Case 3 - micronutrients absorption Flashcards
what are the fat soluble vitamins
A,D,E,K
how are these fat soluble vitamins absorbed
evidence of facilitated diffusion and/or endocytosis at physiological concentrations
what does fat soluble vitamin absorption require
requires optimal fat digestion
what are the water soluble vitamins
B group and C
how are water soluble vitamins absorbed
specific transporters - facilitated and secondary
what is VitB12 absorbed by
endocytosis - requires intrinsic factor and binds which is absorbed
what is Vitamin C coupled to
sodium entry
what are the two routes for Ca2+ absorption
transcellular and paracellular
describe the transcellular route and what is it regulated by
it is on the apical side and this process is regulated by Vitamin D
what is the route of the paracellular route
crosses the epithelium down the electrical gradient
what does Ca2+ absorption enter via
TRPV6
what are the two B group channels involved in calcium absorption and where
B6 in the small intestine
B5 in kidney
what happens once the calcium is inside
it binds to a protein called calbindin
what happens at the basolateral membrane
calcium is removed from the cell via active transport on the calcium pump (PMCA)
this uses ATP to pump calcium out
what is the regulation of calcium usually done by
the active form of Vitamin D: 1,25-dihydroxy-Vitamin D (calcitrion)
what does this bind to
intracellular receptors which triggers transcprtion of the mRNA
what happens to the mRNA
transcribed and codes for 3 proteins: TRPV6 channel, calbinidin protein and the PMCA
what are these proteins unregulated by and what does this do
unregulated by vitamin D to make more Calcium
where is iron absorbed
in the duodenum §
what kind of process is the iron absorption
transcellular process
recount the steps of the iron absorption
- dcytb reduces non heme Fe3+ to Fe2+
- DMT co transports Fe2+ with H+
- heme Fe2+ enters by unknown mechanisms
- heme oxygenate oxidises the Fe2+ in heme and then releases Fe3+
- Fe2+ tranfers to mobilferrin
- Fe2+ leaves the cell via ferroportin (FP1) and after hephaestin oxidises it to Fe3+, the iron binds to transferrin in plasma
what happens to biliverdin
changed into bilirubin
what is the regulation by and where is it produced
regulated by the hormone hepcidin and is produced by the liver
when is it produced
when the body has plenty of iron
what does hepcidin bind to
ferroportin so you have less of these transporters and decreases iron absorption
