Biochemistry

soluble complexes. In the epithelial cells of the intestinal villi, they are split into bile and fatty acids. The released bile acids re-enter directly into the intestinal lumen or go through a more complex path: blood - liver - gallbladder - secreted bile. The constant circulation of bile acids provides a large amount of intake of fats with a relatively limited production of bile acids by the liver (2.8-3.5 g per day). Lipid digestion occurs both in the intestinal cavity (abdominal digestion) and on the mucosa of the small intestine (parietal or contact digestion). In particular, lipase of pancreatic juice (pancreas), catalyzing the hydrolysis of fats, is adsorbed on the cell surface. From epithelial cells of the intestinal wall, fats in the form of the smallest fat droplets surrounded by proteins (chylomicrons) enter the lymph. Chylomicrons are complex lipids. Its structure is spherical particles (100-5000 nm), the outer shell of which is formed by proteins, and the inner shell - by lipids and their derivatives. Chylomicrons - the largest of lipoproteins. They contain 98- 99% of lipids and 1-2% of protein. Being formed in the cells of the intestinal mucosa, they ensure the transport of lipids (triacylglycerols) from the intestine to the lymph. Chylomicrons along the thoracic lymphatic duct enter the bloodstream and arc transported to the fat depot and the liver. Thus, with the help of chylomicrons, exogenous triacylglycerols, cholesterol and partially phospholipids are transported from the intestine to the blood. After 1- 2 hours after a meal, alimentary hyperlipemia is observed, it reaches a maximum value after 4-6 hours after ingestion of fatty foods. After 10-12 hours, the content of triacylglycerols returns to normal, and the chylomicrons disappear from the bloodstream, since they break up into smaller particles under the influence of lipoprotein lipase (a clearing factor) of the inner lining of the vessel walls. Lipoprotein lipase not only breaks down chylomicrons, but also hydrolyzes the triacylglycerols released during this process into glycerol and fatty acids, which can directly enter cells and undergo disintegration processes. Part of the fatty acids enters the blood, where it is adsorbed by serum albumin, then transferred to the organs and is included in the metabolic processes (Fig. 10.2). Part of the fat is directly absorbed into the bloodstream, bypassing the lymphatic system, and enters the liver. After some time, from the liver, the fats pass into the peripheral depot: subcutaneous tissue, omentum, and mesentery. Fats from the "fat depot" are deposited in other tissues, mainly in the liver, where they undergo oxidative cleavage to the final products of metabolism. Plasma proteins provide the transport of fats in the blood: fl- and y-globulins, albumin. 192