Saliva, the watery secretion produced in our mouths, has many functions. It moistens the mouth and tongue, making sure that the mucus membrane does not dry or crack. It also moistens our food so that it can be molded into an egg-shaped mass (or bolus) for swallowing, and it lubricates the bolus so that it can be swallowed easily.
By means of the enzyme ptyalin, which it contains, saliva begins the digestion of carbohydrates inside the food. Saliva also acts as a solvent to make tasting food easier for the taste buds are stimulated only by dissolved substances.
It is a cleansing agent, washing away particles inside the mouth. If salivation is stopped, for instance in the case of a high fever, the mouth becomes dirty and tastes and smells foul. If salivation slows down, our mouths feel dry and we know we need water.
Saliva is secreted in the three pairs of salivary glands. The largest of these are the irregularly shaped parotid glands which are packed tightly into a space between the ear and the top of the jawbone. The glands are encased in an inelastic covering and that is why they are extremely painful if they swell.
The next pair are the sub-mandibular glands which are egg-shaped and lie under the front of the jawbone, and the third pair, the almond-shaped sub-lingual glands, lie on the floor of the mouth between the tongue and the jawbone.