The liver is the largest organ in the human body and one that performs a multitude of important functions, both alone and in concert with other organs. The typical weight of a healthy liver will range from 2 lb to 4 lb (1 kg to 2 kg).
The liver is situated in the upper portion of the abdominal cavity, below the diaphragm, and it forms a part of the biliary system of the body, which is the network that includes a series of ducts, the gall bladder, the bile duct, and the liver. The kidneys are positioned next to the liver. The liver is surrounded by a dense network of connective tissues and blood vessels; the liver is brought into contact with a large amount of the blood present in the cardiovascular system at any time. The liver contains at any given moment over 10%s entire blood supply (approximately 15 oz, or 0.5 l).
The functions of the liver are constant and essential; the liver operates on an involuntary basis, directed by the central control of the body as exercised through the hypothalamus, in combination with the automatic nature of most liver processes. It is for this reason that liver failure or a serious impairment of the liver function is a catastrophic event for the body.
The liver plays an important role in the metabolism of carbohydrates in a number of different ways. The liver acts as a processor in the formation of glucose from a number of different sources. When triglycerides are released to create energy from their storage in the special fat cells, adipose tissue, the triglycerides are broken into two parts: fatty acids, which are applied to energy manufacture, and glycerol, the alcohol sugar. The liver scavenges the glycerol from this process and converts it to glucose.
The liver also converts lactate, or lactic acid, that is produced as a byproduct of the generation of energy. Lactate is also converted into glucose. The glucose converted by the liver is either distributed into the cardiovascular system for energy production, or it is stored in the liver in the form of glycogen. The liver will store other glucose ingested into the body than that which it converts from lactate or glycerol; the liver can store glucose representing as much as 10% of its organ weight for indefinite periods. The liver contains the largest store of glycogen next to that of the skeletal muscles.
The liver and its central role in the production of energy is also evident in its conversion of fats ingested through food products into the triglycerides necessary for storage. The liver is also a permanent reservoir of several important substances, including vitamin B12, iron, and copper.
The fetal blood supply is almost entirely centered on the liver until very late in the gestation period. The liver produces almost all of the red blood cells required by the fetus, until the bone marrow is fully developed.
As the organ through which all of the blood of the gastrointestinal tract will pass, the liver carries out a crucial purification and detoxification role for the entire body. Because the liver is a passageway for a significant quantity of blood, it is an organ that is consequently exposed to an inordinate number of the body's diseases. The liver is a common secondary site for the transference and development of various cancers, a process known as metastasis.
The liver produces the bile that is ultimately passed into the small intestine, where the bile assists in the digestive process by carrying away waste products. When the bile does not properly enter the digestive system, it will cause the blood supply to become tainted with its yellow coloring, a condition known as jaundice.
In addition to jaundice, which is usually a treatable condition, the liver is susceptible to the onset of a number of serious diseases. The most common liver ailment is one of the three types of hepatitis, an inflammation of the organ. Hepatitis is both communicable, and at its most destructive, hepatitis is a fatal condition. Cirrhosis of the liver is a type of cellular destruction of the organ caused by repeated exposure to large amounts of toxin; the most common agent of liver cirrhosis is excessive consumption of alcohol.
Given the importance of the liver to both glucose processing and the general maintenance of good health, liver problems will significantly impact on the ability of an athlete to perform at the highest level. The liver is well insulated within the abdominal structure so that physical damage to the liver by way of a trauma is very rare.