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*”vitamin A” is a group of unsaturated nutritional organic compounds that includes “retinol”, “retinal”, “retinoic acid”, and several provitamin A carotenoids (most notably “beta-carotene”)*
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(“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 necessary for both low-light (scotopic vision) and color vision)
(“vitamin A” also functions in a very different role as retinoic acid (an irreversibly oxidized form of retinol), which is an important hormone-like growth factor for epithelial and other cells)
(in “foods of animal origin” (aka ‘meat’), the major form of vitamin A is an “ester”, primarily “retinyl palmitate”, which is converted to retinol (chemically an alcohol) 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”)
(all forms of vitamin A have a beta-ionone ring to which an isoprenoid chain is attached, called a retinyl group)
(both structural features are essential for vitamin activity)
(the orange pigment of carrots (beta-carotene) can be represented as two connected retinyl groups, which are used in the body to contribute to vitamin A levels)
(“alpha-carotene” and “gamma-carotene” also have a single “retinyl” group, which give them some vitamin activity)
(none of the other carotenes have vitamin activity)
(the carotenoid beta-cryptoxanthin possesses an ionone group and has vitamin activity in humans.
(“vitamin A” can be found in 2 principal forms in foods:)
(“retinol”, the form of vitamin A absorbed when eating animal food sources, is a yellow, fat-soluble substance)
(since the pure alcohol form is unstable, the vitamin is found in tissues in a form of “retinyl ester”)
(it is also commercially produced and administered as esters such as “retinyl acetate” or “palmitate”)
(the carotenes “alpha-carotene”, “beta-carotene”, “gamma-carotene”; and the “xanthophyll beta-cryptoxanthin” (all of which contain beta-ionone rings), but no other carotenoids, function as provitamin A in herbivores and omnivore animals, which possess the enzyme “beta-carotene” (15,15′-dioxygenase) which cleaves beta-carotene in the intestinal mucosa and converts it to retinol)
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(in general, ‘carnivores’ are poor converters of ionone-containing carotenoids, and “pure carnivores” such as cats and ferrets lack “beta-carotene” (15,15′-dioxygenase) and cannot convert any carotenoids to retinal (resulting in none of the carotenoids being forms of “vitamin A” for these species))
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💕💝💖💓🖤💙🖤💙🖤💙🖤❤️💚💛🧡❣️💞💔💘❣️🧡💛💚❤️🖤💜🖤💙🖤💙🖤💗💖💝💘
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*🌈✨ *TABLE OF CONTENTS* ✨🌷*
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🔥🔥🔥🔥🔥🔥*we won the war* 🔥🔥🔥🔥🔥🔥