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the clear, viscid secretion of the salivary glands, with a weakly acid or weakly alkaline reaction (pH 5.6–7.6). A human adult secretes about 1.5 liters of saliva a day, and large farm animals from 40–60 to 120 liters. The composition and quantity of the saliva vary according to the consistency and chemical composition of the substances taken into the mouth and the organism’s functional condition.
Saliva contains 98.5–99.5 percent water, and dissolved anions of chlorides, phosphates, bicarbonates, thiocyanates, iodides, bromides, fluorides, and sulfates and the cations Na+, K+, Ca2+, and Mg2+. It also contains the trace elements Fe, Cu, Mn, Ni, Li, Zn, and others and organic matter, including protein and its fractions (albumin, globulins), amino acids, and mucin. In addition, it contains the enzymes amylase, lactase, ly-sozyme, kallikrein, and parotin, as well as cholesterol, glucose, lactic acid, and vitamins C, B1, B12, H, and K. Saliva helps dissolve the food, thus facilitating the perception of taste and the protection of the teeth against caries. It coats the alimentary bolus, thereby enabling the food to pass easily through the esophagus into the stomach; it also affects the secretory and motor activity of the gastrointestinal tract.
The level of development, habitat, and nature of the food consumed determine the content of certain constituents in the saliva of some animals. In snakes, for example, the saliva contains toxins and serves as a means of defense and attack. In other animals, including annelid worms and some birds, the secretions of the salivary glands are rich in the sticky substances needed to glue together the materials used in building nests. The saliva of bloodsucking animals, such as leeches and mosquitoes, usually contains anticoagulants, for example, hirudin in leeches. Carnivorous animals that feed on live prey may secrete paralyzing toxins in the saliva. Many insects, some mol-lusks (for example, Helix), and vertebrates secrete salivary car-bohydrases. The saliva of some predatory cephalopods contains proteases as well as toxins and mucus.
REFERENCEFiziologiia pishchevareniia. Leningrad, 1974(Rukovodstvo po fiziologii.)
V. D. SUKHODOLO