Updated: 4/25/2014

Carbohydrate Absorption

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Overview
  • Absorption of carbohydrates
    • intestinal epithelial cells in small intestine (enterocytes) absorb only monosaccharides
      • glucose, galactose, and fructose
  • Glucose & Galactose
    • glucose and galactose are absorbed across apical membrane of enterocytes bysecondary active transport
    • glucose and galactose move from intestinal lumen into enterocytes via Na+- glucose cotransporter (SGLT1)
      • SGLT in apical membrane of enterocytes
      • glucose and galactose move up (or against) electrochemical gradient ("uphill")
      • Na+ moves down electrochemical gradient ("downhill")
        • provides energy for uphill movement of glucose and galactose
      • Na+-K+ ATPase in basolateral membrane of enterocytes establishes and maintains Na+ gradient across apical membrane responsible for providing energy for uphill movement of glucose and galactose
    • glucose and galactose move from enterocytes across basolateral membrane to bloodstream by facilitated diffusion (GLUT2)
  • Fructose
    • fructose is absorbed across apical membrane of enterocytes by facilitated diffusion (GLUT5)
      • unlike glucose and galactose, fructose cannot be absorbed against electrochemical gradient ("uphill")
    • fructose moves from enterocytes across basolateral membrane to bloodstream byfacilitated diffusion (GLUT2)
 

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