|Topic Histology of liver And Gall bladder
At the end of the practicle student will able:
To identify the classical lobule of liver.
To explain the arrangement of hepatocytes and sinusoidal space of liver.
To give the different arrangement of hepatic lobules.
To give the normal histology of gall bladder.
It is the largest gland of body.
Covered by connective tissue capsule.
Parenchyma consists of hepatocytes.
Histologically liver consists of innumerable pyramidal lobule
Lobules consists of hepatocytes.
They are located in flat irregular plates that are arranged radially like the spokes of a wheel around a branch of the hepatic vein, called the central vein or central venule since it really has the structure of a venule.
Between these plates of hepatocytes are blood spaces known as liver sinusoids.
Section of Liver (in two dimension)
Hepatocytes are arranged in rows that radiate out from the central vein.
These rows are one cell wide and are surrounded by sinusoidal capillaries or sinusoids.
This arrangement ensures that each hepatocyte is in very close contact with blood flowing through the sinusoids, i.e. bathed in blood.
They are large cells.
Nucleus is large and rounded with prominent nucleolus
25% cells are binucleated.
Cytoplasm is strongly eosinophilic.
There is fine basophilic granularity due to the presence of free ribosomes.
Lipofuscin granules are also present in cytoplasm and increase with age.
The sinusoidal lining cells are endothelial cells, kupffer cells and cells of The endothelial cells lining sinusoids are fenestrated and in most species lack a basal lamina
A narrow space is present between the surface of the hepatocyte and the surface of the endothelial cell.
This is called the space of Disse; it is filled with numerous microvilli from the hepatocytes
The Kuffer cells are found on the luminal surface of endothelial cells.
These are phagocytic cells that remove particulate material and old red blood cells from circulation.
Kupffer cells are members of the mononuclear phagocyte system.
Basic Functional Unit of The Liver
Classical hepatic lobule.
Classical hepatic lobule:
The hepatic lobule is defined as having a central vein (CV) at its center with hepatocytes radiating from it in the form of plates.
The classical hepatic lobule is hexagonal in shape
Terminal branches of hepatic artery, portal vein and bile ductule are located at the angels of hepatic lobule boundary, known as portal triad.
Classical Hepatic Lobule
This lobule is triangular in shape.
Having a triad in the center and three hepatic veins at the corners.
The Hepatic Acinus
It is the functional unit of liver, comprises the territory supplied by each terminal branch of hepatic artery and portal vein and accompanied by bile ductule.
It is diamond shape.
It is situated in adjacent area of two classical hepatic lobules.
Termial branch of hepatic artery and portal vein run transversely in the centre of acinus.
Hepatocytes and sinus radiate towards hepatic venule
The hepatic acinus has three zones.
Hepatocytes in Zone 1 are the first to receive blood and it is high in oxygen.
Hepatocytes in Zone 2 are the second cells to receive blood and it is lower in oxygen.
Hepatocytes in Zone 3 are the last to receive blood from a branch of the hepatic artery and it is lowest in oxygen.
Hepatic Acinus (Zones)
Thus, the cells with the highest metabolic potential are found in Zone 1.
Those with the least are found in Zone 3.
Importantly, the cells in Zone 3 are the most susceptible to ischemic conditions as edges defined by portal canals (PC).
Duct System of Liver
Bile is produced and secreted by hepatocytes into a special "duct" called a bile canaliculus.
This "duct" is actually just a space formed between two hepatocytes that is separated from the connective tissue space around the hepatocytes by the presence of tight junctions.
The bile canaliculi empty into branches of the bile ductules.
In the duct system, bile flows in the direction opposite to the flow of blood in the sinusoids.
Blood Supply of Liver
Functions of Liver
Digestive and Metabolic Functions
Synthesis and secretion of bile
Storage of glycogen and lipid reserves
Maintaining normal blood glucose, amino acid and fatty acid concentrations
Synthesis and release of cholesterol bound to transport proteins
Inactivation of toxins
Storage of iron reserves
Storage of fat-soluble vitamins
Synthesis of plasma proteins
Synthesis of clotting factors
Synthesis of the inactive angiotensinogen
Phagocytosis of damaged red blood cells
Storage of blood
Breakdown of circulating hormones (insulin and epinephrine) and immunoglobulins
Inactivation of lipid-soluble drugs