Arey, Leslie B. Department of Cell Biology and Anatomy, Northwestern University Medical School, Chicago, Illinois.
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Glands located in the mouth that secrete fluids that moisten and lubricate the mouth and food, often initiating digestive activity or performing other specialized functions. Fishes and aquatic amphibians have only solitary mucus (slime)–secreting cells, which are distributed in the epithelium of the mouth cavity. Multicellular oral glands first appeared in land animals to keep the mouth moist and make food easier to swallow. These glands occur in definite regions and have been assigned distinctive names. Some glands of terrestrial amphibians have a lubricative secretion; others serve to make the tongue sticky for use in catching insects. Some frogs secrete a watery serous fluid that contains ptyalin, a digestive enzyme. The oral glands of reptiles are much the same, but are more distinctly grouped. In poisonous snakes and the single poisonous lizard, the Gila monster, certain oral glands of the serous type are modified to produce venom. Also, many of the lizards have glands that are mixed in character, containing both mucous and serous cells. Oral glands are poorly developed in crocodilians and sea turtles. Birds bolt their food in gulps and swallow without chewing; however, grain-eating birds have numerous glands, with some of these glands secreting ptyalin. See also: Digestive system; Enzyme; Gland; Mouth; Poison gland
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