Iron is essential to erythropoiesis and is abundant throughout the body. Two-thirds of total body iron is found in hemoglobin; the other third, mostly in the reticuloendothelial system (liver, spleen, and bone marrow), with small amounts in muscle, serum, and body cells. Adequate dietary ingestion of iron and recirculation of iron released from disintegrating red cells maintain iron supplies. The duodenum and upper part of the small intestine absorb dietary iron. Such absorption depends on gastric acid content, the amout of reducing substances (ascorbic acid, for example) presents in the gastrointestinal tract, and dietary iron intake. If iron intake is deficient, the body gradually depletes its iron stores, causing a decreased hemoglobin level and, eventually, signs and symptoms of iron deficiency anemia.