Now we'll look at the upper digestive system in detail, starting with...

The mouth and pharynx

Food taken into the mouth is broken up physically by chewing (also called mastication). The teeth (32 in total in a normal adult) and tongue start the digestive process by breaking down food particles to a smaller size and smoother consistency.

Swallowing begins when food is gathered on the upper surface of the tongue as a moist mass or bolus. The tongue forces the bolus backwards into the pharynx. The epiglottis , a flap at the top of the larynx, folds over the larynx to prevent food entering the airway.