up mainly of heterochromatin are called closed-face nuclei.

Heterochromatin is regarded as metabolically inactive chromatin (For Example, chromatin in the head of sperm), while euchromatin is active chromatin (chromatin of neurons and liver cells).

The Cell Structure Microphotographs To Show Euchromatic And Heterochromatic Nuclei Photomicrograph Of Neuron And Fibrocytes

Nucleolus

The nucleolus is the spherical body within the nucleus that is stained dark with basic dyes. Some cells contain more than one nucleolus.

  • It contains a protein called nucleostemin. It is a P53 binding protein that regulates the cell cycle and influences cell differentiation.
  • The main role of the nucleolus is to synthesize rRNA and assemble ribosomes.
  • When observed under an electron microscope, it consists of three regions.
  • The innermost pale staining fibrillar center (FC) is surrounded by a dense fibrillar component (DFC) or pars fibrosis, which in turn is bounded by a granular component (GC) or pars granulosa. Pars granulosa contains maturing ribosomes.
  • Transcription of DNA occurs in FC or at the FC-DFC junction. This region contains tips of chromosomes 13, 14, 15, 21, and 22 (the nucleolar organizing regions), where gene loci that encode rRNA are located.
  • Most of the cleavage and modification of RNA occurs in the DFC. While steps involving protein assembly to form preribosomal particles occur in GC.

Here, small and large ribosomal subunits are organized, which migrate to the cytoplasm through nuclear pores.

The Cell Structure Nucleus Of An Interphase Cell Showing Both Types Of Chromatin

Nuclear Matrix

All the material enclosed by the nuclear membrane, excluding chromatin and nucleolus, is called nucleoplasm. At present, nothing much is known about its composition but it seems that it must contain a network of fibrils (karyoskeleton), proteins, and metabolites.

Perineum: Boundaries, Contents, Innervation Notes

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Boundaries And Subdivisions Of Perineum

Boundaries And Subdivisions Of Perineum Definition

The region at the lower end of the trunk, in the interval between the two thighs where external genitalia and anus are located.

Boundaries And Subdivisions Of Perineum Boundaries

Superficial – Anterior – The scrotum in males and mons pubis in females.

  • Posterior- The buttock.
  • Lateral- Upper part of the medial side of the thigh on each side.

Deep – Anterior- Upper part of pubic arch and inferior (arcuate) pubic ligament.

  • Posterior- Tip of the coccyx.
  • Lateral- Ischiopubic rami, ischial tuberosities, and sacrotuberous ligaments.

Subdivisions of perineum

Boundaries And Subdivisions Of Perineum Subdivisions Of Perineum

The perineum is divided into two triangular areas (anal and urogenital triangles) by a transverse line joining the anterior parts of the ischial tuberosities and passing immediately anterior to the anus.

1. The anal triangle (region)

It contains the termination of the anal canal in the midline and ischiorectal fossa on each side. The pudendal canal carrying the neurovascular bundle to the perineum is located in the lateral wall of the ischiorectal fossa.

2. The urogenital triangle (region)

It contains the external urogenital organs. It also contains the superficial and deep perineal spaces.

External Genitalia

Male External Genital Organs

The male genital organs include the penis, scrotum, testis, epididymis, and spermatic cord.

External Genitalia Penis

It is the male organ of copulation. It consists of (1) the attached part called the root and (2) the free part called the body.

External Genitalia External Genitalia Of Male

Root Of Penis

It is located in the superficial perineal pouch. It is made up of two crura and one bulb which are masses of erectile tissue. Each crus is attached to the margins of the pubic arch and covered by ischiocavemosus.

The bulb lying between two crura is attached to the perineal membrane and covered by the bulbospongiosus.

It is pierced by the urethra which shows dilatation in this region called the inrabulbar fossa. The urethra continues anteriorly in the corpus spongiosum located in the body of the penis.

Body Of The Penis

It is continuous with the root of the penis and is completely covered by skin. It has an anterior and posterior surface. It consists of three elongated masses (right and left corpora cavernosa and middle corpus spongiosum) of erectile (cavernous) tissue.

During an erection, the cavernous spaces are excessively filled with blood. Corpora cavernosa are forward continuation of crura and both of them terminate anteriorly in a blunt conical end covered from the front by the glanspenis.

The terminal conical expanded part of the corpus spongiosum. Corpora cavernosa are enveloped by a thick connective tissue covering called the tunica albuginea.

The base of the glans penis is a projected margin (corona glandis) which overhangs an oblique constricted region (neck of penis). Glans is also pierced by the urethra which presents a dilatation in this region called the navicularfossa.

Female External Genital Organs (Pudendum Or Vulva)

These include the following structures;

The mons pubis, the labia majora, the labia minora, the clitoris, the vestibule of vagina, the bulbs of the vestibule and the greater vestibular glands.

Mons Pubis

The rounded eminence present in front of the pubic symphysis formed as a result of the accumulation of subcutaneous fat. It is covered with pubic hairs and in contrast to males, the upper limit of the hair-bearing area is demarcated by a horizontal line.

Labia Majora

These are two thick folds of skin enclosing fat forming the lateral boundaries of the pudendal cleft. Their external surface is covered with hair and the inner surface contains a large number of sebaceous glands.

  • The anterior ends of the two are joined together below the mons pubis forming the anterior commissure. The posterior commissure is formed by the union of the relatively less prominent posterior ends in front of the anus.
  • The gynecological perineum is the area (about 1 inch) located between the posterior commissure and the anus.

Labia Minora

These are two thin folds of skin within the pudendal cleft. Their anterior ends divide into upper and lower layers.

  • The upper layers of two sides join to form the prepuce of the clitoris and the lower layers join to form the frenulum of the clitoris.
  • The posterior ends of the two sides join to form the frenulum of the labia minora. A large number of sebaceous glands are found on the inner surface of the labia minora.

External Genitalia External Genitalia Of Female

Clitoris

It is located in the anterior part of the pudendal cleft. It is homologous to the male penis and erectile but not pierced by the urethra.

  • Like the penis, the body of the clitoris has a pair of corpora cavernosa encloses in a fibrous sheath and separated by a pectiniform septum; however, the corpus spongiosum is absent. Each corpus callosum is attached to the ischiopubic rami.
  • The glans clitoridis which caps the s ends of corpora cavernosa is made up of erectile tissue which is continuous posteriorly with the commissural venous plexus uniting right and left bulbs of the vestibule.
  • The surface of the glans is very g sensitive and plays an important role in sexual responses.

Vestibule Of The Vagina

The space between two labia minora is called the vestibule of the vagina. It has the following features.

  • Urethral orifice. 2.5 cm behind the frenulum of the clitoris
  • Vaginal orifice (introitus).
  • Orifices of the ducts of the greater vestibular glands.
  • Openings of lesser vestibular (mucous) glands.
  • Vestibularfossa- depression between vaginal orifice and frenulum of labia minora.

Bulbs Of The Vestibule

These correspond to two halves of the bulb of the penis. They are oval and made of erectile tissue and are located superficial to the perineal membrane on either side of the vaginal and urethral orifices.

The posterior expanded part is partly overlapped by the greater vestibular glands. The tapering anterior ends of the bulbs are united in front of the urethra by a venous plexus called the bulbar commissure.

Greater Vestibular Glands (Of Bartholin)

These are located in the superficial perineal space on either side of the vaginal orifice and are homologous with the bulbourethral glands (of Cowper) in males.

Each gland is partly overlapped by the bulbs of the vestibule and its long duct (2 cm) opens between the hymen and labium minus.

Anal Triangle

Cutaneous Nerves

  • Inferior rectal nerve (S2, S3, S4): Supplies the skin around the anus and over the ischiorectal fossa.
  • Perineal branch of4th sacral nerve: Supplies the skin posterior to the anus.

Superficial Fascia

It contains a large amount of fat which fills the ischiorectal fossa.

Anal Triangle Structures Of Anal Triangle

Deep Fascia

It forms the inferior fascia of the pelvic diaphragm and the fascia over the obturator intemus below the attachment of the levator ani.

Anococcygeal Ligament Or Body

It consists of fibrofatty tissue intermingled with muscle fibers which are derived from the levator ani and the external anal sphincter. It extends between the tip of the coccyx and the superficial external and sphincter.

Perineal Body

It consists of a fibromuscular node situated in the median plane about 1.25 cm in front of the anal margin and close to the bulb of the penis. Many muscles of the perineum converge. and interlace in the perineal body.

It provides support to the pelvic organs. It is more important in females and when damaged during childbirth it may lead to prolapse of the urinary bladder, uterus, ovary, or even rectum.

External Anal Sphincter

The external anal sphincters surround the anal canal. These are supplied by the inferior rectal nerve and the perineal branch of the 4th sacral nerve. It is under voluntary control and keeps the anus and anal canal closed.

Ischiorectal Fossa

It is a wedge-shaped space (with the base directed downwards and the edge directed upwards) located on each side of the anal canal and below the pelvic diaphragm.

Anal Triangle Ischiorectal Fossa

Ischiorectal Fossa Dimensions

  • Length (anteroposterior)- 2 inches.
  • Width (side to side)- 1 inch
  • Depth (vertical)- 2.5 inches
  • Boundaries
  • Base – skin
  • Edge Apex- line of origin of levator ani from the lateral pelvic wall
  • Anterior-posterior border of the perineal membrane
  • Posterior- lower border of gluteus maximus and sacrotuberous ligament.
  • Lateral-obturator intemus with its fascia and medial surface of the ischial tuberosity.
  • Medial- external anal sphincters and levator ani.

Ischiorectal Fossa Recesses

  • Anterior recess – extends above the perineal membrane to enter the deep perineal pouch and reach the back of the body of the pubis.
  • Posterior recess – extends deep to the sacrotuberous ligament.
  • Horseshoe recess – connects the ischiorectal fossae of two sides behind the anal canal.

Anal Triangle Pudendal (Alcock's) Canal

Spaces And Canals Of The Fossa

Perianal space

It is subcutaneous and contains fat which is enclosed in tight loculi. It is separated from the deep ischiorectal space by a fascial extension called the perianal membrane which passes.

Laterally from the lower end of longitudinal muscle coat (conjoint longitudinal layer). It extends from the white line of Hilton medially to the pudendal canal laterally. The infection of this space is very painful.

Ischiorectal Space

This a large and deep space filled with loosely packed fat. The infection of this space is the least painful. The lunate fascia arches over the ischiorectal fat. The fascia divides the ischiorectal space into,

  • Suprasegmental space – above the fascia.
  • Tegmental space – below the fascia.

Pudendal Canal

A fascial canal in the lateral wall of the pelvis encloses the pudendal nerve and internal pudendal vessels.

The fascia of the canal fuses with,

  • obturatorfascia- laterally
  • lunate fascia – above
  • perianalfascia- medially
  • falciform process of sacrotuberous ligament – below

Contents of the ischiorectal fossa

  • Ischiorectal pad of fat.
  • Inferior rectal nerve and vessels.
  • Posterior scrotal ( or labial, in female) nerves and vessels.
  • Perineal branch of 4th sacral nerve
  • Perforating cutaneous branches of nerves S2, 3
  • Pudendal canal with its contents.

Anal Triangle Applied Anatomy

  • The ischiorectal fossae allow distension of the anal canal during defecation.
  • Abscess formation- Perianal and ischiorectal spaces are common sites of abscess formation.
  • Anorectal fistula (fistula in ano) – Sometimes the abscess may burst medially into the anal canal or rectum or laterally on the surface resulting in anorectal fistula.
  • External sinus- If the abscess bursts externally and does not heal, it results in the external sinus.
  • Prolapse of the rectum- The ischiorectal pad of fat supports the rectum and anal canal and its loss may result in prolapse of the rectum.
  • Ischiorectal hernia- Hmiation of a pelvic organ through the hiatus of Schwalbe (the gap between the tendinous origin of the levator ani and obturator fascia).

Steps Of Dissection Of Ishciorectal Fossa

Place the cadaver in the prone position and expose the lower border of the gluteus maximus. Remove the skin and fascia from the perineum, external anal sphincters, and anococcygeal ligament as well as from the margins of the anus.

  1. Trace and define the boundaries of the ischiorectal fossa. Expose and clean the posterior margin of the perineal membrane and identify and trace the inferior rectal and posterior scrotal (labial) nerve and vessels in the lateral wall of the fossa.
  2. Try to identify the gluteal branches of the posterior cutaneous nerve of the thigh and the perineal branch of S4. Remove all fat from the fossa. Clean and define the pudendal canal on the lateral wall of the fossa and trace the pudendal nerve and internal pudendal vessels.

Urogenital Triangle

Cutaneous innervation

  • Dorsal nerve of penis (or of the clitoris): It supplies the skin of the whole penis (clitoris) except its root.
  • Ilioinguinal nerve and genital branch of genitofemoral nerve: Supply the anterior 1/3rd of the scrotum (or labium majus in females) and the root of the penis.
  • Perineal branch of the posterior cutaneous nerve of the thigh: Supplies the lateral part of the
    urogenital region and lateral part of the posterior 2/3rd of the scrotum (or labium majus).
  • Posterior scrotal (or labial) nerves: Supply the medial part of the urogenital region including labium minus in females and the medial part of the posterior 2/3rd of the scrotum (or labium majus).
  • Perineal branch of the pudendal nerve: Supply the mucous membrane of the urethra.

Urogenital Triangle Layers In Orogenital Triangle

  1. Levator ani
  2. The superior fascia of the urogenital diaphragm
  3. Deep Perineal pouch
  4. Perineal membrane
  5. Superficial perineal pouch
  6. Colles fascia
  7. Skin

Superficial fascia

It consists of two layers:

  • Superficial fatty layer– it is continuous with the superficial fascia of the surrounding region.
  • Deep membranous layer (Colles fascia) – Attachments
    • Posterior- Posterior border of the perineal membrane
    • Sides- Pubic arch below the crus of penis (clitoris in female).
    • Anterior- Continues with the fascia of the scrotum (dartos), of the penis, and with the fascia of the Scarpa (deep membranous layer of the superficial fascia of the anterior abdominal wall).

Deep Fascia

It consists of two layers lining the urogenital diaphragm from its superior and inferior aspects. The inferior layer is thicker and called the perineal membrane.

Urogenital Triangle Inferior Surface Of Pelvic Diaphragm Male

Urogenital Triangle Inferior Surface Of Pelvic Diaphragm Female

Superior Fascia Of Urogenital Diaphragm

  • It is thin and less defined than the inferior fascia
  • It is coextensive with the perineal membrane and attached anteriorly and posteriorly to it.
  • Laterally it is continuous with the obturator fascia.
  • It is pierced by the urethra and continuous with the prostatic fascia.

Deep Perineal Space (Pouch)

It is the space between the superior and inferior fascia of the urogenital diaphragm.

Urogenital Triangle Superior Fascia Of Urogenital Diaphragm Male

Urogenital Triangle Superior Fascia Of Urogenital Diaphragm Female

Urogenital Triangle Deep Perineal Pouch Male

Urogenital Triangle Deep Perineal Pouch Female

Contents of deep perineal pouch

  1. Urethra (membranous urethra in male)
  2. Muscles
    • Sphincter urethrae
    • Deep transverse perineal
  3. Nerves
    • Dorsal nerve of penis (clitoris in female)
    • Muscular branch from perineal nerve
  4. Arteries
    • Initial parts of arteries of the penis (clitoris in females) pass to the superficial perineal pouch
  5. Bulbourethral glands in male

Urogenital Triangle Pudendal Nerve Male

Urogenital Triangle Pudendal Nerve Female

Urogenital Triangle Internal Pudendal Artery Male

Urogenital Triangle Internal Pudendal Artery Female

The Perineal Membrane

It is a thick, triangular sheet of fascia lying across the pubic arch.

  • Its base (posterior border) is continuous
    • Above with the superior fascia of the urogenital diaphragm
    • Below with the code fascia.
    • In the midline connected to the perineal body.
  • On each side- Attached to ischiopubic rami above the attachment of crus of the penis.
  • Anterior border (apex) – Continues with the superior fascia of the urogenital diaphragm and is thickened to form a transverse perineal ligament.
  • The gap between the arcuate pubic ligament and transverse perineal ligament transmits
    • Deep dorsal vein of the penis (clitoris in female)) to the prostatic (vesical in female) venous plexus.
    • Dorsal nerve of penis (clitoris in female).

Structures Piercing The Perineal Membrane

In males

  • Urethra, 1 inch below – the pubic symphysis.
  • Ducts of bulbourethral glands, close to the urethra.
  • Artery and nerve to the bulb of the penis.
  • Urethral artery.
  • Deep artery- of the penis.
  • Dorsal artery of the penis
  • Posterior scrotal nerves and vessels.
  • Branches of perineal nerve supplying superficial perineal muscles

Urogenital Triangle Perineal Membrane Male

Urogenital Triangle Perineal Membrane Female

In females

  • Urethra
  • Vagina
  • Artery and nerve to the bulb of the vestibule
  • Deep artery of clitoris
  • Dorsal artery of the clitoris
  • Posterior labial arteries and nerves.
  • Branches of perineal nerve supplying superficial perineal muscles

Urogenital diaphragm

It is formed by

  • Deep perineal muscles – sphincter urethrae and deep transverse perineal
  • The superior fascia of the urogenital diaphragm
  • The inferior fascia of the urogenital diaphragm (perineal membrane)

Urogenital Triangle Urogenital Diaphragm

Superficial perineal pouch

It is a superficial space in the perineal region located superficial to the perineal membrane.

Urogenital Triangle Superficial Perineal Pouch Male

Urogenital Triangle Superficial Perineal Pouch Female

Urogenital Triangle Boundaries

  • Superficial – Colles’ fascia
  • Deep – Perineal membrane
  • On either side- Ischiopubic rami
  • Anteriorly- Open and continue with the spaces of the scrotum and anterior abdominal wall.
  • Posteriorly- Closed by the union of the perineal membrane with the Colles’ fascia

Urogenital Triangle Contents

  1. The root of the penis (clitoris in females), is made up of a pair of crura and a bulb (only crura in females)
  2. Muscles on each side-
    • Ischiocavemosus
    • Bulbospongiosus
    • Superficial transversus perinea
  3. Nerves
    • Branches of the perineal nerve- posterior scrotal (labial in females), nerve to bulb (in males only), and muscular branches
    • Long perineal nerve- from the posterior cutaneous nerve of the thigh
  4. Arteries
    • Branches of perineal artery- posterior scrotal (labial in female) and transverse perineal
    • Arteries of the penis (clitoris in female) – artery to the bulb (in male only), urethral artery, deep artery of the penis (clitoris in female), and dorsal artery of the penis (clitoris in female).
  5. Greater vestibular glands in females (or, ducts of bulbo-urethral glands in the male).

Pelvis Anatomy Notes

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Introduction To Pelvis

Boundaries Of True Pelvis

The inlet of the bony true pelvis is the demarcation between the pelvis and abdomen proper. Part of the pelvis between the pelvic diaphragm and skin between the upper parts of the medial thigh is called the perineum.

A bony pelvis above the pelvic inlet about the iliac fossa is called a false pelvis. It forms the posterolateral wall of the lower part of the abdomen proper.

Introduction To Plevis Subdivisions Of Abdomen And Pelvis

The true pelvis has got inlet, outlet and cavity. The boundaries of each are as follows.

1. Cavity

  • Anterior
    • Pubic symphysis
    • Pubis (Pelvic surfaces of body and rami)
  • Posterior – Sacrum
  • Pelvic surfaces of ilium and ischium
  • Lateral – Pelvic surfaces of ilium and ischium

2. Inlet

  • Superior margin of pupic symphysis.
  • Pelvic brim. It is comprised of,
    • Sacral promontory – Anterior margin of superior surface of 1st sacral vertebra.
    • All of the sacrum (Lateral part of the base of the sacrum)
    • Linea terminalis
      1. Iliac part – Arcuate line
      2. Pupic part – Pecten pubis and pubic crest

Introduction To Plevis Inlet Of Pelvis

3. Outlet

  1. Inferior margin of the pubic symphysis
  2. Subpubic angle
  3. Ischiopubic rami
  4. Ischial tuberosity
  5. Sacrotuberous ligament.
  6. Tip of coccyx

Introduction To Plevis Oulet Of Pelvis

  1. Inferior Margin Of Public Symphysis
  2. Subpublic Angle
  3. Ischiopublic Rami
  4. Ischial Tuberosities
  5. Sacrotuberous Ligaments
  6. Tip Of Coccyx

Pelvic Wall

Two paired muscles contribute to the wall of the pelvis i.e., piriformis and obturator items.

Pelvic Wall Piriformis

Origin – Pelvic surfaces of middle three pieces of sacrum

Insertion – Upper border of greater trochanter of femur

Nerve – Branches from sacral plexus (L5, Sl,2)

Pelvic Wall Actions

  1. Lateral rotation of the extended thigh.
  2. Abduction of flexed things

Pelvic Wall Lateral Wall Of Polvis Showing Attachments Of Obturator Internus

Pelvic Wall Obturator internus

Origin – Pelvic surface of obturator membrane and adjacent parts of hip bone below the pelvic brim.

Insertion – Medial surface of the greater trochanter.

Nerve – Nerve to obturator intemus (L5, S1,2)

Obturator internus Action

  1. Lateral rotation of the extended thigh.
  2. Abduction of the flexed thigh.

Pelvic Wall Posterior Wall Of Pelvis Showing Attachments Of Piriformis

Floor Of Pelvis (Pelvic Diaphragm)

Coccygeus

This is also called iliococcygeus. It is a triangular muscle. Its apex is attached to the ischial spine. Its base extends to the lateral margin of the lower sacrum and adjacent coccyx. Its posterior surface is covered by a sacrospinous ligament.

Levator Ani

It has two components

Floor Of Pelvis (Pelvic Diaphragm) Medial View Of Right Half Of The Pelvic Diaphragm In Male

iliococcygeus

It arises from the posterior half of the arcus tendinous, a thickening in the obturator fascia along a line from the back of the body of the pubis to the ischial spine.

Fibres extend backwards and downwards to get attached to the side of the coccyx and interlace with the opposite side from the anococcygeal raphe.

Floor Of Pelvis (Pelvic Diaphragm) Superior Surface Of Pelvic Diaphragm In Male

Pubococcygeus

It arises from the posterior surface of the body of the pubis and the anterior half of the acrus tendineus. It is divided into three parts from posterior to anterior.

Floor Of Pelvis (Pelvic Diaphragm) Most Anterior Fiber Of The Pubococcygeus Female And Male

Pubococcygeus proper- It is the main posterior part of the muscle arising from the anterior half of the arcus tendinous. Fibres pass backwards and medially superior to iliococcygeus interlacing with the apposite half at anococcygeal raphe.

Puborectalis – It arises from the posterior aspect of the body of the pubis and continues with that of the opposite side forming a sling at anorectal junction.

Puboprostaticus or pubovaginalis- It passes backwards from the posterior aspect of the body of the pubis and turns medially to fuse with a perineal body behind the prostate in males (puboprostaticus) and vagina in females (pubovaginalis).

The floor of Pelvis Nerves

From above – Perineal branches of 4th sacral nerve.

From below

  1. Inferior rectal nerve.
  2. Muscular branches of the perineal nerve.

The floor of the Pelvis Actions

  1. To support the pelvic viscera.
  2. To fix the perineal body.
  3. Maintenance of continence of bladder and rectum.
  4. Maintains increased intra-abdominal pressure.
  5. Acts as sphincter of rectum, vagina and urethra.
  6. Helps in childbirth during 2nd stage of labour

Pelvic Fascia

According to location, pelvic fascia can be of three types

1. Parietal pelvic fascia

This is located over the pelvic wall and floor and named accordingly,

  • Over pelvic wall
    • Obturator fascia – Covering the obturator intemus.
    • Piriform fascia – Covering the piriformis muscle
  • Over pelvic floor – Thin epimysium – This is also called superior fascia of the pelvic diaphragm.

2. Visceral pelvic fascia

This covers the viscera of the pelvis and is divided into two types.

  1. Over distensible viscera – It is thin to allow distension of viscera For Example., over the urinary bladder.
  2. Over nondistensible viscera – It is well-defined fascia, For Example. over the prostate (Prostatic fascia).

Pelvic Fascia Pelvic Fascia

3. Fascia between the pelvic floor and peritoneum

It can be loose or well-defined ligaments.

  1. Loose areolar tissue – It forms dead space to allow expansion of viscera like the urinary bladder, rectum and uterus (in females).
  2. Ligaments,
    • Condensation around vessels and nerves
      1. Lateral ligament of uterus (Lateral cervical ligament or Mackenrodt’s ligament) – It extends laterally from the cervical region of the uterus to the lateral pelvic wall. It carries uterine
        vessels.
      2. Lateral ligament of the bladder – It extends from the side of the bladder to the region of the arcus tendinous. It carries vesical vessels.
      3. Fascia of Waldeyer – It is the dense connective tissue between the back of the rectum and the front of the sacrum. It holds superior rectal vessels.
    • Independent ligaments
      1. Puboprostatic ligament (in males) or Pubovesical or bulbourethral ligament (in females) Puboprostatic ligament extends from the region of the body of the pubis and the anterior end of the arcus tendinous to the prostatic fascia.
      2. The prosodic ligament extends from the regions of the female urethra to the back of the body of the pubis.
      3. Round ligament of the uterus – It extends from the lateral angle of the uterus to the labium majus. During its course, it passes through the inguinal canal.
      4. Uterosacral alignment – It extends from the side of the cervix to the posterior wall of the pelvis. It raises a fold of the peritoneum called the rectouterine fold which forms the lateral wall of the rectouterine pouch.

Pelvic Peritoneum

Pelvic Peritoneum Parts

  1. Visceral layer – It covers the viscera of the pelvis and receives autonomic innervation.
  2. Parietal layer – It lines the wall of the pelvis and is supplied by the obturator nerve

Pelvic Peritoneum In Male

The Peritoneum is reflected from the junction of the upper 2/3rd with the lower l/3rd of the front of the rectum to the upper part of the posterior surface of the urinary bladder. Here it forms a peritoneal pouch called a rectovesical pouch.

After covering the superior surface of the urinary bladder, the peritoneum is reflected over the posterior surface of the anterior wall of the abdomen. This reflection limits the retropubic space of Retzius between the urinary bladder and the pubis.

Pelvic Peritoneum Pelvic Peritoneum In Male

Pelvic Peritoneum In Female

The peritoneum is reflected from the lower part of the front of the rectum to the posterior fornix of the vagina from where it continues over the posterosuperior and then the anteroinferior surface of the uterus.

Between the rectum and uterus, the reflection forms a rectouterine pouch (of Douglas). From the uterus, it is reflected over the superior surface of the urinary bladder where it forms a ureterovesical pouch between the uterus and the urinary bladder.

Pelvic Peritoneum Pelvic Peritoneum In Male

Pelvic Vessels

Veins Drain Into Internal Iliac Veins

Veins form plexuses about the viscera. These do not possess valves and intercommunicate with each other and with the internal vertebral venous plexus. These venous plexuses are named after the viscera as follows:

  1. Rectal venous plexus – about the rectum.
  2. Uterine venous plexus – to the uterus.
  3. Prostatic-vesical venous plexus – about both prostate and urinary bladder

Pelvic Vessels Arteries

The internal iliac artery splits into anterior and posterior divisions before providing named branches.

1. Anterior division

  1. Three parietal branches (all pass through foramen)
    • Inferior gluteal artery – It passes through the greater sciatic foramen.
    • Internal pudendal artery – It passes through the greater sciatic foramen.
    • Obturator artery – It passes through the obturator foramen
  2. Three visceral branches
    • Superior vesical artery
    • Inferior vesical artery
    • Both vesical arteries supply the urinary bladder
    • Middle rectal artery. It supplies the musculature of the rectum in males. In females, it is replaced by the uterine artery.

Pelvic Vessels Internal Iliac Artery Of Right Side

3. Posterior division

Only three parietal branches appear from it.

  1. Iliolumbar artery – It ascends to supply the lower part of the posterior abdominal wall.
  2. Superior gluteal artery – It enters the gluteal region by passing between the lumbosacral trunk and 1st sacral nerve (ventral ramus) and then through the greater sciatic foramen.
  3. Lateral sacral artery – It descends just lateral to pelvic sacral foramina over the roots of the sacral plexus.

Nerves Of The Pelvis

Obturator Nerve

Follows the medial border of the psoas to reach the obturator canal.

Nerves Of The Pelvis Obturator Nerve In Pelvis

Sacral Sympathetic Trunk

Consists of 4 sympathetic ganglia connected by nerve fibres. Descends about the pelvic sacral foramina.

Inferior Hypogastric (Pelvic) Plexus

Lies in front of the sacrum behind the rectum.

Nerve Of The Pelvis Sacral Sympathetic Trunk And Inferior Hypogastric Plexus

Sacral Plexus Formation

Following nerves from its roots,

  • Lumbosacral trunk (L4,5) – It is formed by the union of ventral rami of the 4th and 5th lumbar nerves. It descends in front of the ala of the sacrum to join the sacral plexus.
  • Ventral rami of upper 4 sacral nerves (S1, S2, S3, S4).

Sacral Plexus Branches

1. Branches from sacral nerves (roots)

  • From behind
    • Nerves to piriformis (S1,2)- Supply piriformis.
    • Perforating cutaneous nerves (S2,3)- Pierce sacrotuberous ligament to appear in the gluteal region.
    • The posterior cutaneous nerve of the thigh (S2,3)- Passes through the greater sciatic foramen.
  • From front
    • Pelvic parasympathetic (splanchnic) nerves (S2,3,4). Also called nervi erigentes. These join the inferior hypogastric plexus.
    • Pudendal nerve (S2,3,4) – Passes through the greater sciatic foramen. Crosses the apex of the sacrospinous ligament.
    • Perineal branch of S4 – Passes between iliococcygeus and iliococcygeus after supplying both.

Nerves Of The Pelvis Sacral Plexus (Branches From Roots)

2. Branches from anterior divisions

  1. Nerve to obturator internus (L5, S1,2)- Passes through the greater sciatic foramen to appear in the gluteal region. Then enters the lesser sciatic foramen to supply the obturator internus and superior gemellus.
  2. Nerve to quadratus femoris (L4,5, S1)- It passes through the greater sciatic foramen to supply the quadratus femoris and inferior gemellus.
  3. The tibial component of the sciatic nerve (L4,5, S1,2,3)- It unites with the common peroneal component to form the thickest nerve of the body (Sciatic nerve).

3. Branches from posterior divisions

  1. Superior gluteal nerve (L4,5, S1) – It passes through the greater sciatic foramen to enter the gluteal region where it supplies the gluteus medius, gluteus minimus and tensor fasciae latae.
  2. Inferior gluteal nerve (L25, S1,2)- It passes through the greater sciatic foramen to supply the gluteus maximus.
  3. Common peroneal component of the sciatic nerve (L4,5, S1,2)- It unites with the tibial component to form the sciatic nerve.

Nerves Of The Pelvis Sacral Plexus (Branches From Divisions)

Nerves of The Pelvis Coccygeal plexus

  • Roots – S4,5, Col
  • Supplies
    • Coccygeus, Levator ani
    • Sacrococcygeal joint
    • Skin over the coccyx

Urinary Bladder

Urinary Bladder Surface Features

It is a muscular vesicle for collection and expulsion of urine.

The shape of an empty bladder is tetrahedral

  • 4 Surfaces.
    • 1 Porterior (Base or fundus)
    • 1 Superior
    • 2 Inferolateral
  • 4 Borders.
    • 2 Lateral
    • 1 Anterior
    • 1 Posterior
  • Neck – It is the lowest conical part.
  • Apex – It is the anterior pointed end.

Urinary Bladder Surface And Borders Of Urinary Bladder

Urinary Bladder Interior

Trigone – A triangular smooth area in the posterior wall.

  • 3 Openings – 2 Ureteric orifices at the upper lateral angles of the trigone.
  • I internal urethral orifice at the lower angle of the trigone.
  • Interureteric crest – It is a transverse mucosal ridge between two ureteric orifices.
  • Uvula vesicae (Male) – Elevation in the posterior wall of the lower angle of trigone produced by a median lobe of the prostate gland.

Urinary Bladder Interior Of Urinary Bladder

Urinary Bladder Relations

  • Peritoneal relations – Peritoneum covers the superior surface
  • Adjacent relations
    • Superior -Coils of intestine
    • Infero-lateral – Obturator intemus and levator ani.
    • Anterior-Cave of Retzius, Fat.
    • Posterior – Male – Seminal vesicle
      • Vas deferens
      • Rectum
  • Female – Vagina and cervix

Urinary Bladder Relations Of Urinary Bladder Male And Female

Urinary Bladder Capacity

120 – 320 ml (in adults).

280 ml of urine → Refelex micturition

More than 500 ml of urine —> Pain

Urinary Bladder Ligaments

  • Median umbilical ligament – Remnant of urachus derived from allantois Lateral ligament – It extends from the side of the urinary bladder to the region of the arcus tendinous. It carries vesical vessels.
  • Pubovesical ligament – It is a fibromuscular band on each side extending from the bladder neck to the inferior aspect of the pubic bone.
  • It is present in both sexes. It is different from the pubovesical ligament of females which is at a lower level and often named pubourethral ligament.

Urinary Bladder Arteries

Superior and inferior vesical arteries. These appear from the internal iliac artery to reach the bladder through the lateral ligament. Pubic branch of an inferior epigastric artery – Supplies the lower part of the bladder.

Urinary Bladder Veins

  • Male – Prostatic vesical venous plexus – It is located at the junction of the bladder neck and base of the prostate gland. This plexus drains into an internal iliac vein.
  • Female – Vesical plexus – It is located at the inferolateral surface of the bladder and drains into an internal iliac vein.

Urinary Bladder Lymphatics

These drain into internal and external iliac lymph nodes.

Urinary Bladder Nerves

  • Efferent
    • Sympathetic – T12-L2
    • Parasympathetic – S2,3,4
  • Afferent – Mainly run through parasympathetic fibres

Urinary Bladder Nervous Control On Micturition

Dissection Steps Of Urinary Bladder And Prostate

Define the peritoneal reflection of the urinary bladder and study the bladder in situ. Identify the rectovesical pouch in males and the rectouterine and uterovesical pouch in females.

  • Remove the peritoneum from the superior surface of the bladder. Make a median section through the pubis symphysis in front and pass through the sacrum and coccyx behind.
  • This will divide the bladder and rectum in males and the bladder, uterus and rectum in females. Identify and study the posterior relations of the bladder in both sexes.
  • In male cadavers, the bladder along with the prostate by blunt dissection, separates it from the surrounding structures and perineum. Examine the gross features of the bladder.
  • To study the interior of the bladder open the bladder by incisions passing along the junction of superior and inferolateral surfaces on both sides and identify the trigone of the bladder, openings of the ureters and the internal urethral meatus.
  • Identify the prostate at the neck of the bladder. Clean the fascia around it and study its gross features.
  • Open the prostate by incising it through the prostatic urethra and identify the lobes of the prostate, uvula vesicae, urethral crest and prostatic sinus. Also identify the prostatic utricle, colliculus seminalis and openings of the ejaculatory ducts.

Urinary Bladder Micturition

The reflex phenomenon at the S2,3,4 level

280 ml of urine —> Afferent (nervi erigentes) —> S2,3,4 segments —> Efferent —> (1) Parasympathetic nerve —> Contraction of bladder and relaxation of sphincter vesicae. (2) Pudendal nerve —> Relaxation of sphincter urethrae —> Micturition.

Prostate Gland

Prostate Gland Definition

Fibro – a muscular and glandular organ in males.

Shape: Pyramidal, base-up, apex down.

Prostate Gland Coronal Sectional View Of Prostate Gland

Prostate Gland Measurements – Anteroposterior – 2 cm, Vertical – 3 cm, Width – 4 cm

Prostate Gland Location: Between the neck of the urinary bladder and the urogenital diaphragm

Prostate Gland Relations

  • The base continues with the neck of the bladder
  • Inferior – urogenital diaphragm
  • Anterior – Cave of Retzius
  • Puboprostatic ligament
  • Lateral – Levator ani
  • Posterior – Fasica of Denonvillier, rectum

Prostate Gland Sagittal Sectional View Of Prostate Gland

Prostate Gland Capsules

True – covering the surface of the gland

False – (Prostatic fascia) – It is external to the true capsule. In between two capsules is the venous plexus

Prostate Gland Lobes Of Prostate Gland

Prostate Gland Lobes

5 in numbers

1. Anterior – Anterior to prostatic urethra

1. Median – Between urethra and ejaculatory duct

1. Porterior- Behind the ejaculatory duct

2. Lateral – Lateral to all the above on each side. The right and left halves fail to fuse completely posteriorly forming a posterior midline groove.

Interior Of The Gland

Interior Of The Gland Zones

  • Inner zone
    • Zone of mucosal glands- Involved in benign prostatic hyperplasia.
    • Zone of submucosal glands
  • Outer zone (Zone of main glands)- Involved in malignancy.

Prostate Gland Zones Of Prostate Gland

Ejaculatory duct. It lies on each side of the midline posteriorly.

Interior Of The Gland Prostatic urethra

  • 3cm in length
  • The widest part of the urethra
  • Urethral crest- posterior, midline, linear vertical elevation.
  • Prostatic sinus – groove on each side of the urethral crest.
  • Verumontanum (Colliculus seminalis) – Rounded elevation in the middle of the urethral crest
  • Utriculus masculinum (‘Prostatic utricle) – A transverse depression in the verumontanum.

Prostate Gland Prostatic Urethra Cross Sectional And Median Sagittal Sectional Views

Prostate Gland Arteries

Inferior vesical and middle rectal arteries.

Prostate Gland Veins

Open into prostatic venous plexus which itself drains into internal iliac veins.

Prostate Gland Nerve

Derived from pelvic plexus (inferior hypogastric plexus)

Prostate Gland Lymphatics

Drain into internal iliac lymph nodes.

Prostate Gland Applied

P/R (Per-rectal) examination- The index finger is introduced into the anal canal and the prostate is palpated through the anterior wall of the rectum.

Normally a midline groove is present and the rectum moves over the prostate freely. In cases of cancer of the prostate, no midline groove is felt and the rectal wall is fixed prostate.

Rectum And Anal Canal

Rectum And Anal Canal Situation: Rectum – Posterior pelvic organ

Anal canal – Posterior perineal organ

Rectum And Anal Canal Extent: Third sacral segment to the anus

Rectum And Anal Canal Measurements

Total length – 15 cm

Rectum

12 cm – 7 cm – over sacrum and coccyx

5 cm – over anococcygeal raphe

Anal canal – 3cm

Rectum And Anal Canal Extent Of Rectum And Anal Canal

Rectum And Anal Canal Curvatures

Rectum And Anal Canal Lateral Curvatures Of Rectum

Rectum And Anal Canal Rectum

  • Antero-posterior curvature (Sacral flexure). It corresponds with the anterior curvature of the sacrum
  • Side-to-side curvature
    • Right- Two curvatures (upper and lower), convex to right.
    • Left- One curvature (middle), convex to left.
  • Junctions of curvatures – These are responsible for folds towards the lumen called transverse folds or rectal valves of Houston or plicae transversals.

Rectum And Anal Proctoscopic Appearance Of Rectum

Anorectal junction

90° Backward bend of the anal canal at its junction with the rectum, produced by puborectalis sling.

Subdivisions

  • Rectum
    • Upper part
    • Lower part (Rectal ampulla)
  • Anal canal
    • Upper 2/3 – Derived from the cloaca.
    • Lower 1/3 – Derived from the anal pit

Rectum And Anal Canal Relations

Relations of Rectum

Peritoneal relations

  • Upper 1/3rd – Anterior and lateral parts covered with peritoneum.
  • Middle 1/3rd – The anterior part is only covered with the peritoneum.
  • Lower 1/3rd- No peritoneum related

Rectum And Anal Canal Rectum And Anal Canal In Relation To Sacrum And Coccyx

Relations of Rectum Adjacent relations

Rectum And Anal Canal Side View Of Rectum And Anal Canal Showing Relations In Male

Rectum And Anal Canal Side View Of Rectum And Anal Canal Showing Relations In Female

Posterior relations

  • Midline
    • Sacrum and coccyx
    • Anococcygeal raphe
    • Medium sacral artery and coccygeal body
    • Ganglion impar
    • Branches of superior rectal artery
    • Fascia of Waldeyer
  • Bilateral
    • Muscles – Piriformis, coccygeus
    • Sympathetic trunk
    • Lateral sacral artery
    • Ventral rami of sacral nerves
    • Pelvic plexus
    • Lymph nodes

Anterior relations

It is different in male and female

  • Male
    • Rectovesical pouch with coils of intestine.
    • Base of the bladder, seminal vesicle, vas deferens, ureter
    • Prostate, fascia of Denonvillier.
  • Females
    • Rectouterine pouch of Douglas
    • Vagina

Rectum And Anal Canal Peritoneal Relations Of Rectum

Relations of Anal Canal

Anterior relations

  • Male
    • Perineal body
    • Membranous urethra
    • Bulb of peni
  • Female
    • Vagina
    • Perineal body
  • Posterior relations
    • Anoccygeal body or ligament
    • Tip of coccyx
  • Lateral relation
    • Ischiorectal fossa

Rectum And Anal Canal Posterior Relations Of Rectum

Rectum and Anal Canal Structure

Rectum And Anal Canal Structure

Rectum and Anal Canal Stability

Rectum And Anal Canal Structural Continuity Between Rectum And Anal Canal

Rectum. The following structures keep the rectum in place:

  1. Fascia of Waldeyer – Between sacrum and rectum
  2. Lateral ligament of rectum-It extends from the rectum to the posterolateral pelvic wall. It holds middle rectal vessels
  3. Pelvic peritoneum – It is reflected from the front of the rectum to the posterior fornix in females and the upper base of the urinary bladder in males and thus forms a rectouterine pouch in females and a rectovesical pouch in males respectively.
  4. Pelvic diaphragm

Anal canal. It is stabilized by the perineal body and anococcygeal body.

Rectum And Anal Canal External Anal Sphincters

Rectum and Anal Canal Arteries

  • Superior rectal artery – It supplies mucosa of the rectum and the upper 2/3rd of the anal canal
  • Median sacral artery – It supplies the posterior aspect of the rectum
  • Middle rectal artery – It supplies muscles of the rectum.
  • Inferior rectal artery – It supplies muscles and lower l/3rd of the mucosa of the anal canal.

Rectum and Anal Canal Veins

  • Superior rectal vein – It drains into the inferior mesenteric vein
  • Middle rectal vein – It drains into the internal iliac vein
  • Inferior rectal vein – It drains into internal pudendal vein

Rectum and Anal Canal Lymphatics

  • Rectum and upper 2/3rd of anal canal
    • Preaortic lymph nodes
    • Internal iliac lymph nodes
    • Sacral lymph nodes

Rectum And Anal Canal Arterial Supply Of Rectum

Lower l/3rd of the anal canal – Medial horizontal chain of superficial inguinal lymph nodes

Rectum and Anal Canal Nerves

Rectum mucosa and internal sphincter of upper 2/3rd of anal canal receive

Autonomic supply —> Sympathetic – T12 – L2 —> Parasympathetic – S2,3,4

Mucosa ofanal canal (lower 1/3rd) – Inferior rectal nerve

External anal sphincter – Subcutaneous —> Inferior rectal nerve (S3,4 ). It is a branch of the pudendal nerve.

Superficial —> Perineal branch of S4

Deep —> Inferior rectal nerve

Pelvic Part Of The Ureter

Length: 15 cm

Pelvic Part Of Ureter Course Of Pelvic Ureter In Male

Pelvic Part Of Ureter Course Of Pelvic Ureter In Female

Pelvic Part Of Ureter Course

It first runs downwards, backwards and laterally and then medially and forward. During its course, it crosses the following structures from above downwards ;

  1. Umbilical artery (superior vesical artery)
  2. Obturator nerve and vessels
  3. Inferior vesical artery
  4. Middle rectal artery (Uterine artery in females)

Intra-vesical part of the ureter is located in the wall of the urinary bladder. Its terminal part is crossed by the vas deferens (in males) or uterine artery (in females).

Pelvic Part Of Ureter Relations Of Pelvic Ureter With Vas Deferens

Pelvic Part Of Ureter Relations Of Pelvic Ureter With Uterine Artery

Seminal Vesicle And Vas Deferens

Seminal Vesicle

  • Form – Sacculated coiled tube.
  • Location – On the posterior surface of the urinary bladder
  • Extent – From terminal ureter to prostate
  • Length
    • 5 cm, when coiled
    • 10-15 cm when uncoiled.
  • Diameter – 3-4 mm

Vas Deferens

Vas Deferens Course

Enters the abdominal cavity through a deep inguinal ring. It then descends to enter the pelvis where it crosses the following structures from above downwards:

  1. Medial umbilical ligament (Obliterated umbilical artery)
  2. Obturator nerve and vessels
  3. Inferior vesical artery
  4. Ureter

Pelvic Part Of Posterior View Of Seminal Vesicle And Vas Deferens

Vas Deferens Terminal Part

It is applied to the posterior aspect of the urinary bladder, medial to seminal vesicle. Here it is dilated from the ampulla of the vas.

Formation Of Ejaculatory Duct

Vas deferens pierces the posterior surface of the prostate gland near its upper border and joins the duct of the seminal vesicle to form the ejaculatory duct. It is 2 cm in length. It opens in the posterior wall of the prostatic urethra.

Vascular Supply

Both seminal vesicles and vas deferens are supplied by vesical arteries and drained by vesicoprostatic venous plexus.

Uterus

The uterus is a muscular organ and is part of the female genital tract. It provides a site for the attachment of the fertilized ovum, responsible for its nutrition, growth and protection. At term, its forceful contraction initiates the expulsion of the foetus.

Uterus Location Of Uterus

Uterus Weight – 30-40 gm

Uterus Size Height – 7.5 cm (Body- 5 cm, Cervix- 2.5 cm)

Width – 5 cm

Thickness – 2.5 cm

Uterus Peritoneal Relations Of Uterus Front And Side Views

Uterus Parts

Body – upper 2/3rd expanded part

Cervix – lower l/3rd cylindrical part

  • Anteversion- Forward bending of the uterus concerning the vagina (about 90°).
  • Anteflexion- Forward bending of the uterus concerning the cervix (about 120°).
  • Long axis – Long axis of the uterus forms an angle of 90 degrees with the long axis of the vagina. This angle opens forward. Roughly, the long axis of the uterus corresponds with the long axis of the pelvic inlet and the long axis of the vagina to the axis of the pelvic cavity and the pelvic outlet.

Uterus Parts Of Uterus F-Fundus, B-Body, C-Cervix

Fundus: Free upper end of the uterus above the entry points of the uterine tubes. It is dome-shaped, directed anteriorly and covered with peritoneum.

Body Of Uterus

1. Surfaces

  • Anterior or vesical surface
    • It is flat and related to the urinary bladder. It is covered with peritoneum and forms the posterior wall of the vesicouterine pouch.
  • Posterior or intestinal surface
    • It is convex and related to the terminal coils of the ileum and sigmoid colon. It forms the anterior wall of the rectouterine pouch and is covered with the peritoneum.

2. Borders

Lateral borders – There are two lateral borders, right and left. Each border is rounded and convex and it provides attachment to the broad ligament of the uterus which connects it to the lateral wall of the pelvis.

The fallopian tube opens in the uterus at its upper end and the uterine artery ascends along it.

3. Cavity

In sagittal and transverse sections it is merely in the form of a slit but in the coronal section, it is triangular with an apex towards the introitus where the uterine cavity becomes continuous with the cervical canal.

Uterus Lumen Of Uterus Transverse, Sagittal And Coronal Sections

  1. Transverse Section
  2. Sagittal Section
  3. Coronal Section

Cervix Of Uterus

Lower 1/3rd, 2.5 cm, cylindrical, less mobile part of the uterus. In the middle, it is a little wider. The lower part of the cervix projects into the upper part of the anterior wall of the vagina.

Cervix Of Uterus Subdivisions

1. Supravaginal part of the cervix

It is related

  • Anteriorly – to the bladder
  • Posteriorly – to the rectouterine pouch containing coils of intestine
  • Sides – to the ureter and uterine artery embedded in the parametrium of the broad ligament

Uterus Bending Of Uterus

2. Vaginal part of the cervix

It projects into the anterior wall of the vagina. The spaces between the cervix and vaginal walls are called the vaginal fornices. The cervical canal opens into the vagina through the external os.

  • In the transverse section, it is circular in outline in nulliparous and becomes transverse (having anterior and posterior lips) in multiparous.
  • The cervical canal extends from the external os to the internal os and thus communicates above with the uterine cavity and below with the vaginal cavity. Along its long axis, it is fusiform in shape.
  • The anterior and posterior walls of the cervical canal show interlocking mucosal folds which resemble branches of a tree (arbour vitae uteri)

Ligaments Of Uterus

1. Peritoneal ligaments

  • Uterovesical fold (anterior)
  • Rectovaginal fold (posterior)
  • Broad ligaments (right and left)-Mesosalpinx and mesometrium are the parts of the broad ligament above and below the ligament of the ovary respectively.

Broad ligament contains,

  • Uterine tube
  • Round ligament of uterus
  • Ligament of ovary
  • Uterine vessels near the attachment to the uterus
  • Ovarian vessels in the infundibulopelvic (suspensory) ligament
  • Uterovaginal and ovarian nerve plexuses
  • Epoophoron
  • Paroophoron
  • Lymph nodes and lymph vessels
  • Dense connective tissue (parametrium) is present on the sides of the uterus.

Uterus Round Ligament Of Uterus

Vestigial remnants present in the broad ligament

Epoophoron

It is a remnant of the cranial part of the mesonephric tubule. It is in the form of 10 -15 parallel tubules in the lateral part of the mesosalpinx.

Paroophoron

It is a remnant of the caudal part of mesonephric tubules. It is in the form of a short rudimentary tubule located in the broad ligament between the ovary and the uterus.

Uterus Lateral Relations Of Uterus

Duct of Gartner

When the duct of the epoophoron becomes much larger is called the duct of Gartner. It can be traced along the uterine tube.

Along the lateral margin of the uterus up to the level of internal os then through the cervix to the lateral wall of the vagina to end in the anterior margin of the hymen.

It represents the mesonephric duct. It may present in the form of a cyst in the anterior or lateral wall of the vagina.

Vesicular appendix

These are derived from the cranial end of the paramesonephric duct in the form of a pedunculated cyst attached to the fimbriated end of the uterine tube. These are also called paramesonephric appendices.

Uterus Ligaments Supporting Uterus

2. Fibromuscular ligaments

  • Round ligaments of the uterus
  • Transfer – 7 cervical ligaments
  • Uterosacral ligaments

Arterial supply

  • Uterine arteries
  • Ovarian arteries

Apart from the uterus the uterine artery also gives branches to

  • Vagina
  • Medial 2/3rd of uterine tube
  • Ovary
  • Ureter
  • Structures present in the broad ligament

Uterus Arterial Supply Of Uterus

Venous drainage

The veins form the plexus along the lateral border of the uterus and drain into the internal iliac vein through uterine, ovarian and vaginal veins.

Lymphatic drainage

Lymphatics of the uterus begin as three intercommunicating networks- endometrial, myometrial, and subperitoneal. These drain into lymph nodes on the side of the uterus. Lymphatic drainage is described to be in three groups.

  1. Upper lymphatics (from the fundus and upper part of the body) – pass to aortic nodes. Some of them pass along the round ligament of the uterus to the superficial inguinal lymph nodes.
  2. Middle lymphatics (from the lower part of the body) – Pass to external iliac nodes.
  3. Lower lymphatics (from the cervix) – Pass to the external iliac, internal iliac and sacral nodes.

Fibromuscular ligaments Nerve supply

The uterus receives both sympathetic and parasympathetic innervation through inferior hypogastric and ovarian nerve plexuses.

Sympathetic (T12, L1)- Produces uterine contraction and vasoconstriction. Also carries pain sensation from the body of the uterus.

Parasympathetic (S2,3,4)- Produces uterine inhibition and vasodilatation. Also carries pain sensation from the cervix.

However, these actions are modified by hormones which have strong action on the genital tract.

Age and reproductive changes

During fetal life – The cervix is larger than the body and the body projects a little above the pelvic brim.

At puberty– Uterus enlarges and descends in the pelvis. Arbor vitae uteri appear in the cervix.

During menstruation – Little enlarged, more vascular and external os swollen.

During pregnancy– Enlarge (due to both hypertrophy and hyperplasia), with advancing pregnancy it becomes thinner. After parturition it involutes.

In old age -It becomes atrophic and dense in texture. The external os obliterates and the lips disappear.

Supports Of Uterus

Primary supports

  1. Muscular
    • Pelvic diaphragm
    • Perineal body
    • Urogenital diaphragm
  2. Fibromuscular or mechanical
    • Uterine axis
    • Pubocervical ligament
    • Transverse cervical ligament
    • Uterosacral ligament
    • Round ligament of uterus

Secondary supports

These are formed by peritoneal ligaments and are of doubtful value.

  • Broad ligaments
  • Uterovesical fold of peritoneum
  • Rectovaginal fold of peritoneum

Role Of Individual Supports

Pelvic diaphragm

It supports the pelvic viscera and also acts against the force due to the rise of intra-abdominal pressure. Some fibres of the pubococcygeus part of the levator ani form a supporting sling and a sphincter for the vagina (indirectly for the uterus and urinary bladder).

During parturition sometimes the pubococcygeus part is tom and it results in loss of support to the vagina which along with the uterus sinks into the vestibule (Prolapse of uterus).

Perineal Body

It is the fibromuscular node to which nine muscles are attached. It acts as an anchor for the pelvic diaphragm and thus maintains the integrity of the pelvic floor.

The efficacy of levator ani as a support is lost when the perineal body becomes unstable due to a tear of the perineal muscle.

Urogenital Diaphragm

The sphincter urethrae form the external sphincter of the urethra. Some of its fibres also get attached to i the wall of the vagina and provide support to it.

Pubocervical Ligaments

These are derived from the pelvic fascia and correspond to the medial and lateral puboprostatic ligaments found in males. Thus they extend from the cervix to the posterior part of the pubis.

Transverse cervical ligaments (of Mackenrodt)

These are fan-shaped condensations of pelvic fascia on each side of the cervix above the levator ani and around the uterine vessels.

They extend from the lateral aspect of the cervix and upper part of the vagina to the lateral pelvic wall. They form a hammock which supports the uterus.

These ligaments are known by many other names – For Example., Lateral cervical ligaments; Paracervical ligaments; Cardinal ligaments; Retinacula uteri; and Sustentaculum of Bonny.

Uterine Axis

The normal position of the uterus is anteverted which is maintained by the uterosacral and round ligaments. This position itself prevents the sagging of the uterus into the vagina.

Increased abdominal pressure further increases its anteverted position by pushing the uterus against the urinary bladder and the pubic symphysis.

Uterosacral ligaments

These are a condensation of pelvic fascia enclosed within the recto-uterine folds (forming the lateral boundaries of the recto-uterine pouch). They connect the cervix to the 2nd and 3rd sacral vertebrae.

These ligaments counter the forward pull of the round ligament on the cervix. Round ligaments and the uterosacral ligaments form a couple that maintains the uterine axis.

Round Ligaments Of Uterus

These are 10-12 cm long, flat fibromuscular bands which lie between two layers of the broad ligament located anterior to the uterine tube.

  • Course- Each ligament begins at the lateral angle of the uterus, runs forward and laterally, passes through the deep inguinal ring, traverses the inguinal canal and merges with the areolar tissue of the labium majus after breaking up into fine filaments.
  • The round ligament keeps the fundus pulled forward and maintains the angle of anteversion against the backward pull of the uterosacral ligament.
  • Canal of Nuck – In the inguinal canal the round ligament is accompanied by a process of peritoneum during foetal life. If it persists after birth, it is known in females as the canal of Nuck.

Uterus Applied Anatomy

  • Retroversion of the uterus – When the uterus comes to lie in a straight line with the vagina.
  • Prolapse of the uterus – When the uterus sags into the vagina due to weakening of support of the uterus.
  • Intrauterine contraceptive device – Insertion of a foreign body into the body of the uterus prevents implantation.
  • Caesarian section – When birth through the vagina is difficult then it is performed by cutting the anterior abdominal wall and the uterus (Roman emperor Julius Caesar was delivered by. this method).
  • Hysterectomy – Surgical removal of the uterus in various conditions.
  • Hysteropexy – Surgical fixation of the unduly mobile uterus.
  • Hysterosalpingography – radiological visualization of the uterus and uterine tube after filling them with radiopaque dye.

Fallopian Tube

It is also called the uterine tube or oviduct. It allows passage of ova from the ovary to the uterus and spermatozoa from the uterus towards the ovary.

Fertilization usually takes place in the lateral 1/3rd of the tube. It is 10 cm long. Its lateral ostium opens into the abdominal cavity.

Fallopian Tube Location Of Fallopian Tube

Fallopian Tube Subdivisions

  • Infundibulum. The pole of the ovary isItscalledlateraltheendovarianis fimbriated. fimbria. One fimbria being longer and attached to the tubal pole of the ovary is called ovarian fimbria.
  • Ampulla – Medial to infundibulum and arches over the upper pole of the ovary. It is thin-walled, tortuous and dilated. It forms the lateral 2/3rd of the uterine tube.
  • Isthmus – Medial to ampulla and forms medial l/3rd of the tube. It is narrow, rounded and cord-like.
  • Interstitial (uterine or intramural) – It lies within the wall of the uterus and opens at the upper angle of the uterine cavity through a narrow uterine ostium (1mm as against 3 mm abdominal ostium)

Fallopian Tube Parts Of Fallopian Tube

Fallopian Lumen Of Fallopian Tube

Fallopian Tube Course And Relations

  • The uterine tube lies in the upper free margin of the broad ligament of the uterus.
  • The part of the broad ligament between the attachment of the mesovarium and the uterine tube is called mesosalpinx. It contains the terminations of the uterine and ovarian vessels and the epoophoron.
  • Ampulla arches over the ovary and is related to its anterior and posterior borders.
  • The infundibulum projects beyond the free margin of the broad ligament.

Fallopian Tube Relation Of Fallopian Tube With Ovary

Fallopian Tube Arteries

  • Uterine artery – supplies the medial two-thirds.
  • Ovarian artery – supplies the lateral one-third.

Fallopian Tube Arterial Supply Of Fallopian Tube

Veins run parallel with the arteries and drain into the pampiniform plexus of the ovary and also into the uterine veins.

Fallopian Tube Lymphatic Drainage

Most of the tubal lymphatics join the lymphatics from the ovary and drain with them into the lateral aortic and pre-aortic nodes. Those from the isthmus accompany the round ligament of the uterus and then drain into the superficial inguinal lymph nodes.

Fallopian Tube Nerve supply

It is supplied by both sympathetic and parasympathetic nerves running along the ovarian and uterine arteries.

Sympathetic nerves – are derived from the hypogastric plexuses. Contains both visceral afferent and efferent. Efferents are vasomotor and to some extent stimulate peristalsis.

Parasympathetic nerves – are derived from the vagus (to the lateral half) and splanchnic nerves (to the medial half). Inhibit peristalsis and produce vasodilatation.

Fallopian Tube Applied

  • Salpingitis – Inflammation of the fallopian tube.
  • Sterility – Inability to produce offspring.
  • Tubal insufflation – Transuterine insufflation of carbon dioxide to test the patency of the fallopian tube.
  • Hysterosalpingography – X-ray study of the uterus and uterine tube after injecting radiopaque material into those organs.
  • Tubal pregnancy – An ectopic pregnancy where implantation has taken place in the uterine tube.
  • Tubectomy and tubal ligation – Surgical methods for female contraception.

Steps Of Dissection Of Female Reproductive System

Clean and identify the female genital organs in situ. Trace the peritoneal reflections in the pelvis and identify the rectouterine pouch, ureterovesical pouch, broad ligament and transverse cervical ligament.

  • Identify structures about the broad ligamentnamely fallopian tubes, ovaries, ligament of the ovary, round ligament of the uterus and uterine artery.
  • Separate the broad ligament from the sides of the pelvis. Pull the uterus towards the pelvic cavity and separate the sides and back of the cervix.
  • Separate the vagina from the perineum and remove the uterus along with the fallopian tube and ovaries after cutting the broad ligament. Study the uterus, fallopian tubes and ovary mass.

Ovaries

These are the female gonads and produce female gametes.

Ovaries Location: Each ovary lies in the ovarian fossa.

Boundaries of the ovarian fossa

  • Anterior- obliterated umbilical artery
  • Posteriorly – ureter and internal iliac artery

Ovaries Location Of Ovary (Ovary Fossa)

Axis of the ovary is.

Vertical in nulliparous and hence has upper and lower poles.

Horizontal in multiparous and therefore has lateral and medial poles

Size: Length: 3 cm. Width: 1.5 cm, Thickness: l cm

Ovaries Borders

  • Anterior – mesovarian border
  • Posterior – free border

Ovaries Mesovarium

Ovaries Relations

1. Peritoneum – covers it entirely except at its anterior border where two layers are reflected as mesovarium on the posterior surface of the broad ligament.

  • Mesovarium– short fold of peritoneum connecting the anterior border of the ovary with the posterior layer of the broad ligament. It transmits nerves and vessels to and from the ovary.
  • Suspensory ligament of ovary (infundibulopelvic ligament) – the lateral part of the broad ligament of the uterus extending from the infundibulum of the fallopian tube and upper pole of the ovary to the external iliac vessels. It contains ovarian nerves and vessels.

Ovaries Ligaments Attached To Ovary

2. Visceral relations

  • Upper or tubal pole – uterine tube and external iliac vessels; appendix on the right side.
  • Lower or uterine pole – pelvic floor, ligament of the ovary.
  • Anterior or mesovarian border – uterine tube, obliterated umbilical artery; forms hilus of ovary.
  • Posterior or free border – uterine tube and ureter.
  • Lateral surface – ovarian fossa lined by parietal peritoneum
  • Medial surface – uterine tube.

Ovarian bursa peritoneal recess between mesosalpinx and medial surface of ovary.

Ovaries Relation Of Ovary With Fallopian Tube

Ovaries Relation Of Ovary With Broad Ligament Of Uterus

Ovaries Arterial supply

  • Ovarian artery – A branch of the abdominal aorta, descending over the posterior abdominal wall and entering the suspensory ligament of the ovary. It sends branches to the ovary through the mesovarium.
  • Uterine artery – gives some branches which reach the ovary through the mesovarium.

Ovaries Arterial Supply Of Ovary

Ovaries Venous drainage

Veins emerge at the hilus and form a pampiniform plexus around the ovarian artery. Near the pelvic inlet, the plexus transforms into a single ovarian vein which ascends on the posterior abdominal wall.

On the right side, it opens into the inferior vena cava and on the left into the left renal vein.

Ovaries Lymphatic drainage

Lymphatics from the ovary freely communicate with those from the fallopian tube and fundus of the uterus. These ascend along the ovarian vessels and terminate in lateral aortic lymph nodes.

Ovaries Nerve supply

It is derived from the ovarian plexus which follows the ovarian vessels. It contains both sympathetic (T10–11) – afferent for pain and vasomotor and parasympathetic (S2,3,4 ) – vasodilator.

Ovaries Applied

  • Prolapse – Downward displacement of the uterus. The cervix sometimes protrudes through the vaginal orifice.
  • Endometriosis – Ectopic endometrium located in various sites throughout the pelvis or the anterior abdominal wall.

Vagina

It is a fibromuscular canal forming the female copulatory organ extending from the vulva to the uterus. It is located behind the bladder and in front of the rectum and anal canal. In an erect posture, it is directed upwards and backwards.

In the supine position, it makes an angle of 75 degrees with the horizontal plane. Its anterior wall is 8 cm and posterior wall is 10 cm long. The diameter of the upper end (vault) is 5 cm and that of the lower end is 2.5 cm only.

Uterus Location Of Uterus

However, it is very distensible and allows passage of the foetal head during parturition. The cervix of the uterus protrudes in its upper end and makes it circular in outline.

  • Below the cervix, the anterior and posterior walls are in contact with each other. In the virgin, the lower end of the vagina is partially closed by an annular fold of mucous membrane called the hymen.
  • In married women, the hymen is represented as rounded elevations around the vaginal orifice, the carunculae hymenale.

Vagina Lumen Of Vagin

  1. Upper 1/3rd
  2. Middle 1/3rd
  3. Lower 1/3rd
  4. Vaginal Orifice

The interior of the upper end of the vagina is in the form of a circular groove that surrounds the protruding cervix and this groove gradually becomes deeper from before backwards.

This groove is divided into 4 parts called the vaginal fornices. The anterior fornix lies in front of the cervix and is the shallowest. The posterior fornix lies behind and is deepest and the lateral fomices lie on either side of the cervix.

Vagina Hymen Of Vagina

Vagina Relations

  • Anterior wall – Bladder and urethra
  • Posterior wall – Recto-uterine pouch, loose connective tissue and perineal body separate it from the rectum and anal canal.
  • Lateral walls – Transverse cervical ligament, pubococcygeus part of the levator ani, urogenital diaphragm and below it to the bulb of vestibule, bulbospongiosus and greater vestibular gland.

Vagina Vestibular Gland

Vagina Arterial supply

Being a very vascular organ, it is supplied by

  • Vaginal branch of the internal iliac artery
  • The cervicovaginal branch of the uterine artery
  • Branches from middle rectal and internal pudendal arteries
  • Vaginal azygos arteries – (anterior and posterior) arising from anastomoses of the above arteries.

Vagina Artery Supply

Venous drainage

The rich vaginal venous plexus joins to form a vaginal vein which accompanies the vaginal artery and drains into the internal iliac vein.

Venous Lymphatic drainage

  • From upper 1/3rd to external iliac lymph nodes
  • From the middle 1/3rd to the internal iliac lymph nodes.
  • From lower l/3rd to the medial group of superficial inguinal lymph nodes.

Venous Nerve supply

  • Lower 1/3rd is sensitive to pain and is supplied by internal pudendal, inferior rectal and posterior labial branches of the perineal nerve.
  • The upper 2/3rd is insensitive to pain and is supplied by sympathetic and parasympathetic nerves derived from inferior hypogastric and uterovaginal plexuses. The fibres which accompany the vaginal artery are known as vaginal nerves.

Venous Applied Anatomy

  • Vaginitis – Inflammation of vagina.
  • Fistulae (abnormal tubular communication)- due to congenital malformation, injury or abscess. It may be between different organs like,
    • vesicovaginal (between vagina and urinary bladder)
    • uterovaginal (between uterus and vagina)
    • rectovaginal (between rectum and vagina)
  • Colpotomy – Incision into the wall of the vagina.
  • Colporrhapy – Repair of vaginal wall.

Bones of the Abdomen Notes

by

Introduction To Abdomen

Abdomen Definition

Part of the trunk below the diaphragm

Abdomen Importance

Abdomen is important to,

  • Physicians
  • Gynaecologists and obstetricians
  • Surgeons

Introduction To Abdomen Subdivisions Of Abdomen Side View

Abdomen Subdivisions

  1. Abdomen proper – Upper (Above the iliac crest) Lower (False pelvis)
  2. Pelvis – True pelvis (Between pelvic inlet and pelvic diaphragm) and Perineum (Below pelvic diaphragm)

Introduction To Abdomen Subdivisions Of Abdomen Front View

Abdomen Bones

  • Lower ribs and costal cartilage
  • Lumbar vertebrae
  • Sacrum and coccyx
  • Hip bones

Introduction To Abdomen Planes Of Abdomen

Abdomen Landmarks

  • Infrastemal/subcostal angle (Anteriorly, between constal margins of two sides).
  • Umbilicus,
  • Costal margin
  • Iliac crest (Superior border of ilium).
  • Tubercle of iliac crest (Along outer lip, 5 cm from anterior superior iliac spine).
  • Anterior superior iliac spine (Anterior extremity of the iliac crest).
  • Inguinal ligament (Between anterior superior iliac spine and pubic tubercle).
  • Pubic tubercle (Lateral end of pubic crest).
  • Pubic crest (Superior border of the body of pubis).
  • Pubic symphysis (In the midline, between the bodies of the pubis).
  • Position of the linea alba (Midline groove between the xiphoid process and pubic symphysis).
  • Linea semilunaris (Curved groove between the tip of 9th costal cartilage and pubic tubercle).

Introduction To Abdomen Surfaces Features Of Anterior Abdominal Wall

Divisions Of Abdomen Into Nine Regions

Two vertical (right and left lateral) and two horizontal (transpyloric and transtubercular) planes divide the abdomen into 9 regions.

A lateral plane passes through the mid-inguinal point (a point on the inguinal ligament between the anterior superior iliac plane and public symphysis).

The transpyloric plane is horizontal midway between the suprasternal notch and public symphysis. The transtunercular plane is a horizontal plane through tubercles of the iliac crest of two sides.

Regions from above downwards.

  • 3 unpaired – Epigastric, Umbilical, Hypochondriac/public
  • 3 Paired – Hypochondriac, Lateral/Lumbar, Inguinal /Iliac

Introduction To Abdomen Nine Regions Of Abdomen

Divisions of the abdomen into four quadrants: by median and supracristal planes. The supracristal plane is a horizontal plane passing through the highest point of the iliac crest of two sides. 4 quadrants with important viscera are as follows;

  1. Upper right quadrant – Liver and gall bladder
  2. Upper left quadrant – Stomach and spleen
  3. Lower right quadrant – Caecum, appendix and ascending colon
  4. Lower left quadrant – Descending colon and sigmoid colon

Introduction To Abdomen Four Quadrants Of Abdomen

Extent Of The Abdomen Proper

  • Apparent
    • Superior – Costal margin
    • Inferior – Anterior – Inguinal ligament
      • Lateral and posterior -Iliac crest
  • Actual
    • Superior – Diaphragm
    • Inferior – Pelvic inlet

Bodily habitus (4 types)

  1. Hypersthenic – 5%
  2. Sthenic – 48%
  3. Hypersthenic – 35%
  4. Asthenic – 12%

Introduction To Abdomen Bodily Habitus

Anterior Abdominal Wall Superficial Structures

Langer’s Lines

These are produced by the directions of bundles of collagen fibres in the dermis.

  • Horizontal in nature.
  • An incision along these lines heal with hair-line scars (Important from a cosmetic point of view)

Anterior Abdominal Wall Superficial Structures Cleavage Lines Of Anterior Abdominal Wall

Cutaneous Nerves

  • Anterior cutaneous branches of,
    • T7-11 intercostal nerves
    • Subcostal nerve (T12)
    • Iliohypogastric nerve (L1)
  • Lateral cutaneous branches of T10 and 11 intercostal nerves

Anterior Abdominal Wall Superficial Superficial Structures(Cutaneous) Arteries And Nerves Of Anterior Abdominal Wall

Cutaneous Arteries

  • Accompanying cutaneous nerves,
    • Anterior cutaneous arteries from superior and inferior epigastric arteries
    • Lateral cutaneous branches of lumbar arteries
  • Branches of the femoral artery (A little below the inguinal ligament),
    • Superficial circumflexiliac artery. (Runs laterally towards the anterior superior iliac spine).
    • Superficial epigastric artery (Runs upwards towards the anterior abdominal wall).
    • External pudendal arteries (Superficial and Deep). These run medially in relation (superficial and deep) to the spermatic cord in males.
  • Branches of external iliac artery (A little above the inguinal ligament).
    • Deep circumflex iliac artery. (Runs towards the anterior superior iliac spine).
    • Inferior epigastric artery (Ascends in the anterior abdominal wall).

Superficial Veins

  1. Radiating veins around the umbilicus
  2. Below the level of the umbilicus – superficial veins drain into a great saphenous vein
  3. Above the level of the umbilicus – superficial veins drain into a lateral thoracic vein
  4. Thoracoepigastric vein -It connects the lateral thoracic vein with a superficial vein of the lower abdomen.
  5. Para umbilical veins – These are located around the round ligament of the liver (ligamentum teres) and connect radiating veins around the umbilicus with the portal vein

Anterior Abdominal Wall Superficial Structures Superficial (Cutaneous) Veins Of Anterior Abdominal Wall

Superficial Veins Applied

  1. Portal obstruction – Caput medusae (Dilated radiating veins around the umbilicus)
  2. Obstruction of superior vena cava – Downward flow of blood in superficial veins
  3. Obstruction of inferior vena cava- Upward flow of blood in superficial veins

Superficial Lymphatics

  1. Above the umbilicus – Superficial lymphatics drain into axillary lymph nodes (Anterior and Posterior groups)
  2. Below the umbilicus – Superficial lymphatics drain into superficial inguinal lymph nodes (Medial and Lateral groups of horizontal chain)

Anterior Abdominal Wall Superficial Structures Lymphatics Of The Anterior Abdominal Wall

Superficial Fascia

1. Superficial Fascia Character

    • Above the level of umbilicus – It is fatty connective tissue
    • Below the level of the umbilicus
      1. Its superficial layer is fatty (Fascia of Camper)
      2. Its deep layer is membranous (Fascia of Scarpa)

2. Superficial Fascia Extent offascia of Scarpa,

Above – Umbilicus

Lateral – Midaxillary line

Below (Step ladder descent). It gets attached to,

  • Iliac crest
  • Holden’s line (1 cm below and parallel to the inguinal ligament)
  • Body of pubis
  • Ischiopubic ramus
  • Posterior margin of perineal membrane

Midline – Fuses with linea alba and pubic symphysis

Anterior Abdominal Wall Superficial Structures Extent Of Fascia Of Scarpa

3. Continuity membranous layer beyond the anterior abdominal wall

  • Into thigh (to Holden’s line)
  • Into perineum – Here it is named Colles’ fascia
  • Over penis – Fascia penis
  • Into scrotum – Dartos muscle

4. Contributes to the fundiform ligament, an elastic sling holding shaft of the pen is

Superficial Fascia Applied

Urethral rupture leads to typical swelling in the lower abdomen and perineal region

Anterior Abdominal Wall Superficial Structures Extravasation Of Urine Sagittal And Midsagittal Sections

Anterolateral Abdominal Muscles

Anterolateral Abdominal Muscles Classification

  • 4 Large muscles
    • 3 Flat muscles
      1. External oblique (EO)
      2. Internal oblique (10)
      3. Transversus abdominis (TA)
    • 1 Strap-like muscle – Rectus abdominis (RA)
  • 2 Small muscles
    • Cremaster
    • Pyramidalis

Anterolateral Abdominal Muscles External Oblique Of Abdomen

Attachments Of Three Flat Muscles Origin

EO – Lower 8 ribs

IO – Inguinal ligament (Lateral 2/3rd)

  • Iliac crest (Anterior 2/3rd of ventral segment)
  • Thoracolumbar fascia

TA – Inguinal ligament (Lateral l/3rd)

  • Iliac crest (Anterior 2/3rd of ventral segment)
  • Thoracolumbar fascia
  • Lower 6 costal cartilages

Anterolateral Abdominal Muscles Internal Oblique Muscle Of Abdomen

Insertion

EO – Muscular – Iliac crest – (anterior 1/2 of ventral segment)

Aponeurotic – Its muscle is replaced by aponeurosis along the lateral border of the rectus abdominis and a line between the umbilicus and anterior superior iliac spine. The pneumatic free border between the anterior superior iliac spine and pubic tubercle forms the inguinal ligament. Aponeurosis extends medially to contribute to rectus sheath and linea alba

IO and TA – These are replaced by aponeuroses before reaching the lateral border of the rectus abdominous. Their aponeuroses derived from inguinal fibres combine to form a conjoint tendon (falx inguinalis) which gets attached to the pubic crest, aponeuroses from the rest of the muscles contribute to the walls of the rectus sheath and linea alba.

Anterolateral Abdominal Muscles Transversus Abdominis Muscle Of Abdomen

Anterolateral Abdominal Muscles Attachments Of Three Flat Muscles To The Iliac Crest And Inguinal Ligament

Attachments Of Rectus Abdominis

Rectus Abdominis Origin

  • Medial tendon – Pubic symphysis
  • Lateral tendon – Pubic crest

Rectus Abdominis Insertion

  • 5th, 6th and 7th Costal cartilages.
  • 3 Tendinous intersections are noticed at the level of xiphoid, umbilicus and in between respectively.

Anterolateral Abdominal Muscles Costal Cartilages

Formation Of Rectus Sheath And Linea Alba

Linea alba – Fibrous band from xiphoid to pubic symphysis

Rectus sheath

  1. Above costal margin – Only anterior wall (Contributed by the aponeurosis of EO only)
  2. Below the costal margin
    • Upper 3/4th
      1. The anterior wall is contributed by the aponeurosis of EO and an anterior layer of the aponeurosis of I0.
      2. The posterior wall is contributed by the aponeurosis of TA and a posterior layer of the aponeurosis of I0.
    • Lower l/4th-It has only the anterior wall contributed by the aponeurosis of all three muscles i.e., EO, IO and TA.

The lower free margin of the posterior wall is called the arcuate line (Linea semicircularis).

Anterolateral Abdominal Muscles Formation Of Rectus Sheath

Pyramidalis

From pubic crest to lower l/4th of linea alba

Anterolateral Abdominal Muscles Pyramidalis

Cremaster

Loops of muscle fasciculi along the spermatic cord derived from IO and TA.

Anterolateral Abdominal Muscles Cremaster

Special features of the aponeurosis of EO

  1. Inferior margin – Poupart’s ligament ( Inguinal ligament)
    • 12 – 14 cm in length
    • Between the pubic tubercle and anterior superior iliac spine.
    • Lateral part – more oblique, rounded
    • Medial part – less oblique, concave upward
  2. Lacunar ligament of Gimbemat – a triangular posterior extension of the medial end of the inguinal ligament.
  3. Pectineal ligament of Astley Cooper – a lateral extension of the posterior margin of the lacunar ligament over the pecten pubis.
  4. Reflected part of an inguinal ligament – an upward and medial extension of the medial end of the inguinal ligament behind the aponeurosis of EO and anterior to conjoint tendon.
  5. Superficial inguinal ring
    • Triangular, having – a base (Pubic crest), lateral crus and a medial crus.
    • Intercrural fibres run across the aponeurotic fibres near the apex.
    • Passage for – Spermatic cord in male. (Round ligament of the uterus in the female.)
    • Ilioinguinal nerve.

Anterolateral Abdominal Muscles Some Special Features Of The Inguinal Region Anterior View

Anterolateral Abdominal Muscles Some Special Features Of The Inguinal Region Sagittal Sectional View

Nerves

EO and RA – T7 -12

IO and TA – T7 -12, Iliohypogastric nerve (LI)

Pyramidalis – Subcostal nerve (T12)

Cremaster – L2 (Gnital branch of genitofermoral nerve)

Functions

EO, IO, TA

  1. Compression of abdominal contents
    • Forced expiration
    • Coughing
    • Sneezing
    • Vomiting
    • Defecation
    • Micturition
    • Parturition (childbirth)
  2. Helps in pushing and weight lifting
  3. Supports the abdominal contents
  4. Rotation of trunk for example. contraction of ipsilateral 10 and contralateral EO produces ipsilateral rotation

RA

  1. Flexion of vertebral column
  2. Protection from blow

Pyramidalis – Tensor of linea alba

Cremaster

  1. Elevatoin of testis for,
    • Protection
    • Cremasteric reflex
  2. Helps in thermoregulation of testis

Special features of the aponeurosis of EO Applied

  1. Hernia
    • Inguinal
    • Umbilical
  2. Surgical Incisions
    • Median incision
    • Paramedian incision
    • Mc Burney’s gridiron incision.

Dissection Steps Of Anterior Abdominal Wall (See volume I of the book for incision numbers)

Place the body in the supine position and give incisions Nos. 3,4,8 and 9. Ensure to encircle the umbilicus while giving incision No. 8. Extend incision No. 9 posteriorly along the iliac crest.

Reflect the skin flaps leaving the superficial fascia on the anterior abdominal wall.

  • Make a transverse incision through the superficial fascia from the anterior superior iliac spine to the median plane and separate the membranous layer of the superficial fascia from the external oblique aponeurosis.
  • Now divide the superficial fascia vertically in the median plane and along the posterior axillary fold. Identify the muscles of the anterior abdominal wall, superficial inguinal ring and spermatic cord.
  • Separate the superficial fascia by blunt dissection. Note the direction of the fibres of the external oblique muscle and define its attachments. Divide the external oblique from the costal margin to the iliac crest and reflect it medially.
  • Now, note the direction of the fibres of the internal oblique muscle. Divide the internal oblique from the costal margin to the iliac crest, reflect it medially and separate it from the transversus abdominis lying deep to it.

Rectus Sheath

Rectus Sheath Definition

Fibrous compartment for rectus abdominis

Linea alba: It is a midline fibrous band from xiphoid to pubic symphysis between the rectus sheaths of two sides

Rectus Sheath Formation

Upper 3/4th

  1. Above the costal margins, it has only anterior walls contributed by the aponeurosis of the external oblique.
  2. Below the coastal margins that both anterior and posterior walls. The anterior wall is contributed by the aponeurosis of the external oblique and the anterior layer of the aponeurosis of the internal oblique.

The posterior layer is formed by aponeurosis of the transverses abdominis and a posterior layer of the aponeurosis of the internal oblique.

Lower l/4th – It has only the anterior wall contributed by aponeuroses of all three flat muscles i.e. external oblique, internal oblique and transversus abdominis.

Rectus Sheath Rectus Sheath Anterior View

Rectus Sheath Features

  1. Anterior wall
    • Complete
    • Fuses with tendinous intersections
  2. Posterior wall
    • Incomplete
    • Free from tendinous intersections

Rectus Sheath Rectus Sheath Sagittal View

Rectus Sheath Function

Increases the efficiency of the rectus abdomen by keeping it in position

Rectus Sheath Contents

Muscles – Rectus abdominis and pyramidalis

Vessels

  • Superior and inferior epigastric arteries
  • Venae commitments

Nerves

  • Lower five intercostal nerves (T7- 11)
  • Subcostal nerve.

Rectus Sheath Applied

  1. Hernia:
    • Umbilical – Congenital (Exomphalos), Acquired
    • Epigastric – Due to the divarication of recti
    • Spigelian – Along linea semilunaris
  2. Incisions
    • Median
    • Paramedian
  3. Zenker’s degeneration

Rectus Sheath Zenkers Degeneration

Dissection Steps Of The Rectus Sheath

Identify the rectus sheath. Open the anterior layer of the rectus sheath medially along the middle fibres of the rectus abdominis.

Identify the rectus abdomen and detach it from the tendinous intersections. Reflect the anterior layer of the rectus sheath medially and laterally.

Lift the rectus abdomin divide it transversely at the middle and turn the parts superior and inferior. Identify the posterior layer of the rectus sheath; superior and inferior epigastric vessels and arcuate line.

Additional layers in the abdominal wall

  1. Fascial linings of the abdominal cavity,
    • Over the anterolateral abdominal muscle – Fascia transversal
    • Over psoas and iliacus – Iliac fascia/Fascia iliac
    • Over diaphragm – Diaphragmatic fascia
    • Over kidney – Renal fascia
    • In the pelvis – Pelvic fascia
  2. Extraperitoneal fat
  3. Peritoneum

Inguinal Canal

Inguinal Canal Definition

The oblique intramuscular passage in the lower part of the anterior abdominal wall.

Inguinal Canal Location

A little above the medial part of the inguinal ligament.

Inguinal Canal Extent

From the deep inguinal ring to the superficial inguinal ring.

Inguinal Canal Extent Of Inguinal Canal

Inguinal Canal Inguinal Rings

Inguinal Canal Length – 4cm

Inguinal Canal Development

  • Occupation of passage by Gubemaculm testis (male) or Gubemaculum of ovary (female)
  • Facilitated by the adaptation of the same passage by,
    • Processus vaginalis and descending testis in male.
    • Processus vaginalis (Canal of Nuck) in female.

Inguinal Canal Gubernaculum Testis

Inguinal Canal Boundaries

Anterior wall

  • Skin
  • Superficial fascia
  • Aponeurosis of external oblique
  • Internal oblique ( in the lateral part)

Inguinal Canal Reconstructive Anatomy Of The Inguinal Canal External Oblique

Inguinal Canal Reconstructive Anatomy Of The Inguinal Canal Internal Oblique

Inguinal Canal Reconstructive Anatomy Of The Inguinal Canal Transversus Abdomins

Inguinal Canal Reconstructive Anatomy Of The Inguinal Canal Fascia Transversalis

Posterior wall

  • Peritoneum
  • Extraperitoneal fat
  • Fascia transversalis
  • Conjoint tendon (Falx inguinalis)
  • Reflected inguinal ligament

Roof – Arched fibres of internal oblique and transversus abdominis

Floor – Inguinal and lacunar ligaments.

Inguinal Canal Contents:

  • Male- Spermatic cord
    • Female- Round ligament of uterus
  • Ilioinguinal nerve

Mechanics of inguinal canal (Factors discouraging inguinal hernia)

  • Obliquity – Superficial and deep inguinal rings don’t oppose each other (except in newborn)
  • The superficial inguinal ring is strengthened by falx inguinal and reflected ligament
  • The deep inguinal ring is strengthened by the internal oblique muscle
  • Increased intra-abdominal pressure — Lowering of arched fibres of internal oblique and
    transversus abdominis — Narrowing the canal (Shutter mechanism)
  • Contraction of internal oblique-Traction of the deep inguinal ring (Valvular safety mechanism).
  • Squatting posture (during defecation and parturition) – Canal compressed by the thigh.

Inguinal Canal Applied

Inguinal hernia

  • Developmental classification
    • Incomplete (Bubonocele)
    • Complete
  • Anatomical classification
    • Indirect
      1. Congenital – Incomplete (Funicular)
      2. Complete (Vaginal)
    • Infantile
    • Acquired
    • Direct – through Hesselbach’s triangle (bounded by linea alba, inguinal ligament and inferior epigastric artery)

Inguinal Canal Direct And Indirect Inguinal Henia

Dissection Steps Of Inguinal Canal

Study the formation of the inguinal canal; its anterior wall, posterior wall, floor and roof and structures passing through it.

Identify the inguinal ligament, superficial inguinal ring, deep inguinal ring, spermatic cord in males round ligament of uterus in females, ilioinguinal nerve and also the conjoint tendon.

Inguinal Canal Boundaries Of Inguinal Canal

Spermatic Cord

Spermatic Cord Definition

Structures which leave or enter the inguinal canal through a deep inguinal ring, together constitute the spermatic cord.

Spermatic Cord Location

  • Upper – Inguinal canal
  • Lower part – Scrotum

Spermatic Cord Extent And Location Of Spermatic Cord

Spermatic Cord Extent

From deep inguinal ring to testis.

Spermatic Cord Constituents

3 Arteries

  1. Testicular artery (From aorta)
  2. Artery of vas deferens (From superior vesical artery – a branch of internal iliac artery)
  3. Cremasteric artery (From inferior epigastric artery)

Spermatic Cord Formation Of Spermatic Cord

3 veins

  1. Accompanying testicular artery (Pampiniform plexus in the scrotum, Venae comitantes in the inguinal canal, Testicular vein in the abdominal cavity)
  2. Vein of vas deferens which ultimately drains into internal iliac vein
  3. Cremasteric vein which drains into the external Iliac vein

3 Nerves

  1. Sympathetic and parasympathetic (autonomic fibres)
  2. Genital branch of genitofemoral nerve
  3. Ilioinguinal nerve

3 More structures

  1. Vas deferens
  2. Remnant of processus vaginalis
  3. Lymphatics

Coverings

  1. External spermatic fascia (Derived from aponeurosis of external oblique)
  2. Cremaster muscle and cremasteric fascia (Derived from internal oblique and transversus abdominis)
  3. Internal spermatic fascia (Derived from fascia transversalis)

Spermatic Cord Covering Of Spermatic Cord And Testis

Spermatic Cord T.S Of Spermatic Cord

Spermatic Cord Applied: Vasectomy

Dissection Steps Of Testis And Spermatic Cord

Make an incision extending from the superficial inguinal ring through the anterolateral aspect of the scrotum. Reflect the dartos muscle from the skin and then reflect the dartos from the loose areolar tissue deep into it.

  • Now, lift the testis and spermatic cord from the scrotum cut the spermatic cord at the level of the superficial inguinal ring and remove it along with the testis. Clean and trace the blood vessels into the testis.
  • Identify the spermatic cord, ductus deferens and testis. Identify the epididymis (its sinus opening laterally) and free the tail and body of the epididymis from the testis. Make a transverse incision through the testis. Examine it with a hand lens.

Scrotum

Scrotum Definition

Cutaneous fibromuscular pouch for testis and their associated structures

Scrotum Scrotal wall

  1. Skin
    1. Thin
    2. Often rugose
    3. Pigmented
    4. Excessive sweat glands
  2. Subcutaneous tissue
    • No fat
    • Dartos muscle (smooth muscle supplied by sympathetic fibres)
  3. External spermatic fascia
  4. Cremasteric fascia and cremaster muscle
  5. Internal spermatic fascia

(Note: All the layers, except skin, form the scrotal septum)

Scrotum Scrotal Wall

Scrotum Functions

  1. Support of testis
  2. Thermoregulation of testis
    • The temperature of the testis is always maintained below body temperature by a system called Cremasterico -Dartos – Venous complex
    • Cremaster undergoes reflex contraction due to excessive cold
    • Dartos windows (the gap between muscle fasciculi) open (relaxed) or close (contracted) in response to hot and cold weather respectively to allow the transfer of heat from testicular arterial blood to the skin via pampiniform plexus. This is called a counter-current heat exchange mechanism.

Scrotum Contents (of each half)

  1. Testis
  2. Epididymis
  3. Constituent of the spermatic cord

Scrotum Pampiniform Plexus

Testis

  1. 5 (length) x 2.5 (width) x 3 (A.P. diameter) cm in size
  2. 10 -14 g in weight
  3. 2 Surfaces (Medial and lateral)
    • 2 Margins (Anterior and Posterior)
    • 2 Poles (Superior and Inferior)
  4. 3 Tunics, from superficial to deep
    • Tunica vaginalis
      1. Parietal layer
      2. Visceral layer
      3. It covers, the testis from all its sides except the posterior.
    • Tunica albuginea, a fibrous coat.
    • Tunica vasculosa, a vascular coat.
  5. Structure
    • Septa from mediastinum testis (thickened tunica albuginea in the posterior part) divide the interior of the testis into 200 – 300 compartments
    • Seminiferous tubules occupy these compartments (1-4 in each compartment)
    • A major part of each seminiferous tubule is coiled except adjacent to the mediastinum, where
      it becomes straight
    • Rete testis – It is a tubular plexus in which seminiferous tubules open
    • Vasa efferentia. These are 6-12 thin tubules connecting the rete testis with the head of the epididymis

Scrotum 3 Tunics

Epididymis

  1. It is located postero-lateral to the testis
  2. It is a coiled single-tube
  3. It has 3 Parts – Head, Body, Tail
  4. Tail continues with vas deferens which are located posterior to the testis and medial to the epididymis.

Nerves

  • Skin-Posterior 2/3rd – S3 – Scrotal nerve. It is a branch of the perineal nerve, which itself arises from the pudendal nerve
  • Perineal branch of the posterior cutaneous nerve of the thigh
  • Anterior l/3rd – LI – Ilioinguinal nerve
  • Dartos – Sympathetic (with the perineal branch of S4 or genitofemoral nerve).
  • Coverings – Genital branch ofGenito-fermoral nerve.
  • Testis – Sympathetic (T10) Preganglionic fibres —> Lesser splanchnic nerve —> Renal and aortic plexuses —> Postganglionic fibres run with testicular artery
  • Epididymis – Sympathetic (T11, L2 and LI )

Arteries

  • Skin – Pudendal arteries – Both superficial and deep external pudendal arteries arise from the femoral artery. The internal pudendal artery arises from the internal Iliac artery.
  • Fibromuscular layers- Cremasteric artery- It is a branch of the external iliac artery.
  • Testis – Testicular artery —It is a branch of the abdominal aorta.

Scrotum Arteries

Veins

  • Skin – Pudendal veins – Both superficial and deep external pudendal veins drain into great
    saphenous vein.
  • Venae comitantes ofinternal pudendal artery- These drain into internal iliac vein.
  • Fibromuscular layers- Cremasteric vein – It is a tributary of the external iliac vein.
  • Testis – Testicular vein- On the right side it drains into the inferior vena cava while on the left side, it enters into the left renal vein.

Lymphatics

  • Skin – Superficial inguinal lymph nodes (Medial group of horizontal chain)
  • Fibromuscular layer- External iliac lymph nodes
  • Testis – Pre- and Para-aortic lymph nodes

Scrotum Venous Drainage Of Testis

Scrotum Lymphatic Drainage Of Testis

Scrotum Incomplete Descent Of Testis

Scrotum Applied

  1. Imperfect descent
  2. Incomplete descent
  3. Maldescent (Ectopic testis)
  4. Testicular pain -Referred to umbilicus due to common segmental (T10) innervation
  5. Malignancy of testis-Involves abdominal lymph nodes
  6. Varicocele of pampiniform plexus
  7. Hydrocele
    • Congenital
      1. Complete type
      2. Incomplete type (Funicular)
    • Infantile
    • Encysted
    • Acquired (Vaginal)
      1. Primary (cause unknown)
      2. Secondary (known cause)

Scrotum Different Types Of Hydrocele

Peritoneum

Peritoneum Definition

The serous membrane lining the abdominal cavity and covering its viscera or connecting the two.

Peritoneum Parts

  1. Parietal layer – It lines the wall of the abdomen and pelvis
  2. Visceral layer – It covers the viscera of the abdomen and pelvis
  3. Folds – These are double layers of the peritoneum which connect the viscera or with abdomen wall. These are of the following types,
    • Connecting mobile viscera with the abdominal wall. This is termed as “MESENTERY”. These are named after viscera For Example.,
      1. of the small intestine – The Mesentery
      2. of the colon – Mesocolon<Transverse mesocolon / Sigmoid mesocolon)
      3. of the appendix – Mesoappendix
    • Connecting stomach with adjacent viscus. This is termed as “OMENTUM”. These are named differently depending on the viscus to which it is connected, For Example.,
      1. With liver – Lesser omentum
      2. With a transverse colon – Greater omentum
      3. With spleen-gastrosplenic omentum
    • Connecting relatively less mobile viscera (For Example., liver) with the abdominal wall.
      1. These are termed “LIGAMENTS” as shown below,
      2. Ligaments of the liver – Falciform, Coronary, Triangular.
      3. Ligament of spleen – Lienorenal ligament

1. Peritoneal Cavity

Potential space between parietal and visceral layers is called the peritoneal cavity which can be broadly divided into,

  1. Greater sac
  2. Lesser sac

Communication between the two sacs is called epiploic foramen or foramen of Winslow.

Arrangement

Developmental correlation

The mesentery of primitive gut,

  • Dorsal – Present thought out the gut
  • Ventral – It is present only in the region of the stomach and proximal duodenum and is therefore called ventral mesogastrium.

Spleen developsin dorsal mesogastrium dividingitinto lienorenal ligament and gastrosplenic ligament.

The liver develops in the ventral mesogastrium dividing it into falciform ligament and lesser omentum.

Peritoneum Major Subdivisions Of Peritoneal Cavity

Peritoneum Developmental Correlations Of Peritoneum

Peritoneum Cross Section Of Embryo Caudal To Foregut (Passing Through Midgut Or Hindgut)

Peritoneum Cross Section Of Embtyo Passing Through Foregut

Peritoneum Cross Section Of Embryo Showing Development Of Spleen And Liver

Peritoneum Cross Section Of Embryo Showing Rotation Of Stomatch With Displacement Of Spleen And Liver

Rotation of the stomach brings the following changes,

  • A smaller sac goes behind the stomach and the lesser omentum
  • Spleen comes to lie in the left hypochondriac region
  • The liver is shifted to the right hypochondriac region

Peritoneum Loss Of Dorsal Mesentery Due To Falling Of Some Parts Of Primitive Gut On The Posterior Wall Of Abdomen

  1. Gut with dorsal mesentery
  2. Fall of gut on the posterior wall
  3. The gut loses its mesentery and becomes retroperitoneal

Peritoneal reflection observed by palpation

Peritoneum Peritoneal Reflexions In The Posterior Wall Of Abdomen

I – Immediately after opening the abdomen one can observe the following;

  1. Liver, Falciform ligament
  2. Gall Bladder
  3. Stomach
  4. Greater omentum

After elevation of the greater omentum following visceral parts are found,

  1. Coils of small intestine
  2. Colons – Transverse, ascending and descending

Peritoneum Appearance Of Abdominal Cavity Immediately After Opening The Abdomen

Peritoneum Appearance Of Abdominal Cavity Greater Omentum Raised Upwards

Peritoneum Peritoneal Relations Of Stomach

2. Further Exploration

1. Vertical disposition

Palpate the posterior surface of the anterior abdomen wall glide your hand upwards from the umbilicus and palpate the following in sequence,

  1. First to the right falciform ligament
    • Anterior abdominal wall —> Diaphragm —> Sperior layer of a coronary ligament —> Liver —> Inferior layer of a coronary ligament —> posterior abdominal wall (having, right kidney, right lateral paracolic gutter, ascending colon, right medial paracolic gutter).
  2. Secondly to the left of the falciform ligament.
    • Anterior abdominal wall —> Diaphragm —> Anterior layer of a left triangular ligament —> Liver —> Lesser omentum —> Stomach —> Greater omentum —> Transverse colon —> Transverse mesocolon —> Posterior abdominal wall (with the pancreas, duodenum, right medial paracolic gutter) —> Right infrasonic compartment —> Right layer of the mesentery —> Jejunum and ileum —> Left layer of the mesentery —> Left infrasonic compartment —> Sigmoid mesocolon and colon —> Rectum.

Peritoneum Vertical Disposition Of Peritoneum Falciform Ligament

Peritoneum Vertical Disposition Of Peritoneum Vertical Disposition Of Peritoneum To The Right Of Falciform Ligament

Peritoneum Vertical Disposition Of Peritoneum Morisons Pouch

Peritoneal reflections (from posterior to anterior pelvis differ in males and females.

Male: Rectum —> Rectovesical pouch —> Urinary bladder

Female: Rectum —> Rectouterine pouch of Douglas —> Uterus and Vagina —> Vesicouterine pouch —> Urinary bladder

From the superior surface of the urinary bladder, the peritoneum continues over the anterior abdominal wall to reach the umbilicus.

Peritoneum Vertical Disposition Of Peritoneum To The Left Of Falciform Ligament Male

Peritoneum Vertical Disposition Of Peritoneum To The Left Of Falciform Ligament Female

2. Horizontal disposition

Pelvis

Fossae

  • Pararectal fossa – By the side of rectum
  • Ovarian fossa – In the lateral wall just anterior to internal iliac vessels
  • Paravesical fossa – By the side of the urinary bladder Ridges.
  • Urogenital ridge – It limits the pararectal fossa laterally in males.
  • Ridge for vas deferens -It limits the paravesical fossa laterally in male
  • Ridge for ureter – Located in the lateral wall of the pelvis just in front of internal iliac vessels
  • Recto-uterine fold – It limits the para-rectal fossa laterally in females.
  • Ridge for round ligament of the uterus – It limits the paravesical fossa laterally in female
  • Broad ligament of the uterus -It connects the side of the uterus with the lateral wall of the pelvis.

Peritoneum Horizontal Disposition Of Peritoneum In Pelvic Cavity Male And Female

Lower abdomen (Below umbilicus)

Anterior abdominal wall

  • Folds
    • Median umbilical fold – Raised by urachus
    • Medial umbilical fold – Raised by obliterated umbilical artery
    • Lateral umbilical fold – Raised by inferior epigastric artery
  • Fossae
    • Supravesical fossa – Between median and medial umbilical folds
    • Medial inguinal fossa – Between medial and lateral umbilical fold
    • Lateral inguinal fossa – Over deep inguinal ring. Just lateral to lateral umbilical fold.
    • Femoral fossa – Over femoral ring

Peritoneum Posterior Aspect Of Lower Anterior Abdominal Wall

Posterior abdominal wall

  • Paracolic gutters
    • Right, about ascending colon.
    • Left, to descending colon. (Both are medial as well as lateral)
  • Colons – Ascending and descending
  • The mesentery and ileum.

Upper abdomen (Above umbilicus)

Peritoneum Horizontal Disposition Of Peritoneum In The Region Of Lower Abdomen

Go towards the left from the falciform ligament on the posterior surface of the anterior abdominal wall and feel the following structures;

Falciform ligament —> Lienorenal ligament —> Spleen —> Gastrosplenic ligament —> Stomach —> Lesser omentum —> Epiploic foremen —> Anterior wall of lesser sac —> Gastrosplenic ligament —> Hilum of spleen —> Lienorenal ligament —> Posterior wall of lesser sac (pancreas, aorta, inferior vena cava) —> Epiploic foramen —> Right kidney —> Right abdominal wall —> Filciform ligament.

Peritoneum Horizontal Disposition Of Peritoneum In The Region Of Upper Abdomen

Dissection Steps Of Peritoneum

Identify the parietal peritoneum and cut it transversely at the level of the umbilicus and turn the upper and lower parts superior and inferior respectively.

  • Examine and identify the peritoneal ligaments falciform ligament and ligamentum teres hepatitis and also the ligaments in the infra umbilical portion from its deeper aspect.
  • Identify the greater omentum and its parts and the lesser omentum and its parts as well as the transverse mesocolon. Note the locations of abdominal viscera in situ; supra-and infracolic compartments as well as epiploic foramen.
  • Pull the stomach down and to the left and the liver up and to the right to locate the epiploic foramen. Pass the index and middle finger of the left hand through it and feel the surfaces.

Peritoneal Recesses And Fossae

1. Doudenal recesses

  • Paraduodenal recess (inferior mesenteric vein is related to it)
  • Superior duodenal recess
  • Inferior duodenal recess
  • Retroduodenal recess

Recesses (1), (2) and (3) are located just to the left of the duodenojejunal junction while recess (4) is lying behind the 4th part of the duodenum.

Peritoneum Peritoneal Recesses In Relation To Duodenum

Peritoneum Peritoneal Recesses In Relation To Caecum

Peritoneum Peritoneal Recesses In Relation To Sigmoid Colon

2. Caecal recesses

  • Superior ileocaecal
  • Inferior ileocaecal
  • Retrocaecal

Recesses 1 and 2 are located about the ileocaecal junction while recess 3 is lying behind the caecum.

3. Intersigmoid fossa

It is enclosed by an inverted ‘V’ shaped attachment of sigmoid mesocolon.

Subphrenic spaces

  • Extraperitoneal
    • Right – Bare area of the liver (Near right suprarenal gland)
    • Left – Near left suprarenal gland and upper pole of left kidney.
  • Intraperitoneal
    • Right
      • Anterior (Between front of the right lobe of the liver, upper layer of coronary ligament and diaphragm).
      • Posterior (Between right kidney, lower layer of coronary ligament and right lobe of the liver. This is also called hepatorenal or Morison’s pouch).
    • Left
      • Anterior (Between front of the left lobe of the liver, anterior layer of left triangular ligament and diaphragm).
      • Posterior (Lesser sac)

Peritoneum Subphrenic Spaces

  1. About the front of the liver
  2. The sagittal section of the upper abdomen to the right of the falciform ligament
  3. The sagittal section of the upper abdomen to the left of the falciform ligament

Lesser Sac

  • The peritoneal cavity behind the stomach and lesser omentum
  • 4 borders
    • Superior – Extends to the diaphragm
    • Inferior – Extends to the greater omentum
    • Left – Extends to the hilum of the spleen
    • Right – Has foramen of Winslow or Epiploic foramen
  • Epiploic foramen – Its boundaries are as follows,
    • Anterior – Free margin of lesser omentum (with portal vein, bile duct and hepatic artery)
    • Posterior – Inferior vena cava
    • Superior – Caudate process of liver
    • Inferior – 1st Part of duodenum
  • Parts
    • Body – Central part. It is the main portion.
    • Vestibular – It is the right extension which joins the body with the epiploic foramen
    • Superior recess – Between body and superior border.
    • Inferior recess – Between body and inferior border.
    • Splenic recess – Between body and left border
  • Relations
    • Anterior – Stomach, lesser omentum, caudate lobe.
    • Posterior – Stomach bed. (Transverse colon, transverse mesocolon, pancreas, left kidney, left suprarenal gland, diaphragm, spleen, splenic artery)
  • Gastropancreatic folds in the posterior wall,
    • Its right portion is produced by the hepatic artery while its left part is raised by the left gastric artery.

Peritoneum Lesser Sac Front View Showing Recesses And Sectional View

Peritoneum Boundaries Of Foramen Of Winslow

Lesser Sac Applied

  • Internal abdominal hernia is common through epiploic foramen which sometimes leads to strangulations
  • Perforation of posterior gastric ulcer leads to communication between the stomach and lesser sac.

Peritoneum Most Dependent Part Of Abdomen And Pelvis During Supine Position

Functions Of Peritoneum

  1. Lubrication
  2. Storage of fat
  3. Folds carry vessels and nerves to and from viscera
  4. Support of viscera
  5. Localization of inflammation
    • The greater omentum is also called abdominal policeman as it covers the inflammatory sites and limits its spread.
  6. Absorption of peritoneal fluid.
  7. To resist the infection by leukocytes and antibodies

Nerves

Parietal peritoneum

  • Diaphragmatic
    • The central part is supplied by the phrenic nerve explaining the referred pain to the shoulder.
    • The peripheral part is innervated by lower intercostal nerves.
  • Over abdominal wall
    • It is supplied by lower intercostal. Iliohypogastric and ilioinguinal nerves
  • Pelvic -It is innervated by the obturator nerve.

Visceral peritoneum

Autonomic nerves supplying the viscera also supply the peritoneum covering it.

Functions of peritoneum Applied

  • Inflammation is termed as peritonitis
  • Pain
    • from parietal peritoneum -It is severe and precisely localized in nature
    • from viscera-It is dull, poorly localized and referred to the anterior midline as shown below.

Peritoneum Functions Of Peritoneum

Greater omentum acts as an “Abdominal policeman”

  • Peritoneal cavity
  • The collection of fluid is called ascites
    • Paracentesis is the procedure to drain excess fluid in the peritoneal cavity
    • Collection of pus in Morison’s and rectovesical pouches is common due to their being
      most dependent parts of the abdominal cavity in supine posture.
    • If there is strangulation of the herniated intestinal loop in the para duodenal fossa, take care of an inferior mesenteric vein in its anterior wall during operation.

Peritoneum Location Of Referred Pain From Different Parts Of Alimentary Canal

Stomach

Stomach Definition

The most dilated part of the foregut is situated between the oesophagus and duodenum.

Stomach Location:

It occupies the following regions – Left hypochondriac, epigastric, umbilical

Stomach Two orifices

  1. Cardiac orifice (Proximal opening). This orifice acts as a physiological sphincter due to the following arrangements,
    • Circular fibres of diaphragm, oesophagus and stomach
    • Phrenico – oesophageal ligament
    • Angulation of the oesophagus with stomach
    • Mucosal folds
  2. Pyloric orifice (Distal opening)
    • It has well well-defined anatomical sphincter i.e., a thick circular muscle coat in the wall.

Stomach Different Parts Of Stomach

Stomach Two borders

  • Lesser curvature- Small, concave, right border. A deep notch in its distal part is called an angular notch.
  • Greater curvature- Large, convex, left border. A depression in its distal part is called sulcus intermedius

Stomach Two Surfaces

  • Anterior – It faces anteriorly and superiorly.
  • Posterior – It faces posteriorly and inferiorly

Stomach Parts

  • Fundus – Part of the stomach above the level of the cardiac orifice.
  • Body – Part of stomach between fundus and angular notch.
  • Pyloric part – Part of stomach distal to angular notch. It has two components.
    • Antrum – proximal portion
    • Pyloric canal – distal portion

Stomach Surface Marking Of Stomach

Stomach Capacity

  • At birth- 30 ml
  • At puberty – 1 litre
  • In Adults – 1.5 litre

Stomach Structure

Stomach Magenstrasse And Magenblaze Of Stomach

Magenstrasse (Gastric canal) – It is a narrow tunnel along lesser curvature produced due to the contraction of oblique fibres of the muscular coat of the stomach.

Magenblaze – It is gas in fundus

Stomach Cardiac Ends Of Stomach Showing Physiological Sphincter

Stomach Musculature Of Stomach

Stomach Relations

1. Peritoneal relations

  • Lesser curvature receives lesser omentum from the liver. It has two parts,
    1. Hepatogastric ligament – Between liver and stomach.
    2. Hepatoduodenal ligament – Between the liver and 1st part of the duodenum
  • Greater curvature receives attachments of greater omentum which has three parts,
    1. Gastrophrenic ligament – Between stomach and diaphragm.
    2. Gastrosplenic ligament – Between stomach and spleen.
    3. Gastrocolic ligament – Between stomach and transverse colon.

Stomach Peritoneal Relations Of Stomach

2. Visceral relations

  • Anterior (LAD)
    • L = Liver
    • A = Anterior abdominal wall
    • D = Diaphragm
  • Posterior – Lesser sac and stomach bed
    (Tickle me please, killing sensations disappear so soon)

T = Transverse colon

M = Mesocolon (Transverse)

P = Pancreas,

K = Kidney (Left)

S = Suprarenal gland (Left)

D = Diaphragm

S = Spleen

S = Splenic artery

Stomach Stomach Bed

Stomach Functions

  1. Temporary storage
  2. Mixing
  3. Partial digestion
  4. Partial absorption
  5. Sense of fullness
  6. HCl secretion
  7. Intrinsic factor secretion (+ Extrinsic factor i.e. B12 = Hemopoietic factor)

Stomach Arteries

Coeliac artery

  • Gastric arteries
    • Right gastric artery. It arises from the hepatic artery and runs towards the left along the right portion of lesser curvature.
    • Left gastric artery. It arises from the celiac trunk and runs retroperitoneally towards the cardiac end where it enters the lesser omentum and follows the lesser curvature to meet its fellow artery.
    • 5 Short gastric arteries arise from the splenic artery to supply the fundus and upper part of the body.
    • Posterior gastric arteries arise from the splenic artery and supply its posterior surface.
  • Gastroepiploic arteries
    • The right gastroepiploic artery arises from the gastroduodenal artery and runs towards the left parallel to and 2 cm from the greater curvature
    • The left gastroepiploic artery is a branch of the splenic artery and runs towards the right gastroepiploic artery.
    • Gastroepiploic arteries supply both the stomach as well as greater omentum.

Stomach Arterial Supply Of Stomach

Stomach Veins

Portal vein

Accompany arteries of the same name and ultimately drain into the portal vein

Stomach Venous Drainage Of Stomach

Stomach Nerves

Parasympathetic

Anterior vagal trunk (Mainly contributed by left vagus)

Branches

  • Gastric
  • Hepatic
  • Pyloric

Posterior vagal trunk (Mainly contributed by right vagus)

Branches

  • Gastric
  • Coeliac

Stomach Innvervation Of Stomach

Functions

  1. Motor to glands
  2. Motor to muscles
  3. Inhibitory to pylorus

Stomach Sympathetic

Fibres originate from the 6th to the 9th thoracic segments of the spinal cord.

These runs in greater (T5-9) and lesser (T9-10) splanchnic nerves to relay in the coeliac plexus. Branches of celiac plexus accompany the branches of the coeliac trunk.

Functions

  1. Motor to vessels
  2. Motor to pylorus
  3. Sensory

Lymphatic drainage

Coeliac lymph nodes ultimately receive lymphatics from the stomach after being interrupted by the following lymph nodes.

  • Left gastric lymph nodes (about the superior left gastric artery) These can be superior, inferior and pericardiac.
  • Right gastroepiploic lymph nodes (About right gastroepiploic artery)
  • Pancreatic – splenic lymph nodes (Concerning the hilum of the spleen)
  • Pyloric lymph nodes (About the pyloric end of the stomach)

Stomach Lymphatic Drainage Of Stomach

Dissection Steps Of Stomach

Identify the organ in situ and note its gross features. Note the cardiac and pyloric ends and their differences. Identify the peritoneal folds of the stomach. Note the vessels in the greater omentum.

  • Tie two ligatures some distance apart right to the pyloric sphincter. Turn the stomach along the right gastric and right gastroepiploic vessels to the left side and then identify the omental bursa.
  • Strip off the peritoneum along the lesser curvature and identify the celiac trunk and its branches; left kidney and suprarenal. Pull the cardiac end down tie 2 ligatures some distance apart and cut in between the two ligatures.
  • Cut at the pyloric end and remove the stomach and while doing so identify the branches of the splenic artery. Study the gross features of the stomach. Identify the pyloric region and sphincter.
  • Note the structures forming the stomach bed. Open the stomach along the greater curvature and examine its interior. Strip off muscles from a part of the stomach and study.

Stomach Applied

  • Gastric ulcers can be treated by vagotomy and partial gastrectomy. The latter removes the gastrin-bearing area of the stomach i.e. anterior part.
  • Gastric malignancy needs radical gastrectomy.
  • Gastroscopy is an endoscopic procedure with the help of a gastroscope to visualize the interior of the stomach.

Spleen

Spleen Definition

Largest single lymphoid organ

Spleen Location

Left hypochondriac region

Spleen Extent

Horizontal – From the side of the rounded vertebral column to the midaxillary line

Vertical – From 9th to 11th rib

Spleen Location Of Spleen Anterior Aspect

Spleen Extent Of Spleen Back

Spleen Development

It develops at the age of the 7th week of intrauterine life in the left leaf of the upper dorsal mesogastrium.

Spleen Development Of Spleen

Weight – 150 g

Spleen Measurements

Thickness = 3-4 cm

Width = 7 cm

Length = 12 cm

Spleen Extremities – Anterior and Posterior

Spleen Borders

  • Superior – It is notched
  • Inferior
  • Intermediate (Margo intermedialis)

Spleen Surfaces

  • Diaphragmatic
  • Visceral

Spleen Borders And Surfaces Of Spleen

Spleen Relations

1. Peritoneal

Most of the surfaces of the spleen are covered with peritoneum except the hilum on the visceral surface which is bare for the passage of splenic vessels and the tail of the pancreas (pancreatic impression).

Ligaments

Spleen Ligaments

Spleen Relations Of Visceral Surface Of Spleen

2. Adjacent relations

  • The diaphragmatic surface is related to,
    • Diaphragm
    • Left lung and costodiaphragmatic recess
    • 9-11 ribs and intercostal space
  • The visceral surface has the following- Impressions
    • Gastric for stomach
    • Renal for the left kidney
    • Colic for left colic flexure

Spleen Relations Of Parietal Surface Of Spleen

Spleen Functions

  1. Phagocytosis (Graveyard)
  2. Immune responses (Guard)
  3. Cytopoiesis (Factory)
    • Lymphopoiesis
    • Haemopoiesis (In foetus)
  4. Erythrocyte storage – (Blood bank)

In humans – it is discharged by elastic recoil.

In lower mammals – it is discharged by contraction of the capsule

Artery

Splenic artery- 5 branches enter the spleen

Vein

Splenic vein- 5 tributaries appear from the spleen

Lymphatic

Pancreaticosplenic lymph nodes in the hilum drain the spleen. Their efferents drain into coeliac lymph nodes.

Nerves

The Coeliac plexus provides innervation to the spleen which is sympathetic.

Spleen Segmentation

84 % — 2 Segments — Superior and inferior

16 % — 3 Segments — Superior, intermediate, inferior

Dissection Steps Of Spleen

Palpate spleen in the left hypochondrium. Push the stomach to the right and identify the upper part of the greater curvature. Identify the fold of the peritoneum extending from there to the hilum of the spleen.

  • Identify the vessels in the gastrosplenic ligament. Push the transverse colon downward on the left including the left colic flexure and push the spleen upwards towards the left dome of the diaphragm and note the fold of the peritoneum extending between the spleen and the left kidney.
  • Examine the organ in situ note its anatomical position and also note the relations. Cut ligaments at the hilum remove the organ and study its gross features including various impressions on its visceral aspect.

Spleen Applied

  • Splenomegaly (Enlargement of spleen )— Spleen is palpated when it is double the size.
    Splenomegaly is noticed in Malaria, Typhoid, Portal hypertension
  • Splenectomy (Surgical removal of spleen). Tail of the pancreas should be saved during operation which is located in the lienorenal ligament.
  • Kehr’s sign

Spleen Kehr's Sign

Small Intestine

Small Intestine Extent

Gastroduodenal (Pyloroduodenal) Junction to Ileocaecal junction

Small Intestine Parts and lengths

  1. Duodenum – 10″ / 25cm
    • 1st / Superior part – 2″
    • 2nd / Descending part – 3″
    • 3rd / Horizontal part – 4″
    • 4th / Ascending part – 1″
  2. Jejunum – 2/5th, 87 240 cm / 2.4 m
  3. Ileum – 3/5th, 12′ / 360cm / 3.6 m

Jejunum and ileum together – 20′ / 6m

Small Intestine Peritoneal Relations Of Different Parts Of Small Intestine

Duodenojejunal Junction is marked by the ligament of Treitz which is a fibromuscular band connecting the junction with the right crus of the diaphragm.

Small Intestine Ligament Of Treitz

Small Intestine Relation

1. Peritoneal relations

1st inch of the superior part of the duodenum is covered by the peritoneum and receives lesser and greater omenta along its superior and inferior borders respectively

Rest of duodenum- Retroperitoneal

The jejunum and ileum are mobile but attached to the posterior wall of the abdomen by a double layer of peritoneum called the mesentery. Features, of the mesentery, are as follows,

  • Fan shaped
  • Free margin – holds jejunum and ileum.
  • The attached margin is called the root of the mesentery, it extends from the left side of the 2nd lumbar vertebra to the right sacroiliac joint. It is 15 cm in length. This root crosses the following structures,
    • Duodenum (3rd part)
    • Aorta
    • Inferior vena cava
    • Right ureter
    • Right psoas
  • The average width of the mesentery is 20 cm
  • Between two layers are enclosed vessels, nerves, lymph nodes and fat.

Small Intestine Root Of The Mesentery

2. Adjacent relations

Duodenum

  • Vertebral relations
    • 1st Part — To the right of 1st lumbar vertebra.
    • 2nd Part — To the right of 2nd and 3rd lumbar vertebrae.
    • 3rd Part — Across the 3rd lumbar vertebra.
    • 4th Part — To the left of the 2nd lumbar vertebra.
  • Structures in vicinity

Small Intestine Duodenum In Relation To The Lumbar Vertebral Bodies

1st Part

  • Superior
    • Epiploic foramen
    • Hepatic artery
    • Lesser sac (related to 1st inch only)
  • Inferior
    • Head of the pancreas
  • Anterior
    • The quadrate lobe of the liver
    • Gall bladder
  • Posterior
    • Common bile duct
    • Gastroduodenal artery
    • Portal vein
    • Inferior vena cava

Small Intestine Posterior Relations Of Duodenum

2nd Part

  • Anterior
    • Gall bladder
    • The right lobe of the liver
    • Transverse colon
    • Coils of intestine
  • Posterior
    • Hilum of the right kidney
    • Right pelvis and ureter
    • Right renal vessels
    • Inferior vena cava
    • Right psoas
  • Lateral
    • The right lobe of the liver
  • Medial
    • Head of a pancreas

Small Intestine Relations Of Duodenum With Pancreas And Some Anterior Structures

The posteromedial wall is pierced by main and accessory pancreatic ducts producing major and minor duodenal papillae respectively on the mucosal surface.

Small Intestine Major And Minor Duodenal Papillae

3rd Part

  • Anterior
    • The root of the mesentery
    • Superior mesenteric vessels
    • Coils of jejunum
  • Posterior
    • Right crus of diaphragm
    • Right psoas
    • Inferior vena cava
    • Aorta
    • Right gonadal artery
    • Origin of inferior mesenteric artery
    • Right ureter
  • Superior
    • Head of the pancreas
  • Inferior
    • Coils of jejunum

4th Part

  • Superior
    • Body of pancreas
  • Anterior
    • Transverse colon and mesocolon
  • Posterior
    • Left psoas
    • Left sympathetic trunk
    • Left gonadal and renal vessels
    • Inferior mesenteric vein
  • Right
    • Beginning of root of mesentery
  • Left
    • Left kidney and ureter

Jejunum and ileum

  • Location
    • Jejunum – Upper abdomen
    • Ileum – Lower abdomen and pelvis

Feature of small intestine

  • Duodenum
    • Most proximal
    • Smallest
    • Widest
    • Most sessile
  • Jejunum and Ileum

Small Intestine Jejunum And Ileum

Small Intestine Relative Features Of Jejunum And Ileum

Small Intestine Mucosa Of Jejunum And Ileum

Meckel’s diverticulum (Ileal diverticulum)

  1. Definition – Persistence of intra-abdominal part of vitello-intestinal duct
  2. Incidence – 3%
  3. Location – 1 meter proximal to ileocaecal junction
  4. Length – 5 cm
  5. Applied
    • Intestinal obstruction is more common.
    • Meckelian diverticulitis – resembles appendicitis
    • Peptic ulcer may occur if the gastric mucosa develops in Meckel’s diverticulum.
    • Littre’s hernia (Herniation of Meckel’s diverticulum)

Arteries of small intestine

  • Ultimate artery
    • Up to the middle of 2nd part of the duodenum – Coeliac trunk
    • Rest of small intestine – Superior mesenteric artery
  • Named branches

Duodenum

  • Supraduodenal artery from gastroduodenal artery.
  • Right gastric artery.
  • Right gastroepiploic artery.
  • Superior pancreaticoduodenal artery
  • Inferior pancreaticoduodenal artery

Small Intestine Parts Of Primitive Gut And Their Arteries

Jejunum and Ileum

12-15 Jejunal and ileal branches of the superior mesenteric artery

Small Intestine Arteries And Veins Of Small Intestine Front And Sectional Views

Veins of small intestine

  • Portal vein – Veins of the small intestine drain into the portal vein directly or indirectly via a superior mesenteric vein.
  • The prepyloric vein is a surgical guide to the pylorus – It drains into the right gastric vein.

Lymphatic drainage of the small intestine.

  • Duodenum
    • Upper part — Pyloric lymph nodes- Coeliac lymph nodes
    • Lower part — Superior mesenteric lymph nodes
  • Jejunum and ileum
    • Mesenteric lymph nodes
      1. Mural lymph nodes (close to intestinal wall)
      2. Intermediate lymph nodes
      3. Juxta-arterial lymph nodes.
    • Superior mesenteric lymph nodes (close to the origin of an artery)

Small Intestine Lymphatic Drainage Of Small Intestine

Nerves of small intestine

  • Ultimate source
    • Sympathetic – T9-10, via splanchnic nerves
    • Parasympathetic – Vagus
  • Supply
    • Upper duodenum – Coeliac plexus
    • Rest – Superior mesenteric plexus

Applied anatomy of the small intestine

1. Duodenum

  • Ulcers
    • Anterior wall – Common
    • Posterior wall – Uncommon. If perforated, causes erosion of the gastroduodenal artery and profuse bleeding
  • Paraduodenal fossa may be site of internal abdominal hernia.
  • Adjacent relations of the duodenum are surgically important.

2. Jejunum and ileum

  • Tumour or cyst of the mesentery is more mobile across the attachment of the mesentery
  • Referred pain is felt usually at the umbilicus
  • Thrombosis/embolism of the superior mesenteric artery leads to gangrene of the small intestine.

Dissection Steps Of Small Intestine

Pull duodenojejunal flexure downwards. Tie two ligatures at the duodenojejunal flexure some distance apart (1″). Cut small intestine between these ligatures. Pass two ligatures 2 inches proximal to the iliocaecal junction and cut the small intestine.

  • Cut the mesentery along the attachment on the posterior abdominal wall. Remove the small intestine and flush its lumen thoroughly.
  • Cut a piece of jejunum and ileum along with the mesentery (about 6 inches in length). Study both parts and note their differences. Open the jejunum and ileum along their antemesenteric border and study the interior.

Pancreas

Pancreas Definition

Lobulated, soft, exo-endocrine gland

Pancreas Length 12 – 15 cm

Pancreas Parts

  • Head with uncinate process
  • Neck (2 cm wide)
  • Body
  • Tail

Pancreas Parts Of Pancreas

Pancreas Relation

  1. Head
    • Margin- Concavity of duodenum
    • Anterior – Transverse colon
    • Jejunum
    • Superior mesenteric vessels (anterior to uncinate process)
    • Posterior- Inferior vena cava
  2. Neck
    • Anterior- Gastroduodenal artery
    • Posterior- Superior mesenteric vein and portal vein
  3. Body
    • 3 Surfaces
    • Anterosuperior
      • Lesser sac and stomach

Pancreas Surfaces And Borders Of The Body Of Pancreas

Anteroinferior

  • Jejunum
  • Two flexures, duodenojejunal and left colic flexures

Pancreas Structures In The Vicinity Of The Pancreas

Posterior

  • Aorta
  • Superior mesenteric artery
  • Left crus of the diaphragm
  • Left renal vessels
  • Left kidney and suprarenal gland
  • Splenic vein

Pancreas Posterior Relations Of Pancreas H-Head, N-Neck, B-Body, T-Tail

3 borders

  • Anterior – Transverse mesocolon
  • Superior- Splenic artery. It has omental tuberosity which is related to liver
  • Inferior – Superior mesenteric vessels

Tail -It passes through the splenorenal (lienorenal) ligament to reach the hilum of the spleen

Ducts of pancreas

Main pancreatic duct – It unites with the common bile duct to form the ampulla of Vater whose wall is marked by the sphincter of Oddi. It opens on the summit of the major duodenal papilla, a smooth elevation in the mucosa of the posteromedial wall of 2nd part of the duodenum.

Accessory pancreatic duct – It opens on the summit of the minor duodenal papilla located in the duodenal mucosa above the major duodenal papilla.

Pancreas Ducts Of Pancreas

Artery

  • Head – Superior and inferior pancreaticoduodenal arteries
  • Rest of pancreas – Splenic artery.

Vein – Veins draining the pancreas open into the portal, superior mesenteric and splenic veins.

Lymphatics

  • Pancreaticosplenic lymph nodes
  • Pancreaticoduodenal lymph nodes
  • Efferents from the above two groups drain into coeliac or superior mesenteric lymph nodes.

Nerves

  • The Coeliac plexus provides autonomic fibres to the pancreas
  • Parasympathetic-> Right vagus — to parenchyma
  • Sympathetic → T7-9 — To parenchyma, Vasomotor

Pancreas Side View Of Some Of The Structures In The Vicinity Of Pancreas

Pancreas Applied

  • Diabetes mellitus – Reduced Insulin — Increased blood sugar
  • Cancer of the head – Persistent obstructive jaundice

Dissection Steps Of Pancreas And Duodenum

Turn the tail and body of the pancreas to the right. Strip the splenic vessels from its posterior surface. Divide the bile duct near the superior part of the duodenum. Remove the duodenum and pancreas as one piece.

  • Make 2 cuts on the posterior surface parallel to the superior and inferior margins of the body of the pancreas. Tease away the lobules of the gland between the cuts to expose the main pancreatic duct which is greyish-white.
  • Note its tributaries (herringbone pattern). Now, expose the accessory pancreatic duct and its tributaries coming from the head of the pancreas. Follow both ducts to the duodenum. Cut open the duodenum vertically along its right wall and wash it.
  • Identify the openings (at major and minor duodenal papilla) on the internal aspect of the posteromedial surface of the 2nd part of the duodenum.

Large Intestine

Large Intestine Extent

From caecum to anal canal

Large Intestine Parts and lengths

Vermiform appendix 2-20 cm, excluded from the total length

Large Intestine Parts Of Large Intestine

Total length- 155 cm

  • Caecum – 5 cm
  • Ascending colon – 15 cm
  • Transverse colon – 45 cm
  • Descending colon – 30 cm
  • Sigmoid colon – 45 cm
  • Rectum and anal canal – 15 cm

(Rectum- 12 cm.; Anal canal – 3cm)

Large Intestine Features

1. General Features

  • Large lumen (wider)
  • Taenia (e) coli. These are three longitudinal muscular bands as follows,
    • Taenia libra
    • Taenia mesocolic
    • Taenia omental

These bands are anterior, posteromedial and posterolateral respectively in the ascending and descending colons. Their positions change in the transverse and sigmoid colon.

  • Sacculations (Haustrations) – These form a series of dilatations separated by constrictions through the colon.
  • Appendices epiploicae – These are a large number of peritoneal sacs along taenia coli.

Large Intestine Measurements Of Caecum

2. Specific features

Caecum – 6 cm (Height) x 7.5 cm (Width)

Posteromedially is the opening of the ileum guarded by the ileocaecal valve. A little below the side opening is a rounded orifice of the vermiform appendix.

Large Intestine Interior Of Caecum

Large Intestine Longitudinal Sectional View Of Ileocaecal Orifice

Types

  • Infantile (Type 1) – 2%
  • Quadrate (Type 2) – 3%
  • Ampullary (Type 3) – 90%
  • Type 4 – 4%

Large Intestine Types Of Caecum

Vermiform appendix

Length – 2 – 20 cm

Shape – Worm-like

Locations of appendix

Retrocaecal – 12 o’clock – position – 65%

Pelvic – 4 o’clock – position – 31%

Subcaecal – 6 o’clock – position – 2%

Preileal – 2 o’clock – position – 1%

Postileal – 1 o’clock position – 0.4%

Paracaecal – 11 o’clock position

Promontoric – 3 o’clock position

Location of the base of the appendix

All three teenage coli converge to it (Surgical importance)

Large Intestine Locations Of Appendix

Surface marking of large intestine

  • The base of the appendix – Lateral trisection of spinoumbilical line.
  • Junction of ileum with large intestine (at caecocolic junction). Junction of right lateral with trans tubercular plane
  • Caecum
  • Right iliac region
  • Ascending colon
  • Right lumbar region
  • Transverse colon
    • Right lumbar region
    • Umbilical region
    • Left lumbar region
    • Left hypochondriac region
  • Descending colon
    • Left hypochondriac region
    • Left lumbar region
    • Left iliac region
  • Sigmoid colon
    • Hypogastric region

Large Intestine Surface Marking Of Large Intestine

Relations of large intestine

1. Peritoneal relations

  • Appendix – It has a mesoappendix formed by a double layer of peritoneum derived from the left leaf of the mesentery.
  • Caecum – It is covered by the peritoneum from all sides. A retrocaecal fossa is usually present.
  • Ascending and descending colons
    • Retroperitoneal – 52%
    • Ascending mesocolon only (Double layer of peritoneum connecting ascending colon with
      posterior wall) – 12%
    • Descending mesocolon only (Double layer of peritoneum connecting descending colon with
      posterior wall). – 22%
    • Both ascending and descending mesocolon – 14%
  • Transverse colon – It has a transverse mesocolon i.e. layer peritoneum connecting the transverse colon with posterior wall.
  • Sigmoid colon – It has a sigmoid mesocolon, which is a double layer of peritoneum holding the sigmoid colon. Its attachment is inverted ‘V’ (A) shaped
    • Upper limb attachment
      1. Along the external iliac artery (Pelvic brim)
      2. Halfway from the sacroiliac joint to the inguinal ligament
      3. 5 cm in length
    • Lower limb attachment
      1. Front of the upper sacrum
      2. From left sacroiliac joint to 3rd sacral segment
      3. 5 cm in length

Large Intestine Peritoneal Relations Of Large Intestine

2. Adjacent relations

  • Anterior relations
    • Transverse colon
      • Anterior abdominal wall.
    • Rest of colon
      • Anterior abdominal wall
      • Coils of small intestine
      • Greater omentum.
  • Posterior relations
    • Caecum
    • 2 Muscles
      • Psoas
      • Iliacus
    • 2 Nerves
      • Lateral cutaneous nerve of thigh
      • Femoral nerve
    • 2 Vessels
      • External iliac artery
      • Gonadal vessels

Large Intestine Posterior Relations Of Caecum, Ascending Colon And Descending Colon

Ascending colon

  • 4 Muscles
    • Psoas
    • Hiatus
    • Quadratus lumborum
    • Transversus abdominis
  • 2 Nerves
    • Iliohypogastric nerve
    • Ilioinguinal nerve
  • 1 Gland
    • Right kidney
  • Transverse colon (Near right colic flexure)
    • Duodenum
    • Head of the pancreas
  • Descending colon – It is related to the following structure on the left side.
    • Muscles – Psoas, Iliacus, Quadratus lumborum, Transversus abdominis
    • Nerves – Subcostal, Iliohypogastric, Ilioinguinal, Genitofemoral, Lateral cutaneous nerve of the thigh, Femoral
  • Vessels
    •  Subcostal
    • External iliac
    • Gonadal

Arteries of large intestine

  • Caecum and appendix
    • Inferior branch of the iliocoic branch of the superior mesenteric artery.
    • Named branches
      • Anterior caecal artery. It descends in the form of caecum
      • Posterior caecal artery. It descends behind the caecum.
      • The appendicular artery arises from this branch.

Large Intestine Arteries Supplying Caecum And Appendix

Large Intestine Arteries Of Large Intestine And Related Lymph Nodes

Colon– Marginal artery of Drummond

  • Formed by colic branches of superior and inferior mesenteric arteries
  • Extent- From the beginning of the ascending colon to the end of the sigmoid colon.
  • Long and short branches appear from the marginal artery and supply wall of the colon including taeniae coli and appendices epiploicae.

Large Intestine Short And Long Branches Of Marginal Artery Of Drummond

Veins of large intestine

  • Superior mesenteric vein (mid gut)
  • Inferior mesenteric vein (hindgut)- It drains into the splenic vein.
  • Superior mesenteric and splenic veins unite to form a portal vein.

Large Intestine Venous Drainage Of Large Intestine

Lymphatics of the large intestine

  • Caecum and appendix
    • Anterior ileocolic lymph nodes
    • Posterior ileocolic lymph nodes
    • Appendicular lymph nodes
    • (Efferents of the above lymph nodes drain into ileocolic lymph nodes → → Superior mesenteric lymph nodes)
  • Colon — Colic lymph nodes
    • Epicolic – over the colon
    • Paracolic – adjacent to colon
    • Intermediate colic
    • Preterminal colic – at the origin of colic arteries
    • (Efferents of the above lymph nodes drain into superior and inferior mesenteric lymph nodes)

Nerves of the large intestine

  1. Up to junctions of right 2/3rd with left l/3rd of transverse colon, it is supplied by autonomic plexus about mid gut artery (superior mesenteric artery) called superior mesenteric plexus.
  2. This plexus receives sympathetic fibres from spinal segments T 10-11 and parasympathetic fibres from the vagus.
  3. The rest of the colon receives autonomic fibres from the inferior mesenteric plexus which accompanies the artery of the hindgut i.e. inferior mesenteric artery. It receives sympathetic fibres from spinal segments T 10-11 and parasympathetic fibres from the hypogastric plexus (S 2,3,4).

Large Intestine Inbervation Of Large Intestine

Dissection Steps Of Large Intestine

Study the large intestine in situ and note its cardinal features. Note the peritoneal covering of the large intestine. Clean and define the caecum and turn it upwards. Identify the appendix and note its position.

  • Note the convergence of all taeniae to the base of the appendix. Note posterior relations of caecum. Cut the lateral wall of the caecum, wash and identify the ileocaecal orifice and orifice of the appendix.
  • Divide the peritoneum along the lateral margin of the descending colon and turn the colon medially. Note the attachment of sigmoid mesocolon. Tie two ligatures at the junction of the descending colon and sigmoid colon.
  • Divide the colon between these ligatures. Remove the large intestine and wash it. Take about a 6″ piece of the large intestine. Open it longitudinally and examine its interior.

Large Intestine Applied

  • Appendix
    • Appendicitis i.e. inflammation of the appendix.
    • Perforation of the appendix. It is a complication of appendicitis.
    • Referred pain from the appendix is felt at the umbilicus due to a common source (T10) of innervation
  • Caecum and colon
    • Cancer of the colon – Partial colectomy is preferred.
    • Diverticulosis – Evagination of mucosa through the wall.
    • Large bowel obstruction. Caecum is full of faeces. (In cases of small intestinal obstruction caecum is empty).

Portal Vein

Portal Vein Length – 8 cm

Portal Vein Commencement

  • Between the neck of the pancreas and the inferior vena cava.
  • Formed by the union of superior mesenteric and splenic veins

Portal Vein Course

Ascends behind the 1st part of the duodenum, in the free margin of the lesser omentum

Portal Vein Termination

At porta hepatis; it terminates by dividing into right and left branches.

Portal Vein Territory Of Drainage

  • Alimentary canal from the lower end of the oesophagus to the upper anal canal
  • Pancreas
  • Spleen
  • Gall bladder
  • Bile duct

Portal Vein Tributaries

  • Splenic vein
  • Superior mesenteric vein
  • Left gastric vein
  • Right gastric vein
  • Paraumbilical vein
  • Cystic vein

Large Intestine Portal Vein And Its Tributaries 1 To 5 Portosystemic Anastomoses

Portal Vein Applied

Obstruction of portal vein leads to,

  • Splenomegaly (enlargement of spleen)
  • Ascites (Collection of fluid in the peritoneal cavity)
  • Varicose veins at the sites of portosystemic anastomoses, i.e.
    • Lower 3rd of the oesophagus (Oesophageal varices)
    • Middle anal canal (Haemorrhoid)
    • Behind retroperitoneal viscera.
    • Bare area of liver
    • Umbilicus (Caput Medusae)
    • Patent ductus venosus.

Dissection Steps Of Portal Vein

Lift the tail of the pancreas from the spleen and separate the body of the pancreas from the posterior abdominal wall. Identify the inferior mesenteric, splenic, superior mesenteric and portal veins over the posterior surface of the pancreas.

Clean and trace the splenic vein to the junction of the superior mesenteric vein behind the neck of the pancreas and note the beginning of the portal vein. Follow the inferior mesenteric vein and note its termination. Trace the various tributaries of the portal vein.

Liver

Liver Peculiarity

Largest gland of the body

Liver Weight

  • Male – 1.4 – 1.8 kg.
  • Female – 1.2 – 1.4 kg.

Liver Situation – Mainly – Right hypochondriac and epigastric regions

Large Intestine Surface Marking Of Liver

Liver Surfaces

  • Superior
  • Anterior
  • Right
  • Posterior
  • Inferior (Visceral)

One border – Inferior

Large Intestine Surfaces And Borders Of Liver Front And Side Views

Liver Relations

1. Peritoneal relations

  • Anterior and superior – Falciform ligament extends from the liver to the anterior wall of the abdomen above the umbilicus
  • Posterior and Inferior – Coronary ligaments – Its upper and lower layers bound the bare area of the liver superiorly and inferiorly respectively.
  • Right triangular ligament. Formed by the union of two layers of the coronary ligament at the extreme right of the bare area.
  • Left triangular ligament. It is located on the back of the left lobe of the liver and is an extension of the left leaf of the falciform ligament.
  • Lesser omentum. Coronary and triangular ligaments connect the liver with the diaphragm while It extends between the liver and lesser curvature of the stomach.

Large Intestine Peritoneal Relation Of Anterosuperior Surface Of Liver

Large Intestine H Arrangement On The Posteroinferior Suface Of Liver Observed From Front After Raising The Inferior Border

Large Intestine Preritoneal Relations On The Posteroinferior Surface Of Liver

Large Intestine Peritoneal Reflection On The Posterior Surface Of Live And Its Mirror Image On The Posterior Wall Of Abdomen

2. Adjacent relations

  • All surfaces (except visceral),
    • Diaphragm – Separates liver from pleural and pericardial cavities as well as lungs and heart.
    • Anterior abdominal wall- Related to the anterior surface.
    • Right suprarenal gland- Related to bare area near inferior vena cava.
    • Superior- Central concavity for heart and pericardium.
    • Posterior- 3 Concavities – which are meant, from right to left,
      • For inferior vena cava
      • For vertebral column
      • For oesophagus
  • Visceral surface is related to the following,
    • Stomach and lesser omentum
    • Duodenum
    • Right kidney
    • Right colic flexure
    • Gall bladder.

Large Intestine Relations Of Posteroinferior Surface Of Liver

Liver Segmentation

The liver is divided into lobes, parts, segments and regions as mentioned below.

1. Right and left lobes

  • Anatomical lobes – Here the criteria is attachment of falciform ligament and therefore caudate and quadrate lobes are parts of the right lobe.
  • Physiological lobes – Here the criteria is the plane of inferior vena cava and gall bladder and therefore caudate and quadrate lobes are parts of the left lobe but the caudate process is excluded.

Large Intestine Segmentation Of Liver

2. Segments, parts and regions

  • 3 Segments in the right lobe – Anterior – intermediates (middle) and posterior 2 Parts in the left lobe – Medial and lateral.
  • Subdivisions in the left lobe
    • Medial part- Anterior region, central region and posterior region.
    • Lateral part- Anterior segment, and posterior segment
  • All subdivisions may be divided into upper and lower

Large Intestine Diagrammatic Presentation Of Segmentation Of Liver

3. Based on drainage by hepatic veins, the liver is divided into 8 surgical segments i.e. from 1 to 8.

Large Intestine Surgical Divisions Of Liver Into 8 Segments (1 to 8) Depending Upon The Drainage By The Hepatic Veins

Liver Blood supply

20% – Hepatic artery

80% – Portal vein

Liver Venous drainage

2-3 Hepatic veins drain into the inferior vena cava.

Lymphatic drainage

1. Superficial lymphatics

  • The left portion of the posterior surface
  • The posterior portion of the inferior surface
  • The middle portion of the superior surface
    • From a, b, and c lymphatics drain into right lateral diaphragmatic and paracardiac lymph nodes, both located above the diaphragm.
  • The right portion of the posterior surface is drained by coeliac lymph nodes about the origin of the coeliac artery.
  • The rest of the liver is drained by hepatic lymph nodes located at porta hepatis.

2. Deep lymphatics

  • Ascending- Right lateral diaphragmatic lymph nodes (Near the entrance of inferior vena cava)
  • Descending- Hepatic lymph nodes

Large Intestine Lymphatic Drainage Of Liver

Nerves

  • Parasympathetic – Vagus – Hepatic branch of the anterior vagal trunk and coeliac branch of the posterior vagal trunk.
  • Sympathetic – T7 -9, via greater splanchnic nerve and coeliac plexus.
  • Nerves follow the hepatic artery to reach the liver.

Liver Applied

  • Hepatitis (inflammation of the liver)
    • Amoebic hepatitis
    • Infective hepatitis (Viral)
  • Icterus / Jaundice – Yellowish pigmentation of skin due to a high level of bilirubin in the blood.
  • Hepatomegaly (Enlargement of the liver) Massive hepatomegaly is observed in cancer and hydatid cysts.
  • Cirrhosis – It leads to portal obstruction

Dissection Steps Of Liver And Gall Bladder

Identify the liver and gall bladder in situ. Pull the liver down and cut the layers of the left triangular and coronary ligaments. Identify and feel inferior vena cava and cut it above and below the liver.

Remove the liver along with the segment of the inferior vena cava. Study the liver for its different lobes, fissures, grooves, ligaments, and porta hepatis. Identify the various parts of the gall bladder and extrahepatic biliary apparatus.

Extrahepatic Biliary Apparatus

Gall Bladder

  1. Pear shaped
  2. Measurement and capacity.
  3. The gall bladder is 3 cm in width and 10 cm in length. Its capacity is approximately 30-50 ml.
  4. 4 parts
    • Fundus – Portion of gall bladder beyond the inferior border of the liver.
    • Body
    • Infundibulum (Hartmann’s pouch) – It is bending in the upper part of the gall bladder which connects the body with the neck.
    • Neck – It is a narrow uppermost part of the gall bladder which turns to the left to continue as a cystic duct.

Extrahepatic Biliary Apparatus Parts Of Gall Bladder And Formation Of Bile Duct

Gall Bladder Relations

  • Peritoneal
    • In the majority of cases, the anterior surface of the body is in contact with the inferior surface of the liver while the rest of it is covered with the peritoneum. Rarely the gall bladder has mesentery.
  • Adjacent relations
    • Anterior
      • Liver,
      • Anterior abdominal wall,
    • Posterior
      • Duodenum
      • Transverse colon
  • Artery– Cystic artery from the right hepatic artery
  • Veins– Cystic vein draining into right branch of portal vein
  • Lymphatics
    • Cystic lymph nodes —» Hepatic lymph nodes —> Coeliac lymph nodes
  • Nerves
    • Coeliac plexus- Sympathetic and parasympathetic
    • Phrenic nerve (via communicating branch with coeliac plexus) – This explains the referred pain to the right shoulder.

Extrahepatic Biliary Apparatus Relations Of Gall Bladder And Common Bile Duct

Function – To store and concentrate the bile.

Applied

  • Inflammation of the gall bladder is called cholecystitis. It can be acute or chronic
  • Stone in the gall bladder is called cholelithiasis
  • + ve Murphy’s sign —» Catch in breath on palpation if the organ is inflamed.

Cystic duct

  • 4 cm in length
  • Connects neck of gall bladder with common hepatic duct

Right and left hepatic ducts

Appear from porta hepatis

Common hepatic duct

  • 4 cm in length.
  • The common hepatic duct unites with the cystic duct to form a common bile duct.

Common bile duct

  • 8 cm in length.
  • 3 parts
    • 1st part – Supraduodenal ( In the free margin of lesser omentum)
    • 2nd part – Retroduodenal ( Behind duodenum)
    • 3rd part – Infraduodenal (Behind the head of the pancreas)

Extrahepatic Biliary Apparatus Termination Of Common Bile Duct

The Sphincter of Boyden guards the terminal part of the common bile duct.

  • It terminates in the substance of the head of the pancreas by joining the main pancreatic duct to form the ampulla of Vater. Ampulla is guarded by the sphincter of Oddi and itself opens on the summit of the major duodenal papilla in the posteromedial wall of 2nd part of the duodenum.
  • Artery
    • The upper part is supplied by the cystic artery
    • The lower part is supplied posterior branch of the superior pancreaticoduodenal artery.

The Diaphragm

The Diaphragm Definition

Musculotendinous partition between thorax and abdomen

The Diaphragm Attachments

Origin (Peripheral attachments)

Sternal – Xiphoid – 2 slips

Extrahepatic Biliary Apparatus Inferior Surface Of The Diaphragm

Costal – Lower 6 costal cartilages

  • Vertebral – Crura – Right crus – It is attached to the upper three lumbar vertebral bodies
  • Left crus – It is attached to the upper two lumbar vertebral bodies
  • Arcuate ligaments – Median – It connects its two cura in front of the 12th thoracic vertebral body.
  • Medial – It connects the 2nd lumbar vertebral body with the 1st lumbar transverse process.
  • Lateral – It connects 1st lumbar transverse process with the 12th rib
  • Insertion (Central tendon) – Trefoil / Trifoliate in nature. It has the following parts
    • Central part – Cruciate node-It is formed due to crossing connective tissue fibres
    • Right leaf
    • Anterior leaf
    • Left Leaf

The Diaphragm Shape

From front – Two domes (Right and Left) and a concavity

  • Both the domes reach the level of the 5th rib (the right dome is higher) and correspond with the
    concavities of the base of the lungs.
  • The middle part fuses with fibrous pericardium.

From side – Inverted T-shaped.

Extrahepatic Biliary Apparatus Shapes Of Diaphragm Front And Side View

The Diaphram Functions

  • Respiration
  • Abdominal strainings
    • Defaecation
    • Micturition
    • Parturition
  • Weight lifting

The Diaphragm Openings

  • Large openings
    • Aortic aperture – It is present at the level of the 12th thoracic vertebral body.
  • Structures passing through it are,
    • Aorta
    • Thoracic duct
    • Vena azygos
    • Lymphatics
  • Oesophageal aperture – It is located at the level of the 10th thoracic vertebra and allows the following structures to pass through it,
    • Oesophagus
    • Anterior and posterior vagal trunks
    • Oesophageal vessels from/to left gastric vessels
  • Venacaval aperture – It is located at the level of the 8th thoracic vertebra. Following structures pass through it,
    • Inferior vena cava
    • Right phrenic nerve
    • Lymphatics

Small Passages – for,

  • Superior epigastric vessels.
  • Lower 5 (7th to 11th) intercostal nerves, 10th and 11th posterior intercostal vessels.
  • Subcostal nerve and vessels.- These pass under lateral arcuate ligaments.
  • Sympathetic chains – These pass under medial arcuate ligaments.
  • Greater and lesser splanchnic nerves- These pierce the crura of the diaphragm.
  • Left phrenic nerve.
  • Hemiazygos vein.

Dissection Steps For Diaphragm

Strip the parietal peritoneum from the undersurface of the diaphragm and identify its various parts and openings. Clean and define the attachments of crura and arcuate ligaments.

  • Clean and define the major openings (caval, oesophageal and aortic) in the diaphragm with structures passing through them. Work out their levels about the thoracic spines.
  • Explore various other minor openings (for superior epigastric vessels, subcostal vessels and nerves, sympathetic trunk and splanchnic nerves) and structures passing through them.
  • Openings for the superior epigastric vessels, lower 5 intercostal nerves and hemiazygos vein may also be located.

The Diaphragm Nerves

  • Motor – Phrenic nerve – (C3, 4, 5)
  • Sensory
    • Central part -Phrenic nerve.
    • Peripheral part – Lower intercostal nerves (T7-11)

Nerves Arteries

  • Inferior phrenic arteries from the abdominal aorta.
  • A musculophrenic artery from the internal thoracic artery.
  • A pericardiacophrenic artery from the internal thoracic artery.

Nerves Applied

Hiatus hernia – Abdominal contents protrude into the thoracic cavity through openings in the diaphragm.

  • Sliding / Oesophagogastric – 85%
  • Rolling / Paraoesophageal – 10%
  • Mixed or Transitional -5%

Extrahepatic Biliary Apparatus Hiatus Hernia

Posterior Wall Of Abdomen

Muscles Of The Posterior Abdominal Wall

1. Quadratus lumborum

Origin – Iliac crest and lower lumbar transverse processes

Insertion – 12th Rib and upper lumbar transverse processes.

Nerve – Directly from lumbar plexus (L 1-4)

Actions – Lateral flexion of spine Respiration

Posterior Wall Of Abdomen Muscles Of Nerves Of The Posterior Abdominal Wall

Thoracic-Iumbar fascia– It has the following three layers

  • Anterior layer – On the anterior surface of quadratus lumboram.
  • Middle layer – On the posterior surface of quadratus lumborum.
  • Posterior layer – Over erector spinae.

Posterior Wall Of Abdomen Thoracolumbar Fascia

2. Psoas major

  • Origin – Bodies and transverse processes of lumbar vertebrae.
  • Insertion – Lesser trochanter of femur.
  • Nerve – Directly from lumbar plexus ( LI-4.)
  • Actions – Lateral flexion of the spine.
  • Flexion and medial rotation of the thigh.

3. lilacs

  • Origin – Iliac fossa.
  • Insertion – Lesser trochanter.
  • Nerve – Femoral nerve.
  • Actions – Flexion and medial rotation of the thigh.

Nerve Supply Of Posterior Abdominal Wall

  • Subcostal nerve
    • Runs laterally under lateral arcuate ligaments.
  • Branches of lumbar plexus ( L1-4)
    • Directly from roots of lumbar plexus for quadratus lumborum and psoas
    • Iliohypogastric nerve (LI) – Runs laterally over the quadratus lumborum muscle
    • Ilioinguinal nerve (LI)- Runs laterally just below the iliohypogastric nerve.
    • Genitofemoral nerve (LI,2). Descends in front of the Psoas major muscle.
    • The lateral cutaneous nerve of the thigh (L2,3). Extends towards the anterior superior iliac spine
    • Femoral nerve (L2,3,4). Descends in the groove between the psoas and iliacus.
    • Obturator nerve – (L2,3,4). Descends along the medial border of psoas.

Posterior Wall Of Abdomen Lumbar Plexus V-Ventral Division, D-Dorsal Division, Ps-Psoas, Qi-Quadratus Lumborum

3. Sympathetic chain

  • Ganglia
  • 4 lumbar ganglia lie in the groove between lumbar vertebral bodies and psoas
    • 4 sacral ganglia lie over sacral feramina or medial to them,
    • 1 ganglion impair is located over the coccyx
  • Grey and white rami communicantes (latter from upper two lumbar ganglia only)
  • Lumbar splanchnic nerves from the lumbar ganglia join the hypogastric plexus.

4. Autonomic plexuses

  1. Coeliac plexus (About coeliac artery from the aorta)
    • The right and left coeliac ganglia in the coeliac plexus on each side of the coeliac artery receive greater (T5-9) and lesser (T10-11) splanchnic nerves.
    • Communicating nerve from phrenic nerve joins coeliac plexus
    • Coeliac branch of posterior vagal trunk also joins oeliac plexus
  2. Phrenic plexus – Follows inferior phrenic artery.
  3. Left gastric plexus -Follows left gastric artery.
  4. Splenic plexus – Follows splenic artery.
  5. Hepatic plexus – Follows hepatic artery.
  6. Renal plexus (Along renal artery) – It has a renal ganglion which receives fibres from the least splanchnic nerve (from the last thoracic ganglion)
  7. Superior mesenteric plexus- Follows superior mesenteric artery.
  8. Abdominal aortic (Intermesenteric) plexus- over the abdominal aorta between origins of
    superior and inferior mesenteric arteries.
  9. Inferior mesenteric plexus- Follows inferior mesenteric artery.
  10. Superior hypogastric plexus- Concerning sacral promontory.
  11. Inferior hypogastric plexus (pelvic plexus)- Behind the rectum, in front of the sacrum.

Dissection Steps Of Posterior Abdominal Wall

Clean the posterior abdominal wall and denude it from all fascia and identify the inferior vena cava and its tributaries, abdominal aorta and its branches.

  • Clean the muscles of the posterior abdominal wall and identify the quadratus lumborum, and psoas major and minor.
  • Clean and trace the subcostal, iliohypogastric, ilioinguinal, femoral and obturator as well as lateral cutaneous nerves on the posterior abdominal wall.

Abdominal Aorta

Extent -From aortic hiatus (T12) to L4 vertebra

Abdominal Aorta Branches

1. Ventral (unpaired) branches.

  • Coeliac artery. Appears at T12 vertebra.
  • Superior mesenteric artery. Appears at Lj vertebra.
  • Inferior mesenteric artery. Appears at L3 vertebra.

2. Lateral (paired) branches. (Actually, these are anterolateral)

  • Inferior phrenic artery- To the inferior surface of the diaphragm.
  • Middle suprarenal artery- To suprarenal gland.
  • Renal artery- To kidney.
  • Gonadal (Testicular or Ovarian) artery- To gonad.

Posterior Wall Of Abdomen Abdominal Aorta And Autonomic Plexuses

3. Dorsal branches

  • Lumbar arteries (posterolateral) – There are four paired lumbar arteries opposite the upper four lumbar vertebrae
  • Median sacral artery (posterior) – Arises from the bifurcation of the aorta and descends in front of the sacrum in the middling.

4. Terminal branches

The aorta terminates at the level of the 4th lumbar vertebra into the right and left common iliac arteries These terminate at the level of the sacroiliac joint into external and internal iliac arteries.

Inferior Vena Cava

Inferior Vena Cava Extent – From L5 vertebra to T8 vertebra (Venacaval orifice)

Inferior Vena CavaTributaries

  1. Common iliac veins – These unite to form the inferior vena cava at the level of the 5th lumbar vertebra.
  2. Lumbar veins, from the abdominal wall. These accompany the lumbar arteries.
  3. Right gonadal (Testicular or ovarian) veins, from right gonad (testis in male and ovary in
    female).
  4. Renal veins, from kidneys.
  5. Right suprarenal vein, from right suprarenal gland.
  6. Right inferior phrenic vein, from under the surface of the right portion of the diaphragm.
  7. Hepatic veins- 3, from liver.

Posterior Wall Of Abdomen Inferior Vena Cava

Lymph Nodes

These are named after their relations with arteries.

  • Internal iliac lymph nodes.
  • External iliac lymph nodes.
  • Common iliac lymph nodes.
  • Lumbar lymph nodes (Along the aorta and inferior vena cava.)
    • Preaortic lymph nodes
      1. Coeliac lymph nodes (With the origin of a coeliac artery).
      2. Superior mesenteric lymph nodes (About the origin of the superior mesenteric artery)
      3. Inferior mesenteric lymph nodes (About the origin of the inferior mesenteric artery)
      4. Efferents from the above lymph nodes form a single intestinal trunk which drains into cistema chyli in its middle.
    • Lateral aortic (Para-aortic) lymph nodes. Their efferents unite to form right and left lumbar trunks which join the lower part of cisterna chyli.
    • Retroaortic lymph nodes (Lying behind the aorta).

Posterior Wall Of Abdomen Abdominal Lymph Nodes

Suprarenal Glands

Suprarenal Glands Location: Near the kidney’s upper pole.

Suprarenal Glands Weight: 5 grams.

Suprarenal Glands Measurements: Height- 5 cm, Width- 3 cm, Thickness- 1 cm.

Suprarenal Glands Coverings: Perinephric fat and renal fascia.

Suprarenal Glands Location And Vascular Supply Of Suprarenal Gland

Differences between two glands

Suprarenal Glands Differences Between Two Glands

Suprarenal Glands Relations Of Suprarenal Glands Anterior And Posterior Relations

Arteries

  • Three in number,
  • Superior suprarenal artery – from the inferior phrenic artery.
  • Middle suprarenal artery – from aorta
  • Inferior suprarenal artery – from renal artery
  • All three arteries enter the gland away from the hilum.

Veins – One in number. It appears from the hilum and drains on the right side into the inferior vena cava and on the left side into the left renal vein.

Lymphatics – Drain into lateral aortic lymph nodes.

Nerves – Preganglionic sympathetic fibres are derived from coeliac plexus (TIO- LI)

Suprarenal Glands Applied

  • Cortex
    • Decreased secretion → Addison’s disease
    • Increase secretion —> Cushing’s syndrome – It causes masculinization in females and feminization in males.
  • Medulla – Phaeochromocytoma – It is a benign tumour leading to an increase in its secretion followed by hypertension.

Kidneys

Kidneys Weight: 135 — 150 grams, (less in females)

Kidneys Measurements: Height-11 cm (>4″), Width-6cm (>2″) Thickness-3cm (>1″).

Kidneys Surface projection

  • Hilum- It lies in a transpyloric plane about 5 cm from the midline.
  • Anterior —> This plane passes through the tips of the 11th costal cartilage.
  • Posterior → This plane passes through the spine of 1st lumbar vertebra

(Note: Right hilum is located a little below and left, a little above the plane)

Upper pole – 2.5 cm from midline.

Lower pole – 7.5 cm from midline.

Size – 4.5 x 11 cm

Kidney Surface Marking Of Kidney Anterior And Posterior Surfaces Of Bodies

Hilum and renal sinus: Hilum is a concavity along the medial border of the kidney to receive renal vessels. Deep to the hilum is a space for the renal pelvis, major and minor calyces, renal vessels and some connective tissue. This space is called the renal sinus.

Kidney Hilum And Renal Sinus Of Kidney Anterior And Cross Sectional Views

Coverings of kidney

Kidney Covering Of Kidney Sagittal Sectional Cross Sectional Views

Capsule – It is immediate connective tissue covering.

Perinephric (perirenal)fat – It is a fatty layer next to the capsule.

Renal fascia – It is a well-defined membrane over perinephric fat. This fascia along with perinephric fat also encloses the suprarenal gland.

The fascia on the front and back of the kidney, meet laterally but continue downwards and medially without meeting with each other. Medially they fuse with adventitia of great vessels i.e. renal vessels, inferior vena cava and abdominal aorta.

Paranephric (pararenal) body – This is fatty aggregation in the paravertebral gutter behind the kidney.

Kidneys Relations

  • Posterior relations are almost symmetrical on two sides.
    • 4 muscles
    • Quadratus lumborum
    • Diaphragm
    • Psoas major
    • Transversus abdominis
  • Subcostal nerve and vessels
  • Medial and lateral arcuate ligaments
  • Hiohypastric and ilioinguinal nerves
  • Ribs- 12th (on both sides) and 11th (on left side only)

Kidney Anterior Relations Of Kidney

Kidney Posterior Relations Of Kidney

Anterior relations are different on two sides

  • Right kidney 
    • Right suprarenal gland
    • Duodenum
    • Liver
    • Right colic flexure
    • Right colic artery
    • Small intestine (Coils of jejunum)
  • Left kidney
    • Left suprarenal gland
    • Spleen
    • Stomach
    • Pancreas
    • Jejunum
    • Descending colon

Kidney Arteries

  • Renal artery – It divides into anterior and posterior divisions. The former is further divided into four branches.
  • Vascular segmentation of kidney – Based on arterial supply, the kidney is divided into 5 segments:
    • Apical segment
    • Superior segment
    • Middle segment
    • Inferior segment
    • Upper 4 segments are supplied by 4 branches of anterior division.
    • Posterior segment- Supplied by posterior division.
  • Bloodless line of Brodel (1901) – It is a vertical line along the lateral border of the kidney. An incision along this line results in relatively less bleeding.

Kidney Vascular Segmentation Of Kidney

  1. Arteries Of Kidney
  2. Lateral View Of Right Kidney
  3. Medial View Of Left Kidney

Kidney Brodels Bloodless Line

Kidney Vein

Renal vein

Kidney Lymphatics

Drain into para-aortic lymph nodes.

Kidney Nerves

Sympathetic (T12-L1)

Preganglionic fibres are derived from least splanchnic and lumbar splanchnic nerves which relay into renal ganglion. Postganglionic fibres further run a course in the renal plexus before supplying the kidney.

Kidney Lymphatic Drainage Of Kidney

Dissection Steps Of Kidneys And Suprarenal Glands

Remove fat and fascia from the anterior surface of the kidneys and suprarenal glands. Indentify kidney and suprarenal in situ, and renal vessels. Identify the opening of the suprarenal vein, gonadal vein and renal vein on the left side.

  • Clean and trace the ureters. Note their relations at the hilum. Mobilise both the kidneys and turn them medially. Separate suprarenals from the renal fascia and note their relations. Remove suprarenals and note the differences in their shape.
  • Cut the ureters at the lower poles of the kidneys and the renal vessels 2 cm from the hilum and remove them. Study the posterior relations.
  • Cut one kidney along its lateral border into two halves (anterior and posterior) and study the cut sections for the cortex, medulla, pyramid, calyces and pelvis of the ureter.

Kidneys Applied

  • Congenital anomalies,
    • Congenital polycystic kidney
    • Horseshoe kidney
    • Pelvic kidney
  • Acquired – Renal stones.
  • IVP – Intravenous pyelography. Introducing intravenous radio-opaque fluid and visualising the kidney, ureter and urinary bladder in the radiograph.

Kidney Horse Shoe Kidney

Ureters

Length: 30 cm

Diameter: 3 mm

Commencement: Continuation of renal pelvis.

Termination: Ends by entering the base of the urinary bladder.

Two parts

  • Abdominal part – 15cm
  • Pelvic part – 15 cm

Ureters Posterior Relations Of Abdominal Part Of Ureter

Ureters Relations

The posterior relation is symmetrical on two sides, i.e.,

  • Psoas,
  • Tips of lower 4 lumbar transverse processes.
  • Genitofemoral nerve

Ureters Formation Of Renal Pelvis Cross And Longitudinal Sectional Views

Anterior relations arc differently on two sides, as given below,

Ureters Anterior Relations Are Different On Two Sides

Ureters Anterior Relations Of Abdominal Part Of Ureter Right And Light Ureters

Surface projection (on the anterior abdominal wall)

Hilum Of kidney to public tubercle

Ureters Constructions

  • At Commencement- At the tip of the transverse process of the second lumbar vertebra.
  • At Middle- At the pelvic brim over the sacroiliac joint
  • At the Lower end Slight medial to the ischial spine

Ureters Surface Marking Of Ureter

Ureters Arteries

Upper abdominal part

It is supplied by branches from the renal artery, abdominal aorta and gonadal artery.

Lower abdominal part

It is supplied by branches from the common iliac artery.

Pelvic part

It is supplied by branches from vesical arteries, and uterine arteries (in females).

Ureters Anterior Relations Supply And Lymphatic Drainage Of Ureter Lymph Nodes

Ureters Lymphatics

  • Upper abdominal part – Lymphatics drain into lateral aortic lymph nodes.
  • Lower abdominal part – Lymphatics drain into common iliac lymph nodes.
  • Pelvic part – Lymphatics drain into common iliac lymph nodes, external iliac lymph nodes and internal iliac lymph nodes.

Nerves are derived from the following autonomic plexuses

  1. Renal plexus.
  2. Aortic plexus.
  3. Superior hypogastric plexus.
  4. Inferior hypogastric plexus.

Sympathetic – T10 — LI

Parasympathetic – S2,3,4

Ureters Applied

  • Renal or ureteric colic – Pain is referred to the testis (T10 segment) or medial side of the thigh (LI segment).
  • Obstruction of the ureter may result in hydronephrosis- dilatation of calyces.
  • Pyelography. In this procedure kidney, ureter and urinary bladder are visualized by using radioopaque fluid. The drug can be introduced by intravenous injection (descending pyelography) or by catheter into the ureter (ascending pyelography).

Bones Of Thorax Notes

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Bones Of Thorax And Abdomen

The following bones constitute the thorax:

  1. Sternum: Bone of anterior wall of thorax
  2. Twelve thoracic vertebrae: Bones of the posterior wall of the thorax. These are named after 1st thoracic vertebra to the twelfth thoracic vertebra from above downwards
  3. Twelve pairs of ribs: Bones of lateral walls of the thorax

The following bones constitute the abdomen and pelvis:

  1. Five lumbar vertebrae: Bones of the posterior abdominal wall. These are named from 1st lumbar vertebra to the fifth lumbar vertebra from above downwards.
  2. Sacrum and coccyx: These together with hip bones form a bony pelvis or pelvic girdle and form the skeleton of the pelvis and gluteal region.

The total number of bones in the thorax and abdomen are as follows:

  1. Thorax -37
  2. Abdomen and pelvis- 9

Note: Two hip bones are common to both lower limbs and pelvis

Reference diagrams to make incisions for dissection

Bones Of Thorax And Abdomen Landmarks And Incisions Ventral Incisions

Bones Of Thorax And Abdomen Landmarks And Incisions Dorsal Incisions

Thoracic Cage Framework

The thoracic cage is an osseoligamentous framework formed by 12 thoracic vertebrae posteriorly, sternum anteriorly and 12 pairs of ribs and costal cartilages on each side.

The posterior wall is longer as compared to the anterior wall making upper and lower openings of the thoracic cavity oblique.

Thoracic Cage Framework Shape Of The Thoracic Cage, Side View

The upper opening (anatomists call it thoracic inlet and clinicians name it thoracic outlet) faces upwards and forwards.

It is bounded by the highest (1st) thoracic vertebra posteriorly, the superior border of manubrium stem anteriorly (sternum consists of 3 pieces from above downwards namely manubrium stem, body and xiphisternum) and the inner border of highest (1st) rib and its costal cartilage on each side.

  • The lower opening (thoracic outlet) faces forward and downwards. It is bounded anteriorly by the xiphisternal joint.
  • Posteriorly by the last (12th) thoracic vertebra and the 12th pair of ribs and on each side by lower 6 (7th to 12th) costal cartilages. Boundaries formed by ribs and costal cartilages are also called coastal margins.

Which form a subcostal angle below the xiphoid process anteriorly. The lower opening is occupied by a musculotendinous partition between the thorax and abdomen called ‘the diaphragm’.

Thoracic Cage Framework Boundaries Of Inlet (Upper Opening Of Thoracic Cage)

Thoracic Cage Framework Boundaries Of Outlet (Lower Opening Of Thoracic Cage)

The thoracic cavity is not circular in outline, but compressed anteroposteriorly and due to the forward projection of thoracic vertebral bodies it becomes reniform (kidney-shaped) in shape.

  • The 12 thoracic vertebrae follow the primary curvature (concavity forward i.e., the original foetal curvature) to provide adequate room for the vital thoracic organs.
  • Ribs are curved bones whose posterior ends invariably articulate with the vertebrae and the anterior ends extend forwards variably. 1st rib fuses with the upper part of the lateral border of the manubrium stem (synostosis).
  • 2nd to 7th ribs end a short distance from the side of the sternum, the gap being filled by the costal cartilages (thus upper 7 ribs are vertebrosternal).
  • The anterior ends of the 8th to 10th ribs are similarly replaced by the costal cartilages but instead of reaching the sternum they articulate with the costal cartilages just above (thus, the 8th to 10th ribs are vertebrochondral).

The lower two ribs are replaced by small costal cartilages at their anterior ends, which do not articulate with adjacent costal cartilages (thus, the 11th and 12th ribs are vertebral).

Thoracic Cage Framework Outline Of Thoracic Cavity

Thoracic Cage Framework Thoracic Cage

Between 12 pairs of ribs and costal cartilages are 11 pairs of intervals called the intercostal spaces. The obliquity of the spaces corresponds with the obliquity of the ribs.

Their width gradually reduces from above-downwards as those of coastal cartilages. The intercostal spaces are occupied by the intercostal muscles.

Joints Of Thorax

Sternal Joints

Three pieces of sternum (manubrium, body and xiphisternum) meet at two junctions, the manubriostemal and xiphisternal. Both the joints thus formed are secondary cartilaginous (symphyses) in nature.

Thoracic Cage Framework Sternal Joints

Sternocostal Joints

Only true ribs (upper seven, vertebrosternal) reach the sternum but indirectly through the costal cartilages to form sternocostal (truly speaking osteochondral) joints.

1st costal cartilage forms a primary cartilaginous joint with the side of the upper part of the manubrium. 2nd costal cartilage meets with the sternum at the manubriostemal joint (level of sternal angle) forming a synovial joint.

Its cavity is divisible into two by an intra-articular disc. 3rd to 6th costal cartilages meet with the side of the body of the sternum while the 7th reaches the side of the xiphisternal joint, each forming a single synovial joint cavity.

Interchondral Joints

Adjacent surfaces of6th to 9th costal cartilages form synovial interchondral joints. Each joint is supported by medial and lateral interchondral ligaments.

Thoracic Cage Framework Sternocostal And Interchondral Joints

Costochondral Joints

These are primary cartilaginous joints between the concavities at the anterior ends of long ribs and convexities at the lateral ends of corresponding costal cartilages.

Thoracic Cage Framework Costochondral Junctions

Costovertebral Joints

Joints Of The Heads Of The Ribs

The head of a typical rib articulates with the upper border of the corresponding vertebral body and the inferior border of the vertebral body above; i.e., levels with the intervertebral disc.

The synovial joint thus formed is strengthened by the radiate ligament that connects the front of the head of the rib with the adjacent vertebral border and intervertebral disc.

Thoracic Cage Framework Joints Of Heads Of Ribs

The cavity of the joint is divided into upper and lower compartments by an intra-articular ligament which connects the crest of the head with the intervertebral disc.

Costotransverse Joint

It is a synovial joint formed between the articular facet of the tubercle of the rib and the costal facet on the front of the lateral part of the transverse process of the corresponding vertebra. The joint is strengthened by three costotransverse ligaments.

The inferior costotransverse ligament connects the front of the corresponding transverse process medial to the joint.

A similar ligament lateral to the joint is called the lateral costotransverse ligament. The superior costotransverse ligament connects the superior border of the neck of the rib with the transverse process of the vertebra above.

Thoracic Cage Framework Constotransverse Joints And Ligaments

Joints Of The Vertebral Column

Joints Of The Vertebral Bodies

Bodies of the adjacent vertebrae form secondary cartilaginous joints. Adjacent surfaces are covered with hyaline cartilages with intervening intervertebral discs.

  • The latter has concentric fibrous laminae in the periphery (annulus fibrosus) and gelatinous mass in the centre (nucleus pulposus).
  • Joints strengthened by vertical fibrous bands all along the vertebral column, anterior and posterior to the vertebral bodies called anterior and posterior longitudinal ligaments.

Thoracic Cage Framework Joints Of The Vertebral Bodies And Arches

Joints Of The Vertebral Arches

Zygapophyseal Joints

These are plane synovial joints between the adjacent superior and inferior articular processes. articular surfaces are oblique and located along a horizontal arc therefore allowing rotational movements in the thoracic region.

Intervertebral Syndesmosis

Gaps between the adjacent laminae of the thoracic vertebrae are filled by the ligamentum flava. The spines of the adjacent vertebrae are held together by the interspinous ligaments.

The supraspinous ligament is an elongated band connecting the tips of the spines. Intertransverse ligaments connect the adjacent transverse processes.

Intrinsic Muscles Of Thoracic Wall

The muscles are arranged in three layers, external (external intercostal), middle (internal intercostal), and internal (stemocostal is, intercostales intimi and subcostales).

1st two are smaller and occupy the intercostal spaces while the innermost is larger and covers the inner surfaces of the ribs.

Intrinsic Muscles Of Thoracic Wall Intrinsic Muscles Of Thoracic Wall

Intrinsic Muscles Of Thoracic Wall Attachments

External intercostal muscles connect the adjacent border of the ribs. In the anterior part, its fibres downwards and forwards.

In an intercostal space, the external intercostal extends from the tubercle to the anterior end of the rib. The muscle is replaced by the external intercostal membrane between the costal cartilages.

Intrinsic Muscles Of Thoracic Wall Extent Of External And Internal Intercostal Muscles

The internal intercostal muscle is attached to the upper border of the rib below and the costal groove of the rib above.

  • Towards the posterior end, its fibres run downwards and backwards. In an intercostal space, it extends from the angle of the ribs to the anterior end of the intercostal space.
  • The side of the sternum. Beyond the angle posteriorly, it is represented by the internal intercostal membrane.

Intrinsic Muscles Of Thoracic Wall Intrinsic Muscles And Neurovascular Bundle Of The Thoracic Wall

The three components of the innermost layer i.e., stemocostal (also called the transverse thoracic), intercostales intima and the subcostales, occupy approximately the anterior 1/4th.

Middle 2/4th and the posterior 1/4th of the intercostal spaces respectively. Fibres of the stemocostal are attached to the posterior surface of the lower half of the sternum and extend upwards and laterally towards the 2nd to 6th pairs of the costal cartilages.

Intrinsic Muscles Of Thoracic Wall Sternocostalis

Intercostalis intimi connects the inner surfaces of the adjacent ribs while subcostales extend between the inner surfaces of distant ribs. The direction of fibres in both these muscles is the same as that of internal intercostals.

Intrinsic Muscles Of Thoracic Wall Dissection Steps

Remove the remains of the serratus anterior and pectoral muscles. Choose one intercostal space and cut through the external intercostal muscle and external intercostal membrane along the lower border of the space.

  • Turn the muscle upward identify the internal intercostal muscle and note the direction of its fibres both anteriorly and posteriorly and concerning the external intercostal muscle.
  • Expose and identify the lateral cutaneous branch of the intercostal nerve trunk deep into the internal intercostal muscle. Cut the internal intercostals, expose and follow the intercostal nerve forward and backwards with the accompanying intercostal vessels.
  • Identify the innermost intercostal muscles and note their arrangement. Remove the intercostal muscles and membranes from the anterior part of the 1st and 2nd intercostal spaces and expose the internal thoracic artery lateral to the sternum.
  • Trace this artery into the 6th intercostal space and note its terminal branches, namely superior epigastric and musculophrenic arteries.

Intrinsic Muscles Of Thoracic Wall Nerves

Intercostal nerves

Intrinsic Muscles Of Thoracic Wall Actions

External intercostals and the interchondral parts of the internal intercostals elevate the ribs i.e., help in inspiration, while rest depresses the ribs and helps in expiration.

The tone of the intercostal muscles prevents in-drawings and budging of the intercostal spaces during inspiration and expiration respectively.

Intrinsic Muscles Of Thoracic Wall Applied Anatomy

  1. The needle should be introduced near the upper border of the ribs to avoid injury to the main intercostal and vessels which run in the costal groove.
  2. Retraction of intercostal spaces is evident along with stridor, dyspnoea and cyanosis in cases of obstruction of major passages.
  3. Structural (fixed) scoliosis is always accompanied by rotation of vertebrae (i.e., there is some kyphosis). Asymmetrical paralysis of the intercostal muscles is one of the many causes of this condition.

Intrinsic Muscles Of Thoracic Wall Preferable Site Of Introduction Of Needle Into The Thorax

Respiratory Movements

These are the movements of the ribs and diaphragm which are responsible for the act of respiration.

  • The former is responsible for the increase in the anteroposterior and transverse diameters while the latter causes an increment of the vertical diameter during inspiration. All diameters are reduced during expiration.
  • Thoracic respiration involves movements of the thoracic cage. Movements of the diaphragm, as during quiet respiration result in ‘abdominal respiration.
  • Normally, the anterior abdominal wall moves forwards and backwards during inspiration (depression of the diaphragm) and expiration (elevation of the diaphragm) respectively.
  • Since the anterior ends of ribs lie at a lower level than the posterior ones, their elevation also 1 moves them forward, an action responsible for the increase in the anteroposterior diameter during inspiration.

Such movements elevate the sternum with angulation of 7° at the manubriostemal joint. This phenomenon is also called ‘pump handle movement.

Respiratory Movements Diameters Of The Thorax

Respiratory Movements Abdominal Respiration

Respiratory Movements Pump Handle Movement An Experimental Model Showing Roles Of Intercostal Muscles During Respiration

Respiratory Movements Pump Handle Movement Up And Down Movements Of Sternum During Respiration

The lateral parts on the ribs are relatively lower than their ends. Therefore, these parts when elevated during inspiration also move laterally thereby increasing the thoracic transverse diameter.

This phenomenon is markedly noted in the lower ribs during forced inspiration and is often called “bucket handle movement”.

Respiratory Movements Bucket Handle Movement Position Of Thoracic Wall And Diagram During Respiration

Respiratory Movements Bucket Handle Movement Movements Of Lateral Parts Of The Ribs (5th Downwards) During Respiration Position Of Handle Of A Buket

Intercostal Nerves

The ventral rami of the 1st to 11th thoracic nerves continue in the neurovascular plane (between internal intercostal and innermost intercostal thoracic muscles) as intercostal nerves.

Usually 3rd to 6th have similar features and are called ‘typical intercostal nerves’. The rest are atypical due to some differentiating features.

Atypical Intercostal Nerves

First Intercostal Nerve

It contributes to the lowest root of the brachial plexus.

Second Intercostal Nerve

Its lateral cutaneous branch (intercostobrachial nerve) supplies the floor of the axilla and the upper medial part of the arm.

Seventh To Eleventh Intercostal Nerves

These continue in the anterior abdominal wall after supplying the intercostal spaces and therefore are thoracolumbar.

Typical Intercostal Nerve

It runs in the neurovascular plane in the costal groove below the intercostal vessels (remember VAN: vein, artery and never) and provides the following branches

  1. Rami communicantes. Two small nerves connect the posterior part of the intercostal nerve with the adjacent ganglion of the sympathetic chain.
    • Most often the lateral one is the white ramus communicans conveying preganglionic fibres to the ganglion and the medial one is the grey ramus communicans receiving postganglionic fibres from the ganglion.
  2. Muscular branches. Numerous branches supply the intrinsic muscles of the thorax
  3. Collateral branches. It usually appears at the angle of the rib and then runs in the lower part of the intercostal space along the upper border of the rib.
  4. Pleural branches. Conveying branches to the parietal pleura.
  5. Lateral cutaneous nerve. It pierces the muscles along the midaxillary line divides into the anterior and posterior branches and supplies the skin of the lateral thoracic region.
  6. Anterior cutaneous branch. It pierces the internal intercostal muscle and external intercostal membrane to appear by the side of the sternum and supply the skin of the front of the thorax.

Intercostal Nerves Atypical Intercostal Nerves

Intercostal Nerves Typical Intercostal Nerve

Intercostal Nerves Course Of The Collateral Branch Of The A Typical Nerve

Intercostal Nerves Applied Anatomy

  1. Herpes zoster: A viral disease of the spinal root ganglion which is the most important cause of intercostal neuralgia (severe cutaneous pain along the distribution of a nerve).
  2. Tube thoracostomy: The preferred site for insertion of the tube during thoracostomy is the 4th or 5th intercostal space at the anterior axillary line. The introduction of a tube at a further lower level might damage the diaphragm or enter the abdominal cavity causing injury to the liver, spleen or stomach.
  3. Intercostal nerve block. The nerve should be blocked before the emergence of lateral cutaneous nerve. The needle is directed towards the lower border of the rib and the tip is pushed towards the subcostal groove.
  4. Pain in the vertebral region may follow the course of the neurovascular bundle.

Internal Thoracic Mammary Vessels

Internal Thoracic Artery

  • Origin– Subclavian artery.
  • Course– The artery descends behind the costal cartilage by the side of the sternum.
  • Termination– It terminates at the level of the 6th intercostal space into two terminal branches.

Branches

  1. Pericardiophrenic artery. It accompanies the phrenic nerve during its course over the fibrous pericardium.
  2. Pericardial branches. They supply the fibrous pericardium and parietal layer of the serous pericardium.
  3. Perforating arteries. These accompany the anterior cutaneous branches of the intercostal nerve I and appear by the side of the sternum.
  4. Mediastinal branches. These supply the structures in the anterior mediastinum including the thymus.
  5. Sternal branches. Supply the sternum and sternocostal muscle.
  6. Anterior intercostal arteries. A pair of anterior intercostal arteries, upper and lower, run laterally in each of the upper six intercostal spaces and anastomose with the posterior intercostal artery and its collateral respectively.
  7. Terminal branches
    • Musculophrenic artery. It runs along the costal margin above the peripheral attachment of the diaphragm.
    • Paired anterior intercostal arteries for the 7th to 9th intercostal spaces originate from this branch.
    • Superior epigastric artery. This artery enters the rectus sheath and descends behind the rectus abdomen to supply the anterior abdominal wall.

 

Internal Thoracic (Mammary) Vessels Intercostal Nerves Internal Thoracic (Mammary) Artery

Internal Thoracic (Mammary) Vessels Branches Of The Internal Thoracic Artery

Internal Thoracic Vein

It is formed at the level of 3rd costal cartilage by the union of venae comitantes of the internal thoracic artery. It ascends medial to the artery and ends in the brachiocephalic vein.

Intercostal Vessels

Intercostal Arteries

Posterior Intercostal Arteries

Intercostal Vessels Posterior Intercostal Arteries

There are 11 pairs of posterior intercostal arteries, i.e., one in each space. Those for the upper two spaces originate from the superior intercostals artery, a branch of the costocervical trunk which itself arises from the subclavian artery.

3rd to 11th posterior intercostal arteries are the direct branches from the descending thoracic aorta.

Intercostal Arteries Applied Anatomy

  • A needle should not be introduced into the thoracic wall medial to costal angle as it might risk the posterior intercostal artery due to its oblique course.
  • In cases of coarctation of the aorta, dilated and tortuous intercostal arteries produce notches in the ribs, a phenomenon which can be easily appreciated in a chest radiograph.

Anterior Intercostal Arteries

There are two (upper and lower) intercostal arteries in the upper nine intercostal spaces. In the upper six spaces, these originate from the internal thoracic artery.

While those for the 7th to 9th spaces appear from the musculophrenic artery. There are no anterior intercostal arteries in the 10th and 11th intercostal spaces.

Intercostal Vessels Anastomosis Between Anterior And Posterior Intercostal Arteries

Intercostal Veins

Posterior Intercostal Veins

  • There are 11 pairs of posterior intercostal veins, i.e., one in each intercostal space. The first (highest) intercostal vein of two sides drains into the corresponding brachiocephalic vein.
  • 2nd and 3rd posterior intercostal veins unite to form superior intercostal veins which on the right and left sides drain into azygos and brachiocephalic veins respectively.
  • Next 8 (i.e., from 4th to 11th) posterior intercostal veins drain into the azygos vein on the right side. On the left side.
  • The posterior intercostal veins from 4th to 8th spaces join the accessory hemiazygos and those from 9th to 11th join the hemiazygos vein. Both accessory azygos and hemiazygos veins ultimately drain into the azygos vein.

Intercostal Vessels Posterior Intercostal Veins

Intercostal Veins Applied Anatomy

In the obstruction of the superior vena cava, the azygos veins provide an alternative route for the return of venous blood because these veins and their tributaries connect the two venae cavae.

Anterior Intercostals Veins

These accompany the corresponding arteries and end in the internal thoracic or musculophrenic veins.

Subdivisions Of The Thoracic Cavity

The thoracic cavity is divisible into a midline part called the mediastinum and two lateral parts (right and left) occupied by the corresponding pleura and lung.

Subdivisions Of The Thoracic Cavity Subdivisions Of The Thoracic Cavity

Pleura

The pleura is a serous membrane (a fibrous membrane lined by simple squamous epithelium) around each lung. Since the pleural sac is invaginated by the corresponding lung from the medial side, the pleura on each side is divided into the following parts;

  1. Visceral (pulmonary)- It intimately covers the lung.
  2. Parietal pleura- It lines the walls surrounding each lung.
  3. Connecting pleura- It connects the visceral with the parietal pleura.

Pleura Subdivisions Of The Thoracic Cavity Development And Subdivisions Of The Pleura

Parietal Pleura

The parietal pleura is subdivided into different parts according to their relations.

  1. Costovertebral pleura – It lines the thoracic cage, i.e., ribs, intercostal spaces, sternum and the vertebral column.
  2. The mediastinal pleura covers the midline septum (mediastinum) between the sternum anteriorly and the vertebral bodies posteriorly.
  3. Diaphragmatic pleura-It covers the dome of the diaphragm.
  4. Cervical pleura (cupola or dome)– It is the part of the pleura beyond the inner margin of the 1st rib. It lies under the suprapleural membrane (Sibson’s fascia) at the root of the neck.

Margins And Their Reflection

  1. Anterior margin (sternal reflection)-The line extends on both sides from the sternoclavicular joint to the middle of the sternal angle and then descends vertically on the sternum up to the level of the 4th costal cartilage.
    • On the left side, the line makes a bold curvature beyond the sternal margin and descends to the 6th costal cartilage. On the right side, the line descends vertically to the xiphisternal joint.
  2. Inferior margin (costodiaphragmatic reflection)-The line of reflection extends laterally from the lower end of the anterior margin and meets with the midclavicular line at the 8th rib, and the midaxillary line at the 10th rib.
    • Lateral to the upper border of erector spinae at the 12th rib and a point 2 cm lateral to the upper border of the 12th thoracic spine.
  3. Posterior margin (vertebral reflection) – It is a vertical line from the posterior end of the inferior margin to a point 2 cm lateral to the 2nd thoracic spine.

Pleura Pleural Reflection

Pleural Recesses

The lungs do not extend as far anteriorly as well as inferiorly as the pleural reflections resulting in the formation of costomediastinal and costodiaphragmatic recesses respectively.

A recess therefore is a narrow space between the adjacent parietal pleurae. Recesses allow expansions of the lungs during inspiration.

Pleura Pleural Recesses

Fasciae Holding The Parietal Pleurae

  1. Endothoracic fascia– It is loose areolar tissue which separates the parietal pleura from the rib cage, vertebrae and diaphragm.
  2. Suprapleural membrane (Sibson’sfascia)-This fascia diverges from the front of the 7th cervical transverse process to the inner border of the first rib. The cervical pleura is attached to it. It prevents the bulging of the apex of the lung with each inspiration.
  3. Phrenicopleural fascia– It is endothoracic fascia between the diaphragmatic pleura and muscles of the diaphragm.

Pleura Superpleural Membrane (Sibson's Fascia)

Connecting Pleura

It is the site where the parietal pleura meets with the visceral pleura. Connecting pleura encircles the lung root. Below the root of the lung, the connecting pleura hangs down as an empty fold, the pulmonary ligament.

It provides a dead space into which the lung root descends during inspiration and also allows the expansion of pulmonary vessels, especially the inferior pulmonary vein.

Vessels And Nerves

  1. Parietal pleura– It receives blood supply from the internal thoracic, musculophrenic, and intercostal vessels. Lymphatics drain into the parasternal, intercostal, posterior mediastinal and diaphragmatic lymph nodes.
    • Mediastinal and the central parts of the diaphragmatic pleura are innervated by the phrenic nerve while the rest receives nerve supply from the intercostal nerves.
  2. Pulmonary pleura-It a part and parcel of the lung tissue and therefore its supply is like that of the lung. Its blood vessels are derived from the bronchial vessels.

Its lymphatics drain into the lymph nodes of the lung. It is innervated by the autonomic fibres and therefore insensitive to general stimuli.

Pleura Functions

The pleura acts as a bursa and therefore minimizes the friction between the lung and thoracic wall.

Negative pressure (-10 to -20 mm Hg) in the pleural cavity helps in the expansion of the lung during respiration and prevents its collapse.

Pleura Applied Anatomy

  • Inflammation of pleura is called pleuritis or pleurisy.
  • The pleural cavity being a potential space, is prone to the collection of air or fluid in pathological conditions:

Pleura Pathological Conditions

The cervical pleura is at risk during incision in the region of the root of the neck due to the obliquity of the inlet of the thorax.

  • At three sites the parietal pleura extends beyond the costal margins, i.e., the right xiphisternal angle and costovertebral angles of both sides. An abdominal incision at these sites may endanger the pleura.
  • Costodiaphragmatic recesses are separated from the upper poles of the corresponding kidney at the costovertebral angles, a fact to be noted in incisions and wounds in this region.
  • Aspiration needles and drainage tubes for removing fluid or air from the pleural cavity are passed through the chest wall close to the upper border of the rib to avoid injury to the intercostal nerve and vessels which run along the lower border.
  • 4th intercostal space just in front of the midaxillary line is often chosen as there is no major structure here and the level avoids domes of the diaphragm.
  • Referred pain from the pleura is a common observation. Pain is referred to the shoulder from phrenic nerve territory and to the abdomen from lower costal and peripheral diaphragmatic pleurae.

Right And Left Mediastinal Views

Features Of Right And Left Surfaces Of The Mediastinum

Right and left mediastinal views are mirror images of the impressions on the medial surfaces of right and left lungs respectively. Some of the relations are very specific for right and left views. These are as follows:

Right Mediastinal View

  1. Right atrium
  2. Inferior vena cava
  3. Superior vena cava
  4. Right brachiocephalic vein
  5. The upper four structures occupy the anterior part of the mediastinal view just behind the sternum.
  6. Azygos vein- It is a vertical vein over the vertebral bodies behind the heart. Reaching the level of sternal angle it arches forwards above the root of the right lung to enter the superior vena cava.
  7. Trachea- It lies in the upper part of the mediastinum in a plane posterior to the superior vena cava and right brachiocephalic vein.

Left Mediastinal View

  1. Left ventricle- It lies in the anterior part of this view just behind the sternum.
  2. Arch of aorta- It arches over the root of the left lung.
  3. Descending thoracic aorta – It is a continuation of the arch of the aorta and lies just behind the heart.
  4. Left common carotid artery.
  5. Left subclavian artery.
  6. Above two arteries ascend from the arch of the aorta of which the former is more anterior. :
  7. Thoracic duct- It is a vertical lymphatic duct lying in the upper part of this view in a more posterior plane, even behind the subclavian artery.

Right And Left Mediastinal Views Right Mediastinal View

Right And Left Mediastinal Views Left Mediastinal View

Dissection Steps For Mediastinum And Heart In Situ

Define the boundaries and subdivisions of the mediastinum. Clean the pericardium and note the phrenic nerve and pericardiophrenic artery.

  • Cut the fibrous pericardium on both sides in front of phrenic nerves vertically and join the lower ends of the incision by a transverse cut about 1 cm above the diaphragm.
  • Define and note the attachments of the pericardium to the superior vena cava, aorta and pulmonary trunk. Now, maintaining small flaps on these structures cut through them.
  • Identify the various pericardial sinuses and correlate them with their development. Remove the fibrous pericardium and study the heart in situ. Note its anatomical position. Identify coronary arteries and major cardiac veins.

The following additional features are alike on the two sides.

  1. Pericardium. Covers the heart and occupies a large area behind the body of the sternum.
  2. The root of the lung. Structures entering into or appearing from the lung constitute its root. It is located behind the upper part of the fibrous pericardium.
  3. It is covered by the connecting pleura which is loose and hanging below- called the pulmonary ligament.
  4. Sympathetic chain. It descends by the side of the vertebral column.
  5. Intercostal nerves and vessels. These occupy the intercostal spaces close to the lower border of the ribs.
  6. Phrenic nerve.
  7. Pericardiophrenic artery.
  8. The above two structures descend vertically over the fibrous pericardium.
  9. Vagus nerve. The right vagus crosses the trachea obliquely to reach the back of the root of the right lung.
  10. The left vagus crosses the left surface of the arch of the aorta to reach the posterior surface of the root of the left lung. (Phrenic-front and Vagus-behind).
  11. Oesophagus. It is prominently visible on the right side behind the trachea in the upper part and front of the azygos vein in the lower part.
  12. On the left side, it is crossed by the thoracic duct in the upper part. It is also visible between the lower part of the fibrous pericardium and the descending thoracic aorta.

Lungs

Lungs are essential organs of respiration. Each lung resembles the shape of a half cone and thus has a base, an apex, three borders and two surfaces.

Lungs Resemblance Of Lung With A Half Cone

Base. It is deeply concave and faces downwards to rest over the corresponding dome of the diaphragm.

Apex. It is conical and directed upwards towards the root of the neck.

Lungs Borders

  • Anterior border. It is a sharp border related to the anterior thoracic wall. Its lower part is marked by a deep concavity called a cardiac notch in the left lung.
  • Posterior border. It is rounded and forms the junction of the costal and medial surfaces and corresponds to the heads of the ribs.
  • Inferior border. It is a convex sharp border directed downwards to the costodiaphragmatic recess.

Lungs Surfaces

  • Costal surface. This surface is related to the rib cage and the sternum.
  • Medial surface. This surface is marked by the hilum, i.e., a depression where structures enter or come out of the lung. The medial surface is divisible into two parts.
    • Vertebralpart. It is the posterior part of the medial surface and is related to the vertebral bodies and intervertebral discs.
    • Mediastinal part. It is the large anterior part of the medial surface related to the mediastinum.

Lungs Cross Sectional View Of Lung

Side Determination Of Lung

The sides of the lungs are determined based on the following simple morphological features.

  1. Sharp anterior border faces forward.
  2. Deep concave base faces inferiorly
  3. The surface has hilum faces medially.

Fissures And Lobes

Right lung. Two fissures (oblique and transverse) divide the right lung into three lobes, superior, middle and inferior.

Left lung. There is only one fissure (oblique) in the left lung which divides it into two lobes, superior and inferior. The lower part of the superior lobe is also called the lingula which corresponds with the middle lobe of the right lung.

Lungs Medial Aspect Of Right Lung

Lungs Medial Aspect Of Left Lung

Surface Marking Of Lungs

Apex

It is marked by a line with bold convexity upwards formed by the union of three points, sternoclavicular joint, a point 2.5 cm above the medial l/3rd of clavicle and medial trisection of clavicle.

Anterior Border

Right lung. It is marked by a vertical line formed by the joining of the following three points.

  1. Right stemocalvicular joint.
  2. Midpoint of the sternal angle.
  3. 6th right costochondral junction.

Left lung. It is formed by the union of the following points.

  1. Left sternoclavicular joint.
  2. Midpoint of the sternal angle.
  3. 4th left chondrostemal junction.
  4. A point on the 6th costal cartilage, 2.5 cm from the left margin of the sternum.

This line becomes concave between points 3 and 4 to represent the cardiac notch.

Lungs Some Relative Features Of Two Lungs And Their Explanation

Inferior border. It is formed by the union of the following four points.

  1. 1st point is different for the two lungs. For the right lung, it is present on the right 6th chondrostemal junction, while for the left it is located on the 6th costal cartilage 2.5 cm from the left margin of the sternum.
  2. Crossing of midclavicular line and 6th rib.
  3. Crossing of midaxillary line and 8th rib.
  4. At the level of the 10th thoracic spine, 2 cm from the midline.

Lungs Surface Making Of Lung And The Pleural Reflection Anterior View

Posterior border. It is represented by a vertical line formed by the union of the following two points.

  1. 2 cm from the midline at the level of the T10 spine.
  2. 2 cm from the midline at the T2 spine.

Lungs Surface Making Of Lung And The Pleura Of Right Side Posterior View

Dissection Steps For The Removal Of Lung

Cut through the rib cage on both sides in the anterior axillary line. Reflect the flap upwards and identify the heart with the pericardium in situ, the lung with pleura in situ, the mediastinum, the internal thoracic artery and its terminal branches.

  • Identify the morphological differences, fissures and lobes. Pull the lung laterally and look at the root of a lung on its medial aspect for the arrangement of structures at the hilum.
  • The pulmonary ligament and various impressions, and structures related to it. Cut through the root close to the lungs remove the lung and study.

Oblique Fissure

Join the following points to mark the oblique fissure.

  1. 2 cm lateral to the 2nd thoracic spine.
  2. 3 cm lateral to the nipple.
  3. 6th costal cartilage, 7.5 cm from the middle plane.

The oblique fissure roughly corresponds with the medial border of the scapula if the corresponding side of the arm is raised above the head.

Transverse Fissure Of The Right Lung

It is represented by a horizontal line at the level of the 4th costal cartilage, extending from a point on the anterior median line to the midaxillary line.

Relations Of Lung

Lungs Relations Of Lung

Lungs Medial Relations Of Lung Right Lung

Lungs Medial Relations Of Lung Left Lung

Hilum Of The Lung

It is a depressed site on the medial aspect of the lung joined by its root. Remember, the root is different from the hilum as the former is composed of structures which enter or leave the lung.

Major tubular structures can easily be identified based on their locations as shown below.

Lungs Hilum Of The Lung

Bronchial arteries and hilar (broncho-pulmonary) lymph nodes are closely associated with bronchi.

Anterior and posterior pulmonary plexuses of autonomic nerves occupy respective sides of the lung root and are observed in the hilum.

Differences Between Two Lungs

Lungs Differences Between Two Lungs

Tracheobroncheal Tree

Lungs Tracheobroncheal Tree

Lungs Tracheobroncheal Tree From Trachea To Tertiary Bronchi

Lungs Tracheobroncheal Tree Tertiary Bronchi To Alveoli

Lungs Tracheobroncheal Tree Surface Appearance Of Subdivisions Of Lung

Bronchopulmonary Segments

It is defined as the developmental, structural and functional unit of the lung. It consists of a tertiary bronchus and the lung tissue supplied by it.

There are ten bronchopulmonary segments in the right lung. This number is less on the left side due to compression by the leftward deviated position of the heart which causes either fusion of adjacent segments or suppression of the same.

The number and names of these segments are very specific as shown below.

Lungs Bronchopulmonary Segments

Lungs Bronchopulmonary Segment

Bronchoscopy

Bronchoscopy is the direct visualization of the interior of the tracheobronchial tree up to the level of the bronchiole with the help of an instrument called the bronchoscope. The visual appearance of the respiratory passage at different levels is shown below.

Lungs Bronchoscopic Picture Of Tracheobranchial Tree

Lungs Arteries

  • Pulmonary arteries. One on each side forms a capillary plexus around the alveoli to facilitate gaseous exchange and supply nutrition (alveoli get oxygen from the atmosphere).
  • Bronchial arteries. One on the right side (arising from the 3rd right posterior intercostal artery) and 11 two on the left side (arising from the descending thoracic aorta), supply nutrition as well as oxygen to the rest of the pulmonary tissue.

Lungs Veins

  • Pulmonary veins. Two from each lung, a superior and an inferior pulmonary vein.
  • Bronchial veins. These drain into the azygos vein on the right side and into the accessory hemiazygos vein on the left side.

Dissection Steps For Bronchopulmonary Segments

Identify the principal bronchus. Remove the substance of the lung piecemeal starting from the principal bronchus. Identify the lobar and segmental bronchi.

Lungs Vascular Planes In The Lung

Lymphatic Drainage

Lymphatics. Superficial lymphatic vessels form superficial (subpleural) plexus. Deep lymphatics follow the pulmonary vessels.

Lymph nodes. Lymphatics are interrupted by the following lymph nodes

  1. Pulmonary lymph nodes- located in the interior of the lung.
  2. Hilar (bronchopulmonary) lymph nodes- located at the hilum of the lung.
  3. Tracheobronchial lymph nodes- located at the bifurcation of the trachea. These may be superior or inferior.
  4. Para tracheal lymph nodes – found in the trachea. Their efferents ultimately form corresponding bronchomediastinal lymph trunk which opens at the jugulo-subclavian junction.

The vessels of the lung should always be considered in terms of bronchopulmonary segments which are isolated by the connective tissue intersegmental septa.

  • Intrasegmental septa demarcate the lobule (primary and secondary) of the lung. It is interesting to note that the veins follow inter as well as intrasegmental septa and drain many adjacent segments.
  • The bronchial tree, pulmonary artery and bronchial artery run in the centre of the lobule. Lymphatics follow both septa as well as the bronchial tree.

Lungs Lymphatic Drainage Of The Lung

Lungs Innervation

The lung is supplied by the anterior and posterior pulmonary plexuses which are located on the front and back of the root of the lung respectively.

Both sympathetic and parasympathetic fibres innervate the lung. The former are derived from the 2nd to 5th thoracic spinal segments. Parasympathetic fibres come from the vagus nerve.

Functionally, stimulation of the sympathetic fibres causes bronchodilation and vasoconstriction while parasympathetic fibres result in bronchospasm, vasodilatation and increased secretion by the bronchial glands.

Lungs Applied Anatomy

Medicolegal importance. The presence of air in the lung observed during postmortem confirms the
live birth of the baby.

  • The lobe of the Azygos vein. Rarely azygos vein descends through the apex of the right lung and occupies the depth of the parietal pleural fold (mesoazygos).
  • This is responsible for the matchstick appearance in the chest radiograph (P-A view). The lung tissue medial to the mesoazygos is termed the lobe of the azygos vein.
  • A stab wound above the clavicle might damage the apex of the lung.
  • A foreign body in the trachea usually enters the right principal bronchus because of its relatively larger lumen and vertical position as compared to the left bronchus.

Surgical removal of the diseased lung or its part is a common procedure.

Lungs Surgical Removal Of The Diseased Lung

Bronchography. The tracheobronchial tree can be visualized by taking a radiograph of the chest after introducing radio-opaque dye (For example., diagnosis aqueous) into it.

  • Pulmonary thromboembolism. This is a common postoperative complication in which a thrombus detached from the site of operation blocks the pulmonary artery. The patient usually undergoes respiratory distress which commonly proves fatal.
  • Bronchogenic carcinoma. Its frequency is 30% of all common cancers occurring in men.
  • The metastatic intracerebral abscess is sometimes a well-recognized complication of lung abscess.
  • The two commonest signs of lung injuries are haemoptysis (sputum with blood) and subcutaneous emphysema (air under the skin).
  • Aspiration pneumonia (inhaled vomitus). It is a common postoperative chest complication.
  • Atelectasis (collapse of the lung). It is also a postoperative complication which may be segmental, lobar or massive.

Referred abdominal pain due to diaphragmatic inflammation caused by pleuropneumonia should always be differentiated from peritonitis as the rebound pain (pain in the abdomen when the pressure over the abdominal wall is suddenly released) is a specific sign of peritonitis.

Lungs Azygos Lobe Of The Lung

Mediastinum

It is defined as the median septum in the thoracic cavity between the two pleural cavities.

The horizontal plane at the level of the sternal angle (which corresponds to the intervertebral disc between the 4th and 5th thoracic vertebrae) divides the septum into an upper part (superior mediastinum) and a lower part (inferior mediastinum).

The inferior mediastinum is further subdivided into the following three regions;

  1. Middle mediastinum. Partly occupied by the fibrous pericardium.
  2. Anterior mediastinum. Part anterior to the fibrous pericardium.
  3. Posterior mediastinum. Part behind the fibrous pericardium.

Mediastinum Subdivisions Of The Mediastinum

Anterior Mediastinum

Anterior Mediastinum Boundaries.

Anterior– Body of sternum.

Posterior– Fibrous pericardium.

Anterior Mediastinum Contents.

  1. Thymus
  2. Lymph nodes
  3. Loose areolar tissue
  4. Pericardial branches of the internal thoracic artery
  5. Sternopericardial ligaments.

These ligaments are usually two in number (superior and inferior) connecting the sternum with the fibrous pericardium.

Anterior Mediastinum Anterior Mediastinum

Anterior Mediastinum Thymus

It is a primary central lymphatic organ as well as an endocrine gland. It develops from the 3rd pharyngeal pouch. Though single, it is comprised of two asymmetric lobes called the thymic bodies.

It occupies the lower neck and upper thorax (up to 4th costal cartilage). At puberty, it is most prominent and weighs about 30 grams.

It is only 10 g at birth and middle age. It is the site of the production of T lymphocytes as well as factors and hormones.

Anterior Mediastinum The Thymus

Pericardium

The pericardium is the covering of the heart. Its outer component is tough and inelastic and called the fibrous pericardium. The inner component, called serous pericardium is comprised of two parts.

The one which lines the inner surface of the fibrous pericardium is called the parietal layer and the other which covers the heart is termed the visceral layer.

Fibrous Pericardium

It is derived from the septum transversum and extends from the 2nd to the 6th costal cartilage. It is said to have;

  1. Base. It faces inferiorly and is pierced by the inferior vena cava.
  2. Apex. It is directed upwards and is pierced by the ascending aorta, pulmonary trunk and the superior vena cava.
  3. Four surfaces
    • Anterior surface. Related to the anterior mediastinum.
    • Posterior surface. Related to the posterior mediastinum and is pierced by four pulmonary veins.
    • Right lateral surface. Related to right lung and pleura.
    • Left lateral surface. Related to left lung and pleura.

The fibrous pericardium is fixed to the central tendon of the diaphragm, adventitia of great vessels (except the inferior vena cava which is free from it) and the sternum (by the sternopericardial ligaments).

The fibrous pericardium protects the heart and provides a slippery surface for the movements of both the heart and lungs.

Serous Pericardium

  1. Truly speaking, it is a bursa around the heart to allow its free movement. The pericardial cavity may be divided into three parts
  2. Main ‘general’ cavity.
  3. Transverse sinus. It is located between the pulmonary trunk and the ascending aorta anteriorly and the superior vena cava and left atrium posteriorly.
  4. Oblique sinus. It is a cul-de-sac behind the left atrium whose opening is directed downwards and towards the left between the inferior vena cava and the left inferior pulmonary vein. It allows atrial pulsation.

The heart invaginates into the pericardial cavity from its posterior aspect. Steps involved in the formation of the pericardial sinus are shown.

Pericardium Subdivisions Of The Pericardium

Pericardial Vessels And Nerves

  • The fibrous pericardium and the parietal layer of the serous pericardium receive arterial supply from the internal thoracic artery through its pericardial, musculophrenic, and pericardiophrenic branches and also from branches of descending thoracic aorta.
    • Pericardial veins drain into the azygos system. Their nerve supply comes from the branches of the phrenic nerve.
  • The visceral layer of serous pericardium is supplied by the coronary arteries and drained by the coronary sinus. It receives autonomic innervation from the vagus and the sympathetic trunk similar to the heart.

Pericardium Applied Anatomy

  • Pericarditis. It is inflammation of the pericardium. It leads to chest pain. It produces characteristic ‘pericardial rub’, a high-pitched sound heard on auscultation, due to the friction between two inflamed pericardial layers.
    • A chronic condition in which due to excessive fibrosis, the dilatation of the heart is restricted, is called ‘constrictive pericarditis’.
  • Pneumopericardium. Entry of air into the pericardial cavity is sometimes a complication of pneumothorax.
  • Pericardial effusion. It is a collection of clear fluid in the pericardial cavity. When too much, it restricts the cardiac dilatation, a condition called the ‘cardiac tamponade’.
  • Haemopericardium. The blood can enter the pericardial cavity either due to a stab wound of the heart or perforation of the infarcted and fibrosed thin wall of the heart.
  • Pericardiocentesis. It is the procedure to drain excess fluid in the pericardial cavity.
    • The needle is preferably introduced in the left 5th or 6th intercostal space adjacent to the sternum or left xiphicostal angle. These sites are devoid of pleura.
  • Transverse pericardial sinus is surgically very important as it helps in temporary ligation of the ascending aorta and the pulmonary trunk for cardiopulmonary bypass.
    • This is needed in coronary bypass surgery.
  • Exposure of the superior and inferior vena cava. Both the venae cavae are preferably exposed from inside the pericardial cavity, i.e., by opening it.

Pericardium Development Of Pericardial Sinuses

Heart

Heart Surface Features

The heart is a hollow conical muscular organ.

Heart Measurement

Base to apex – 12 cm

Maximum transverse diameter – 8 cm

Anteroposterior – 6 cm

Heart Weight

Male – 300 g

Female – 250 g

Heart Surfaces And Borders

Base. It is posterior. It is formed mainly by the left atrium.

Apex. It is directed forward and towards the left (opposite the base). It is formed by the left ventricle.

Heart Orientation Of The Heart In The Body

Borders. It has four borders.

  • Superior border (clinicians consider it as the base). It is formed by atria.
  • Inferior border. Formed by ventricles.
  • Right border. Formed by the right atrium.
  • Left border. Formed by the left ventricle.

Heart Anterior View Of The Heart

Surfaces

  • Sternocostal surface. It faces forward. It is formed from right to left by right atrium, right ventricle (2/3rd) and left ventricle (l/3rd).
  • Diaphragmatic surface. It faces inferiorly. It is formed mainly by the left and right
    ventricle contributing 2/3rd and l/3rd of this surface respectively.
  • Right and left surfaces. These are also called the pulmonary surfaces.

Grooves and sulci

  • Interatrial groove. It is located between right and left atria.
  • Atrioventricular sulcus. It is the junction between the atria and the ventricles. This is also called the coronary sulcus.
  • Interventricular groove. It is the junction between two ventricles. Its sternocostal component is called the anterior interventricular sulcus.
  • The groove on the inferior surface is called the posterior interventricular sulcus.
  • The site where the coronary sulcus meets with the posterior interventricular sulcus is called the ‘crux’ of the heart.

Heart Posterior View Of The Heart

Heart Inferior View Of The Heart

Surface Projection Of The Heart

Mark the following points

Point 1. The lower border of the left 2nd costal cartilage is 1.2 cm from the side of the sternum.

Point 2. The upper border of the right 3rd costal cartilage is 1.2 cm from the side of the sternum.

Point 3. Right 6th costal cartilage, 1.2 cm from the side of the sternum.

Point 4. Midpoint of the xiphisternal joint.

Point 5. The apex of the heart, 5th left intercostal space, just medial to the midclavicular
line.

Join the above-mentioned points to draw the heart on the surface of the chest.

1 + 2 = Upper border of the heart.

2 + 3 = Right border of the heart.

3 + 4 + 5 = Inferior border of the heart.

5 + 1 = Left border of the heart.

Heart Surface Making Of The Heart

Heart Applied Anatomy

  • The heart deviates to one side with the mediastinal shift. Mediastinum is pushed to the opposite side by the tumours in the lung or pulled towards the same side by fibrosis or collapse of the lung.
  • Cardiomegaly. The heart is enlarged due to multiple conditions, For example., aortic stenosis, aortic regurgitation and hypertension.
  • Cardiac dullness. The heart can be mapped out by tapping the front of the thorax (percussion).
  • The central area of the heart which is not covered with the lung can easily be detected by light percussion. This is called superficial cardiac dullness.
  • Forceful percussion is needed to map out the exact size of the heart, i.e. even that part of the heart which is covered with the lung. This is called deep cardiac dullness.

Arterial Supply Of The Heart

Two arteries supply the heart. These are called the right and left coronary arteries.

These originate from two of the ascending three outpouchings (anterior, right posterior, and left posterior aortic sinuses)at the commencement of the ascending aorta.

The right coronary artery emerges from the anterior aortic sinus while the left one appears from the left posterior aortic sinus.

Heart Origin Of The Coronary Arteries

Right Coronary Artery

Course. The artery appears between the pulmonary trunk and the right auricle and runs a rightwards course in the right portion of the coronary sulcus on the sternocostal surface of the heart.

After winding around the inferior margin of the heart it runs a leftwards course on the diaphragmatic surface of the heart to reach the crux.

Branches

  • Conus branch – for the upper portion of the right ventricle.
  • Periventricular branch- for the front of the right ventricle.
  • Right marginal branch. It runs towards the left close to the inferior margin of the heart.
  • Nodal branches. In the majority of the cases, it emerges from the right coronary artery.
  • SA node -55%
  • AV node- 90%
  • Small branches to the ascending aorta, pulmonary trunk and the right atrium.
  • Terminal branches. At the crux of the heart, the right coronary artery terminates into a transverse branch (which continues into the left portion of the coronary sulcus to anastomose with the circumflex branch of the left coronary artery).
  • And posterior interventricular artery (which runs into the posterior interventricular sulcus and anastomoses with the anterior interventricular branch of the left coronary artery).

Left Coronary Artery

Course. It appears between the pulmonary trunk and the left auricle. It runs a leftward course in the left portion of the coronary sulcus.

At the upper end of the anterior interventricular sulcus, the artery terminates.

Branches. Two terminal branches are emerging from the left coronary artery.

Heart Coronary Arteries Anterior View

Heart Coronary Arteries Posterior View

Anterior Interventricular Artery

It descends in the anterior interventricular sulcus and winds around the inferior margin of the heart to run in the posterior interventricular sulcus and anastomose with the posterior interventricular branch of the right coronary artery.

Circumflex Artery

It continues leftwards in the coronary sulcus and after winding around the left margin of the heart, runs a rightwards course to anastomose with the transverse branch of the right coronary artery.

It gives a descending branch along the left margin of the heart called the left marginal artery.

Heart Termination Of Right And Left Coronary Arteries A Relative Presentation

Heart Arterial Supply Of The Interventricular Septum

Schlesinger’s Grouping Of Arterial Pattern

Schlesinger divided the heart into three groups depending upon the relation of the coronary arteries with the crux of the heart as shown below

Heart Schlesingers Grouping Of Arterial Pattern

Collateral Circulation

Cardiac anastomosis

  • Myocardial anastomosis. Branches of the coronary arteries anastomose in the substance of the cardiac muscle.
  • Intercoronary anastomosis. Branches of coronary arteries anastomose in the sulci, i.e. in the epicardial fat.

Extracardiac Anastomosis

Such anastomosis is noticed at the site where great vessels of the heart pierce the fibrous pericardium. Anastomosis takes place between the branches of coronary arteries on one hand and the vasa vasorum of great vessels or the pericardial arteries on the other hand.

Heart Collateral Circulation In The Heart

Collateral Circulation Applied Anatomy

Angina pectoris. It is chest pain due to the narrowing of coronary arteries or its branches. Pain is usually produced when the lumen of a coronary artery is reduced to Vl or l/3rd of its original size.

Myocardial infarction. It is the ischaemia of the heart due to complete obstruction of the coronary arteries or its branches. The following three arteries are usually involved in descending order of their frequency-

  1. Anterior interventricular artery.
  2. Right coronary artery.
  3. Circumflex artery.

Coronary angiography. It is a visualization of the coronary arteries and their branches in a radiograph after introducing a radio-opaque dye. The dye is pushed with the help of an intravascular catheter at the level of the aortic sinus during the diastolic phase of the heart.

Coronary angioplasty. In this case, a small balloon at the tip of an intravascular catheter is carried at the site of the narrowing of the coronary artery and inflated to dilate.

The artery allows the resumption of normal blood flow to the cardiac tissue. Thrombokinase is also introduced to dissolve the clot.

Coronary bypass surgery. In this operation, normal blood flow is resumed in the coronary artery or its branches distal to the site of obstruction.

This can be achieved either by providing a bridge of venous graft (usually the great saphenous vein) across the obstruction or connecting an adjacent artery (usually the internal thoracic artery) with the diseased artery distal to the obstruction.

Venous Drainage Of The Heart

The following veins drain the heart.

1. Coronary sinus. It is a wide venous channel, 2-3 cm in size, located in the posterior part of the coronary sulcus. It opens into the right atrium between the inferior vena cava and right atrioventricular orifices. Its opening is guarded by a small valve called the Thebesian valve.

Heart Opening Of The Coronary Sinus In The Right Atrium

Tributaries

  • Great cardiac vein. It accompanies the anterior interventricular artery and circumflex artery to continue with the upper part of the coronary sinus. It is interesting to note that the blood flows in the same direction in this vein as well as the circumflex artery.
  • Small cardiac vein. It accompanies the right marginal artery and winds around the inferior border of the heart to enter the terminal part of the coronary sinus.
  • Middle cardiac vein. It accompanies the posterior interventricular artery and joins the middle of the coronary sinus.
  • Oblique vein of Marshall. It descends from the back of the left atrium.
  • Posterior ventricular veins. These drain the posterior surface of the left ventricle.
  • Left marginal vein. It ascends close to the left border of the heart and joins the upper part of the coronary sinus.

Heart Venous Drainage Of Heart Posterior View

Heart Venous Drainage Of Heart Anterior View

2. Anterior cardiac veins. Usually, two, run towards the right from the front of the right ventricle and drain directly into the right atrium.

3. The besian veins (venae cordis minimae). These are numerous small veins located in the wall of the heart and opening directly into the cardiac chambers. The majority of these are located in the wall of the right atrium.

Dissection Steps For The Blood Supply Of The Heart

Remove the visceral pericardium from the surface of the heart and identify the right coronary artery between the pulmonary trunk and the right auricle.

  • The left coronary artery between the pulmonary trunk and left auricle and coronary sinus in the posterior part of the coronary sulcus.
  • Scrape the fat present in the anterior interventricular sulcus and left part of the coronary sulcus and identify the anterior interventricular branch of the left coronary artery great cardiac vein and circumflex branch of the left coronary artery.
  • Trace the anterior interventricular artery to the diaphragmatic surface of the heart. Remove the fat from the coronary sulcus and identify the right coronary artery; trace it to the anterior aortic sinus.
  • Trace the posterior interventricular branch of the right coronary artery on the diaphragmatic surface in the posterior interventricular groove with the accompanying vein. Note the coronary dominance.
  • Identify the crux of the heart and clean and trace the coronary sinus in the posterior part of the coronary sulcus.

Innervation Of The Heart

Nature – Autonomic

Source – Sympathetic. 3 cervical and upper 5 thoracic sympathetic ganglia (T1– T5). Parasympathetic – Vagus.

Nerve Plexuses

  • Cardiac Plexuses
    • Superficial cardiac plexus. This is located in the concavity of the arch of the aorta to the right of the ligamentum arteriosum.
    • It receives only two cardiac branches. 1st is derived from the left superior cervical sympathetic ganglion and 2nd is the lower of the two cardiac branches of the left vagus.
    • Deep cardiac plexus. It is located on the posterior and right surface of the arch of the aorta. It is divisible into right and left halves.
    • All the rest of the cardiac branches from sympathetic ganglia, vagus and recurrent laryngeal nerves contribute to its formation.
  • Coronary Plexuses
    • Right coronary plexus. It accompanies the right coronary artery. It receives fibres from the superficial cardiac plexus and the right half of the deep cardiac plexus.
    • Left coronary plexus. It receives fibres mainly from the left half of the deep cardiac plexus.

Distribution

  • Efferent Fibres
    • Parasympathetic fibres. These supply the SA node, AV node, atria and fine branches of the coronary arteries.
    • Sympathetic fibres. These supply the atria, ventricles and large branches of the coronary arteries.
  • Afferentfibres.
    • Pressure sensations from the great vessels run into the vagus. Pain fibres from the heart follow the sympathetic nerves.

Heart Innervation Of The Heart

Functions

  • Sympathetic.
    • Acceleration of the heart.
    • Coronary artery dilatation.
  • Parasympathetic
    • Slows the heart.
    • Causes coronary artery constriction.

Innervation Of The Heart-Applied Anatomy

Cardiac pain is referred to the medial side of the arm. This is because the heart receives sympathetic fibres from the segments of the spinal cord (T1-T5) whose major portion (T1 – T3) also supplies the medial side of the arm.

Chambers Of The Heart

There are four chambers in a heart, the right atrium, the right ventricle, the left atrium and the left ventricle. Both the right chambers constitute the right heart while the left ones form the left heart.

Though the atrium and ventricles of the same side communicate with each other through the atrioventricular orifice, the atria and ventricles themselves are separated by a complete interatrial and interventricular septum respectively.

The Right Atrium

External Features

It occupies the extreme right part of the heart. A vertical sulcus (sulcus terminalis) connects the front of the superior vena cava with that of the inferior vena cava.

The sulcus demarcates its right smooth part (derived from sinus venosus) from the left rough part (derived from the primitive atrium). The extension of the rough part upwards and towards the left forms its auricular appendage.

Heart External Features Of The Right Atrium

Internal Features

The sulcus terminalis corresponds with a vertical ridge (crista terminalis) when observed from inside the cavity of the right atrium. This ridge again demarcates the interior of the cavity into an anterior (rough part) and a posterior (smooth part).

Rough part – It is marked by transversely running ridges called the musculi pectinati.

Smooth part – This is also called sinus venarum. It shows the following features.

  • Opening of the superior vena cava – It is present at its upper end.
  • Opening of the inferior vena cava – It is present at its lower end. It is marked by an incomplete valve.
  • Tricuspid orifice – This is the largest opening in the right atrium allowing three fingers to pass. It is located anteriorly.
  • Opening of the coronary sinus. This is a small opening located in the posterior wall between the tricuspid and inferior vena caval orifices allowing only a little finger to pass. It is guarded by a valve called the Thebesian valve.
  • Fossa ovalis. This is a thumb-sized depression in the posterior wall. It represents the septum primum of the developing interatrial septum.
  • Limbusfossa ovalis. It is a crescent margin demarcating the anterosuperior aspect of the fossa ovalis. It represents the inferior free margin of the septum secondum.
  • Intervenous tubercle. This is a faint elevation between the fossa ovalis and the superior vena canal orifice.
  • The tubercle probably plays an important role in directing the blood from the superior and inferior vena cavae (to the right ventricle and left atrium respectively) during foetal circulation.
  • Triangle of Koch. This is a small triangular location for the atrioventricular node. This is bounded by the septal leaf of the tricuspid valve, the opening of the coronary sinus and the tendon of Todaro.

Heart Internal Features Of The Right Atrium

Dissection Steps For Right Atrium

Remove the heart by cutting through the ascending aorta and pulmonary trunk. Note its anatomical position. Identify the external features of the heart – apex, base, borders and surfaces and sulci/ grooves.

  • Dissect the arch of the aorta beyond the branches of the aortic arch. Now cut the left pulmonary artery beyond ligamentum arteriosum.
  • Open the right atrium by giving a longitudinal incision from the lower end of the superior vena cava along the sulcus terminalis up to the opening of the inferior vena cava in the right atrium.
  • Remove the blood clots if any reflect the flap to the left side and study the interior of the right atrium for various features – openings, rough and smooth surfaces and their developmental correlation.

The Left Atrium

External Features

It is located posterior and to the left of the right atrium. Two right and two left pulmonary veins join the upper halves of their corresponding margins.

An extension from its lower half winds around the left border of the infundibulum to appear on the sternocostal surface of the heart. This is called the auricular appendage.

Heart External Features Of The Left Atrium

Internal Features

Roughpart. It is the auricular appendage showing elongated ridges. It’s derived from the primitive atrium.

Smooth part. The rest of the atrium is devoid of ridges. It is derived by the incorporation of pulmonary veins. The upper halves of its margins are marked by the opening of a pair of corresponding pulmonary veins.

Heart Internal Features Of The Left Atrium

The Right Ventricle

External Features

It contributes to the 2/3rd of the sternocostal surface and l/3rd of the diaphragmatic surface of the heart. Its sternocostal surface is triangular with a base towards the inferior border and an apex towards the pulmonary trunk.

Its junction with the right atrium is marked by the coronary sulcus while its junction with the left ventricle is marked by the anterior (on the sternocostal surface) interventricular sulcus.

Internal Features

These are described under the following 4 headings.

  1. Inflow orifice (right atrioventricular orifice).
  2. Inflow tract (rough part).
  3. Outflow tract (smooth part).
  4. Outflow orifice (pulmonary orifice).

Right Atrioventricular Orifice

It is the largest opening of the heart. It connects the right atrium with the right ventricle and directs the blood to flow forward and towards the left.

  • A fibrous ring (annulus) along its margin provides attachment to the tricuspid valve whose three cusps are named anterior (largest), septal (smallest) and posterior.
  • The junction of three cusps (commissures) are named after the cusps, i.e., anteroseptal, posteroseptal and anteroposterior.

Heart Interior Of The Right Ventricle

Heart Cups And Commissures Of The Tricuspid Valve

Dissection Steps For Chambers Of The Heart

Make a T-shaped incision in the right ventricle in such a way that the vertical limb passes through the ventricular wall and the horizontal limb below the infundibulum. Open the cavity of the right ventricle study its interior and note the thickness of its wall.

  • Note the shape of the cavity and bulging of the interventricular septum to the right. Note the right atrioventricular opening, smooth and rough parts of the cavity, chordae tendineae and cusps of the tricuspid valve. Identify the septomarginal (moderator) band
  • Make an inverted T-shaped incision in the left ventricle in such a way the vertical limb passes through the ventricular wall and the horizontal limb through the inferior border up to the apex and opens the cavity.
  • Study the interior note the thickness of its wall and compare it with the right ventricle. Note the rough and smooth parts, mitral opening and its cusps. Note the membranous and muscular parts of the interventricular septum.
  • To open the left atrium 2 horizontal incisions are given through the pulmonary veins. Open the chamber and study its interior.
  • Note openings of 4 pulmonary veins, smooth and rough parts, and left atrioventricular orifice from the atrial aspect. Locate the positions of the sinoatrial node, atrioventricular node and a bundle of His.

A cusp consists of a fibrous core covered by endothelium. The cusps are not uniform in thickness. Its central part is thinnest (clear zone) while the attached part (basal zone) and marginal part (rough zone) are relatively thicker.

All the cusps receive the attachment of fibrous thread-like structures (chordae tendinae) from the ventricular wall, along their margins and on their ventricular surfaces.

Heart Zones Of The Cusps Of The Tricuspid Valve

Heart Attachments Of The Chordae Tendinae In Right Ventricle

Rough part

It is the lower part of the right ventricle marked by a large number of elevations called the trabeculae camera. These elevations are of three types;

  1. Ridges – elongated elevations attached to the wall all along its length,
  2.  – elongated elevation attached at its ends only (For Example., septomarginal/moderator band),
  3. Papillary muscles – conical elevations. Papillary muscles provide chordae tendineae to the cusps. Papillary muscles are arranged in three groups named, anterior, posterior and septal according to their relation with the ventricular walls.

Chordae tendineae from each group extend towards the commissure and get attached to the adjacent cusps.

Heart Types Of Elevations In The Right Ventricular Chamber

Heart Rough Part

Smooth Part

It is the upper part of the right ventricle devoid of the trabeculae camera. This is tunnel-shaped and therefore called the infundibulum or conus arteriosus.

The demarcation between the rough and smooth parts is the supraventricular crest (posteriorly) and the septomarginal band (anteriorly). The latter (also called the moderator band) extends from the interventricular septum to the anterior papillary muscle.

Pulmonary Orifice

It is located at the upper extreme of the right ventricle. A fibrous ring (annulus) along its margin provides attachment to the pulmonary valve.

This valve consists of three cusps named according to their attachments, i.e., right anterior, left anterior and posterior. The centre of the cusp margin is marked by a fibrous nodule with thin crescentic areas lateral to it called lunules.

Heart Pulmonary Cusps(Opened)

The Left Ventricle

External Features

The left ventricle contributes to a l/3rd of the sternocostal surface, 2/3rd of the diaphragmatic surface, the left border and the apex of the heart. Its wall is three times thicker than that of the right ventricle – a fact correlated with the blood pressure inside its chambers.

Internal Features

This is also described under similar 4 headings as follows,

  1. Inflow orifice (left atrioventricular orifice)
  2. Inflow tract (rough part)
  3. Outflow tract (smooth part)
  4. Outflow orifice (aortic orifice)

Left Atrioventricular Orifice.

It connects the left atrium with the left ventricle and directs the blood to flow forward and towards the apex of the heart. Its margin is marked by a fibrous ring (annulus) which receives attachment from a bicuspid (mitral) valve.

As the name suggests, the valve consists of two cusps, anterior (larger) and posterior (smaller). Truly speaking, the former is anteromedial and the posterior is posterolateral in position. Their two commissures therefore are anterolateral and posteromedial.

Heart Caediac Valves Observed From Behind (From Atrial Side)

The posterior cusp is typical in the sense that it shows all three zones (rough, clear and basal) in its wall and receives attachment of chordae tendineae along its margin as well as on the ventricular surface.

The anterior cusp is atypical as its wall shows only two zones (rough and clear) and it receives attachment of chordae tendineae along its margin only.

Rough Part

It is the lower part of the left ventricle marked by the trabeculae camera, but here only two types of elevations are noticed, i.e., ridges and papillary muscles (bridges are lacking).

  • Papillary muscles are grouped into anterior and posterior which provide chordae tendineae to the adjacent cusps of the bicuspid valves.
  • Chordae tendineae from the anterior group extend towards the anterolateral commissure while those from the posterior group proceed to the posteromedial commissure.

Heart Interior Of The Left Ventricle

Smooth Part

It is the upper part of the left ventricle devoid of trabeculae camera. This is also called the aortic vestibule. It is located between its anterosuperior wall, the anterior cusp of the bicuspid valve and the membranous part of the interventricular septum.

Aortic Orifice

It connects the aortic vestibule with the ascending aorta. Attached to the fibrous ring (annulus) is an aortic valve which consists of three semilunar valvules or cusps.

Three cusps are named according to their orientation i.e., anterior, right posterior and left posterior. Nodule and lunule are similarly appreciated as in the pulmonary cusps.

Applied Anatomy Of The Chambers Of The Heart

  • Atrial septal defect. Normally the foramen ovale (an opening in the interatrial septum during intrauterine life) closes after birth. A minor defect is compatible with life but a large opening needs surgical intervention.
  • Ventricular septal defect. The defect is usually noticed in the region of the membranous part of the interventricular septum.
  • A large defect will push a lot of blood from left to right resulting in right ventricular enlargement. The defect is corrected surgically.
  • Pulmonary valve stenosis. Narrowing of the pulmonary orifice restricts the blood flow from the right ventricle to the pulmonary trunk. Increased load on the right ventricle results in its hypertrophy.
    • Pulmonary valve incompetence. It results in pulmonary regurgitation and during diastole, a murmur (an abnormal sound) can be heard.
  • Mitral valve stenosis and regurgitation. The mitral valve is a common site of valvular disease. It may be narrowed (stenosis) or unable to close during systole (regurgitation).
    • Both conditions produce murmur, the former during diastole (diastolic murmur) and the latter during systole (systolic murmur).
    • Aortic valve incompetence is usually congenital and results in a systolic murmur and left ventricular hypertrophy.
  • Enlarged left atrium. Since the oesophagus forms the immediate posterior relation of the left atrium, a compression effect is observed in the ‘barium-swallow-radiograph’ in case of left atrium enlargement.

Structures Of The Walls Of The Heart

Fibrous Skeleton Of The Heart

Functions

  1. Ensures electrophysiological discontinuity between atrial and ventricular musculature.
  2. Provides attachments for the myocardium.
  3. Maintains the cardiac position.
  4. Forms base for the attachment of valves.

Components

  1. Fourfibrous rings
    • Tricuspid valve annulus.
    • Mitral valve annulus.
    • Pulmonary valve annulus.
    • Aortic valve annulus.
  2. Two fibrous trigones. These are thickenings in the aortic annulus.
    • Rightfibrous trigone. It is the central fibrous body and forms a structural and functional
      link between aortic, mitral and tricuspid orifices.
    • Leftfibrous trigone. It connects the aortic annulus with the mitral valve annulus.
  3. Two tendons
    • Tendon ofinfundibulum. It is a fibrous connection between the aortic annulus and the pulmonary annulus.
    • Tendon of Todaro. It is a curved fibrous band between the mitral valve annulus and the tricuspid valve annulus. It is subendocardial in the right atrial wall and lying in its concavity is the atrioventricular node.

Membranous part of the interventricular septum. It is the posterior part of the interventricular septum close to the junction of the mitral valve annulus and tricuspid valve annulus. Its inferior margin is related to the atrioventricular bundle.

Heart Fibrous Skeleton Of The Heart

Musculature Of The Heart

Actual and ventricular musculatures are completely separated from each other by a fibrous skeleton. In both cases, muscle fibres form superficial and deep laminae.

Heart Musculature Of The Heart

Atrial Musculature

Superficial fibres. These encircle two atria transversely, i.e., across the cardiac long axis.

Deep fibres.

  • Looped deep fibres. These arise from the superior margin of the tricuspid and mitral valve annulus and after making a loop, get attached to the inferior margin of the corresponding annulus.
  • Annular deepfibres. These are circular fibres adjacent to the termination of venae cavae.

Ventricula Musculature

  • Superficial fibres. These fibres arise from the tricuspid as well as mitral valve annulus and run spirally around the heart till they reach the apex of the right and left ventricles.
    • These fibres make a whirl (called a vertex) at the corresponding apex and then run very deep to continue with the papillary muscles.
  • Deepfibres. These fibres are located in the interventricular septum and connect the papillary muscles of the two ventricles.

Heart Deep Fibres Of The Ventricular Musculature

Conduction System Of The Heart

Specialized cardiac muscles organize to form this system to control the rate of heartbeat. Components of this system are as follows.

  1. Sinuatrial node. This is also called a ‘pacemaker’ because the impulses are initiated here. This is named sinoatrial because originally it is a part of ‘sinus venosus’ which is absorbed later to form part of the right atrium.
    • The node is subepicardial in the junctional region between the superior vena cava and the right atrium at the upper end of the sulcus terminalis.
  2. Atrioventricular node. It is subendocardial and located in the posterior wall of the right atrium just above the opening of the coronary sinus.
  3. Atrioventricular bundle of His. It runs along the inferior margin of the membranous part of the interventricular septum. It terminates into two crura.
  4. Right crus. It runs in the interventricular septum, mostly subendocardially, towards the right ventricular chamber.
    • The majority of it passes to the anterior papillary muscles and the anterior wall of the right ventricle through the moderator band, and is then distributed via their fine branches called the Purkinje fibres.
  5. Left crus. It pierces the interventricular septum to reach its left aspect and immediately splits into multiple bands. These are distributed to the left ventricle via their Purkinje fibres.
  6. Accessory tracts. There are three specialized tracts which connect the SA node with the AV node. These are called the internodal tracts.
    • Anterior internodal tract. It is one of the branches of the interatrial bundle of Bachmann arising from the SA node. The tract runs to the left, anterior to the opening of the superior vena cava and descends to join the AV node.
    • Middle internodal tract of Wenckebach. It passes along the posterior margin of the opening of the superior vena cava and then descends along the limbus fossa ovalis to join the AV
      node.
    • Posterior internodal tract of Thorel. It descends in the crista terminalis and runs to the left along the attached margin of the valve of the inferior vena cava to enter the AV node.

Heart Conducting System Of Heart

Applied Anatomy Of The Conducting System Of Heart

  • Injury to the AV node and AV bundle. Damage to the conducting system is usually caused by the ischaemia resulting from coronary artery disease.
  • Heart block is caused by damage to the AV node or AV bundle as the impulses are unable to reach the ventricle from the SA node. A pacemaker implantation is usually useful in such cases.
  • Artificial cardiac pacemaker. The instrument is useful in the cardiac block. It has three components; a battery, a wire and an electrode. Battery is inserted subcutaneously whereas electrode is passed in the right ventricle through the venous channel and inserted subendocardially.
  • Cardiac massage. It is applying pressure over the lower part of the sternum and then releasing it. The process is repeated at regular intervals and is found to be very useful in reviving the heart in cases of cardiac arrest.
  • Abnormal heart rate. A pulse rate above 100 beats/min in adults is said to be ‘SINUS TACHYCARDIA’ and below 60 beats/min is considered to be ‘SINUS BRADYCARDIA’.
  • Extrasystole. It is due to ectopic beat arising from foci in the heart which stimulates the heart before the next sinus beat is due. Extra systole therefore comes prematurely and is followed by a pause.

Superior Mediastinum

Superior Mediastinum Boundaries

Anterior – Sternum (monubrium stemi)

Posterior – Upper 4 thoracic vertebral bodies.

Lateral – Mediastinal pleurae

Superior – Inlet of the thorax

Inferior – Horizontal plane at the level of the sternal angle.

Superior Mediastinum Boundaries Of The Superior Mediastinum

Superior Mediastinum Contents

Retrosternal structures

  1. Sternothyroid.
  2. Sternohyoid
  3. Thymus.
  4. Superior vena cava
  5. Brachiocephalic vein
  6. Left superior intercostal vein

 

Superior Mediastinum Structures In The Superior Mediastinum

Prevertebral structures

  1. Longus colli
  2. Trachea
  3. Oesophagus
  4. Left recurrent laryngeal nerve
  5. Thoracic duct

Intermediate Structures

  1. Arch of aorta
  2. 3 branches of the arch of the aorta (brachiocephalic, left common carotid and left subclavian)

Paired nerves and plexuses

  1. Vagus nerve – right and left
  2. Phrenic nerve- right and left
  3. Cervical cardiac branches from the left superior cervical ganglion and left vagus.
  4. Cardiac plexuses – superficial and deep

Superior Mediastinum TS Through Superior Mediastinum

Arch Of Aorta

The Arch of the aorta commences at the level of the sternal angle as a continuation of the ascending aorta. It courses backwards and towards the left to terminate as a descending thoracic aorta at the same level.

Arch Of Aorta Surface Marking

The Arch of the aorta is related to the posterior surface of the lower half of the manubrium stem. It is marked by joining the right and the left ends of the sternal angle with an upward bold convexity reaching the midpoint of the manubrium.

Superior Mediastinum Surface Making Of The Arch Of Aorta

Arch Of Aorta Curvatures

  • In vertical plane
    • Superior- convex
    • Inferior- concave
  • In horizontal plane
    • Right- concave
    • Left- convex

Superior Mediastinum Curvatures Of The Arch Of Aorta

Arch Of Aorta Branches

From proximal to distal these are-

  1. Brachiocephalic artery
  2. Left common carotid artery
  3. Left subclavian artery

Superior Mediastinum Arch Of Aorta Anterior View

Arch Of Aorta Relations

  • Superior
    • Three branches of the arch of the aorta
    • Left brachiocephalic vein
  • Inferior
    • Ligamentum arteriosum
    • Bifurcation of the pulmonary trunk and left pulmonary artery
    • Left principal bronchus
    • Left recurrent laryngeal nerve
    • Superficial cardiac plexus
  • Anterior and to the left
    • Left vagus
    • Left phrenic
    • Two cervical cardiac branches to the superficial cardiac plexus
    • Left superior intercostal vein
  • Posterior and to the right
    • Trachea
    • Oesophagus
    • Thoracic duct
    • Left recurrent laryngeal nerve

Superior Mediastinum Transverse Section Of Thorax

Superior Mediastinum Applied Anatomy

  • The left brachiocephalic vein is located in the lower neck of children. This is of great importance in operations like tracheostomy.
  • Anomalies of the branches of the arch of the aorta. In about 27% of cases left common carotid artery originates from the brachiocephalic artery.
    • In 2.5% of cases, the right common carotid and right subclavian arteries arise independently from the arch.
    • The presence of two brachiocephalic arteries and the origin of the vertebral artery from the arch is also often observed.
  • Abnormal arterial conditions cause pressure on the trachea and oesophagus.
    • Retro-oesophageal right subclavian artery. In such cases, the right subclavian artery is the distalmost branch of the arch of the aorta.
    • Double aortic arch. Two aortae arise from a vascular ring around the trachea and oesophagus.
    • Aortic aneurysm. It is a localized dilatation of the aorta.
  • Coarctation of aorta. It is an abnormal narrowing (stenosis) of the aorta diminishing blood flow to the lower part of the body.
  • Patent ductus arteriosus. Ductus arteriosus (communication between the left pulmonary artery and arch of the aorta during intrauterine life) is soon fibrosis to form ligamentum arteriosum.
    • If it persists (patent ductus arteriosus), there is mixing of oxygenated and deoxygenated blood. The surgical ligation of the duct corrects the problem.

Superior Mediastinum Coarctation Of Aorta

Superior Mediastinum Patent Ductus Arteriosus

Posterior Mediastinum

Posterior Mediastinum

Posterior Mediastinum Boundaries

  • Anterior
    • Tracheal bifurcation
    • Pulmonary vessels
    • Pericardium
    • Diaphragm
  • Posterior – Lower eight thoracic vertebra
  • Sides – Mediastinal pleurae
  • Inferior – Diaphragm

Posterior Mediastinum Boundaries Of The Posterior Mediastinum

Posterior Mediastinum Contents

  • Vertical structures
    • Descending thoracic aorta
    • Azygos, hemiazygos and accessory hemiazygos veins
    • Oesophagus
    • Thoracic duct
    • Vagus
    • Splanchnic nerves (greater, lesser and least)
  • Horizontal structures
    • Right posterior intercostal arteries
    • Posterior intercostal veins
    • Terminal parts of hemiazygos and accessory hemiazygos veins
    • Right to left course of thoracic duct

Posterior mediastinal lymph nodes

Inter-relationship of the contents

In general, horizontal structures pass behind the vertical structures.

Posterior Mediastinum Inter Relationship Between The Contents Of The Posterior Mediastinum

Descending Thoracic Aorta

It is a continuation of the arch of the aorta at the level of the intervertebral disc between the 4th and 5th thoracic vertebrae. It descends to the left of the midline in the upper part while in the midline in the lower part.

Posterior Mediastinum Descending Thoracic Aorta

Posterior mediastinal lymph nodes Relations

  • Posterior
    • Terminal part of hemiazygos vein
    • Accessory hemiazygos vein
  • Posterior and to the right
    • Azygos vein
    • Thoracic duct
  • Posterior and to the left
    • Hemiazygos vein
    • Accessory hemiazygos vein
  • Sides
    • Mediastinal pleurae
  • Anterior
    • Root of the left lung
    • Pericardium
    • Oesophagus
    • Diaphragm

Posterior mediastinal lymph nodes Branches

  • One right and two left bronchial arteries.
  • Pericardiophrenic branches
  • Lower 9 pairs of posterior intercostal arteries
  • Superior phrenic arteries
  • Three oesophageal arteries
  • Mediastinal arteries
  • Subcostal arteries

Dissection Steps For The Posterior Mediastinum

Define the boundaries of the posterior mediastinum. Identify and divide the ligmentum arteriosum. Trace the left recurrent laryngeal nerve branches to the deep cardiac plexus located in front of the tracheal bifurcation.

  • Clean and identify the descending thoracic aorta and note its branches. trace the upper part of the thoracic duct to its termination at the left Jugulosubclvian junction. Trace the posterior Intercostal veins to the azygos, hemiazygos and accessory hemiazygos veins.
  • Clean and identify the sympathetic chain about the heads of the ribs and note the different splanchnic nerves. Note the various structures at the level of T4.

Oesophagus

It begins at the level of the 6th cervical vertebra as a continuation of the pharynx in the midline. It descends to the left of the midline but comes to lie in the midline at the level of the 5th thoracic vertebra.

Reaching the level of the 7th thoracic vertebra it gradually turns to the left till it reaches the level of the 10th thoracic vertebra where it pierces the diaphragm. It terminates by joining the stomach at the level of the 11th thoracic vertebra.

The oesophagus is approximately 25 cm in length. It is divided into three parts according to its location, i.e., cervical, thoracic and abdominal. Normally four constrictions are noted in the oesophagus.

Posterior Mediastinum Oesophagus

Vascular supply is tabulated below.

Posterior Mediastinum Vascular Supply

Posterior Mediastinum Oesophagus..

Innervation

The oesophagus receives autonomic innervation as tabulated below.

Posterior Mediastinum Innervation

Oesophagus Applied Anatomy

  • Dyspepsia – difficulty in swallowing. It is a serious symptom usually due to benign or malignant tumours of the oesophagus.
  • Oesophageal injury – though rare, but very important because of its fatal outcome. Injury to the oesophagus is usually accompanied by injury to the trachea due to its immediate anterior relation.
  • Tracheo-oesophageal fistula – This is the most common congenital anomaly of the oesophagus. Associated oesophageal atresia is a usual combination. In the majority of anomalies, the trachea communicates with the distal part of the oesophagus.
  • Oesophageal cancer – It reduces the lumen of the oesophagus. The patient develops dysphagia when the lumen is reduced by 30 to 50%. Involvement of recurrent laryngeal nerve causes hoarseness of voice.

Azygos System Of Veins

Azygos vein

It commences in the abdomen by the union of right ascending lumbar and right subcostal veins. It enters the thorax by passing through the aortic hiatus to the right of the thoracic duct. Its tributaries are:

  • 2nd to 11th right posterior intercostal veins
  • Hemiazygos and accessory hemiazygos veins.
  • Veins from the thoracic viscera.

Posterior Mediastinum Azygos System Of Veins

Accessory Hemiazygos Vein

It is a vertical vein in the upper part of the thorax on the left side of the vertebral column. It receives left 4th to 8th posterior intercostal veins.

It descends from the level of the 4th left intercostal space to the 8th thoracic vertebral body where it crosses to the right to join the azygos vein.

Hemiazygos vein

Its commencement is like azygos vein i.e., left subcostal and left ascending lumbar veins unite to form it. It enters the abdomen by piercing the left crus of the diaphragm.

It ascends to the left of the vertebral column till it reaches the 8th thoracic vertebral body where it turns to the right to join the azygos vein. During its course, it receives 9th to 11th left posterior intercostal veins.

Thoracic Duct

This is the largest lymphatic channel in the body which drains almost the whole body except the right upper limb and right half of the head neck and thorax.

  • It ascends from the upper part of the cistema chyli (a lymphatic sac lying vertically in the abdomen against the upper two lumbar vertebrae) and enters the thorax through the aortic hiatus.
  • It ascends to the right of the midline till it reaches the level of the sternal ‘ angle.
  • During this part of the course, it lies anterior to the lower thoracic vertebral bodies, posterior to the oesophagus, to the right of the descending thoracic aorta and to the left of the azygos vein.
  • At the sternal angle, it turns to the left and then ascends to the left of the midline to reach the root of the neck.
  • At the level of the 7th cervical vertebra, it again turns to the left to drain into venous blood at the junction of the left internal jugular and left subclavian veins.
  • The thoracic duct measures approximately 18″ (45 cm). It is beaded in appearance due to the presence of multiple valves in it.

Posterior Mediastinum Course f The Thoracic Duct

Accessory Hemiazygos Vein Applied Anatomy

  • Laceration of thoracic duct – The thoracic duct is colourless, therefore it is difficult to visualize it during surgical procedures and therefore prone to injury during operation in the posterior mediastinum.
  • Lymph (chyle) may enter the pleural cavity, this condition is called chylothorax.
  • Variation of the thoracic duct. There are two lymphatic vessels during intrauterine life running parallel to each other and draining symmetrically in the root of the neck.
  • Since the thoracic duct is the persistence of part of both these channels, anomalous thoracic duct (For Example., double thoracic duct) may be noticed in adults.

Posterior Mediastinum Development Of Thoracic Duct (Vessels Shown With The Dotted Lines Disappear)