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thirst,sensation indicating the body's need for water. Dry or salty food and dry, dusty air may induce such a sensation by depleting moisture in the mucous membranes of the mouth and throat. Relief through ingestion of water is only temporary, however, if thirst results from a generalized depletion of water in the system. About three fourths of the body is composed of fluids, and the average adult requires 2 1-2 qt (2.4 liters) of fluid per day, supplied by water, other beverages, and foods. Depriving the body of water interferes with its metabolism and functions, causing dehydration, which is eventually fatal. The unnatural thirst that accompanies fever, diabetes, and other disorders is caused by a rapid reduction of the body fluids. The sensation of thirst is controlled by osmoreceptors in the hypothalamus in the brain. Dehydration of the cells triggers the posterior pituitary to releast the antidiuretic hormone (ADH).
the urge to drink, the physiological state that regulates intake of water into the bodies of animals and humans.
Intensity of thirst is determined by the duration of water deprivation, water losses in urine and perspiration, and the quantity of table salt consumed. In humans thirst is manifested by a sensation of dryness in the mouth and throat. It is conditioned by the thirst center—a set of nerve cells located in various sections of the central nervous system (the hypothalamus, the limbic-reticular system, the cerebral cortex) and associated with complex reflex reactions arising after stimulation of the central and peripheral interoceptors that respond to changes in osmotic pressure and volume of extracellular and intracellular fluids. Usually, the appearance of thirst precedes dehydration of the body, and relief of thirst occurs long before the entry of the water imbibed into the tissues, merely as a result of the act of drinking, the wetting of the mouth and throat, and the distension of the stomach walls. Thirst may also arise during digestion, since during this process water from body tissues enters the lumen of the digestive tract. Considerable intensification of thirst is observed in certain nervous and endocrine diseases, disorders of the water-salt metabolism, changes of the electrolyte con-tent in the blood, and edemas of cardiac origin.
REFERENCESKravchinskii, B. D. Fiziologtia vodno-solevogo obmena zhidkostei tela. Leningrad, 1963.
Handbook of Physiology. Section 6: Alimentary Canal. Vol. 1: Control of Food and Water Intake. Baltimore, 1967.
V. G. KASSIL’