DEPRESSORY REACTIONS (lat. depressio suppression) — the active reactions of an organism directed to a lowering of arterial pressure.
Of river were opened by I. F. Tsion and K. Ludvig in 1866 in experiences on rabbits at irritation of the central end of the cut aortal nerve. As at irritation of a nerve decrease (depression) in arterial pressure was noted, this nerve received the name n. depressor. Morfologo-fiziol. researches showed that n. depressor is formed by preferential afferent fibers going from baroreceptors of an aortic arch. Afterwards D. of river were received at irritation of a nerve of a carotid sine, increase in pressure in vessels of lungs, intestines, spleen, auricles and other internals.
Nerves which irritation causes D. of river received the name «buffer nerves» as the name «Depressor Nerves» not absolutely precisely reflects their afferent functions.
Of river were considered earlier as special Depressory reflexes which adaptive value was not clear. However afterwards this point of view changed a little.
Of river arising in a complete organism of hl. obr. in response to increase in the ABP, are carried out by the principle of self-control by special functional system (see. Arterial pressure ). Any increase in the ABP caused by action on an organism physical is normal., emotional or other factors, some span adaptive is. After cancellation of these factors of the ABP decreases and returned to the initial level defining the normal course of metabolism in an organism.
The initiative role in D.'s formation by the river in this functional system belongs to baroreceptors of large vessels which as show fiziol, experiments, perceive any increases in the ABP in an organism. In experiments with registration of activity of single fibers of aortal and sinus nerves the general are established fiziol, properties of baroreceptors. Baroreceptors of vessels are specialized and each of them perceives changes of the ABP only in certain limits. They differ from each other and on the speed of adaptation, some of them perceive the pulsing, bystry, and other static slow changings of the ABP. There are receptors answering vibration of a vascular wall. It is established that baroreceptors are more actively excited by sharp increase in the ABP, than gradual. Besides, they give a bigger gain of impulsation at increases of the ABP at the same size, but from the bigger initial level (fig). The properties of baroreceptors described above define especially active turning on of mechanisms of self-control (see. Self-control of physiological functions ), than above and more abruptly the ABP rises. If in normal conditions in an aortal nerve the reniform impulsation in beat of cordial reductions, synchronous with systolic waves of the ABP is registered, then at increase in pressure in a vascular bed the frequency of an impulsation increases. Against the background of high figures of the ABP from buffer nerves action potentials not only in a systole, but also in a diastole are registered, i.e. the continuous impulsation is observed. Impulsation, extending to cells of a vasomotor center of a myelencephalon, leads to pessimal braking of its vasoconstrictive department (see. Vasomotor center ). As a result of decrease in tonic influences on arterioles of a number of internals vessels of these bodies extend. At the same time due to excitement of a dorsal kernel of a vagus nerve action of the heart is slowed down, the speed of a blood-groove, volume of the circulating blood etc. decrease. All these processes also lead to decrease in the ABP.
At long keeping of pressure at the increased level the continuous impulsation of an aortal nerve through a nek-swarm time is replaced by reniform again. So-called reconfiguration of baroreceptors is observed. This phenomenon still is finally not understood. There are all bases to think that reconfiguration baroretseptorog is connected with the fact that the baroreceptors perceiving the pulsing pressure get to a zone of static constantly high pressure. In these conditions reaction joins the baroreceptors answering the pulsing waves at a high level of the ABP.
The phenomenon of reconfiguration of baroreceptors, certainly, has adaptive value. At the same time conditions for the incidental overweight of pressor vascular influences necessary for adaptive activity of an organism are created. However at long increase in the ABP there is an adaptation of the baroreceptors which got to a zone of not fluctuating pressure to the subsequent loss of the receptor properties by them.
Of river can be caused in animals not only a reflex way at primary irritation of baroreceptors of vessels, but also at direct electric irritation of certain structures of c. N of page: myelencephalon, front hypothalamus, partition, bazomedialny amygdala and so forth. All this specifies that along with system of pressor educations in structures of a brain there is specially organized depressor system. Nervous elements of this system are capable both to perceive pressor and Depressor influences, and to create at their excitement D. of river. In some structures of a brain (a myelencephalon, a hypothalamus) there are neurons on which convergence of pressor and depressor vozbuzhdeniye is carried out.
In a human body all the time occurs a peculiar fight pressor and D. of river. However in normal conditions cumulative effect of D. of river is always stronger than any pressor influences. It means that any incidental pressor reactions, the caused physical. or emotional factors, immediately are eliminated with protective depressor mechanisms of self-control. In this remarkable property D. of river the so-called golden rule of norm (P. K. Anokhin) is shown, according to Krom in a healthy organism the maximum protection is always stronger than maximum deviations. M. F. Rumyantseva and N. B. Altukhova (1972) showed that the pressor reaction caused by stimulation of the emotsiogenny center of a hypothalamus is returned to initial level depressor mechanisms of self-control even in the conditions of section of both aortal and vagus nerves, cervical sympathetic nerves, a spinal cord at the level of an upper chest vertebra, a bilateral deafferentation of sinocarotid area i.e. when the vast majority of nervous depressor mechanisms is almost eliminated. M. M. Rasulov (1972) established that the Depressory reactions caused by electric irritation of an aortal nerve or depressor areas of a myelencephalon are stronger than ABP of the pressor reactions, equal on changes, caused by stimulation of the emotsiogenny centers of a hypothalamus.
Depressor excitement are capable to reduce also already developing pressor reaction. However in the conditions of the long pressor influences connected with emotional or physical. tension, the fluctuations of size ABP caused by alternation of pressor and depressory reactions (a so-called tranzitorny hypertension) can be observed. At last, in the conditions of long and continuous tonic pressor influences on vessels at stable emotional stressorny states of D. of river are exhausted that results in overweight in an organism of pressor mechanisms and to developing of steady arterial hypertension (see arterial hypertension). For strengthening in these conditions of insufficient function of depressor devices the increasing development is gained by special electric stimulators of sinocarotid area, a so-called baropeysinga.
Some D. of river are applied in clinic with the diagnostic purpose, napr, a reflex of Chermak which is that during the pressing falling of the ABP and delay of heartbeat happens fingers on area of an upper third m. sternocleidomastoideus slightly below than a corner of a mandible to feeling of a pulsation of a carotid artery (irritation of a carotid sine and vagal trunk). Srednenormalny delay of pulse on 6 — 12 beats per minute is considered. More considerable delay of pulse indicates dominance of a parasympathetic tone. At such subjects along with D. river dizziness and a loss of consciousness can be observed. Increase in a tone of a vagus nerve is noted, e.g., at patients with defeats of coronary vessels and bilious ways.
Mechanisms of peripheral vasodilating influences still are adequately not studied. A determinal factor is vascular tone (see) and metabolic mechanisms of its regulation. There are separate data showing that the irritation of chorda tympani leads to vasodilatation of submaxillary gland and language, and irritation of n. pelvicus — to vasodilatation of cavernous bodies of generative organs. In some bodies, napr, in skeletal muscles, expansion of arterioles happens at irritation of sympathetic nerves. Except the nervous mechanism, the ruble takes part in D.'s implementation a number of humoral factors.
Reactions of various vessels to the same substance can be various. E.g., coronary arteries of small diameter under the influence of adrenaline and noradrenaline extend, and large arteries can extend and be narrowed. This effect is caused by dominance in large vessels of a-, an in small — beta and adrenergic receptors. In a medulla of kidneys vasodilating substance of the lipidic nature — Medullinum is formed. In a number of fabrics the special vasodilating substances which received the name are found prostaglandins (see). From submaxillary and pancreatic glands, lungs, skin and other bodies active vasodilating polypeptide — bradykinin which is formed during the splitting of one of globulins of a blood plasma under the influence of the enzyme which is in fabrics — kallikrein (K.F.3,4.4.21) is received. Except such vasodilating substances as acetylcholine, a histamine, in an organism also others are synthesized, napr, at hard work in skeletal muscles — vasodilating metabolites: milk to - that, ATP, carbonic acid, potassium ions, etc. The significant role in a vazodilatation belongs to a local hypoxia, changes of osmotic pressure.
Mechanisms of effect of humoral substances on D. of river are quite difficult. E.g., the adrenaline having preferential systemic pressor effect in a certain dose increases sensitivity of aortal baroreceptors, facilitating thereby Depressory reactions. Acetylcholine in certain doses can reduce or strengthen effect of adrenaline.
See also Pressor reactions .
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K. V. Sudakov.