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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)
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(“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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*👨🔬🕵️♀️🙇♀️*SKETCHES*🙇♂️👩🔬🕵️♂️*
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💕💝💖💓🖤💙🖤💙🖤💙🖤❤️💚💛🧡❣️💞💔💘❣️🧡💛💚❤️🖤💜🖤💙🖤💙🖤💗💖💝💘
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*🌈✨ *TABLE OF CONTENTS* ✨🌷*
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🔥🔥🔥🔥🔥🔥*we won the war* 🔥🔥🔥🔥🔥🔥