Vitamin and Mineral Absorption

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