Fig. 3

Iron metabolism. This figure summarises the main events in the iron metabolism. In small intestine lumen, iron is found in heme or ionic form. Heme-bound-Fe²⁺ enters the enterocyte via a heme transporter and is exposed to heme oxygenase, which frees the iron from heme and oxidises it to the Fe³⁺ form. Free Fe³⁺ in the intestinal lumen is reduced to Fe²⁺ thanks to the duodenal cytochrome B or dietary antioxidants. Fe²⁺ can enter the enterocyte through DMT1 (Divalent metal transporter 1). In enterocytes, iron can be stored in mucosal ferritin, or it can be effluxed into blood through ferroportin which is regulated by hepcidin. Once effluxed, Fe²⁺ is oxidised to Fe³⁺ by hephaestin or ceruloplasmin and is transported bound to plasma transferrin. Very little amounts of iron are transported in the free form. On the site of tissue cells, plasma transferrin binds to transferrin receptor 1 and enters the cells. Tissues can also uptake Fe²⁺ iron through DMT1. However, Fe³⁺ from the blood first needs to be converted to Fe²⁺ by SDR2 or STEAP2 on cells membranes