Chemical digestion

Some food molecules are too large and insoluble to be absorbed from the digestive system. Chemical digestion breaks these molecules into smaller, soluble molecules. Digestive enzymes speed up the chemical reactions that break the large molecules down.

The small products can dissolve in the fluid in the digestive system and pass through its lining into the body. This transfer is called absorption. Digestion therefore makes the molecules small and soluble enough to be absorbed.

Amylase in digestion

Amylase is a digestive enzyme that breaks down starch, a large carbohydrate in food, into smaller sugars. These include maltose, a reducing sugar.

The salivary glands secrete amylase into the mouth. As food is chewed and mixed with saliva, the amylase begins to break down its starch.

The pancreas also secretes amylase into the small intestine. There, it continues to break down starch that remains in the food.

Proteases in digestion

Proteins are made of chains of amino acids. Proteases are digestive enzymes that break these chains down into amino acids.

Protein digestion begins in the stomach, where proteases are secreted and act on proteins. Digestion continues in the small intestine. The pancreas secretes proteases into the small intestine, and the small intestine also secretes proteases. These enzymes act in the small intestine to continue breaking down proteins into amino acids.