The liver is a large organ with several functions (see Biology of the Liver and Gallbladder: Liver), only some of which are related to digestion.
The nutrients of food are absorbed into the intestinal wall, which is supplied with many tiny blood vessels (capillaries). These capillaries flow into veins that join larger veins and eventually enter the liver as the portal vein. This vein splits into tiny vessels inside the liver, where the incoming blood can be processed.
Blood in the liver is processed in two ways: Bacteria and other foreign particles absorbed from the intestine are removed, and many nutrients absorbed from the intestine are further broken down so they can be used by the body. The liver performs the necessary processing at high speed and passes the blood, laden with nutrients, into the general circulation.
The liver manufactures about half of the body's cholesterol; the rest comes from food. About 80% of the cholesterol made by the liver is used to make bile. The liver secretes bile, which is stored in the gallbladder until it is needed.
Last full review/revision August 2006 by Nicholas J. Shaheen, MD, MPH