Liver is the largest gland in the body, which weight is approximately 1.5-kg and it lies in the upper right side of the abdominal cavity just below the diaphragm. It is heavier in males than females. It plays a vital role in digestion and excretion. The basic anatomical and histological structure of the liver is described below.
Anatomically liver has been divided into two main lobes- Right lobe and Left lobe which are separated by the falciform ligament. The right lobe is much larger and it differentiated into- Caudate lobe, Quadrate lobe and Right lobe proper. Left lobe is much smaller than the right one. The right and left part of the liver have their own blood supply from the hepatic artery and portal vein and their own venous and biliary drainage. The structural and functional units of liver are Hepatic lobules, containing hepatic cells. The mammalian liver also containing Kupffer cells (which are one type of phagocytic cell) and Fat storage cells.
Liver is encapsulated by a connective tissue layer. The liver tissue comprises about one lac hexagonal areas which consist of hepatic lobules.
- Each hepatic lobule is made of columns of hepatic cells or hepatocytes. These cells form a one cell thick plates. In between two hepatocytes bile canaliculi are present.
- These hepatic cell plates are tunnelled by a communicating system of lacunae called sinusoids, which open into a central vein present in the centre of the hepatic lobules. It
- Blood sinusoids are lined by the endothelial cells. The Kupffer cells (the macrophage type cells) are found at a regular interval in between the endothelial cells.
- Portal triads consisting a branch of portal vein, portal artery and interlobular bile duct, present on the peripheral region of each hepatic lobule. Portal triad is also known as hepatic triad. Liver receives about 1500mL blood/min from the portal vein, portal artery and hepatic vein.
- Presently, acinus is considered as the functional unit of liver. Each acinus has been considered to have three zones. Zone-1 refers to the central portion of the acinus, Zone-2 refers to the intermediate zone situated between the Zone-1 and Zone-3 and the Zone-3 refers to the peripheral most part of the acinus.
NOTES: The liver possess considerable regeneration power. Original liver mass is restored within 6-8 weeks of removal of up to ¾ of liver. This occurs due to an active mitotic division of the cells.