Lipid metabolism is the metabolism of fats and fat - like substances. Lipid metabolism consists of four stages: splitting, absorption, intermediate and final exchanges.
Lipid metabolism: cleavage. Most lipids that are part of food are absorbed by the body only after preliminary cleavage. Under the influence of digestive juices, they are hydrolyzed (broken down) to simple compounds (glycerol, higher fatty acids, sterols, phosphoric acid, nitrous bases, higher alcohols, etc.), which are absorbed by the mucous membrane of the digestive canal.
In the oral cavity, lipid-containing food is mechanically crushed, mixed, moistened with saliva and transformed into a food lump. The crushed food masses enter the stomach through the esophagus. Here they mix and leak through gastric juice. Gastric juice contains a lipolytic enzyme called lipase, which can break down emulsified fats. From the stomach, food masses in small portions enter the duodenum, then into the skinny and ileum. Here the process of lipid breakdown is completed and the products of their hydrolysis are absorbed. Bile, pancreatic juice, and intestinal juice are involved in lipid breakdown.
Bile is a secret that is synthesized by hepatocytes. Bile contains bile acids and pigments, breakdown products of hemoglobin, mucin, cholesterol, lecithin, fats, some enzymes, hormones, etc. Bile is involved in the emulsification of lipids, their breakdown and absorption; contributes to normal intestinal motility; exhibits a bactericidal effect on the intestinal microflora. Bile acids are synthesized from cholesterol. Fatty acids reduce the surface tension of fat droplets, emulsifying them, stimulate the excretion of pancreatic juice, and also activate the action of many enzymes. In the small intestine, food masses leak out with pancreatic juice, which includes sodium bicarbonate and lipolytic enzymes: lipases, cholinesterases, phospholipases, phosphatases, etc.
Lipid metabolism: absorption. Most lipids are absorbed in the lower part of the duodenum and in the upper part of the jejunum. Food lipid cleavage products are absorbed by the epithelium of the villi. The suction surface of the epithelial cell is increased due to microvilli. The final products of lipid hydrolysis are composed of small particles of fat, di- and monoglycerides, higher fatty acids, glycerol, glycerophosphates, nitrogenous bases, cholesterol, higher alcohols and phosphoric acid. In the large intestine, lipolytic enzymes are absent. The mucus of the colon contains a small amount of phospholipids. Cholesterol, which is not absorbed, is restored to fecal coprosterol.
Lipid metabolism: intermediate metabolism. In lipids, it has some features that lie in the fact that in the small intestine immediately after absorption of the cleavage products, lipid resynthesis inherent in humans occurs.
Lipid metabolism: final metabolism. The main end products of lipid metabolism are carbon dioxide and water. The latter is excreted in the composition of urine and sweat, partially feces, exhaled air. Carbon dioxide is secreted predominantly by the lungs. The final exchange for individual lipid groups has its own characteristics.
Disorders of lipid metabolism. Lipid metabolism is impaired in many infectious, invasive and non-communicable diseases. The pathology of lipid metabolism is observed in violation of the neurohumoral regulation of the processes of cleavage, absorption, biosynthesis and lipolysis. Among disorders of lipid metabolism, obesity is most often recorded.
Obesity is a predisposition of the body to excessive weight gain due to excess fat deposition in the subcutaneous tissue and other body tissues and intercellular space. Fats are deposited inside fat cells as triglycerides. The number of lipocytes does not increase, but only their volume increases. It is such hypertrophy of lipocytes that is the main factor in obesity.