PLATE 52 • PAROTI D G LAN D KEY A, acinus AC, adipose cell AL, acinar lumen CT, connective tissue ED, excretory duct ID, intercalated duct PC, plasma cells S, striations of duct cells StD, striated duct
The sublingual glands are the smallest of the paired major salivary glands. Their multiple small ducts empty into the submandibular ducts as well as directly onto the floor of the mouth. The sublingual gland resembles the submandibular gland, in that it contains both serous and mu-cous elements. In the sublingual gland, however, the mucous acini predominate. Some of the predominant mucous acini have serous de-milunes, but purely serous acini are rarely present. Saliva includes the combined secretions of all the major and minor salivary glands. The functions of saliva include moistening dry foods to aid swallowing, dissolving and suspending food materials that chemically stimulate taste buds, buffering the contents of the oral cavity through its high concentration of bicarbonate ion, digestion of carbohydrates by the digestive enzyme -amylase (which breaks the 1–4 gly-coside bonds and continues to act in the esophagus and stomach), and controlling the bacterial flora of the oral cavity because of the pres-ence of the antibacterial enzyme lysozyme. Saliva is a source of calcium and phosphate ions essential for normal tooth development and maintenance. It also contains antibodies, no-tably salivary sIgA. Salivation is part of a reflex arc that is normally stimulated by the ingestion of food, although sight, smell, or even thoughts of food can also stimulate salivation.
Sublingual gland, human, H&E ×160.
This figure shows a sublingual gland at low power. The mucous acini (MA) are conspicuous because of their light staining. Critical examination of the mucous acini at this relatively low magnification reveals that they are not spherical structures but, rather, elongate or tubular structures with branch ing outpockets. Thus, the acinus is rather large, and much of it is usually not seen within the plane of a single section. The serous component of the gland is composed largely of demilunes, but occasional serous acini are present. As noted earlier, some of the serous
Sublingual gland, human, H&E ×400.
Note that through a fortuitous plane of section the lumen of a mucous acinus (MA) (upper right) is seen joining an intercalated duct (ID). The juncture between the acinus and the beginning of the intercalated duct is marked by an arrowhead. The intercalated duct is composed of a flattened or low columnar epithelium similar to that seen in the other salivary glands. The intercalated ducts of the sublingual gland are extremely short, however, and thus are usually difficult to find. The intercalated duct seen in this micrograph joins with one or more other intercalated ducts to become the intralobular duct (InD), which is identified by its columnar epithelium and relatively large lumen. The point of transition from intercalated to intralobular duct is not recognizable in the micrograph, however, because the duct wall has only been grazed and the shape of the cells cannot be determined.
demilunes may be sectioned in a plane that does not include the mucous component of the acinus, thus giving the appearance of a serous acinus.
The ducts of the sublingual gland that are observed most frequently in a section are the intralobular ducts. They are the equivalent of the striated duct of the submandibular and parotid glands but lack the extensive basal infoldings and mitochondrial array that creates the striations. One of the intralobular ducts (InD) is evident in this figure (upper right). The area within the rectangle includes part of this duct and is shown at higher magnification in figure below.