Saliva

saliva

Thick, colourless fluid constantly present in the mouth, composed of water, mucus, proteins, mineral salts, and amylase, an enzyme that breaks down starches. One to two litres are produced daily by the salivary glands. Small amounts are continually discharged into the mouth, but the presence, smell, or even thought of food increases flow. Saliva's main function is to keep the inside of the mouth moist, making speech more fluid, dissolving food molecules for taste, and easing swallowing. It also helps control the body's water balance, since lack of it stimulates thirst when water intake has been low. Saliva reduces dental caries and infection by removing food debris, dead cells, bacteria, and white blood cells.

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saliva

the secretion of salivary glands, consisting of a clear usually slightly acid aqueous fluid of variable composition. It moistens the oral cavity, prepares food for swallowing, and initiates the process of digestion

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saliva [sə′lī·və]

(physiology)

The opalescent, tasteless secretions of the oral glands.

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Saliva 

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.

REFERENCE

Fiziologiia pishchevareniia. Leningrad, 1974(Rukovodstvo po fiziologii.)

V. D. SUKHODOLO