Fat digestion
The fat digestion is the digestion of fats and fat-like substances in the body. The fats relevant in connection with the energy supply are the so-called. Triglycerides , formed by dehydration from one molecule of glycerine and - hence their name - three identical or different molecules of fatty acid . We ingest the following lipids through food :
- Triglycerides (i.e. fats, vegetable oils, etc.)
- Fatty acids of different size and saturation
- Cholesterol (in eggs, meat, etc.)
Fat digestion in humans
absorption
In the stomach , the fats from the food are determined by the peristaltic movements in the chyme (chyme) emulsified . At the same time, the lipase breaks down fats by 15%.
In the intestine , the peristaltic movements of the intestine enable further emulsification of the fats. The bile juice (which is formed in the liver and stored in the gall bladder ) forms tiny fat droplets ( see also: emulsifier ). This configuration allows the lipases to work optimally, and the surface on which the lipase attacks is also considerably increased. The pancreatic lipase out in the presence of colipase (from Pro-colipase by the action of trypsins originated) and calcium ions. One or two fatty acid molecules are hydrolytically separated from the triacylglyceride step by step , so that finally two free fatty acid molecules and a 2- monoacylglyceride are formed. The second important lipase that works in the small intestine is bile salt-activated lipase , which also breaks down triglycerides, but above all cholesterol esters .
From the fatty acid molecules and the 2-monoacylglycerides, micelles arise in the intestinal lumen , which attach to the brush border membrane, from where their content is absorbed into the enterocytes either passively or, in the case of free fatty acids, also carrier-mediated through the phospholipid membrane . Fat-soluble vitamins such as vitamins A, D, E and K can only be absorbed in this way, i.e. together with fats. If there is a lack of pancreatic lipase as a result of exocrine pancreatic insufficiency , maldigestion occurs, often accompanied by light, foul-smelling and voluminous diarrhea (“fatty stool”, steatorrhea ). Those affected show chronic weight loss and a deficiency in fat-soluble vitamins can occur in the long term ( hypovitaminosis ).
transport
Re-esterification then takes place in the intestinal cells , i. H. the free fatty acids are re- esterified with the monoglycerides to form triglycerides with elimination of water . Hydrophobic substances, however, cannot easily be transported further in the blood as an aqueous medium. From the resulting triglycerides, cholesterol therefore, Cholesterinestern, phospholipids, apolipoprotein and fat-soluble vitamins initially nascent chylomicrons formed, which subsequently was added to vesicles of the Golgi apparatus and by exocytosis into the lymphatic system are eliminated. About 80% of the chylomicrons get into the blood via the lymphatic system, from where the triglycerides finally reach the following destinations:
- Liver for storage, processing and oxidation.
- Myocytes (muscle fibers) and the like a. Organs where the fats are oxidized for energy. The muscles are also able to store a certain amount of triglycerides.
- Fat cells for storage.
Individual evidence
- ↑ Georg Löffler, Petro E. Petrides, Peter C. Heinrich (Eds.): Biochemistry and Pathobiochemistry. 8th, completely revised edition. Springer Medicine, Heidelberg 2007, ISBN 978-3-540-32680-9 , p. 1057.
- ^ Heinrich Kasper: Nutritional medicine and dietetics. 10th, revised edition. Elsevier, Urban & Fischer, Munich et al. 2004, ISBN 3-437-42011-9 , pp. 14-16.