Where is iron absorbed
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Iron Absorption in the Human Body
Iron is a crucial element for various physiological functions, including oxygen transport, energy metabolism, and cell division. Understanding where and how iron is absorbed in the human body is essential for addressing iron deficiency and related disorders.
Primary Site of Iron Absorption: Duodenum and Proximal Jejunum
Research indicates that iron absorption occurs predominantly in the duodenum and the proximal jejunum. Studies have shown that the duodenum is the most efficient site for iron absorption, with absorption efficiency decreasing as the iron moves further along the small intestine . This is particularly evident in iron-deficient individuals, where enhanced absorption extends distally to about the mid-jejunum.
Mechanisms of Iron Absorption
Heme and Non-Heme Iron
Iron in the diet exists in two forms: heme and non-heme iron. Heme iron, derived from hemoglobin and myoglobin in animal products, is absorbed intact by the intestinal mucosa and then cleaved by mucosal heme oxygenase to release inorganic iron. Non-heme iron, found in plant-based foods, is absorbed through a different mechanism involving the divalent metal-ion transporter 1 (DMT-1) .
Transport and Regulation
Once inside the enterocytes, iron is transported across the basolateral membrane into the bloodstream by ferroportin, in conjunction with the ferroxidase hephaestin, which oxidizes ferrous iron to facilitate its binding to plasma transferrin. The regulation of iron absorption is tightly controlled by the liver-derived peptide hepcidin, which binds to ferroportin, leading to its internalization and reducing iron absorption .
Factors Influencing Iron Absorption
Dietary Influences
The bioavailability of iron is influenced by various dietary factors. Enhancers such as ascorbic acid and proteins can increase iron absorption, while inhibitors like calcium, phytates, and polyphenols can decrease it. The form of iron in the diet also plays a significant role, with heme iron being more readily absorbed than non-heme iron due to fewer luminal chelators binding to it .
Systemic and Local Influences
Iron absorption is also affected by systemic factors such as iron status, hypoxia, erythropoiesis, and inflammation. These factors influence hepcidin expression, which in turn regulates iron absorption. Local factors within the enterocytes, such as the iron concentration, also play a crucial role in modulating iron uptake .
Conclusion
Iron absorption primarily occurs in the duodenum and proximal jejunum, facilitated by specific transport mechanisms for heme and non-heme iron. The process is tightly regulated by systemic and local factors to maintain iron homeostasis. Understanding these mechanisms and influences is vital for developing strategies to combat iron deficiency and related disorders.
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