From Big Medical Encyclopedia

PLASTICITY OF PHYSIOLOGICAL FUNCTIONS — property of cells, bodies and fabrics to change the level of the functioning for ensuring maintenance of constancy of internal environment of an organism.

Ideas of P. f. t. an organism began to develop in the first half of 17 century when the fr. scientist R. Descartes proved the reflex principle of reaction of an organism and its parts on changes of the environment. In the middle of 19 century the fr. physiologist M. Flurans at a research of a role of various structures of a brain in implementation of autokinesias for the first time put forward idea of plasticity of nerve centers. At the end — the 19th beginning of 20 century it is mute. the scientist A. Beta formulated the concept about some fiziol, mechanisms which are the cornerstone of plasticity of nervous tissue. Its experiments with cross-linking of nerves of opposite extremities at dogs showed a possibility of recovery of normal movements for the account of «reeducation» of nerve centers. In 1930 — 1934 P. K. Anokhin formulated and proved the theory of functional system of an organism in which plasticity not only nerve centers, but also fiziol, functions of various bodies which are mutually promoting obtaining adaptive result, useful to an organism (is shown see. Functional systems ).

P.'s borders f. t. are defined by specific features of each organism (genetic, age, sexual), and also a spetsializirovannost of the separate cells and bodies realizing specific fiziol, functions. Genotype (see) sets P.'s limits f. t., including limits of normal adaptation of organisms to conditions of the environment. In turn P. f. t. is that mechanism which provides adaptation of an organism to exercise, mental, emotional and other stresses.

Item f. t. can be implemented at the molecular, cellular, fabric, organ and system levels, however the range of plasticity will be always limited by functionality of any structure of an organism, to-rye are characterized by the speed of elementary processes (see. Lability ). At the molecular, cellular and fabric

levels P. f. t. it is shown, first of all, in changes of intensity of the energy balance necessary for ensuring implementation of the genetic program of biosynthesis of the proteins which are a structural basis of activity of a cell. At all variety of P. f. t. in an organism power ensuring various manifestations of life activity is universal. Initial splitting of feedstuffs to the level of the substrates suitable for energy release, comes to the end with a cycle of Tricarboxylic acids with formation of the main amount of energy (see. Metabolism and energy ). The final stage of all power turning into to a cell is carried out with the participation of oxygen. Any hypoxia inevitably leads to exhaustion of power fund of a cell and disturbance of all types of exchange, turning on also the mechanism of biosynthesis of proteins. Therefore in the course of evolution there were special systems of providing an organism with oxygen.

At the level of a complete organism normal life activity is characterized by relative dynamic constancy of internal environment (see. Homeostasis ), to-rye are provided with the functional systems of an organism having high ductility. Plasticity of functional systems is shown in their ample opportunities in various ways to provide achievement with an organism of specific adaptive results (see. Adaptive reactions ). At failure of one or several components of functional system ensuring its net adaptive result can be carried out by other logging-in components. So, nerve and humoral pathways of the alarm system about existence of requirement or about achievement of result can interchange each other. E.g., in case of removal of a stomach and switching off of a considerable part of chemoceptors the alarm system about food requirement of an organism is carried out in preferential humoral way. However the most effective interchangeability is carried out in effector executive mechanisms of functional systems due to the joint action of nerve and humoral pathways of regulyation of functions (see. Neurohumoral regulation ).

Broad range of the regulating impacts on physiological processes from c. the N of page is possible thanks to pronounced plasticity of nerve centers, and the brain has the greatest plasticity in early ontogenesis. According to P. K. Anokhin, «ontogenesis of a brain moves towards ecology» — i.e. first of all there is a development of those nerve centers, to-rye provide survival and the most adequate adaptation of the developing organism to living conditions, reorganization of the processes happening in a nervous system in the direction of development of adaptive behavior with accurately controlled biologically useful result. Various modifications of behavior of an organism most of neurophysiologists are explained with plastic changes of activity of neurons in the presence of the general predeterminirovannost of a nervous system. Similar changes can be connected as with increase in the quanta of a mediator allocated by synapses and with sensitization of a hemoretseptivny zone of a postsynaptic membrane to constant number of quanta. At the level of the central neurons plastic changes are shown in fluctuations of their convergent capacity.

Any regulating influences of c. N of page on activity of these or those bodies and fabrics are possible thanks to P. f. t. Own range of any kind of activity of body is programmed in the fabric, and change of level of functioning is defined by specifics and selective sensitivity to nervous and humoral influences.

Item f. t. separate bodies it can be carried out due to inclusion in work or switching off of some part of cellular structures. So-called circulatory capillaries on duty, air cells, nephrons, neuromotor units are known. Change of one on duty functioning elements with others, and also inclusion additional is the important adaptive mechanism of an organism to conditions of intense activity.

Stability fiziol. functions of an organism of the adult it is very relative, and with age their plasticity decreases, though is unequal in various fabrics and bodies. There are homeostatic parameters, rather fast changing in various conditions of life activity of an organism. Arterial pressure, level of sugar in blood, lung ventilation at the corresponding loadings can change during several tens seconds. At the same time thanks to mechanisms of self-control of their change are unsharp with age and are shown generally in decrease in reliability of mechanisms of a homeostasis (see. Self-control of physiological functions ). There is a group of functions of stabler, but slowly and naturally changing with age — visual acuity and hearing, rate of propagation of pulse wave, a muscle tone, etc. More frequent reductions of heart, more low blood pressure, higher content of water are inherent to a young organism, e.g. With age at people the vital and total capacity of lungs, the maximal lung ventilation naturally decrease, there is a decrease in intensity of tissue respiration and oxygen absorption, concentration of sugar in blood increases. At men with age the minute volume of heart naturally decreases that is caused by change of systolic volume and reduction of heart rate (see. Blood pressure ). In parallel with it the systolic arterial pressure, peripheric resistance to a blood flow and time of blood circulation increases.

Item f. t. consider as important fiziol, the property providing adaptation (see) live organisms and the person to various living conditions and activity.

Plastic changes fiziol, functions, coming in an organism under the influence of various factors of a natural or artificial origin are widely investigated (change of climatic conditions, physical activity, structure and properties of food, a lack or excess of oxygen of air, zero gravity). Important theoretical and applied value has studying of mechanisms of adaptive biocontrol by visceral functions at animals and the person on the basis of P. f. t. Studying of specific mechanisms of plasticity of nerve centers will help to carry out the directed correction of an intracerebral homeostasis in the long term.

In the conditions of any pathology of P. f. t. it is sharply limited, and into the forefront compensatory and vicarious processes act (see. Vicarious processes , Compensatory processes ).

See also Brain, physiology .

Bibliography: Adolphus E. Development of physiological regulyation, M., 1971; Anokhin P. K. Sketches on physiology of functional systems, M., 1975; Burl-e r F. Aging and an old age, the lane with Franz M., 1962; You and l of e in with to and y H. H. Ecological physiology of a brain, L., 1979 * Meerson F. Z. Plastic ensuring functions of an organism, M., 1967; it she, Adaptation, stress and prevention, M.’ 1981; Frolkis V. V. Regulation’ adaptation and aging, JI., 1970.

Yu. A. Fadeyev.