Maximum iron absorption occurs in
Iron is absorbed from upper small intestine mainly duodenum. In diet, iron occurs in two forms, haem iron and inorganic (non-haem) iron.

Haem iron is better absorbed than inorganic iron, but the major fraction of diet is inorganic iron. Inorganic iron is mostly in ferric form; needs to be reduced to ferrous form because iron is absorbed in ferrous form.

After absorption, ferrous form is once again oxidized to ferric form inside enterocytes.

A fraction of absorbed iron is rapidly delivered to plasma transferrin.
However, most of the iron is deposited in the enterocytes as ferritin,
some to be transferred more slowly to plasma transferrin, and some to be lost when senescent mucosal cells (enterocytes) are sloughed into the intestine.

Iron absorption is regulated according to the demand, e.g., when there is iron deficiency, absorption increases.

This regulation is mediated by “iron metabolism regulatory hormone”, i.e., hepcidin that inhibits iron absorption. When there is iron deficiency, the concentration of hepcidin falls and there is increase iron absorption. Hepcidin also decreases the release of iron from storage sites.
Duodenum
Jejunum
Ileum
Caecum