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Structures of vitamin A
- all-trans B carotene - diet, plant
- all-trans retinol - blood
- retinyl palmitate - storage *most in diet*
- all-trans retinoic acid - *ACTIVE*, most functions
- 11-cis retinal - *ACTIVE*, vision
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Sources of vitamin A
- Preformed: liver, milk, fortified cereal
- Pro-vitamin A carotenoids
: green leafy veggies, yellow & orange fruits/veggies
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Digestion of vitamin A
Retinyl ester + retinyl ester hydrolases → fatty acids + retinol
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Absorption of vitamin A
- Occurs in duodenum & jejunum
- Requires micellePassively diffuses into enterocyte
- Attaches to CRBPII (retinol binding protein)
- Converted to retinyl ester by LRAT (lectin retinol acetyltransferase)
- Packaged into chylomicron and sent to lymph
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Digestion of carotenoid
- Released from food (harder to get out of food than retinyl esters)
- Solubilized in micelle
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Absorption of carotenoids
- Requires micelle
- Taken across by protein
- Converted to beta-carotene by BCO1
- Cleaved by BCO2 into retinalAttached to CRBPII
- Converted to retinyl ester by LRAT, put into chylomicron & carried to lymph
- OR
- Taken across by protein
- Packaged into chylomicron & to lymph
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