How does the liver function?
The liver is the largest organ of the human body. It is like a big factory that metabolises nutrients, produces a large number of proteins and other substances essential for the structure and function of the whole organism. In addition, the liver has a detoxifying function. Its multiple roles as the central metabolic organ make the liver function essential for survival. To fulfil its role, the liver requires good blood perfusion and considerable energy. The weight of the liver is between 1500 to 2000 gram, thus constituting 2 % of the total body weight. Yet, in order to be able to fulfil its complete role, the liver requires about 20 % of our oxygen supply.
Without a functioning liver, the body can only survive for a few hours. As a safeguard against such a catastrophe, the organ has considerable reserves: Only one third of the total liver volume is required to fulfil all its functions sufficiently. In addition, the liver can regrow. Nutrients reach the liver from the intestine via the portal vein. Nutrients are usually taken up by the liver cells and used there for further functions. At the same time, the blood from the intestine is cleaned and detoxified by passing the tissue filter of the liver.
The main liver cells are called hepatocytes. These cells have the ability to destroy or eliminate toxic material and at the same time to use the nutrients to build proteins and other substances. Ingested proteins are split into the individual amino acids and the re-synthesized into new proteins required by the body. Carbohydrates, which usually reach the liver from the intestine in the form of glucose, can be stored in the liver and are brought back into the circulation when required as energy supply. This function is crucial for a balanced blood sugar level preventing diabetes mellitus. Ingested fat components are used by liver cells for the production of a variety of substances such as transport molecules or material to build cell walls. On the other hand, the liver can use superfluous energy to build new fatty acids for energy storage.
Detoxification of blood
Without the liver the body would be overwhelmed by toxic substances within a short period. For example, toxic ammonia resulting from protein metabolism in the body can be taken up by liver cells and metabolized to non-toxic urea and subsequently excreted in the urine. Similar mechanisms apply to a variety of other toxic waste from metabolic processes of the body. In addition, external substances such as drugs are also metabolised in the liver and eventually excreted either via bile or via urine.
The liver as a gland
The liver is the largest digestive gland producing about half a litre of bile every day. Bile is secreted into the duodenum and partly stored in the gall bladder, to be excreted when a larger meal is consumed. Bile consists of enzymes and salts, which are required for the digestion and absorption of fat in the intestine. In addition, the liver produces a number of hormones. These regulate various body functions such as cell division, tissue growth and repair.
Storage function of the liver
The liver is not only a metabolic and secretory organ, but also a storage organ. The vitamins A, D, E and K require bile for absorption and are then stored in the liver. Also vitamin B12 and essential elements such as iron, copper and zinc are stored in the liver. These and other substances can be provided by the liver to other tissues of the body shuttled by specific transport molecules, which are also synthesised and secreted by the liver.