Biochemistry

Н,с CH, CHj I н г с< " n-(CH=CH-OCH,) f -CH-CH- нА/ 4 CH, ha CH, H 2 (СН=С-СН=СН)-[Г A ch , A A ch 2 CH, I P-caiotene H. During the hydrolysis of a- and ү -carotcnes, one molecule of vitamin A is formed, since these provitamins contain one P-ionon ring. Retinol deficiency. Vitamin A deficiency in human food leads to A- avitaminosis: vision weakens (twilight or “ night blindness ” ), epithelial tissues of the skin and mucous membranes are affected (dryness, desquamation of the epithelium), including the cornea of the eye (its dryness and inflammation - xerophthalmia). In addition, with vitamin deficiency, growth is delayed, body weight drops and general exhaustion of the body is observed. Dryness of the skin and mucous membranes, contributing to the penetration of pathogenic microbes into the body, leads to dermatitis, bronchitis, and catarrh of the respiratory tract. The carotene breakdown into vitamin A molecules is carried out mainly in the wall of the small intestine and in the liver. In this connection, in liver diseases, the main source of vitamin A should be animal sources of vitamin A, and not p- carotene. Daily intake of retinol is 1.5-2.5 mg for adults. A third of this amount should be provided due to retinol, the rest - due to carotenes. The need for vitamin A increases with work associated with visual stress, with chemicals that irritate the mucous membranes of the eyes, upper respiratory tract, skin, under exposure to dust and low temperatures. The need for retinol also increases with various diseases of the skin and mucous membranes. Sources. Retinol enters the body in the fonn of retinol or in the form of carotenes. Retinol is found in butter, eggs, and caviar. It is slightly less in sour cream, cream, cheese, fatty cottage cheese and fatty fish. The content of vitamin A depends on the season of the year: it is twice as much in butter and eggs in the summer-autumn period than in winter-spring period. Provitamin retinol - P-carotene is found in large quantities in orange-colored vegetables, berries, fruits and butter. They are sea buckthorn, carrots, garden rowan, red pepper, parsley, apricots, pumpkin, tomatoes, chokeberry, green peas, melon, quince, cherry, currant. Carotene of plant products is reliably protected 264