This occurs in the duodenum and proximal jejunum and depends on:
The dietary iron content;
Bioavailability of the dietary iron;
Absorption by mucosal cells, which depends on the extent of the body iron stores and the erythropoietic activity of the bone marrow.
About 10% of the normal dietary intake of 10-20 mg of dietary iron is absorbed daily. Ferric iron is converted in the presence of gastric acid by ferric reductase in the duodenal brush border to ferrous iron. Absorption is facilitated by the divalent metal transporter 1 protein, which transports ferrous iron from the gut lumen over the apical border of the enterocyte. After an oral iron load, down-regulation of iron absorption (mucosal block) by the enterocytes ensues. This is presumably created by intracellular iron accumulation in the enterocyte, and operates even in the presence of systemic iron deficiency states.
Factors affecting the bioavailability of iron include:
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