Roof of oral cavity. The hard palate, which contains bone, is bisected into right and left halves by a raphe. Anteriorly, in the fatty zone, the submucosa of the hard palate contains adipose tissue; posteriorly, in the glandular zone, there are mucous glands within the submucosa. Neither the raphe nor the gingiva contains a submucosa; instead, the mucosa is attached directly to the bone. The soft palate has muscle instead of bone, and its glands are continuous with those of the hard palate in the submucosa. (Based on Bhaskar SN, ed. Orban's Oral Histology and Embryology. St. Louis: CV Mosby, 1991.)
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The cells of the mucosal epithelium are similar to those of the epidermis of the skin and include keratinocytes, Langerhans' cells, melanocytes, and Merkel's cells.
The lamina propria contains blood vessels, nerves that send bare axon endings into the basal layers of the epithelium, and encapsulated sensory endings in some papillae. The sharp contrast between the numerous deep papillae of the alveolar mucosa and the shallow papillae in the rest of the lining mucosa allows easy identification of the two different regions in a histologic section.
A distinct submucosa underlies the lining mucosa except on the inferior surface of the tongue. This layer contains large bands of collagen and elastic fibers that bind the mucosa to the underlying muscle; it also contains the many minor salivary glands of the lips, tongue, and cheeks. Occasionally, sebaceous glands not associated with a hair follicle are found in the submucosa just lateral to the corner of the mouth and in the cheeks opposite the molar teeth. They are visible to the eye and are called Fordyce spots. The submucosa contains the larger blood vessels, nerves, and lymphatic vessels that supply the subepithelial neurovascular networks in the lamina propria throughout the oral cavity.
Specialized mucosa is restricted to the dorsal surface of the tongue, where it contains papillae and taste buds.
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