Absorption of products of digestion

• Structure of ileum:

  • Ileum is adapted to the function of absorbing the products of digestion
  • Walls of the ileum are highly folded and possess finger-like projections called villi.
  • They have thin walls lined with epithelial cells on the other side of which is a rich network of blood capillaries.
  • Villi increases the surface area of the ileum, accelerating the rate of absorption.
• Villi

  • Situated at the interface between the lumen of the intestines and the blood and any other tissues in the bodies
  • Increases surface area of diffusion
  • Very thin walled, reducing distance of which diffusion takes place
  • Containing muscles so they are able to move helps maintain diffusion gradient because their movement mixes the contents of ileum, ensures that as products of digestion are absorbed from food adjacent to villi, new material rich products of digestion replace it
  • Well supplied with blood vessels so blood can carry away absorbed molecules maintaining a diffusion gradient
  • Epithelial cells lining the villi possess microvilli, fingerlike projections of cell surface membrane increasing surface area
• Absorption of triglycerides;

  • Once formed during digestion, monoglycerides and fatty acids remain associated with bile salts which initially emulsified the lipid droplets into structures called micelles.
• Absorption of triglycerides process

  1. movement of material within lumen of ileum, micelles come into contact with epithelial cells.
  2. micelles break down releasing monoglycerides and fatty acids, as they are non- polar they diffuse across cell surface membranes into epithelial cells.
  3. Monoglycerides and fatty acids are transported to the endoplasmic reticulum where they are recombined, to reform the triglycerides.
• Absorption of triglycerides after reformation entering Golgi.

  1. In the golgi, triglycerides associate with cholesterol and lipoproteins to form chylomicrons
  2. Chylomicrons move out of epithelial cells by EXOCYTOSIS.
  3. Chylomicrons enter lymphatic capillaries called lacteals, then passed into the bloodstream.
• Absorption of amino acids and monosaccharides

  Same namely diffusion and co transport