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serous membrane[′sir·əs ′mem‚brān]
(also tunica serosa), a connective-tissue membrane covered with an epithelial layer; it is approximately 1 mm thick and lines the body cavities of man and animals. Depending on its location, a serous membrane is called peritoneum, pleura, pericardium, or epicardium.
A serous membrane develops from a mesodermal derivative, or splanchnotome, which borders the secondary cavity of the body, or the coelom. The serous membrane produces and absorbs serous fluid and facilitates the movement and maintains the shape of the internal organs it surrounds, separates, or connects. It performs a protective function as a serohematolym-phatic barrier and is composed of several layers of dense and fibrous connective tissue. A serous membrane’s surface layer facing toward the body cavity is composed of a flat layer of epithelium called mesothelium.
The total extent of the body’s membranes is great. In man, the peritoneum covers approximately 20,400 cm2. A serous membrane is usually smooth, shining, transparent, and elastic; it becomes rough, dull, and thick during such inflammatory processes as peritonitis, pleurisy, and pericarditis, which cause functional disorders in the membrane. The growth of a serous membrane during pathological processes is accompanied by the formation of the commissures or by the adhesion and concrescence of the membrane’s layers.
V. V. KUPRIIANOV