The enzymes in saliva initiate the digestion process of ingested food and break down food particles that accumulate in dental crevices, protecting teeth from bacterial decay. Saliva also functions as a lubricant, permitting swallowing and preventing desiccation of the digestive tract.
In addition to predigestion, other species, such as birds, use saliva as an adhesive in the construction of nests. The venomous saliva of cobras and vipers is used in hunting. Some species of spiders and caterpillars create thread from salivary glands.
The lubricating properties of saliva enable it to coat food and prevent mechanically induced trauma during eating, swallowing and speaking. This lubrication also insures the continual flow of food along the digestive tract without adhering to its inner linings.
Saliva contains the enzyme amylase, which when aided with the mechanical effect of chewing leads to the breakdown of starch into simple sugars, such as maltose and dextrin. This decompositional effect accounts for only 30 percent of the starch digestion process. Saliva also contains lipase, which initiates the digestion of fat.
Insufficient production of saliva leads to dental caries and gum disease. The production of insufficient saliva is called xerostomia and is a side effect of many medications and narcotics.