Bile | The function of the liver

Bile

The liver is the producer of bile (up to 1 liter/day). The bile is a mixed fluid consisting of fat (cholesterol), bile acids, bile dyes, bile salts and other substances. It is used both for excretion of unnecessary, possibly toxic substances and to assist in the digestion of high-fat food.

Cholesterol is the main component of bile. Although it can be produced by the body, it cannot be broken down again, so its excretion is necessary. Cholesterol can be excreted either coupled to various amino acids (building blocks of proteins) as bile acid (the majority), or as cholesterol itself.

Bile dyes are predominantly the breakdown substances of the red blood cells. They are further processed by the liver. The bile is stored in the gallbladder until it is released during food intake.

The liver mainly contains substances that are little or not at all soluble in water, but instead in fat (lipophilic substances). This can be explained by the fact that only water-soluble substances can enter the urine. The body uses this increased occurrence of fat-soluble substances in the bile to digest high-fat food.The gall bladder is connected to the small intestine via the bile duct. In the small intestine, the bile mixes with the digestive substances of the pancreas and the food pulp. The bile dissolves (emulsifies) the fatty parts of the food to allow the digestive proteins of the pancreas to work.

Formation of lipoproteins

Lipoproteins belong to the blood proteins. They are all (with one exception) produced in the liver and act as transporters for fatty acids and cholesterol in the blood, which otherwise could not be found in the blood due to their chemical composition. There are four different classes of lipoproteins: chylomicrons (the exception that is not produced in the liver), VLDL, LDL and HDL: chylomicrons are produced in the intestine.

Their function is to transport the fat freshly absorbed from food through the lymphatic system into the blood and then into the consuming tissues, especially adipose tissue and muscles. These tissues contain special proteins (lipoprotein lipase) which break down the fats into their individual components and thus enable them to be absorbed by the target cells. The remains of the fat transporters are further processed in the liver.

The VLDL are formed in the liver. Their task is to transport the fatty acids newly produced in the liver when there is an energy surplus into the body. Similar to chylomicrons, they are also broken down by proteins near their target cells and the fatty acids are absorbed into the cells.

LDL: These famous lipoproteins are mainly cholesterol transporters. They bring cholesterol from food and the liver to the other cells of the body. They are famous as “bad” Cholesterin therefore, since they can favour the emergence of arteriosclerosis (arteriosclerosis) in higher concentrations.

The LDL is absorbed as a whole into the target cells and is only broken down in the cell. HDL: This lipoprotein, also known as “good” cholesterol, has the task of collecting cholesterol in the body and transporting it to the liver for excretion via the bile. Therefore, a high concentration of HDL can dispose of superfluous cholesterol and thus inhibit the development of arteriosclerosis.