Short notes on the basic structure and functions of liver
The liver is composed of a large number of hexagonal lobules. Each lobule is about 1 mm in diameter. At the centre of each lobule runs a small branch of the hepatic vein. The cells of the liver are arranged in one celled thick sheets around the central vein. There are certain spaces between the cells of these plates wherein lie sinusoids.
These sinusoids are blood Vessels with incomplete walls. They are irregular in shape and wider than blood capillaries. They are lined by certain specialised cells called Kupffer cells which are phagocytic in action and remove cell debris and bacteria in the blood. Each lobule receives the branches of hepatic artery and the portal vein. The blood vessels form small branches and enter the sinusoids.
The liver cells are polyhedral in shape and have two surfaces that face the sinusoids and several surfaces in contact with other cells. The most important secretion of the liver is the bile. This is secreted by the liver cells and drains into minute cannals called bile canaliculi which lie between the walls of the cells.
The bile canaliculi join to form intralobular ductules which unite to form the right and the left hepatic ducts. These two ducts unite to form the common hepatic duct. This runs downwards for about three centimeters where it is joined by the cystic duct which comes from the gall bladder and continues downwards as the common bile duct. This common bile duct enters the duodenum at a small papilla called the ampulla of Vater.
The bile consists of bile pigments and bile salts. The salts present in the bile are sodium glycocholate and sodium taurocholate. The bile pigments are bilirubin and biliverdin. Bile is a golden yellow bitter fluid secreted by the human body to the tune of 500 to 1000 ml. daily about 86% of it is water.
Functions of the liver:
1 .During embryonic development R.B.Cs are formed in the liver.
2. Liver stores Vitamin A, B and C.
3. It stores the iron from the destroyed R.B.C.
4. It produces heparin for preventing coagulation of blood in the body.
5. Fibrinogen, blood protein is produced for blood clotting.
6. 1/5th of total volume of blood of the body is stored in the liver.
7. Liver plays an important role in carbohydrate metabolism. It stores glycogen and releases it as glucose into blood at times of need, like fasting.
8. It deals with fat metabolism, converting extra carbohydrates into fat.
9. Bile helps in saponification of fat.
10. It is the graveyard for old, worn out R.B.Cs. Bile pigments are formed from haemoglobin.
11. Liver brings about deamination of proteins. The unwanted amino acids are converted into urea, thus toxic substances are rendered harmless and are sent into blood to be expelled through the kidneys.
12. Liver excretes toxic substances.