Outline for Final exam

Outline for Final exam - Outline for Final Vitamin A Not...

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Outline for Final: Vitamin A: Not found in plant kingdom. Fat soluble vitamin B-carotene- precursor. Not biologically active B-caroteine> Retinal. 50% cleavage efficiency. So need twice as much B. C. as retinal. Retinal then gets converted to retinol (biologically active form) When looking at BC and retinol, need to consider the efficiency of cleavage and ALSO how it is absorbed. BC. From diet, only 15% absorption. So in order to get 1 microgram retinol, need to consume 12!!! Micrograms of BC from diet BUT if you are consuming BC from supplements, only need 2 micrograms because 100% absorption, and 50% cleavage efficiency Retinaldehyde reductase: enzyme that converts retinal to retinol Retinol combines with palmitate to form RE (retinol ester) BC and retinol can diffuse into entrocyte (RE must be converted to retinol before entering). But only RE and BC can diffuse into lymph. So RE must be converted to retinol to go into cell, but then must be converted back to RE to be diffused into lymph system RE combines with Chylomicron when in lymph. (Process driven by normal absorption of fat) Once RE in in chylomicron, they move to the liver. There RE are hydrolyzed to retinol, and the retinol then binds to RBP (retinol binding protein). SO RBP can trap some Vitamin A in the liver 11-cis-retinal- triggers Vision Light hits this (11-cis-retinal [Rhodopsin complex]), then it changes shape and releases all-trans- retinal and opsin. How is vision activated? Activating enzymes reduced CGMP > which then reduces uptake of Sodium >then negative charges in cell accumulates causing an electrical impulse ---hyperpolerization in rod cells caused from rhodopsin decomposition Vitamin A results in Nyctalopia (night blindness) With Vitamin A deficiency, normal mucus secreting cells become keratinized Takes a while to show deficiency (over a year) Deficiency level=under 10µg/100ml Healthy level = 50µg/100ml At high levels, Vitamin A is very toxic!! B-carotene is not toxic at high levels
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RDA for vitamin A: 3,000 IU or 900µg/100ml/day retinol **If you consume too much Vitamin A, you will exceed capacity of RBP (retinol bound protein) to carry Vitamin A. Then you will end up with a HUGE percent of vitamin A being transported in blood in the form of RE (retinol esters). RE are toxic to membranes Rickets,- calcium deficiency. From lack of vitamin D, which is synthesized in the skin Vitamin D is actually a hormone. Don’t need to consume Vitamin D as long as you get enough sun exposure. In the presence of UV light: 7-dehydrocholesterol -> Vitamin D3 [cholecalciferol. Made in the skin] Ergosterol -> Vitamin D2 [ergocalciferol. From plants] If you see D2, must have consumed D2 from diet Recommendation: 400IU/day No difference between D2 and D3, affects status the same D2, binds to chylomicron in blood. This doesn’t happen with D3 D3- vitamin D binding protein Lumisterol- accumulates in skin upon further exposure to sun. prevents Vitamin D toxicity Toxicity occurs at levels of 20,000 to 50,000 µg/day
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Outline for Final exam - Outline for Final Vitamin A Not...

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