Saliva includes the combined secretions of all the major and minor salivary glands
Most saliva is produced by the salivary glands. A smaller amount is derived from the gingival sulcus, tonsillar crypts, and general transudation from the epithelial lining of the oral cavity. One of the unique features of saliva is the large and variable volume produced. The volume (per weight of gland tissue) of saliva exceeds that of other digestive secretions by as much as 40 times. The large volume of saliva produced is undoubtedly related to its many functions, only some of which are concerned with digestion.
Saliva performs both protective and digestive functions
The salivary glands produce about 1200 mL of saliva a day. Saliva has numerous functions relating to metabolic and nonmetabolic activities. These include
• Moistening the oral mucosa
• Moistening dry foods to aid swallowing
• Providing a medium for dissolved and suspended food materials that chemically stimulate taste buds
• Buffering the contents of the oral cavity, because of its high concentration of bicarbonate ions
• Digesting carbohydrates with the digestive enzyme a-amylase that breaks 1-4 glycosidic bonds and continues to act in the esophagus and stomach
• Controlling the bacterial flora of the oral cavity by use of lysozyme (muramidase), an enzyme that lyses the mu-ramic acid in certain bacteria (e.g., staphylococci).
The unique composition of saliva is summarized in Table 15.1.
Saliva is a source of calcium and phosphate ions essential for normal tooth development and maintenance
Calcium and phosphate in the saliva are essential for the mineralization of newly erupted teeth and for repair of precarious lesions of the enamel in erupted teeth. In addition, saliva serves several other roles in protecting the teeth. Proteins in saliva cover the teeth with a protective coat called the acquired pellicle. Antibodies and other antibacterial agents retard bacterial action that would otherwise lead to tooth decay. Patients whose salivary glands are irradiated, as in the treatment of salivary gland tumors, fail to produce normal amounts of saliva; these patients typically develop rampant caries. Anticholinergic drugs used
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