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Overview
  • Overview
    • dietary carbohydrates include polysaccharides, disaccharides, and monosaccharides
      • intestinal epithelial cells absorb only monosaccharides
        • glucose, galactose, and fructose
  • Digestion of dietary polysaccharides
    • salivary secretions
      • salivary α-amylase initiates digestion of polysaccharides in mouth
        • digests interior α-1,4 glycosidic linkages, yielding 3 disaccharides
          • α-limit dextrins, maltose, and maltotriose
      • salivary α-amylase plays a minimal role in digestion of carbohydrates
        • low pH of gastric contents quickly inactivates salivary α-amylase
    • pancreatic secretions
      • pancreatic juices are secreted into lumen of duodenum of small intestine
      • pancreatic α-amylase initiates digestion of polysaccharides in the small intestines
        • digests interior α-1,4 glycosidic linkages, yielding 3 disaccharides
          • α-limit dextrins, maltose, and maltotriose
    • intestinal mucosa
      • intestinal brush border enzymes initiate digestion of disaccharides to monosaccharides
        • α-dextrinase catalyzes α-limit dextrins → glucose
        • maltase catalyzes maltose → glucose
        • sucrase catalyzes maltotriose → glucose
      • intestinal epithelial cells absorb glucose, a monosaccharide
  • Digestion of dietary disaccharides
    • dietary disaccharides include trehalose, lactose, and sucrose
    • dietary disaccharides do not require α-amylase digestion
    • intestinal brush border enzymes initiate digestion of disaccharides to monosaccharides
      • trehalase catalyzes trehalose → glucose + glucose
      • lactase catalyzes lactose → glucose + galactose  
      • sucrase catalyzes sucrose → glucose + fructose
    • intestinal epithelial cells absorb glucose, galactose, and fructose, all monosaccharides
 

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