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Absorption of vitamins and minerals

Folic acid. Biologically active form of folic acid - tetrahydrofolic - the most important component in the reactions of "one-carbon" transfer in the synthesis of thymidine nucleic acid from deoxyuridine. A deficiency of folic acid leads to the development of macrocytic anemia. Folate is found in green vegetables and fruits and comes in the form of pteroyl polyglutamate. Absorption occurs mainly in the jejunum (Fig. 6-20). Pteroyl polyglutamate is hydrolyzed into monomers of pteroyl glutamate by the microvillus enzyme, a conjugase, and is transferred into the cell with a special protein that has maximum activity at a pH of 5.5-6.0. Inside the enterocyte, pteroyl glutamate is shortened, methylated, and converted into 5-methyltetrahydrofolic acid, which leaves the cell through the basolateral membrane section using a carrier and enters the capillary plexus of the villi first and then the liver through the portal vein.



Vitamin B12. Vitamin B12 (cyanocobalamin) is a coenzyme for the metabolism of amino acids. A deficiency of vitamin B12, due to the reserves in the liver, usually occurs 1-3 years after the violation of its receipt. The occurrence of deficiency leads to the development of macrocytic anemia and degeneration of nerve fibers. Vitamin B12 is part of the food only of animal origin and is completely absent from plant foods. In the stomach, released from food under the action of hydrochloric acid, vitamin B12 combines with the R-protein of saliva. After splitting in the duodenum R-protein pancreatic



Fig. 6-20.

Absorption of vitamins and minerals in the small intestine

. (By YamadaT., A1-pers DH, Owyang S., Powell DW, Silverstein FE, eds. Textbook of Gastroenterology, 2nd ed. Philadelphia: JB Lippincott, 1995; 1: 479.)



Vitamin B12 binds with proteases to the internal factor (HF) produced by the parietal cells of the stomach (Fig. 6-21). The alkaline environment in the duodenum enhances the connection of HF — B12, as a result of which vitamin B12 becomes resistant to the action of proteolytic enzymes. The VF-B12 molecule is then absorbed in the ileum with the help of special receptors in the presence of calcium ions. The mechanism of the capture of vitamin B12 by the enterocyte is unknown, however, after leaving the enterocyte, vitamin B12 in the blood binds to transcobalamin II carrier protein and enters the portal blood flow of the liver.



Iron. Iron is a cofactor for the synthesis of hemoglobin, myoglobin and porphyrins. It enters the body as part of the food of animal (hemin iron) or plant (non-heme iron) origin. Heminic iron is directly absorbed in the duodenum and in the proximal jejunum. Negeminov iron comes mainly in the form of trivalent ions (Fe3 +) and is not soluble in the alkaline environment of the small intestine. AT



Fig. 6-21.

Sequential cobalamin absorption steps

(Cb). R is R-protein; IF is an internal factor. (By Yamada T., Alpers DH, Owyang S., Powell DW, Silverstein FE, eds. Textbook of Gastroenterology, 2nd ed. I ^ iladelphia: JB Lippincott, 1995; 1: 470.)



In the stomach, acid converts ferric iron into ferrous iron (Fe2 +), which dissolves in an alkaline medium and therefore is easily absorbed. The absorption of non-heme iron depends on the components of the food that can solubilize iron (vitamin C) or firmly combine with it (phosphates, vegetable proteins).
Enterovascular microvilli of the duodenum have high affinity receptors for the transport of iron into the cell. In addition, there appear to be several iron-binding proteins in the cell that have not yet been isolated. Then the iron leaves the cell in the capillary plexus of the villi. In the blood, iron binds to transferrin, a protein that has two iron binding sites. In tissues, iron accumulates in the form of ferritin - a molecule that binds up to 4500 iron atoms.



Vitamins A, D, E, K. These vitamins are fat-soluble and are absorbed approximately as well as dietary fats. Full absorption depends on the formation of micelles, the presence of an alkaline pH value and the state of the lymphatic system of the intestine. Absorption occurs mainly in the jejunum.

Vitamin A is necessary for the growth and differentiation of cells and is the precursor of the visual pigment - rhodopsin. Vitamin A deficiency leads to xerophthalmia, a syndrome that causes irreversible blindness. Sources of vitamin A are pigment? -Carotene, which are rich in fresh vegetables, and retinyl esters contained in meat. By passive diffusion,? -Carotene enters the enterocyte, which splits? -Carotene into two molecules of retinaldehyde and converts retinaldehyde into retinol. Retinol esters, the main source of which are food products of animal origin, are split into retinol by pancreatic esterase and also enter the enterocyte by passive diffusion. In the cell, retinol binds to a special cellular retinol-binding protein II and is re-esterified by acetyl-CoA-retinol acyltransferase to retinyl esters. This process is similar to the mechanism of cholesterol absorption. Retinyl esters are inserted into the chylomicron lipoproteins and enter the lymphatic system.

Vitamin D regulates calcium absorption in the small intestine. Its deficiency leads to the development of rickets and osteomalacia, a violation of bone mineralization. Vitamin D is synthesized in the skin by UV light from 7-dihydrocholesterol. In addition, vitamin D comes from food, after which (ergocalciferol) is absorbed by enterocytes and leaves them in the composition of chylomicrons. Received vitamin D is in an inactive form until it is hydroxylated in the liver and in the kidneys.

Vitamin E is necessary for cell membranes as an antioxidant, its action is especially important for nervous tissue. Vitamin E deficiency is combined with progressive neurological disorders, manifested as cerebellar disorders. The most active form of vitamin E is α-tocopherol, and its main sources are vegetables and bread products. Vitamin E enters the small intestine in the form of esters and is hydrolyzed to the non-esterified form of pancreatic esterase. Then, vitamin E is absorbed according to the principle of the mechanism of passive diffusion, is embedded in the chylomicrons, and with them enters the lymphatic system.

Vitamin K is a cofactor for? -Carboxylation of glutamic acid, which is necessary for the synthesis of blood coagulation factors II, VII, IX, X and anticoagulants - proteins C and S, in the liver. Vitamin K deficiency leads to impaired blood coagulation (in the coagulogram, the main symptom is an increase in prothrombin time). Vitamin K is synthesized in the intestine by microorganisms, and also enters the body with plant food (green vegetables). Like other fat-soluble vitamins, vitamin K is absorbed by passive diffusion and enters the lymphatic system as part of the chylomicrons.
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Absorption of vitamins and minerals

  1. Hygienic importance of minerals and vitamins in the diet of the population
    Minerals and vitamins play a very important and at the same time peculiar role in the vital activity of the organism. First of all, they are not used as energy materials, which is a specific feature for proteins, fats and carbohydrates. Another distinctive feature of these nutrients is the relatively very insignificant quantitative need for them in the body. Enough
  2. The value of vitamins and minerals for the growth and development of the child
    For the normal development of the body, children should have enough vitamins in their diet. They not only protect the body from diseases associated with them, but also are components of the tissues. Without vitamins, enzymes are not formed, and, consequently, all reactions occurring in the body are delayed, normal metabolism is disturbed, digestion and blood formation are affected, and
  3. Diseases associated with a lack of vitamins and minerals
    Hypovitaminosis A (A hypovitaminosis) occurs when there is a lack of vitamin A in the body (retinol, retinal, retinoic acid), it is clinically manifested by growth retardation, development, reduction of natural resistance and local immune protection, increased peeling of the epidermis and dermatitis, metaplasia and keratinization of the mucous membranes and glands. More often the disease is registered in
  4. Minerals
    Mineral substances are essential nutrients that must be ingested. The value of minerals in human nutrition is very diverse: 1. Mineral substances in the body are included in the complex of substances that make up the living protoplasm of cells, in which the main substance is protein. 2. Mineral substances are part of all the extracellular and interstitial
  5. The main mechanisms of absorption and transport of substances
    Chyme is advanced from the duodenum along the entire small intestine for complete digestion and absorption by villi and microvilli. The muscular wall of the small intestine consists of the inner circular and outer longitudinal layers and performs at least two types of contractions: segmentation and peristalsis. Segmentation causes chyme mixing, moving intestinal contents
  6. The exchange of water and minerals
    The human body is 60% water. Adipose tissue contains 20% of water (from its mass), bones - 25, liver - 70, skeletal muscles - 75, blood - 80, brain - 85%. For the normal functioning of the body, which lives in a changing environment, it is very important the constancy of the internal environment of the body. It is created by blood plasma, tissue fluid, lymph, the main part of which is water, proteins and
  7. Minerals and trace elements (minerals)
    Minerals are inorganic constituents of food. Many of them play an important role in the body, and their constant intake with food is necessary. The mineral composition of food includes more than 60 macro-and micronutrients. ___________ __ conduction of nervous excitement to muscles Iron hematopoiesis (composed of hemoglobin, 60% of total Fe in the body), anemia, rapid fatigue
  8. DETERMINATION OF THE GENERAL CONTENT OF MINERAL SUBSTANCES (ASH)
    The total content of mineral substances in the material under study is determined by its ashing, that is, organic substances are burned with free access of air. During combustion, carbon, hydrogen, and partially oxygen evaporate in the form of carbon dioxide and water vapor, and mineral elements in the form of oxide compounds remain in the so-called raw ash. Course of determination
  9. ROLE OF VITAMINS IN THE EXCHANGE OF SUBSTANCES
    Vitamins are not drugs or metabolic stimulants, but they are always needed, and often their lack causes some diseases. The secret is that vitamins are part of enzymes, and a decrease in the content of vitamins in the body leads to disruption of normal enzymatic activity. Normally, the animals are not able to produce some vitamins on their own,
  10. The value of fats, carbohydrates and minerals in human nutrition. The norms of these components of food and the sources of their entry into the human body
    As mentioned in the previous lecture, fats are substances that perform in the body mainly energy function. In this regard, fats are superior to all other components of food (carbohydrates and proteins), since their combustion releases 2 times more energy (1 g of fat forms 9.3 kcal, while 1 g of protein and the corresponding amount of carbohydrates is only 4, 3 kcal). However biological
  11. The value of vitamins in human nutrition. Food - sources of vitamins
    For a long time, mankind has noticed that with a long monotonous diet, in cases of exclusion of some products from the diet, especially during long expeditions, quite often various diseases occurred. At first glance, there was no first cause. However, with the accumulation of this experience, it became clear that in food there are some specific components in very small quantities,
  12. Production and absorption of cerebrospinal fluid
    Inhalation anesthetics affect the production and absorption of cerebrospinal fluid. Enflurane increases the formation of fluid and prevents its absorption, which, with a lower elongation of the intracranial system, causes an increase in ICP. Halothane interferes with the absorption of cerebrospinal fluid and slightly reduces its formation. Isoflurane promotes absorption and, therefore, is
  13. Impaired digestion and absorption in the intestine
    The main processes of digestion and absorption of proteins, fats and carbohydrates occur in the small intestine. The total surface of the epithelial cells of the mucous membrane of the fine ganglion (enterocytes), which provide these functions, increases significantly due to the numerous microvilli located on the apical part of the enterocytes and forming the so-called brush border. Microvilli covered
  14. Iron absorption
    Absorption occurs mainly in the duodenum and the initial part of the jejunum. With iron deficiency in the body, the absorption zone extends in the distal direction. The daily diet usually contains about 10-20 mg of iron, but only 1-2 mg is absorbed in the gastrointestinal tract. Absorption of heme iron significantly exceeds inorganic intake. About
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