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in animals and man, the secretion of mucous glands. In amphibians mucus is secreted onto the skin, whereas in invertebrates and other vertebrates it is secreted into the internal cavities of many organs, where it coats the mucous membranes.
Mucus is immunologically and bactericidally active. It protects organs and integumentary tissues from mechanical injuries and facilitates the movement of food along the digestive tract. Certain annelids, mollusks, ascidians, and other animals feed on food particles that adhere to the mucus when water is filtered through it.
Chemically, mucus is a complex mixture of glycoproteins, which account for approximately 40 percent of its dry weight. For example, mucus secreted by gastric and intestinal mucous epithelia is an aqueous solution of acid mucopolysaccharides, which are similar or identical to the mucopolysaccharides of connective tissue, neutral glycoproteins, which contain a large quantity of fucose, and acid glycoproteins, which contain sialic acids. Hyaluronic acid is a major constituent of synovia.
Mucus is important in maintaining cellular fluid and ion balances. In mammals it is a constituent of the developing embryo’s connective tissue, although at birth it is found only in the umbilical cord.
REFERENCESKhimiia uglevodov. Moscow, 1967.
Kretovich, V. L. Osnovy biokhimii rastenii, 5th ed. Moscow, 1971.
Schlegel, H. Obshchaia mikrobiologiia. Moscow, 1972. (Translated from German.)
N. D. GABRIELIAN