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Vitamin and Mineral Absorption

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Topic updated on 06/24/17 3:02pm

Overview
  • Vitamin B12 (Cobalamin)
    • absorption occurs in terminal ileum
      • requires intrinsic factor (IF)
    • gastrectomy
      • IF deficiency as a consequence of loss of parietal cells
        • IF deficiency → vitamin B12 deficiency
          • may cause pernicious anemia
            • treatment is vitamin B12 administered by injection
  • Iron (Fe)
    • absorption occurs in duodenum
    • absorption across apical membrane of intestinal epithelial cells occurs as free iron (Fe2+)
      • in intestinal epithelial cells, free iron (Fe2+) binds apoferritin
        • iron-ferritin complex is transported across basolateral membrane into bloodstream
          • in bloodstream, iron binds transferrin and is transported from intestine to storage sites in liver
    • absorption across apical membrane of intestinal epithelial cells may also occur as heme iron
      • in intestinal epithelial cells, heme iron (iron bound to hemoglobin) is digested by lysosomal enzymes
        • releases free iron (Fe2+), which binds apoferritin
  • Folic acid (folate)
    • absorption occurs in the jejunum
    • small reserve pool stored in the liver


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