One of the liver’s primary jobs is to store energy in the form of glycogen, which is made from a type of sugar called glucose. The liver removes glucose from the blood when blood glucose levels are high. Through a process called glycogenesis, the liver combines the glucose molecules in long chains to create glycogen, a carbohydrate that provides a stored form of energy. When the amount of glucose in the blood falls below the level required to meet the body’s needs, the liver reverses this reaction, transforming glycogen into glucose.
Another crucial function of the liver is the production of bile, a yellowish-brown liquid containing salts necessary for the digestion of lipids, or fats. These salts are produced within the lobules. Bile leaves the liver through a network of ducts and is transported to the gallbladder, which concentrates the bile and releases it into the small intestine.
Vitamins are also stored in the liver. Drawing on the nutrient-rich blood in the hepatic portal vein, the liver collects and stores supplies of vitamins A, D, E, and K. The B vitamins are also stored here, including a two- to four-year supply of Vitamin B12.
The liver also functions as the body’s chemical factory. Several important proteins found in the blood are produced in the liver. One of these proteins, albumin, helps retain calcium and other important substances in the bloodstream. Albumin also helps regulate the movement of water from the bloodstream into the body’s tissues. The liver also produces globin, one of the two components that form hemoglobin—the oxygen-carrying substance in red blood cells. Certain globulins, a group of proteins that includes antibodies, are produced in the liver, as are the proteins that make up the complement system, a part of the immune system that combines with antibodies to fight invading microorganisms.
Many other chemicals are produced by the liver. These include fibrinogen and prothrombin, which help wounds to heal by enabling blood to form clots, and cholesterol, a key component of cell membranes that transports fats in the bloodstream to body tissues.
In addition to manufacturing chemicals, the liver helps clear toxic substances, such as drugs and alcohol, from the bloodstream. It does this by absorbing the harmful substances, chemically altering them, and then excreting them in the bile.