Oral cavity

The oral cavity consists of the mouth and its structures, which include the tongue, teeth and their supporting structures (peridontium), major and minor salivary glands, and tonsils

The oral cavity is divided into a vestibule and the oral cavity proper. The vestibule is the space between the lips, cheeks, and teeth. The oral cavity proper lies behind the teeth and is bounded by the hard and soft palates superiorly, the tongue and the floor of the mouth inferiorly, and the entrance to the oropharynx posteriorly.

Each of the three major salivary glands are paired structures; they include the

• Parotid gland, the largest of the three glands, located in the temporal region of the head. Its excretory duct, the parotid (Stensen's) duct, opens at the parotid papilla, a small elevation on the mucosal surface of the cheek opposite the second upper molar tooth.

• Submandibular gland, located in the submandibular triangle of the neck. Its excretory duct, the submandibular (Wharton's) duct opens at a small fleshy prominence (the sublingual caruncle) on each side of the lingual frenulum on the floor of the oral cavity.

• Sublingual gland, lying inferior to the tongue within the sublingual folds at the floor of the oral cavity. It has a number of small excretory ducts; some enter the submandibular duct, and others enter individually into the oral cavity.

The parotid and submandibular glands have relatively long ducts that extend from the secretory portion of the gland to the oral cavity. The sublingual ducts are relatively short.

The minor salivary glands are located in the submucosa of the oral cavity. They empty directly into the cavity via short ducts and are named for their location i.e., buccal, labial, lingual, and palatine.

The tonsils consist of aggregations of lymphatic nodules that are clustered around the posterior opening of the oral and nasal cavities

Lymphatic tissue is organized into a tonsillar ring (Waldeyefs ring) of immunologic protection located at the shared entrance to the digestive and respiratory tracts. This lymphatic tissue surrounds the posterior orifice of the oral and nasal cavities and contains aggregates of lymphatic nodules that include

• Palatine tonsils, or simply the tonsils, which are located at either side of the entrance to the oropharynx between the palatopharyngeal and palatoglossal arches

• Tubal tonsils, which are located in the lateral walls of the nasopharynx posterior to the opening of the auditory tube

• Pharyngeal tonsil, or adenoid, which is located in the roof of the nasopharynx

• Lingual tonsil, which is located at the base of the tongue on its superior surface

The oral cavity is lined by a masticatory mucosa, a lining mucosa, and a specialized mucosa

The masticatory mucosa is found on the gingiva (gums) and the hard palate (Fig. 15.1). It has a keratinized and, in some areas, a parakeratinized stratified squamous epithelium (see Fig. 15.2). Parakeratinized epithelium is similar to keratinized epithelium except that the superficial cells do not lose their nuclei and their cytoplasm does not stain intensely with eosin. The nuclei of the parakeratinized cells are py-knotic (highly condensed) and remain until the cell is exfoliated (see Fig. 15.2). The keratinized epithelium of the masticatory mucosa resembles that of the skin but lacks a stratum lucidum. The underlying lamina propria consists of a thick papillary layer of loose connective tissue that contains blood vessels and nerves, some of which send bare axon endings into the epithelium as sensory receptors, and some of which end in Meissner's corpuscles. Deep to the lamina propria is a reticular layer of more dense connective tissue.

As in the skin, the depth and number of connective tissue papillae contribute to the relative immobility of the masticatory mucosa, thus protecting it from frictional and shearing stress. At the midline of the hard palate, in the palatine raphe, the mucosa adheres firmly to the underlying bone. The reticular layer of the lamina propria blends with the periosteum, and thus there is no submucosa. The same is true of the gingiva. Where there is a submucosa underlying the lamina propria on the hard palate (see Fig. 15.1), it contains adipose tissue anteriorly (fatty zone) and mucous glands posteriorly (glandular zone) that are continuous with those of the soft palate. In the submucosal regions, thick collagenous bands extend from the mucosa to the bone.

Lming mucosa is found on the lips, cheeks, alveolar mucosal surface, floor of the mouth, inferior surfaces of the tongue, and soft palate. At these sites it covers striated muscle (lips, cheeks, and tongue), bone (alveolar mucosa), and glands (soft palate, cheeks, inferior surface of the tongue). The lining mucosa has fewer and shorter papillae so that it can adjust to the movement of its underlying muscles.

Generally, the epithelium of the lining mucosa is nonker-atinized, although in some places it may be parakeratinized. The epithelium of the vermilion border of the lip (the reddish portion between the moist inner surface and the facial skin) is keratinized. The nonkeratinized lining epithelium is thicker than keratinized epithelium. It consists of only three layers:

• Stratum basale, a single layer of cells resting on the basal lamina

• Stratum spinosum, which is several cells thick

• Stratum supei-ficiale, the most superficial layer of cells, also referred as the surface layer of the mucosa

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