Function of the stomach Physical digestion Food is churned in the stomach.
Chemical digestion Food is mixed with a strong acid called hydrochloric acid and with protein-digesting enzymes. The acid helps to break up the food and kill many of the germs present. It also enables the digestive enzymes in the stomach to work. The enzymes break down protein into simpler molecules. The mixture is now called chyme and is passed into the small intestine.
10.8 The small intestine
The first section of the small intestine is involved in digestion. The second section is involved in absorption.
Stomach
Structure of the small intestine The small intestine is adapted for digestion and absorption in the following ways: It is approximately 6 metres long. This provides a large surface area for digestion and absorption. Millions of tiny glands release digestive enzymes into the small intestine. Millions of tiny finger-like projections called villi provide a huge surface area to aid absorption of nutrients. The villi are one cell thick and have a rich blood supply which allows nutrients to be absorbed into the bloodstream. This is where the digestive and circulatory systems interact.
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Fig. 10 Food passes from the stomach into the small intestine.
Small intestine
Absorption The process by which nutrients move from the digestive system to the bloodstream.
Digestion The process of breaking down food into simpler molecules.
Villi
Villi Tiny finger-like projections.
Capillaries
Fig. 11 The small intestine has a huge surface area due to its millions of villi.
Fig. 12 A cross section of the small intestine showing several villi with a dense capillary network.
