Normal Liver Function and Physiology

The liver is an organ present in vertebrates and some other animals. It plays a big role in metabolism and has a number of functions in the body, including glycogen storage, decomposition of red blood cells, plasma protein synthesis, and detoxification. This organ also is the single largest gland in the human body. It lies below the diaphragm in the thoracic region of the abdomen.

It produces bile, an alkaline compound which aids in digestion, via the emulsification of lipids. It also performs/ regulates a wide variety of high-volume biochemical reactions requiring very specialized tissues.

The liver produces and excretes bile (a greenish liquid) required for emulsifying fats. Some of the bile drains directly into the duodenum, and some is stored in the gallbladder.

The liver performs several roles in carbohydrate metabolism:

- Gluconeogenesis (the synthesis of glucose from certain amino acids, lactate or glycerol)
- Glycogenolysis (the breakdown of glycogen into glucose). Note that muscle tissues can also do this.
- Glycogen sis (the formation of glycogen from glucose)

In the first trimester fetus, the liver is the main site of red blood cell production. By the 32nd week of gestation, the bone marrow has almost completely taken over that task. The liver is responsible for immunological effects- the reticuloendothelial system of the liver contains many immunologically active cells, thus acting as a 'sieve' for antigens carried to it via the portal system.

The liver produces albumin, the major osmolar component of blood serum.
Currently, there is no artificial organ or device capable of emulating all the functions of the liver. Some functions can be emulated by liver dialysis, an experimental treatment for liver failure.

Some of the major liver functions include:

- Removing/ excreting body wastes and hormones as well as drugs and other foreign substances These substances have entered the blood supply either through production by metabolism within the body or from the outside in the form of drugs or other foreign compounds. Enzymes in the liver alter toxins so they can be more easily excreted in urine

- Synthesizing plasma proteins, including those necessary for blood clotting Most of the twelve clotting factors are plasma proteins produced by the liver. If the liver is damaged or diseased, it can take longer for the body to form clots. Other plasma proteins produced by the liver include albumin which binds many water-insoluble substances and contributes to osmotic pressure, fibrogen which is key to the clotting process, and certain globulins which transport substances such as cholesterol and iron.

- Producing immune factors and removing bacteria, thus helping the body fight infection The phagocytes in the liver produce acute-phase proteins in response to microbes. These proteins are associated with the inflammation process, tissue repair, and immune cell activities.

Other important but less immediate functions include:

- Producing bile to aid in digestion Bile salts aid in fat digestion and absorption. Bile is continuously secreted by the liver and stored in the gallbladder until a meal, when bile enters the beginning of the small intestine

- Excretion of bilirubin Bilirubin is one of the few waste products excreted in bile. Macrophages in the liver remove worn out red blood cells from the blood. Bilirubin then results from the breakdown of the hemoglobin in the red blood cells and is excreted into bile by hepatocytes. Jaundice results when bilirubin cannot be removed from the blood quickly enough due to gallstones, liver disease, or the excessive breakdown of red blood cells

- Storing certain vitamins, minerals, and sugars The liver stores enough glucose in the form of glycogen to provide about a day's worth of energy. The liver also stores fats, iron, copper, and many vitamins including vitamins A, D, K, B12

- Processing nutrients absorbed from digestive tract The liver converts glucose into glycogen, its storage form. This glycogen can then be transformed back into glucose if the body needs energy. The fatty acids produced by the digestion of lipids are used to synthesize cholesterol and other substances. The liver also has the ability to convert certain amino acids into others.

Note that one of the liver's most interesting abilities is self-repair and the regeneration of damaged tissues. In clearing the body of toxins, the liver is damaged by exposure to harmful substances, showing why this capability is important. It also gives hope that if a failing liver can be supported for a certain period of time, it might regenerate fully and allow the patient to survive and thus regain a normal life