vitamins - VITAMINS MAGGIE MURPHY [email protected] OVERVIEW...

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VITAMINS! MAGGIE MURPHY OCTOBER 25, 2007 [email protected]
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OVERVIEW Organic compounds Cannot by synthesized by human cells Supplied precursors-->vit A, niacin Microorgansims--> vit K, biotin, folate, vit B12 – Chol. Precursor--> cholecalciferol (vit D 3 )
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CLASSIFICATION Fat Soluble: A,D,E,K Always Dress Every Ken Water Soluble: C, Bs (I.e. thiamin, riboflavin, niacin, pantothenic acid, biotin, folic acid, vit B 6 , vit B 12 )
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VITAMIN A Food Sources Liver Egg yolk Margarine (fortified) Milk-fortified Fish (tuna, sardines, herring) Cod liver oil
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Functions Vision Cellular differentiation Growth Reproduction Immune system functions Bone development
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Structure Retinol Animal origin: usually as retinyl palmitate Retinol-->retinal (same biological properties) Retinal--> retinoic acid
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Structure Carotenoids Plant origin Beta-carotene Essentially 2 molecules of retinal attached tail to tail
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Digestion & Absorption Dietary vit A as retinyl ester Emulsification of fat (micelles taken up) Retinyl esters hydrolyzed in lumen or brush border of cell *Retinol must be esterified to leave mucosa Newly formed esters incorporated into chylomicrons (enter lymphatic system)
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Vit A Liver Uptake & Metabolism Some retinyl esters removed from chlyomicrons by tissues (remnants remain though) Chylomicron remnants deliver retinal esters to the liver Retinal esters taken up by liver parenchymal cells Within cell, retinol binds cellular retinol-binding protein (CRBP)
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Liver Uptake & Metabolism When liver stores adequate, plasma vitamin A levels constant Only when stellate cells cannot accept more retinol for storage can hypervitaminosis occur
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Storage 90% of vit A is stored in the LIVER (remainder in fat deposits, lungs, kidney)
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Vision Retinyl esters are hydrolyzed to retinol Retinol moves into pigment epithelium **converted to all-trans retinyl esters (stored in pigment epithelium) 11-cis retinol in pigment epithelium is converted to 11-cis retinal Binding protein transports 11-cis retinal to photoreceptor (rod) cell
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Vision In the rod cells, 11-cis retinal binds to the protein opsin to form rhodopsin Rhodopsin detects small amt. of light important for night vision All trans-retinal must be converted back to 11-cis retinal to regenerate rhodopsin
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Night Vision 1) Light hits rhodopsin 2) 11-cis retinal photoisomerized to all- trans retinal 3) All trans-retinal released from opsin **when light contacts our eyes, an electrical impulse is sent to optic nerve & then brain for vision in low light
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Deficiency Children: poor dark adaptation, xerosis, keratomalacia, growth failure Adults: night blindness, xeroderma
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VITAMIN D Food sources Few concentrated sources Fatty fish & fish liver oil Mushrooms (only source for vegans) Sun!!
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NOMENCLATURE Calciferol (vit D) – Cholecalciferol (vit D 3 ) – Ergocalciferol (vit D 2 ) Irradiated for supplements & fortified foods
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Synthesis Skin UV light – 7-dehydrocholesterol-->previtamin D 3 2-3 days later… Previtamin D 3 -->Vitamin D 3 ---> Bloodstream
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Hydroxylation Liver
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