Introduction
Iron homeostasis is a crucial physiological process that maintains a balance between iron absorption, storage, and utilization in the body. It is essential for various cellular functions, including oxygen transport, DNA synthesis, and electron transport. This complex process involves multiple organs, cells, and molecules that work together to regulate iron levels and prevent disorders such as anemia and iron overload.How is iron absorbed in the body?
Iron absorption primarily occurs in the
duodenum of the small intestine. Dietary iron exists in two forms: heme iron and non-heme iron. Heme iron, found in animal products, is more readily absorbed than non-heme iron, which is present in plant-based foods. The absorption process involves several steps:
Reduction: Non-heme iron (Fe3+) must be reduced to its ferrous form (Fe2+) by
ferric reductase on the enterocyte surface.
Transport: Fe2+ is transported into enterocytes via the
DMT1 (divalent metal transporter 1).
Storage and Export: Inside enterocytes, iron can be stored as ferritin or exported into the bloodstream via
ferroportin. Hepcidin, a liver-produced hormone, regulates ferroportin activity.
Liver: The liver produces
hepcidin, which inhibits iron export by binding to ferroportin, leading to its degradation. The liver also stores excess iron in the form of ferritin and hemosiderin.
Spleen: The spleen recycles iron from senescent red blood cells, releasing it back into the circulation for reuse.
Bone Marrow: The bone marrow utilizes iron for the synthesis of hemoglobin in developing red blood cells.
Intestine: The duodenum absorbs dietary iron and regulates its entry into the bloodstream.
Iron Regulatory Proteins (IRPs): These proteins bind to iron-responsive elements (IREs) on mRNA, controlling the translation of proteins involved in iron metabolism, such as ferritin and
transferrin receptor.
Ferritin: Ferritin stores excess iron within cells and releases it when needed, preventing free iron from catalyzing the formation of harmful free radicals.
Transferrin: Transferrin transports iron in the blood to various tissues, where it binds to transferrin receptors on cell surfaces for uptake.
Iron Deficiency Anemia: This condition arises from inadequate iron intake or absorption, leading to reduced hemoglobin synthesis and impaired oxygen transport. Symptoms include fatigue, weakness, and pallor.
Hereditary Hemochromatosis: A genetic disorder causing excessive iron absorption and accumulation in tissues, leading to organ damage. Symptoms may include joint pain, liver disease, and diabetes.
Anemia of Chronic Disease: Chronic inflammation or infection can increase hepcidin levels, reducing iron availability for erythropoiesis and resulting in anemia.
Conclusion
Iron homeostasis is a finely tuned process involving multiple organs, cellular mechanisms, and regulatory proteins. Proper maintenance of iron levels is essential for various physiological functions, and its dysregulation can lead to significant health issues. Understanding these mechanisms at the histological level provides insights into the diagnosis and treatment of related disorders.
