Digestion

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Digestion happens in two main ways – physical and chemical digestion.

Physical digestion occurs in the mouth where the teeth break up the food into smaller pieces. Chemical digestion is caused by digestive enzymes that are released at various points along the digestive system. Most enzymes work inside cells controlling reactions. Some enzymes pass out of cells and work in the digestive system. These enzymes digest our food, making the molecules small enough to be absorbed.

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The food is moved along the gut by contractions of the muscle in the lining of the intestine. This process is called peristalsis.

The rate of digestion

To make the digestive enzymes work at an optimum rate the digestive system provides the best conditions:

• Each enzyme has a different optimum pH. Protease in the stomach works best at about pH 2, but a different protease made by the pancreas works best at about pH 9.

• Physical digestion helps to break the food into smaller particles, thereby increasing the surface area of the food particles. Bile salts emulsify fat droplets, breaking them into smaller droplets so lipase can work faster.

Be careful not to say that bile salts break down fats. Make sure that you say ‘fat droplets’ otherwise it sound like bile salts are doing the same job as lipase.