THIRST

From Big Medical Encyclopedia

THIRST — set of the feelings which are expressed in the insuperable aspiration to drink water and causing the corresponding behavioural reactions in the person and animals. treats the main biol, to motivations (see. Motivations ), providing preservation of life both separate organism, and look in general

. arises at reduction of water resources of an organism or disturbance of a normal ratio between water and mineral salts (hl. obr. sodium chloride). Fiziol. reaction to emergence. drink of water is. Thus, state. promotes maintenance on a fixed level of a water balance and electrolytic balance in an organism (see. Water salt metabolism , Homeostasis ).

There are many theories explaining fiziol, mechanisms of formation and a satisfying. They can be divided into the theories considering. as the peculiar «general feeling» caused by changes of composition of blood, and the theory according to the Crimea. there is a result of «locally» arising feelings of dryness of an oral cavity and throat. Differently explain also mechanisms of a satisfying. The authors considering. as «the general feeling», explain a satisfying. shifts in a condition of internal environment (ingress of water from a digestive tract in blood and fabrics) while supporters of «peripheral» theories point to a huge role of change of a condition of receptors of an oral cavity and throat (their moistening), and also interoceptors of a stomach at its filling.

Third group of theories. make so-called central theories which supporters concentrated the main attention on studying of departments of c. N of the page regulating level of consumption of water an organism. Practically all researchers who support either «general», or «peripheral» theories., recognize the extreme importance of c. N of page in formation. and its satisfying, however studying of the central mechanisms Zh. at these authors was not a subject of special researches.

The theory uses the greatest recognition., to-ruyu it is possible to call the theory of multiple factors. In our country I. N. Zhuravlev who began the researches in the field of physiology was a founder of this theory. in the late thirties. In a basis of the ideas of mechanisms of formation. and its satisfying And. N. Zhuravlev put I. P. Pavlov's concept about the food center as sets of those departments of c. the N of page, to-rymi is regulated receipt in an organism of the liquid and solid matters necessary for vital chemism (see. Food center ).

Studying mechanisms of formation and a satisfying. in experiences on dogs with a fistula of a stomach or the cut gullet, I. N. Zhuravlev paid attention that even at considerable degree of dehydration created by water restriction. at dogs it could be «temporarily satisfied» only with imaginary drink of water or filling by water of the rubber bulb placed in a stomach. This pattern is so accurate that the amount of water, the drunk dog at imaginary drink, can serve as an objective and exact indicator of intensity., i.e. degrees of drinking excitability. At the same time the size of imaginary drink does not reflect the true need of an organism for water: only at small degree of dehydration it appears equal true requirement of an organism; after a long exception of water of a diet the animal can mnimo drink such amount of water, a cut several times exceeds necessary for recovery of water balance. It is big even at natural receipt it in a stomach (at «natural» drink) about what it is possible to judge by substantial increase of a diuresis after drink of ad libitum (at will). These facts demonstrate that in formation. and in its satisfying an important role is played by factors as the general, and a local order, and depending on conditions relative value of that and others can be various.

Regulation of level of consumption of water an organism is carried out by the special drinking center (I. N. Zhuravlev) which by analogy with the food center of I. P. Pavlov is considered as a complex system of the nervous educations which are widely presented in various «floors» of a brain. Allocation of such concept was buttressed up by facts clear interaction of this center with other nerve centers, willows of t. h with food, regulating consumption of power substances.

The theory of multiple factors in an origin. received confirmation. It is established that. it can be caused by increase in osmotic pressure of blood or intracellular dehydration. In a hypothalamus, and also in a number of internals the specific receptors reacting to change of osmotic pressure of blood are found (see. Osmotic pressure , Osmoreceptors ). Excitement of these receptors brings those departments of a brain which are a part of the system of the drinking center to a state of activation, creating feelings. and corresponding behavioural reactions. At the same time there is an excitement of supraoptic and paraventrikulyarny kernels of a hypothalamus and the strengthened receipt in blood of the antidiuretic hormone promoting preservation by an organism of water resources (see. Vasopressin ).

Thirst can also arise at reduction of volume of extracellular liquid without noticeable changes of an osmotic condition of blood and fabrics. The mechanism of activation of the drinking center in these cases is connected with excitement of volyumoretseptor (receptors of volume) located in the right auricle and venas cava. Andersson (V. of Andersson, 1953) managed to observe for the first time. at goats at an injection of 0,1 ml of 1,5 — 2% of solution of sodium chloride in front kernels of a hypothalamus. In the subsequent experiences of Andersson, and also numerous works of other researchers it was shown that. in animals it can be caused by electric or chemical irritation of lateral hypothalamus (see).

Various disturbances of level of consumption of water, up to total absence of feeling. (adipsia), were noted at damages of a mesencephalon, lateral hypothalamus, subkomissuralny body, many structures of limbic system, and also new bark. At the same time also different short-term disturbances of consumption of feedstuffs were quite often noted. Detailed studying of a role of a hypothalamus by methods of irritation or destruction of its kernels led to a conclusion that the areas «responsible» for water consumption and food, apparently, block each other.

Relationship and interrelations of the drinking center of a hypothalamus with the neurosecretory kernels connected with regulation of removal of water from an organism, the drinking center, the centers of thermal control as well as integration of various «floors» of the drinking center still is completely not studied. Numerous cases of disturbance of level and the mode of water consumption are not clear, with to-rymi it is necessary to face in clinic. However various observations demonstrate that. as the symptom can have huge diagnostic value [Holmes (J. N of Holmes), 1964]

. can be not only normal fiziol, reaction to change of conditions of internal environment of an organism, but also a symptom at various patol, states. The increased thirst (see. Polydipsia ) it is characteristic of diseases of kidneys and the heart which is followed by hypostases, endocrine diseases etc. At other diseases the adipsia can take place (e.g., at mentally sick). The adipsia can be also the cause of various functional disturbances (headaches, locks, etc.).


Bibliography: K. M bulls. Chosen works, t. 1, page 271, M., 1953; Lakomkin A. I. and Myagkov I. F. Hunger and thirst (In physiological aspect), M., 1975, bibliogr.; Pavlov I. P. Complete collection of works, t. 3, page 120, M., 1949; Experimental materials on physiology of thirst, under I. N. Zhuravlev's edition, etc., Kharkiv, 1954; F i t z s i m about n s J. T. Thirst, Physiol. Rev., v. 52, p. 468, 1972; Y e r-n e y E. B. The antidiuretic hormone and the factors which determine its release, Proc. Roy. Soc. (Lond.), ser. B, v. 135, p. 25, 1947; Wolf A. V. Thirst, Springfield, 1958.

A. I. Lakomkin.

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