The sublingual glands, the smallest of the paired major salivary glands, are located in the floor of the mouth anterior to the submandibular glands. Their multiple small sublingual ducts empty into the submandibular duct as well as directly onto the floor of the mouth. Some of the predominant mucous acini exhibit serous demilunes, but purely serous acini are rarely present (Fig. 16.27c and Plate 53, page 567). Intercalated ducts and striated ducts are short, difficult to locate, or sometimes absent. The mucous secretory units may be more tubular than purely acinar.
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
FIGURE 16.26 • Electron micrograph of the basal portion of an acinus. This electron micrograph shows the basal portion of two secretory cells from a submandibular gland. A myoepithelial cell process is also evident. Note the location of the myoepithelial cell process on the epithelial side of the basal lamina. The cytoplasm of the myoepithelial cell contains contractile filaments and densities (arrows) similar to those seen in smooth muscle cells. The cell on the left with the small nucleus is a lymphocyte. Having migrated through the basal lamina, it is also within the epithelial compartment. Arrowheads, cell boundaries; asterisks, basolateral folds. 15,000.
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 1,200 mL of saliva a day. Saliva has numerous functions relating to metabolic and nonmetabolic activities, including these:  Moistening the oral mucosa Moistening dry foods to aid swallowing Providing a medium for dissolved and suspended food ma terials 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 -amylase, which breaks one to four 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 muramic acid in certain bacteria (e.g., staphylococci)
The unique composition of saliva is summarized in Table 16.1.
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 to treat some forms of heart disease also significantly reduce salivary secretion, leading to dental caries.
Saliva performs immunologic functions.