A vital organ, the liver carries out hundreds of essential chemical processes, adjusts the levels of many substances in the blood, and produces a digestive juice called bile. The liver is the body’s heaviest organ, weighing about 3 1/2 lb (1.5 kg).
The liver is made up of thousands of lobules—tiny hexagonal units about 1/25 in (1 mm) wide. Each is surrounded by a network of incoming blood vessels. Blood filters through the lobule and drains away through a vein in the middle.
Unlike other organs, the liver receives blood from two major blood vessels. The hepatic artery brings oxygen-rich blood from the heart. The hepatic portal vein brings blood rich in digested nutrients from the intestine. This means excess nutrients can be removed and stored before blood circulates around the body.
The liver carries out so many tasks that scientists compare it to a chemical factory. It filters blood from the intestines and removes excess food and iron for storage or for conversion into other substances. It also removes debris, destroys poisons, worn-out blood cells, and alcohol, and manufactures vitamin A and many other chemicals vital to the body.
The liver makes a greenish-brown liquid called bile, which is stored in a pouch called the gall bladder and emptied into the small intestine, where it makes fats mix with water and so helps digestion. Bile consists of water, bile salts, acid, cholesterol, and a pigment called bilirubin, which gives feces their color.