The digestive system

The stages of digestion

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The mouth


Digestion starts in the mouth where teeth break up food into small pieces. The incisors cut, the canines tear and the molars crush food. This mechanical transformation is called mastication.


The salivary glands are also found in the mouth. They secrete saliva.

Saliva moistens food, making it easier to break up. This process is called insalivation. Once transformed, the food is referred to as a bolus of food. Saliva contains enzymes that start the chemical digestion process. Salivary amylase, for example, breaks down certain complex carbohydrates, such as starch and glycogen.


Taste buds help us determine how food tastes. Taste buds are the small bumps on the tongue.

Since taste buds are only sensitive to substances that have been dissolved, saliva plays an important role in the perception of taste. Food must be soaked with saliva for us to sense what it tastes like. The tongue is a very powerful muscle that propels the bolus of food towards the back of the mouth so it can be swallowed.

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