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The oral cavity is lined by a mucosa composed of nonkeratinizing stratified squamous epithelium, continuous with the skin at the lips and with the pharyngeal mucosa posteriorly. Specialized structures in the oral cavity include the following:
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The taste buds, which are specialized nerve endings with afferents in the ninth (posterior tongue) and seventh (anterior tongue) cranial nerves.
The teeth, which are embedded in the maxilla and mandible. The part of the mucosa that is reflected onto the bone in relation to the teeth is called the gingiva (gum).
Three major pairs of salivary glands, plus numerous minor salivary glands. The parotid glands are composed almost entirely of serous cells and are situated in front of and below the ear. They secrete saliva through a duct (Stensen's duct) that opens in the cheek adjacent to the molar teeth. The seromucous submandibular gland lies beneath the mandible and opens by a duct (Warthin's duct) into the floor of the mouth. The sublingual gland, also seromucous in type, is situated in the floor of the mouth and empties through 10–20 small ducts.
Lymphoid tissue, which guards the pharyngeal opening (Waldeyer's ring). The tonsils, which are situated between the faucial pillars and adenoids in the nasopharynx, are the largest collections of lymphoid tissue.
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The function of the oral cavity is to accept food and begin the process of digestion. Mastication, aided by the lubricant action of the saliva, converts the food into a bolus that is propelled back by the tongue muscles into the pharynx for swallowing. Saliva contains (a) amylase, which may initiate carbohydrate digestion; (b) lysozyme, which has bactericidal properties; and (c) secretory IgA. The salivary gland epithelium synthesizes “the secretor piece,” which complexes with IgA produced by plasma cells in the gland stroma.
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The oral cavity is richly supplied with sensory nerve endings, and pain is a feature of almost all diseases that affect the mucosa. Pain in diseases of the teeth occurs only when pain-sensitive fibers in the root of a tooth are involved.
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Changes of the Oral Mucosa
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Alterations of the mucosa include ulceration, vesicular lesions (blisters), and changes in color. Oral ulcers occur in many diseases, including infections, allergy, trauma, and neoplasms. Vesicular lesions occur in infections (eg, herpesvirus infections) and immunologic diseases such as pemphigus vulgaris and erythema multiforme that primarily affect the skin. White plaques on the mucosa (leukoplakia) occur in hyperplastic and neoplastic conditions, and melanin pigmentation occurs in many systemic diseases (Table 31-1).
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