The Liver or hepar is the largest gland in the body, weighing about 1200 to 1600 gms, and situated in the top right side of the abdominal cavity. It is reddish brown in color and is divided by fissures into four lobes. One lobe on the left side called left lobe and on the right side there are three lobes namely, the right lobe, quadrate lobe and caudate lobe.

The gall bladder is a pear-shaped structure, situated on the ventral side of the liver. It is about 10 to 15 cms long and about 2.5 cms in diameter. Bile, secreted by the liver remains stored in the gall bladder and therefore the gall bladder is known as the store house of bile.

Histology of Liver

Liver is a compact mass of glandular cells or hepatic cells arranged in a more or less definite pattern, usually forming lobules. Each lobe of the liver is made up of a number of hepatic lobules, which are incompletely separated from each other by the thin layer of connective tissue called Glisson’s capsules. The connective tissue contains branches of portal vein, hepatic artery, bile duct and lymphatic vessel. Each hepatic lobule consists of a mass of polyhedral hepatic cells which are arranged radially like the spokes of a wheel and are called hepatic cords. Some specialized Kupffer cells are also present in the liver, which help in killing many germs. The hepatic cords are separated by hepatic or liver sinusoids.

Blood supply to the Liver

The hepatic portal vein and hepatic artery supply blood to the liver and blood is collected from the liver by the hepatic veins. The hepatic portal vein is divided into several branches to form inter lobular veins which are found around the lobules. Sinusoids arise from the interlobular veins and run through the lobules between hepatic strands and join into a central or intralobular vein. All the intralobular veins meet together and form the hepatic veins which finally join with the post caval vein.

Bile passages

Bile is secreted from the liver cells. The bile passages begin as spaces between the hepatic cells, called bile canaliculi. The bile canaliculi pass through the center of each hepatic strand. The canaliculi connect with interlobular bile ducts found at the periphery of the hepatic lobule. The interlobular bile ducts join to form progressively large ducts called hepatic ducts. In this way, several hepatic ducts arise from various lobes of the liver and join together to form common hepatic duct. The cystic duct from the gall bladder and the common hepatic duct join to form the common bile duct.

Gall bladder

It is situated in the groove of right central lobe. It is a thin walled, elongated sac like structure. A large cystic duct arises from the gall bladder. The gall bladder acts as a storage reservoir for the bile which is secreted by the liver. Through the large common bile duct, the bile is brought into proximal part of the duodenum.

Composition of bile

A chemical analysis of bile shows that it contains water, the bile salts, the bile pigments, inorganic salt, mucin, lipids and traces of urea and carbon dioxide. The lipase is said to be present in the bile.

The bile salt namely sodium taurocholate and sodium glycocholate are manufactured solely by the liver cells and the most important physiological functions of the bile are due to the presence of these salts. The bile pigments are bilirubin and biliverdin. The colour of the bile is primarily due to the presence of these pigments. The bile pigments are considered to be excretory products and their ultimate source is haemoglobin of worn out red blood corpuscles.

General function of the Liver

Liver is not only a digestive gland but also acts as a master laboratory, performing various other important functions which are as follows:

-         Liver plays its role in the metabolism of carbohydrates e.g. storage of excess of sugar in the form of glycogen, maintenance of constant sugar level in the blood, elaboration of glycogen from non-glucose sources and the formation of glucose from glycogen.

-         It plays a role in the metabolism of lipids, conversion of carbohydrates to fat and so on.

-         It plays a role in protein metabolism i.e. aminoacid synthesis, removal of absorbed aminoacids from the blood, deamination of amino acids, formation of urea and so on.

-         It produces heparin, an anticoagulant which prevents coagulation of blood in the blood vessels.

-         It produces fibrinogen which helps in the clotting of blood.

-         It produces red blood corpuscles in the foetus of mammals.

-         It is responsible for the destruction of worn out red blood corpuscles.

-         It contributes to the secretion of lymph.

-         It stores iron, copper, glycogen, vitamins, enzymes and hormones. Vitamin A and D are stored in the liver and it also manufactures vitamin A and K.

-         It is the most important center for heat production in the body.

-         It prevents anaemia.

-         The Kupffer cells of the liver destroy the germs of many diseases.

-         It helps in removing various unwanted substances like carbolic acid from the blood coming from alimentary canal.

-         It changes amino acids into albumin which regulates the salt water balance in the body, without which animal can not survive.