Introduction
The liver is the largest and most important metabolic organ of the body. It takes on a wide range of tasks from the breakdown of harmful substances, to the utilization of food components, to the synthesis of new enzymes and proteins that are essential for the body’s survival. A loss of liver function can lead to life-threatening metabolic disorders.
General tasks
Via the portal vein (vena porta), substances that have been absorbed into the blood from the intestine reach the liver. Depending on the needs of the body, the components are used differently. Thus, the liver always ensures that the other organs are first supplied with sufficient nutrients before it stores any itself.
If there is enough in the body, the liver stores sugar in the form of glycogen, for example. If the blood sugar level drops, the liver can release glucose from this depot again. Fat, vitamins and protein components (amino acids) can also be stored in the liver.
The liver can then produce various vital proteins from the amino acids. These include coagulation factors, which are important for blood clotting, or C-reactive protein, which plays an important role in inflammation and is also considered an inflammation parameter in the blood count. The liver also produces proteins that can transport fat-soluble substances (fats, hormones) in the blood.
The body’s own cholesterol is also produced to a large extent in the liver, which is also a component of bile, which is also produced in the liver. However, the liver is not only responsible for the formation of substances, but also for the breakdown of harmful substances (detoxification). For example, the liver breaks down ammonia and instead forms the harmless urea from it.
Alcohol and medicines, as well as other toxins, are also broken down in the liver by various enzymes. These include alcohol dehydrogenase and cytochrome P450. Another important task of the liver is the breakdown of aged or defective cells (for example old erythrocytes).
The liver also coordinates the general excretion of substances via the intestines and kidneys. Water-insoluble substances are excreted through the bile, which passes into the gastrointestinal tract, and water-soluble substances into the blood, which is then filtered through the kidneys. The liver therefore has important tasks in many different areas.
Tasks for the digestion
The most important function of the liver for digestion is the production of bile. Every day the liver produces about 700 ml of bile, which is then transported through the bile ducts to the gall bladder where it is stored. The bile consists of lecithin, bile salts, cholesterol, (conjugated) hormones coupled with glucuronic acid and bilirubin (part of the blood pigment, gives the bile its yellow-green colour).
The bile is released from the gallbladder during meals and is used to digest fats and neutralise the acidic gastric juice. It is also used to excrete various substances such as cholesterol and bilirubin. If fats enter the small intestine with food, they stimulate the production of the hormone cholecystokinin in the mucous membrane of the small intestine.
This causes the gallbladder to tense up and the bile to be released into the intestines. The bile salts form so-called micelles (spherical lumps) with the fat-soluble components of food, such as free fatty acids, vitamins and cholesterol. These substances can thus be transported in the blood and are thus available to the body.
From the blood, these substances can now be absorbed by all organs and thus be used for energy production/provision or for the production of enzymes and other important substances. In addition, the bile ensures that the gastric acid that passes from the stomach into the duodenum with the chyme is neutralised in order to protect the mucous membrane of the intestines. The bile also promotes the secretion of pancreatic fluid, which in turn is important for digestion.
The pancreatic fluid contains enzymes that can break down fats, proteins and carbohydrates so that they can be absorbed through the intestinal mucosa. The liver is therefore very important for digestion, because without the bile it would be difficult to absorb the fat-soluble food components. These are essential for many functions of the body (hormone production, enzymes).
