CHEMOCEPTORS (srednevek. Arab al-kimiya; Greek chymeia and chemeia art of alloyage of metals - r receptors; a synonym of a hemotsepto-ra) — the vocational sensitive educations perceiving influences of chemical irritants and transforming them to nervous signals.
Process of interaction of a chemical incentive with a receptor membrane chemo - the sensory cell leading to excitement of neuron is called chemoreception. The mechanism of this process is a little studied. Consider that for. chemoreception the special macromolecules which are a part of a membrane of chemoceptors are responsible. So, from the fabric of language of mammals containing flavoring receptors the membrane fractions including macromolecules capable to interact with sweet and bitter substances are allocated.
Among chemoceptors distinguish the exteroceptors perceiving chemical irritations from the outside (flavoring and olfactory receptors), and the interoceptors perceiving changes of chemical composition of blood, a lymph and other fabrics. Excitement of flavoring receptors causes a feeling of taste (see), and olfactory receptors — a smell (see). Excitement of chemoceptors of internals is not always followed by emergence of accurate figurative perceptions. The subjective feelings arising at the same time were called by I. M. Sechenov «system feelings) — hunger, thirst etc. (see Interoception).
Mo Rfo of l ogiches ki chemo receptors
are very various. From chemoceptors of internals the arterial chemoceptors located in the trunk arterial mains — in a carotid artery and in an aortic arch are most in details studied. Chemoceptors of an internal carotid artery are concentrated in a carotid glome (see Paragangliya). Chemoceptors of an aortic arch represent separate accumulations of cells. The carotid glome has complex capillary structure with a numerous arteriovenous anastomosis. Such anastomosis considers distinctiveness of fabric chemoceptors. Between capillaries cells of two types are located: cells of the I type are filled with the electronic and dense vesicles containing biogenic amines (see); the cells of the II type surrounding them with the cytoplasmatic shoots do not contain biogenic amines. On cells of the I type form synoptic contacts of the termination of fibers carotid sinus nervag the glossopharyngeal nerve which is a branch (see), to-ry contains both afferent, and efferent fibers. Actually in a carotid glome cells of the I type and free hemochuv-stvitelny nerve terminations are considered as chemoceptors.
Arterial chemoceptors react to change of concentration in blood of oxygen, carbonic acid and hydrogen ions. A hypoxia (see; a hypercapnia (see), the blood which are followed by changes of chemical structure (see Blood), lead to emergence of the cardiovascular and respiratory reflexes directed to normalization of composition of blood and maintenance of a homeostasis (see). Therefore the main function of these chemoceptors is participation in regulation of the lung ventilation (see) providing an optimum ratio of oxygen and carbonic acid in blood. Carotid chemoceptors play a large role in regulation of breath (see), than the aortal chemoceptors participating preferential in regulation of activity of cardiovascular system (see).
The mechanism of stimulation of arterial chemoceptors is connected with features of blood supply of body. So, the impulsation in a sinus nerve caused by irritation of chemoceptors of a carotid glome depends not so much on the partial tension of oxygen and carbonic acid in an arterial blood how many from concentration of oxygen and hydrogen ions in fabric of the most carotid glome. Excitement of arterial chemoceptors can happen also under the influence of nek-ry inorganic and organic matters. Use of lobeline is based on it, e.g., (see) for stimulation of breath. Fiziol. value of the chemoceptors localized in fabrics and bodies (a liver, a stomach, intestines, etc.), consists in perception by bodies and fabrics of concentration of nutrients, hormones, osmotic pressure of blood and signal transmission about their changes in c. N of page.
Disturbance of chemoreception can be caused patol. processes in bodies and fabrics where chemoceptors (e.g. are located, at glossites, a glossodynia), and also patol. processes in other fiziol. systems of an organism. So, e.g., secondary disturbance of functions of flavoring chemoceptors is observed at hron. diseases went. - kish. path (gastritises, colitis, etc.).
Experimental methods of studying of chemoceptors of internals are based on registration of the reflex reactions arising in response to impact of these or those chemical substances on bodies and fabrics or at their perfusion through gumo-ralno the isolated bodies (see Perfusion). For a research of chemoceptors use also electrophysiologic registration of pulse activity from the afferent fibers departing from bodies and fabrics (see the Electrophysiology).
See also Receptors.
Bibliography: Lebedeva V. A. Furs
nizm of chemoreception, M. — JI., 1965; With and - m about y l about in V. O. Some problems of carotid chemoreception, in book: Touch systems, Morpho-physiological and behavioural aspects, under the editorship of G. V. Ger-shuni, page 76, L., 1977; Physiology of blood circulation, under the editorship of E. B. Babsky, etc., L., 1980; Handbook of sensory physiology, ed. by E. Neil, v. 3, pt 1, V. a. o., 1972; The peripheral arterial chemorecep-tors, ed. by M. J. Purves, Cambridge, 1975.
A. I. Esakov.