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Enzymes are used in the digestive system to break large, complex, insoluble food molecules into small, simple, soluble molecules so they can be absorbed into the bloodstream.

The small intestine (ileum)

Food is digested in the mouth, stomach and finally in the ileum by amylase, protease and lipase.

The main function of the ileum is the absorption of digested food products into the bloodstream, so they can be transported to the cells of the body.

Adaptation of the ileum for absorption:

• Large surface area – due to being long and folded.
• Thin – digested food doesn’t have to travel far to reach the blood.
• Permeable – digested food can pass through easily.
• Good blood supply – to maintain the concentration gradient for diffusion between the ileum and bloodstream.
• Villi – finger like projections that further increase surface area.

Features of the villi that aid absorption:

• Good blood supply – a villus has a large network of capillaries. Once blood becomes high in digested food products it is transported away and replaced with blood that is low in digested food products. This maintains the concentration gradient necessary for diffusion between the ileum and bloodstream.
• Lacteal – a tube that absorbs the products of fat digestion before returning them to the blood.
• Single layer of surface epithelium cells – this reduces the diffusion distance that digested food products have to travel in order to enter the bloodstream.
• Permeable – digested food can pass through easily.