Our salivary glands produce somewhere in the region of 1.5 to 2 litres of saliva every day. 90% of this is from the three pairs of major salivary glands. The submandibular glands are located beneath the floor of the mouth, the sublingual glands under the tongue and the two parotid glands on either side anterior to the ear. They secrete saliva through excretory ducts into the oral cavity. We also have a large number of minor salivary glands in the buccal mucosa, the throat and on the lips.
Saliva secretion rates vary greatly throughout the day and reach their highest levels when we are eating. Saliva is also produced at night, as if the flow of saliva were to dry up, the consequences would be unpleasant. As the excretory ducts for the salivary glands end in the oral cavity, which is full of bacteria, only a continuous flow of saliva can prevent bacteria from entering the ducts.
Saliva plays various roles that aid digestion. First of all, it liquefies the food chewed into little pieces by the teeth, facilitating transport to the oesophagus and swallowing. The enzymes in saliva also help to digest food. As well as electrolytes and enzymes, saliva also contains immunoglobulin, especially immunoglobulin A. This acts as a defence against infection in the oral cavity.