mucous membrane(redirected from Mucosal tissue)
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(also mucosa), a membrane 0.5–4 mm thick that lines the inner surfaces of the digestive and respiratory organs, the urogenital system, the accessory sinuses of the nose, the middle ear, and the excretory ducts of glands. The name “mucous membrane” is derived from mucus, a glandular secretion that keeps the surfaces of mucous membranes moist.
A mucous membrane consists of one or more epithelial layers, a connective-tissue layer, a muscle plate formed by smooth muscle cells, and a tunica submucosa. The tunica submucosa, which is on the external side of the muscle plate, consists of a flexible layer of areolar tissue that separates the mucous membrane from the tissues underneath. Depending on the functions of the particular organ, mucosal epithelium may be multilay-ered and flat or monolayered and cylindrical, prismatic, cubical, or ciliated (in the airways). Its surface may be smooth, plicate, or villous; for example, in the small intestine the mucous membrane forms folds, villi, and crypts.
Located in the mucous membrane and tunica submucosa are glands, terminal nerve branches, blood and lymphatic vessels, and masses of lymphoid tissue, for example, follicles and tonsils. Mucous glands may be unicellular or multicellular. Unicellular mucous glands consist of goblet cells located between surface epithelial cells. Multicellular mucous glands may be simple tubular or alveolar glands, which are found in the stomach and small intestine, or complex mucous glands, which are found in the digestive tract and the airways.
V. V. KUPRIIANOV