The salivary glands (along with other mucous membranes in the mouth cavity) are responsible for secreting saliva, a clear, alkaline, semi-viscous liquid which helps in the digestion of food. The salivary glands include the large parotid gland and the smaller submaxillary and sublingual glands. When food is smelled or tasted, or often even thought of, the salivary glands begin their secretion to prepare the mouth for the food.
Salivation at the thought or sense of food is one example of a Pavlovian response, named after the scientist which investigated such reflexes in dogs. Mumps, an inflammatory glandular infection, affects the salivary glands (in addition to others), resulting in difficulty chewing and swallowing. Saliva also performs a cleaning function, serving to keep exfoliated epithelial cells, most bacteria, and food particles away from the teeth.
Saliva keeps the mouth lubricated for articulation and speech and also helps to moisten food to assist in swallowing. Enzymes in saliva begin digestive breakdown of the food even before it reaches the stomach. A number of toxins (including lead, mercury, and other heavy metals) are secreted in the saliva and the body's water balance regulation is also assisted by salivary secretion.