Bile acids
The bile acids (Engl. Bile acids ) are an important end product of cholesterol metabolism and are used for digestion of fats and fat resorption . Bile acids belong to the group of steroids .
Education and occurrence
The bile acids are formed in the hepatocytes of the liver from cholesterol through hydroxylation reactions and oxidative shortening of the side chain on ring D (five-membered ring). The most important bile acids are cholic acid and chenodeoxycholic acid . These are not free in the bile , but rather as so-called " conjugated bile acids" in the form of their amides with taurine or glycine and - due to the bile's alkaline pH - mainly as their anions ( bile salts ). The bile acids are transferred to amino acids with the help of the enzyme bile acid-CoA: amino acid-N-acyltransferase .
Components of the bile
Bile consists of 82% water, as well as hydrogen carbonates , bile acids, bile pigments (such as bilirubin ), phospholipids (such as lecithin ), cholesterol and the end metabolites of drugs and steroid hormones .
function
The bile acids are essential for fat digestion . They have the ability to considerably reduce the surface tension of the water ( surfactants , emulsifiers ). They emulsify the water-insoluble constituents in the intestinal tract (especially lipids ) and increase the vulnerability to enzymes . The emulsification of water-insoluble compounds is an important prerequisite for their absorption .
However, this also means that after surgical removal of the ileum - in which 98% of the bile salts are absorbed in order to return them to the enterohepatic circulation - or if the ileum is infected by the chronic inflammatory bowel disease Crohn's disease , these bile salts are prematurely excreted in the stool and thereby the digestion and absorption of fat is severely disturbed. This leads to voluminous fatty stools and a malabsorption syndrome .
If the ratio of bile acid to cholesterol in the gallbladder drops below 13: 1 (norm = 20: 1), cholesterol can precipitate, so that gallstones (cholesterol stones ) can form.
The increased accumulation of bile acids is probably involved in the carcinogenesis of colon cancer .
The rest of the taurocholic acids
The rest of the glycocholic acids
Medical application
The semi-synthetically obtained dehydrocholic acid is used as a medicinal substance to stimulate bile secretion ( choleretic ).
literature
- E. Buddecke: Outline of biochemistry. W.de Gruyter
- G. Löffler: Biochemistry and Pathobiochemistry. Springer publishing house
Individual evidence
- ↑ Entry on bile acids. In: Römpp Online . Georg Thieme Verlag, accessed on June 7, 2014.
- ↑ Debruyne PR et al .: The role of bile acids in carcinogenesis. Mutat Res . 2001 Sep 1; 480-481: 359-69, PMID 11506828 .
- ↑ Hermann J. Roth u. Helmut Fenner: Drugs . Thieme, Stuttgart a. New York 1988. pp. 596-599.
