维生素a缺乏症（Vitamin A deficiency）.docVIP

维生素a缺乏症（Vitamin A deficiency） [brief introduction of vitamin A] Unsaturated one element alcohol; a fat soluble vitamin. Because humans or mammals lack vitamin A, they are prone to dry eye diseases, so they are also called anti dry eye alcohol. Known as vitamin A, there are two kinds of A1 and A2, A1 exists in the animal liver, blood and the eye of the retina, also known as retinol, natural vitamin A in this form mainly exists. A2 is found mainly in the livers of freshwater fishes. Vitamin A1 is a fat soluble yellowish flaky crystalline with a melting point of 64 DEG C and a melting point of vitamin A2 at 17~19 DEG C, usually of a golden oily substance. Vitamin A is a beta alcohol containing beta Angelica ketone ring. The difference between the chemical structure of vitamin A2 and the A1 is only a double bond on the 3,4 site of the beta lime ketone ring. Vitamin A molecules have unsaturated bonds, chemical properties of lively, easy to be oxidized in the air, or damaged by ultraviolet radiation, and lose physiological effects, so vitamin A preparations should be installed in the brown bottle to avoid light preservation. Whether it is A1 or A2, it can react with three antimony chloride, showing dark blue, which can be used as a basis for quantitative determination of vitamin A. Many plants, such as carrots, tomatoes, green leafy vegetables, and corn, contain carotenoids, such as alpha, beta, gamma carotene, yellow pigment, lutein, and so on. Some carotenoids have the same ring structure as vitamin A1, which can be converted into vitamin A in vivo. It is called vitamin A, and beta carotene contains the ring structure of two vitamin A1, and the conversion rate is highest. A molecule of beta carotene, plus two molecules of water, produces two molecules of vitamin A1. In animals, this process of water oxidation is catalyzed by beta -15, 15 - oxygenase, mainly in the small intestine mucosa of animals. Vitamin A, produced in food or produced by beta carotene cleavage, is co