Absorption is the movement of digested food molecules through the wall of the intestine into the blood or lymph.

The small intestine is the region where digested food is absorbed. Most absorption happens in the ileum. This is the longest part of the small intestine and is between 2-4 metres long. The small intestine has a large internal surface area for absorption to happen quickly and efficiently.

The villi

The villi (one is called a villus) are tiny, finger-shaped structures that increase the surface area. They have several important features:

  • wall just one cell thick - ensures that there is only a short distance for absorption to happen by diffusion and active transport
  • network of blood capillaries - transports glucose and amino acids away from the small intestine in the blood
  • internal structure called a lacteal - transports fatty acids and glycerol away from the small intestine in the lymph
The lacteal, a long, relatively thin structure, is surrounded by blood capillaries. On one side they are oxygenated, on the other they are deoxygenated. They are encased in a lining.

The hepatic portal vein transports absorbed food from the small intestine to the liver.