As red blood cells age, they are ingested by scavenger cells called macrophages, mainly in the liver, spleen, and bone marrow. The recycled iron from old red blood cells remains stored in these macrophages or is released back into the circulation bound to transferrin for storage in the liver or for production of new red blood cells in bone marrow.
Once the iron you ingest becomes soluble, it is absorbed in the duodenum, the first part of your small intestine that connects to your stomach.1
The absorption process in the duodenum begins with iron uptake, when iron passes through a membrane of cells called enterocytes that line the intestine.2,3 Then, iron is transferred from enterocytes into the plasma.2 A protein called transferrin attaches to the iron and helps transport it throughout your body.4
Iron later passes to your bone marrow, where it is used to make hemoglobin and red blood cells, which circulate in your body and help supply oxygen to your organs and tissues.5
When you absorb more iron than your body needs for immediate purposes, some of it is stored in your cells as ferritin (ferritin is a storage protein for iron in your cells).6 These stores can supply iron when your body needs it later and will be depleted before iron deficiency begins.6
1 Barton JC. Iron deficiency. In: Rakel RE, Bope ET, eds. Conn’s Current Therapy. Amsterdam, the Netherlands: Saunders/Elsevier; 2008:385-389.
2 Trinder D, Fox C, Vautier G, Olynyk JK. Molecular pathogenesis of iron overload. Gut. 2002;51(2):290-295.
3 Roy CN, Enns CA. Iron homeostasis: new tales from the crypt. Blood. 2000;96(13):4020-4027.
4 Huebers HA, Josephson B, Huebers E, Csiba E, Finch CA. Occupancy of the iron binding sites of human transferrin. Proc Natl Acad Sci USA. 1984;81(14):4326-4330.
5 Iron [definition]. In: Venes D, ed. Taber’s Cyclopedic Medical Dictionary. 20th ed. Philadelphia, PA: F.A. Davis Company; 2005.
6 Centers for Disease Control and Prevention. Recommendations to prevent and control iron deficiency in the United States. MMWR Recomm Rep. 1998;47(RR-3):1-36. http://www.cdc.gov/MMWR/preview/mmwrhtml/00051880.htm. Accessed April 9, 2008.