Iron homeostasis. (A) Normal metabolic pathway of non-heme iron through dietary absorption across the enterocyte and red blood cell (RBC) recycling by macrophages. Non-heme iron is transported across ferroportin, bound to transferrin and transported to the bone marrow to promote erythropoiesis. (B) Iron metabolism in an absolute iron-deficient state. There is less iron to transport to the bone marrow resulting in decreased erythropoiesis. (C) Iron metabolism in a functional iron-deficiency state. Hepcidin disables ferroportin, thus sequestering iron in the enterocyte and macrophage resulting in decreased erythropoiesis.