Iron absorption

• 1. Site of Absorption
  • Primarily occurs in the duodenum and proximal jejunum
• 2. Forms of Dietary Iron
  • Heme iron (from animal sources, e.g. meat):
    • Absorbed directly via heme transporter (HCP1)
    • More efficiently absorbed and less affected by dietary factors
  • Non-heme iron (from plant sources):
    • Exists mostly as ferric iron (Fe³⁺) → must be reduced to ferrous (Fe²⁺) form to be absorbed
    • Less efficiently absorbed; influenced by other dietary components
• 3. Steps in Absorption
  • Gastric acid lowers pH:
    • Helps solubilize iron and reduces Fe³⁺ to Fe²⁺
  • Duodenal cytochrome B (Dcytb):
    • Reduces ferric (Fe³⁺) to ferrous (Fe²⁺) iron on enterocyte brush border
  • Divalent metal transporter 1 (DMT1):
    • Transports Fe²⁺ across the apical membrane into the enterocyte
  • Inside the enterocyte:
    • Some Fe²⁺ is bound to ferritin for intracellular storage
  • Ferroportin (on basolateral membrane):
    • Transports Fe²⁺ into bloodstream
  • Hephaestin or ceruloplasmin:
    • Oxidize Fe²⁺ back to Fe³⁺ for binding to transferrin in plasma
• 4. Regulation
  • Hepcidin (produced by liver):
    • Downregulates ferroportin → blocks iron export → decreases absorption