1.Facilitated diffusion
2.Active transport
3.Passive transport
4.Both active and passive transport
Solution
Description:
By means of both and passive transport, folic acid absorbed in the proximal jejunum.
Steps in the absorption of folate:
1st step: Hydrolysis of pteroyl polyglutamates into pteroyl monoglutamate by conjugase enzyme situated inthe intestinal mucosa
2nd step: Absorption of pteroyl monoglutamate through active carrier mediated transport. Pharmacologic doses of folate are also absorbed passively by facilitated diffusion i.n addition to this
After absorption from the lumen into the entercyte intracellular enzymes reduce and methlate then monoglutamate to produce metabolically active form of folic acid
This form is then absorbed into circulation by simple diffusion
majority of the vitamins are absorbed through passive means.
The only vitamin that depends on active transport for its absorption is cyanocobalamin
The only other vitamins for which active mechanism of absoption is known include folic acid and thiaming
Ref:Understanding medical physiology: A Texbook for medical sudents By R.L.Bijlani,M.D.,4th edn,page 340