Vitamin A , a bi-polar molecule formed with bi-polar covalent bonds between carbon and hydrogen, is linked to a family of similarly shaped molecules, the retinoids , which complete the remainder of the vitamin sequence. 更多

Vitamin A , a bi-polar molecule formed with bi-polar covalent bonds between carbon and hydrogen, is linked to a family of similarly shaped molecules, the retinoids , which complete the remainder of the vitamin sequence. Its important part is the retinyl group, which can be found in several forms. In foods of animal origin, the major form of vitamin A is an ester , primarily retinyl palmitate , which is converted to an alcohol ( retinol ) in the small intestine. Vitamin A 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 ] less