iron metabolism, a series of processes involved in the entry of iron into the body and its absorption, transport, storage, use in the formation of hemoglobin and other iron compounds, and eventual excretion.nce in the blood, iron cycles between the plasma and the reticuloendothelial or erythropoietic system. For hemoglobin synthesis, plasma iron is delivered to the normoblast, where it remains up to 4 months, trapped in the hemoglobin molecules of a mature red cell. Senescent red cells then deteriorate and break down.