Absorption in the small intestine

• The human small intestine have a length of around 5m. This provides a very large surface are for absorption of the products of digestion.
• the interior of the small intestine is covered with millions of villi. Villi massively increase the surface area for the absorption of molecules.

  
• Microvilli on the surface of villi increase the surface area even more.

  
• Villi have a very good blood supply so the bloodstream rapidly removes the products of digestion. This increases the concentration gradient.
• Villi have a thin membrane which ensures a short diffusuion path.
• Microvilli, capillaries and a thin membrane mean that there is a rapid rate of diffusion.
• Any molecules which cannot be absorbed by diffusion are absorbed by active transport.