Distribution of iron in the human body. The adult human body contains approximately 3 to 5 g of iron, corresponding to ∼55 mg/kg for males and ∼44 mg/g for females. Over 70% of body iron is present as heme within hemoglobin (Hb) of developing erythroblasts (bone marrow) and mature erythrocytes (circulating blood). Iron in skeletal muscle is contained primarily in myoglobin. Hb- and Mb-derived iron plays a key role in oxygenation and is therefore referred to as “functional iron”. Significant fractions of body iron are distributed within tissue macrophages (∼5%) and liver hepatocytes (∼20%). All cells in the body contain small amounts of iron for metabolic purposes (not shown). Transferrin binds and carries iron in the circulation, transporting it to various tissues, especially to developing erythroblasts in the bone marrow (bone marrow erythroblasts acquire more than 80% of plasma iron). RES, reticuloendothelial system.
