Exam - Vitamin A Flashcards
supplement label for Vit A
supports night vision, eyesight and skin health
what is Vit A a general term for
retinoids
what are the major forms of Vit A in the body
retinol
retinal
retinoic acid
retinyl ester
what are precursors for Vit A
carotenes (provitamin A)
what are carotenes
type of carotenoid - pigments produced in plants
what are animal livers rich in
retinol and retinyl ester
what are orange and dark green vegetables rich in
B-carotene
what are retinyl esters rich in
milk and eggs
what is retinyl ester made of
retinol + fatty acid
what does retinyl esterase do
cleaves the fatty acid from retinol for absorption
what are retinol and B-carotene incorporated into
mixed micelles
how are retinol and B-carotene absorbed
passive diffusion
what do low retinol-RBP stimulate
hepatic retinyl esterase
why does retinol always travel with RBP
it is an alcohol and would otherwise degrade cells
what percentage of dietary retinol is absorbed
70-90%
what percentage of B-carotene is absorbed
20-50%
2 fates of B-carotene
- incorporated into chylomicrons as is
- converted into a retinyl ester in intestinal cells and then incorporated into chylomicrons
what does liver RBP synthesis depend on
persons Vit A status
what is retinoic acid important for
the control of growth hormone expression
what is growth hormone important for
growing and differentiating tissues
what is keratin
major protein in all epithelial cells whose expression is regulated by RA
what occurs in stem cells when vitamin A is present
- RA differentiates the stem cells into epithelial cells
- mucus secretion and keratinization to determine how cells will divide/function
how often are cells replaced with stem cells
every 3-5 days
what occurs in stem cells when vitamin A is deficient
poor differentiated function
keratinization but little mucus secretion
what can occur with a vitamin A deficiency and impaired epithelial cell differentiation
in cornea: Xerophthalmia
in lungs: respiratory infection
in GI tract: diarrhea
in skin: folliculosis
how many cases of blindness are there per year due to vitamin A deficiency and impaired epithelial cell differentiation
0.5 million
how many deaths per year are there due to vitamin A deficiency and impaired epithelial cell differentiation
1-3 million
what is xerophthalmia
not enough mucus to form protective layer on cornea so viruses and bacteria can penetrate
consequences of vitamin A deficiency
- night blindness
- impaired epithelial cell differentiation
- impaired growth
- impaired fertility
- fetal development defects (deficiency and toxicity)
how many children are Vit A deficient
100-140 million
what is RAE
retinol activity equivalents
why is there no upper limit for B-carotene
it prevents deficiency but does not cause toxicity - only used when we need it
what is the most severe consequence of vitamin A toxicity
liver cell death
