TOPIC 3

• Digestion


  Large insoluble molecules hydrolyzed into smaller soluble molecules which can then be absorbed across cell membranes and into the bloodstream
• Molecules digested


  • Carbohydrates
  • Lipids
  • Proteins
• Amylases


  Enzymes that hydrolyze carbohydrates
• Carbohydrate digestion


  1. Amylases in saliva hydrolyze polysaccharides into disaccharides

  2. Disaccharidases in small intestine hydrolyze disaccharides into monosaccharides
• Protein digestion


  1. Endopeptidases hydrolyze peptide bonds within the protein chain

  2. Exopeptidases hydrolyze peptide bonds at the ends of the chain

  3. Dipeptidases hydrolyze dipeptides into amino acids
• Lipid digestion


  1. Lipase hydrolyzes triglycerides into fatty acids and glycerol

  2. Bile salts emulsify lipids to increase surface area for lipase
• Micelles


  Spheres made of fatty acids, monoglycerides and bile salts that deliver lipids to epithelial cells
• Villi and microvilli


  • Increase surface area for absorption in small intestine
  • Contain capillary network to maintain concentration gradient
• Monosaccharide and amino acid absorption

  By co-transport (active transport)
• Lipid absorption


  • Fatty acids and monoglycerides diffuse into epithelial cells
  • Resynthesized into triglycerides and packaged into chylomicrons
  • Chylomicrons released by exocytosis and absorbed into lymphatic system