Vitamin A is a group of nutritionally unsaturated hydrocarbons, which include retinol, retinal, retinoic acid and several provitamin A carotenoids among which beta-carotene is the most important. Vitamin A has multiple functions, it is important for growth and development, for the maintenance of the immune system and good vision. Vitamin A is needed by the retina of the eye in the form of retinal, which combines with protein opsin to form rhodopsin the light-absorbing molecule, that is necessary for both low-light and color vision. Vitamin A also functions in a very different role as an irreversibly oxidized form of retinol known as retinoic acid, which is an important hormone-like growth factor for epithelial and other cells. In foods of animal origin, the major form of vitamin A is an ester, primarily retinyl palmitate, which is converted to retinol in the small intestine. The retinol form functions as a storage form of the vitamin, and can be converted to and from its visually active aldehyde form, retinal. The associated acid, a metabolite that can be irreversibly synthesized from vitamin A, has only partial vitamin A activity, and does not function in the retina for the visual cycle. Retinoic acid is used for growth and cellular differentiation. Wikipedia [ - ]

Vitamin A is a group of nutritionally unsaturated hydrocarbons, which include retinol, retinal,... [ + ]