Vitamin A

vitamin, class of molecules with related biological function

thumb|upright=1.4|A 3-dimensional stick diagram of β-carotene thumb|Carotene is responsible for the orange colour of carrots and the colours of many other fruits and vegetables and even some animals. thumb|Lesser flamingo|Lesser flamingos in the [[Ngorongoro Crater, Tanzania. The pink colour of wild flamingos is due to astaxanthin (a carotenoid) they absorb from their diet of brine shrimp. If fed a carotene-free diet they become white.]]

β-Carotene (beta-carotene) is an organic, strongly colored red-orange pigment abundant in fungi, plants, and fruits. It is a member of the carotenes, which are terpenoids (isoprenoids), synthesized biochemically from eight isoprene units and thus having 40 carbons.

Tretinoin, also known as 'all-trans retinoic acid (ATRA'), is a medication used for the treatment of acne and acute promyelocytic leukemia. For acne, it is applied to the skin as a cream, gel or ointment. For acute promyelocytic leukemia, it is effective only when the RARA-PML fusion mutation is present and is taken by mouth for up to three months. Topical tretinoin is also the most extensively investigated retinoid therapy for photoaging.

Retinal (also known as retinaldehyde) is a polyene chromophore. Retinal, bound to proteins called opsins, is the chemical basis of visual phototransduction, the light-detection stage of visual perception (vision).

α-Carotene (alpha-carotene) is a form of carotene with a β-ionone ring at one end and an α-ionone ring at the opposite end. It is the second most common form of carotene.

lack of vitamin A in blood and tissues

Human disease