Absorption

• Small intestine


  Main site of absorption
• Villi and microvilli


  • Significance in absorption
• Absorption of small soluble molecules


  1. Undergoes physical and chemical digestion

  2. Takes place in the small intestine
• Absorption occurs in


  • Ileum
  • Colon
• Ileum


  • Adapted for absorption
  • Extremely large internal surface area (around 30 square meters)
  • Has circular folds
  • Covered with millions of tiny finger-like projections called villi
  • Villi lined with epithelial cells
  • Epithelial cells have microvilli on outer membranes to increase surface area even more
• Absorption of small soluble molecules

  1. Pass through epithelial cells of villi

  2. Through walls of capillaries (only one cell thick)

  3. Into blood

  4. Capillaries merge into veins

  5. Nutrients transported to liver

  6. Converted to other molecules or stored
• Absorption of fats


  1. Fatty acids and glycerol molecules reform into fats in epithelium of villi

  2. Fats move into fluid in lactils

  3. Lactils flow into lymphatic system

  4. Then into blood