The Liver

What is the Liver?

The liver is the largest internal organ in the body. It is a multi-functional organ, playing a role in metabolism. It acts as a storage organ for carbohydrates, blood, vitamins and iron. It also removes drugs, hormones and other toxic substances from the circulation.

Where is the Liver situated?
It is situated almost entirely beneath the ribs on the right side of the chest wall. The upper part of the liver is molded to the undersurface of the muscular partition called the diaphragm. The liver is a large organ stretching from the right side of the abdominal cavity to the spleen on the left.

How can we describe the Liver?
The liver is brown in color and is somewhat like a pyramid. It has three surfaces and an apex. The apex is directed towards the spleen on the left. Functionally the liver is divided into the right, left, caudate and the quadrate lobes.

Internal structure of the Liver

The liver consists of thousands of functional units called as lobules. The lobules are tiny blood processing units of about 1 mm. diameter. Each lobule is built around the central structure of the lobule called as the central vein. The lobules contain sinusoids, which are pouch-like structures that store and process the blood flowing through them. These sinusoids are lined with liver cells that secrete bile. Another group of cells called as the Kupfer cells also line the sinusoids. These cells are capable of destroying bacteria and other foreign matter in the blood.

A triad of hepatic artery, portal vein and bile duct surrounds each lobule. The central veins ultimately join to form the hepatic veins and drain into the hepatic veins. The hepatic veins finally drain into the inferior vena cava, the major blood vessel draining into the right atrium.

The bile ducts from each lobule ultimately to form the right and left hepatic ducts. These join to form the common hepatic duct. The common hepatic duct then joins the cystic duct of the gall bladder forming the common bile duct.

The portal circulation : The liver forms a part of the important portal system. The blood supply to the liver is via the portal circulation. The liver is supplied with oxygenated blood by the hepatic artery. But this constitutes only 30% of the total blood supply it receives. The rest comes from the portal vein. The portal vein actually arises from the small intestine. It contains venous blood that is nutrient rich in nature, which is derived from the absorbed food. This blood goes to the liver via the portal vein for processing. The portal vein sends blood to each lobule of the liver from where the blood is processed and then drained into the hepatic veins as mentioned above.

Functions of the Liver

The liver performs many functions. These are listed below in brief :

• Digestion : The liver produces bile, which is stored in the gall bladder. Bile contains bile salts that assist in emulsifying of the fat present in the blood into fatty acids, thus aiding in digestion of food. The liver also produces various digestive enzymes.
• As a storage organ : the liver performs the functions of storage of carbohydrates, vitamins; especially vitamins A, D and B12 and iron.
• Metabolism : the liver takes part in the fat, carbohydrate and protein metabolism.
• The liver also produces certain substances that are required for normal clotting to take place. These are fibrinogen, prothrombin, factor 7 etc.

In addition to all these functions the liver also performs the action of excretion of drugs, hormones and other chemicals in the body. Thus it detoxifies the body as a whole.