The food you eat is broken down in your gut to form simple sugars such as glucose, amino acids, fatty acids and glycerol. These food molecules need to be made available to your body cells to provide fuel for respiration.
- The molecules must move from the inside of your small intestine into your bloodstream. They do this by a combination of diffusion and active transport.
- During digestion your food is broken down into a soluble form so that are they small enough to pass freely through the walls of the small intestine into the blood vessels.
- During digestion there is a very high concentration of food molecules in the gut and a much lower concentration in the blood.
The lining of the small intestine is folded into thousands of tiny finger-like projections known as villi. These greatly increase the uptake of digested food by diffusion.
- Only a certain number of digested food molecules can diffuse over a given surface at any one time. The villi increase the surface area available for diffusion many times.
- The lining of the small intestine has a rich blood supply, which produces a steep concentration gradient for efficient diffusion.
- The villi have thin walls (only one cell thick) so there is only a short distance across which diffusion takes place.
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