Absorption

• The ileum is adapted to absorb the products of digestion as:

  • wall of the ileum is folded and has finger-like projections called vili
  • thin walls
  • lined with epithelial cells, on the other side of which is a rich network of capillaries
• The vili is adapted for absorption as:

  • increase surface area for diffusion
  • thin walled, reducing diffusion distance
  • contain muscle so can move. Maintains diffusion gradient
• Absorption of amino acids and monosaccharides: absorbed via co-transport and diffusion
• Absorption of triglycerides:

  • monoglycerides and fatty acids combine with bile salts that initially emulsify the lipid droplets
  • forms micelles
  • these break down into monoglycerides and fatty acids
  • these diffuse into the cell membrane of epithelial cells
  • they then move into the endoplasmic reticulum
  • triglycerides are reformed
• Following the reformation of triglycerides:

  • triglycerides go with the Golgi apparatus where they associate with cholesterol and lipoproteins to form structures called chylomicrons
  • these move out of epithelial cells by exocytosis
  • they enter lymphatic capillaries called lacteals
  • the chylomicrons go into the bloodstream