The mechanism of iron absorption and its regulation
Linder, M.C.; Munro, H.N.
Federation Proceedings 36(7): 2017-2023
1977
ISSN/ISBN: 0014-9446 PMID: 324817 Document Number: 115774
Fe transport across the intestinal mucosa begins with adsorption of ionic Fe in the lumen of the small intestine to receptors in the brush border of the mucosal cells. The Fe then passes into the cell by an energy-dependent process. Within the mucosal cytosol, the Fe is probably transported to the serosal surface as a compound of low mol. wt., perhaps chelated with amino acids, in equilibrium with iron-poor ferritin in the cytosol, although protein carriers have also been suggested. Part of the Fe in the mucosal cell is then transferred across the serosal cell membrane by a process that probably does not require energy and involves attachment to transferrin for transport in the plasma. The remaining Fe is returned to the gut when the mucosal cells are shed from the villus. The Fe status of the individual subject, his erythropoietic rate, and other factors within the body regulate the process of Fe absorption, particularly at the level of transfer across the serosal surface. The intermediate components in these regulatory processes have not been identified, but serum ferritin may be involved. These factors seem to have a rapid effect on serosal transfer of Fe, but more slowly modulate the number of brush border receptors, probably at the time of cell reproduction in the crypts, so that after a time lag this leads to a change in the capacity of the small intestine for Fe absorption across the mucosal surface. In addition, Fe can pass in the reverse direction from the plasma into the mucosal cell to enter mitochondria and to stimulate ferritin formation. It can also be actively extruded into the gut lumen, especially in the lower regions of the small intestine.