9.3 - Absorption

The Adaptations of Ileum and Villus in the Absorption of Digested Food

Ileum is the predominant site of nutrient absorption. The adaptive characteristics of the digestive system include:

• Epithelial cells lining in the wall of the small intestine
• 6m long small intestine
• The intestinal lining is highly folded and covered with villi
• Epithelial cells of villi have microvilli

Figure 4 - Numerous numbers of villi increase the surface area for absorption. Villi are only one-cell thick and are covered by a network of blood capillaries for efficient nutrients absorption. Villi also contain lacteals which absorb fatty acids and glycerol.

The end products of digestion are absorbed from the small intestine into the bloodstream or lymphatic system.

Digested food

• Glucose, galactose

  • Methods of absorption: Active transport
  • Absorbed through epithelial cells into blood capillaries

• Fructose

  • Methods of absorption: Facilitated diffusion
  • Absorbed through epithelial cells into blood capillaries

• Amino acids

  • Methods of absorption: Active transport
  • Absorbed through epithelial cells into blood capillaries

• Vitamins B and C

  • Methods of absorption: Absorbed together with water
  • Absorbed through epithelial cells into blood capillaries

• Water

  • Methods of absorption: Osmosis
  • Absorbed through epithelial cells into blood capillaries

• Fatty acids, glycerol

  • Methods of absorption: Simple diffusion
  • Absorbed through epithelial cells into lacteal

• Vitamins A, D, E, K

  • Methods of absorption: Simple diffusion
  • Absorbed through epithelial cells into lacteal