Villi
- These absorb the soluble molecules of food.
- There are millions of villi covering the interior of the small intestine. Villi massively increase the surface area of the small intestine so more diffusion of substances can take place.
- Each villus has a good network of blood capillaries. A steep concentration gradient is created as there is a lower concentration of soluble food molecules in the blood than the small intestine. This means diffusion takes place much faster.
- There is only a single layer of cells between the contents of the small intestine and blood vessels in the villus. There is a very short distance in which molecules need to diffuse so diffusion is quicker.
- All of these things makes the diffusion of food molecules as efficient as possible.
Evidence for importance of villi
- People with coeliac disease lose villi and cannot absorb products of digestion properly. They become very thin as a result.
- This shows villi are essential for efficient absorption.