Thirst

THIRST, a peculiar sensation that urges a person to drink and is an important regulator of the body's water balance. Thirst belongs to the so-called general sensations. When the body is water-depleted, the sensation of thirst, initially weak, becomes increasingly persistent and in the end can become a source of extreme suffering. Thirst can arise under different conditions. 1. A mild degree of thirst is clearly localized in the oral cavity and pharynx as a sensation of dryness and stickiness of their mucous membranes, and occurs when breathing through the mouth, especially when rapid (prolonged conversation, singing, feverish state, etc.). In this case, thirst can be represented as a consequence of the exhaustion of the secretory activity of the mucous glands of the mentioned cavities; moistening them, for example with a mouthful of water, usually stops the sensation of thirst. 2. After a heavy meal, especially a salty one or one with a significant consumption of alcoholic beverages, a strong thirst is often felt, which is subjectively localized not only in the oral cavity but also in the esophagus and even in the region of the stomach. Objectively, thirst is manifested by periodic contractions of the esophagus (L. R. Müller) at the level of the tracheal bifurcation (analogous to the contractions of an empty stomach during hunger). It is probable that under these conditions thirst is, on the one hand, a consequence of the depletion of tissues with water (after abundant digestive secretion), and on the other hand, a consequence of the enrichment of the intestinal epithelium, the capillaries of the intestine, and the capillaries of the portal vein with absorption products (relative water depletion), which must lead to a disturbance of the osmotic and colloidal properties of the blood and tissues of this area; the changes in the water regime of the tissues that arise signal the sensation of thirst, which ceases after sufficient introduction of water. However, here, as with thirst from drying of the throat, the sensation of thirst, if unsatisfied, gradually ceases due to the movement of water from other tissues, which are richer in water, into the tissues that have become depleted by it (absolutely or relatively). 3. The strongest sensations of thirst, persistently demanding satisfaction, are observed when the body suffers from large or small significant losses of water; therefore, all moments leading to such losses excite thirst, namely: profuse diarrhea (dysentery, cholera), profuse sweating (for example, during mechanical work, at high t°, especially in a dry atmosphere), polyuria in various forms of diabetes, which, as is known, reaches enormous sizes (8–10 L pro die). In these cases, the sensation of thirst is not limited to sensations of dryness in the mouth, throat, etc., but turns into more acute sensations of "burning," and if prolonged and unsatisfied, passes into a general, ill-defined sensation, and in far-reaching cases, extremely painful. The idea that thirst is a consequence of the depletion of the whole organism with water still cannot be considered indisputable. The decisive factor for the occurrence of thirst is apparently an increase in the concentration in the blood and especially in the tissues of table salt, urea, and other substances. Thus, it has been clinically established that painful thirst can arise even in the presence of large excesses of water in the body, for example, in cardiac and even in renal edemas. By cryoscopy, in these cases it is possible to detect a lowering of the freezing point of serum (down to 0.64), despite the presence of edemas. Experimentally, it is possible to induce the sensation of thirst after the injection of hypertonic solutions of table salt, calcium chloride, urea, and glucose (Leschke). The vegetative nuclei of the medulla oblongata and the gray nuclei of the diencephalon are centers that receive irritations of an unknown nature ("tissue thirst") and project them to the periphery through the vegetative nervous system in the form of the aforementioned subjective and objective phenomena (dryness in the mouth and pharynx, contractions of the esophagus, etc.). The latter are perceived as a psychologically conscious sensation of thirst. Thus, a significant role in the regulation of thirst also belongs to the influence of the cerebral cortex (resp. psyche). Satiety of thirst is possible not only by means of drinking, but also by means of distraction of attention and even by suggestion. The occurrence of thirst is therefore conditioned by the state of the body's water-salt reserves (preliminary feeding, the degree of loss of water and salts by the body), as well as its nervous-psychic set (habits, vegetative excitability, organic irritants in the brain). In other words, the physiological norms of fluid necessary to prevent or satisfy thirst depend on a number of causes and therefore fluctuate within wide limits—from 0.5 L to 3–4 L. Pathological intensification of thirst—polydipsia—is observed as a symptom of a number of diseases and, like thirst itself, can be conditioned by various causes. The most acute polydipsia is observed in sugar diabetes and especially in non-sugar diabetes. It is necessary, however, to emphasize that polydipsia in non-sugar diabetes is a secondary phenomenon, regardless of whether one considers the primary polyuria (Bauer and Aschner) or the damage to the diencephalon and the disturbance of tissue osmotic regulation (Reschke, Veil) as the basic pathogenetic factor. Feil and Regnier showed (on themselves) that with prolonged abundant drinking, even in a healthy person, the strongest polydipsia can artificially develop; its cause is also hyperosmia of the blood, which arose as a result of sharply intensified diuresis. Finally, in patients with a shrunken kidney, who excrete a large amount of urine of low specific gravity (polyuria with hyposmaturia), polydipsia is observed due to the simultaneous tendency to increase the osmotic pressure of the blood. Intensified thirst is observed

was mentioned, in cardiac and renal patients with edemas, as well as in feverish patients. Among healthy people, polydipsia is most often observed in individuals with intensified heat dissipation and sweating, for example, those employed in hot shops (see).