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Vitamin A is an essential human nutrient. Its important part is the retinyl group, which can be found not in a single compound, but in several forms. In foods of animal origin, the major form of vitamin A is an alcohol (retinol), but can also exist as an aldehyde (retinal), or as an acid (retinoic acid). Precursors to the vitamin (provitamins) are present in foods of plant origin as some of the members of the carotenoid family of compounds.[1]
All forms of vitamin A have a Beta-ionone ring to which an isoprenoid chain is attached. This structure is essential for vitamin activity.[1] The orange pigment of carrot - Beta-carotene - can be represented as two connected retinyl groups. Retinyl group, being attached to a protein, is the only primary light absorber in visual perception, and the compound name is related to retina of eye.
Vitamin A may be found in various forms:
retinol, the animal form of vitamin A, is a yellow, fat-soluble, vitamin with importance in vision and bone growth. Since the alcohol form is unstable, the vitamin is usually produced and administered in a form of retinyl acetate or palmitate.
other retinoids, a class of chemical compounds that are related chemically to vitamin A, are used in medicine.
词典释义vitamine 维生素（一般情况下用这个或者省略末尾的e）vitamin(e) 维生素；维他命auxohormome维生素nutramin(e)[医] 维生素（别名）citrin 维生素P，柠檬素双语例句1.新鲜水果和蔬菜提供植物纤维素和维生素。
Fresh fruit and vegetables provide fibre and vitamins.2.我建议你在日常饮食中补充些维生素E和维生素A。I suggest supplementing your diet with vitamins E and A.满意请采纳❤。
1. Vegetables contain many vitamins.
2. Many people took part in the
activities, including some of the students
3. Students can have access to the library.
4. ThE reference book is designed for college
students
5. Students are not permitted to play mobile phone in
class.
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vitamin:
Any of various fat-soluble or water-soluble organic substances essential in minute amounts for normal growth and activity of the body and obtained naturally from plant and animal foods.
维生素：
各种脂溶性或水溶性生命物质之一，少量的这种物质对生命体的生长和活动至关重要，通常从植物食物中取得
爱延续泉泉
维生素英文是vitamin。
读音：/ ˈvɪtəmɪn /
表达意思：维生素，维他命；维生素片，维生素丸。
词性：通常在句中作名词，作为主语或宾语。
固定搭配：vitamin d维生素D（抗佝偻病维生素）；钙化醇。
例句
1、He was put on a high dosage of vitamin C.
他在大剂量服用维生素C。
2、Milk, oily fish and eggs all contain vitamin D.
牛奶、油性鱼类和鸡蛋全都含维他命D。
3、They sell vitamin supplements at the pharmacist's.
那药店卖维生素补剂。
邱shannon
维生素英文是vitamin。
vitamin，英语单词，主要用作为名词，作名词时意为维生素。
维生素的短语搭配
vitamin c 维生素C。
vitamin e 维生素E；生育酚；抗不育维生素。
vitamin d 维生素D（抗佝偻病维生素）；钙化醇。
vitamin a 维生素A；维他命A。
vitamin k 维生素K。
vitamin b complex 复合维生素B。
vitamin p [医]柠檬素。
vitamin deficiency 维生素缺乏；维生素缺乏症。
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