Figure 1.

Absorption of haem and non-haem iron through the duodenal enterocyte. Non-haem absorption pathway: Ferric iron (Fe³⁺) is first reduced to ferrous iron (Fe²⁺) by the enzyme, Duodenal cytochrome B (DcytB). Fe²⁺ can then be absorbed across the apical surface via the divalent metal transporter 1 (DMT1) and exported via ferroportin. Haem absorption pathway: Haem iron is absorbed directly into the enterocyte through haem carrier protein (HCP1). Once inside the enterocyte, haem iron can either be released into plasma via the FLVCR1 receptor or be converted to Fe²⁺ through the enzyme haem oxidase (HO). Before exportation, Fe²⁺ is oxidized back to its Fe³⁺ form via Hephaestin. Hepcidin controls ferroportin and will inhibit iron export in the presence of inflammation. Facilitators of iron absorption include ascorbic acid, citrate and amino acids while inhibitors include phytate, tannins and antacids.