Vitamin A

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  1. 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
  2. Sources of vitamin A
    • Preformed: liver, milk, fortified cereal
    • Pro-vitamin A carotenoids: green leafy veggies, yellow & orange fruits/veggies
  3. Digestion of vitamin A
    Retinyl ester + retinyl ester hydrolases → fatty acids + retinol
  4. Absorption of vitamin A
    • Occurs in duodenum & jejunum
    • Requires micelle
    • Passively 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
  5. Digestion of carotenoid
    • Released from food (harder to get out of food than retinyl esters)
    • Solubilized in micelle
  6. Absorption of carotenoids
    • Requires micelle
    • Taken across by protein
    • Converted to beta-carotene by BCO1
    • Cleaved by BCO2 into retinal
    • Attached to CRBPII 
    • Converted to retinyl ester by LRAT, put into chylomicron & carried to lymph
    • OR

    • Taken across by protein
    • Packaged into chylomicron & to lymph
Card Set:
Vitamin A
2013-10-07 00:28:33
Nutrition micronutrients

How vitamin A is digested, absorbed, metabolized, ect in the human body
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