ADAPTATION

From Big Medical Encyclopedia

ADAPTATION (late lat. adaptatio — adaptation) — adaptation of a live organism to constantly changing living conditions in external environment developed in the course of evolutionary development. Without And. maintenance of normal life activity and adaptation to various environmental factors would be impossible: climatic and temperature (see Acclimatization), to a hypoxia (see Adaptation to height), zero gravity (see), to impact on an organism of infectious agents (see Immunity) etc. And. has great vital value for a human body and animals, allowing not only to transfer considerable and jumps in the environment, but also to actively reconstruct the physiological functions and behavior according to these changes, sometimes and being ahead of them.

Thanking And. constancy of internal environment of an organism (see the Homeostasis), such constants of blood as acid-base equilibrium, osmotic pressure, etc. is maintained.

In the conditions of excessive or adverse long effects for an organism of factors there can come considerable deviations of constants limits of admissible borders that leads to disturbance of a normal course of physiological functions and development of pathological process.

In addition to maintenance of constants of internal environment with the help And., reorganization of various functions of an organism providing its adaptation to exercise, emotional and other stresses is carried out.

And. can lead to change of a form of behavior that is especially brightly shown on the example of the animals falling into hibernation under unfavorable conditions of existence.

In processes And. advanced organisms, in addition to c. N of page, take great interest sympathoadrenal and gipotalamo-pituitary systems.

At emergence of morbid conditions And. plays an essential role in development of various compensatory changes in an organism, the protective mechanisms counteracting a disease.

Unlike And., in a broad sense the term «adaptation» is used for designation of process of change of level of sensitivity of that of a pla of other analyzer (see) under the influence of adequate irritation — so-called physiological adaptation (see visual adaptation, Adaptation acoustical). In this case And. is the difficult sum of the processes proceeding both in receptors (see) and in the central neural structures. And. it can be expressed both by decrease, and sensitization. The last sometimes is called a sensitization. So, sensitivity of an eye to light in the dark increases, and at effect of light goes down.

Physiological adaptation. One of types physiological And. is And. receptors, expressed in decrease in frequency of impulses in the departing afferent fiber, despite constant action of an irritant. Time, during to-rogo occurs such decrease in frequency of impulses, or speed And., variously for different receptors and for the same class of the receptors which are in bodies with various function (a wall of an aorta, a wall of a bladder.

Receptors of a muscle spindle adapt within several minutes, skin tactile the recipe ry — within several seconds, Pachini's little bodies located in a mesentery — during several milliseconds. Baroreceptors of a carotid sine and an aortic arch at constant irritation also adapt. At periodic irritations they signal about change of blood pressure what is a necessary condition of its constancy.

Mechanism A. receptors it is difficult. As the basis of activity of a receptor is made by the generator potential, irritating nerve terminations and the defiant category of impulses, And. receptors depends on accommodation of nerve terminations to constant action of potential.

Since Nernst (1908) works it is known that at long irritation the increase in a threshold of stimulation occurring happens electric current of a constant or at its slow increase as it is proved in a crust, time, owing to changes of ion permeability of a membrane.

Akkomodativny ability of nerve terminations determines speed And. (see Accommodation). Sensitive fibers possess smaller accommodation, than motive. In turn sensitive fibers, the innervating slowly adaptive stretch receptors (muscle spindles or receptors of a throat), differ in the minimum akkomodativny properties.

And. receptors depends not only on accommodation, but also on primary processes of reception, e.g. a condition of a light-sensitive pigment. Besides, And. receptors it is constantly regulated by efferent influences from c. N of page, arriving to them on fibers of a sympathetic nervous system and special centrifugal ways.

About a state physiological And. judge by change of limit of sensibility of analizatorny system depending on change of intensity of an incentive. Research A. eyes is called an adaptometriya (see visual adaptation).

Cellular adaptation — adaptation of cells to conditions of the environment directed to survival and reproduction. At the highest animals and plants And. goes, as a rule, at the level of a complete organism; participation of cells in this process makes only its component. Everything stated below belongs to the elementary organisms.

Cellular adaptation is conditionally divided on gene and phenotypical. Genotypic And. arises owing to selection of cells with the certain genotype causing endurance; phenotypical And. arises as defense reaction on action of a disturbing factor. In the latter case the large role is played by intensity and terms of influence. Strong influence can lead of a cell to death before approach And. At action of a weak irritant (subthreshold force) or at its slow increase there can be a so-called cross stability, i.e. cells become less sensitive not only to this irritant, but also to other agents.

The stability which arose under the influence of a weak irritant can remain and after its action stops. It comes to light after repeated use of the same agent. Speed of change of resistance of a cell, as well as duration And., considerably varies. Degree And. cells — increase or reduction of the threshold of sensitivity — provides the level of active function (e.g., functions of receptors).

The mechanisms which are the cornerstone And., depend by nature cells and character of a disturbing factor. In certain cases cells are capable to change the damaging substance by physical. - chemical binding of the agent or by his chemical transformation in less toxic form. Bacterial cells can synthesize the special enzymes splitting toxicant (induction of a penicillinase in culture of the stafilokokk steady against penicillin). Increase in resistance of a cell to an irritant can be caused by increase in stability of proteins of cytoplasm due to changes of conformation of chains of protein or by formation of a complex enzyme — substrate, pl due to synthesis of new proteins.

Biophysical mechanisms adaptation. The biophysics considers adaptive reaction of a cell or a metaphyte from the point of view of their organization as the system opened in relation to the external environment which thus is freely exchanging with the last energy and substance. At the same time the dynamic equilibrium of processes of inflow and outflow of substance and energy provides the necessary level of a stationary state of live system, constancy of internal environment and various gradients on its borders defining normal functioning of cells and the whole organism in these conditions (see. Biological system). For maintenance of a stationary state the live system uses the principle of a feed-back (see), or a dynamic autostabilization that allows live system to choose as if automatically that mode of speeds of exchange reactions which provides an optimal variant of adaptation to external environment. E.g., at increase of functional activity of a cell (increase in heat production, production of osmotic or mechanical work, etc.) in its mitochondrions there is a deficit of ATP and ADF and phosphorus which in turn accelerate process of biosynthesis of ATP in a respiratory chain collect.

Adaptation reaction of live system represents transition from one stationary level of exchange reactions to another, but as process of exchange consists of reaction chains with the general chemical intermediaries, such transition is connected usually with the extreme phenomena — flash of observed process or its temporary delay (see. Adaptation syndrome ).

Adaptation of living cell is a consequence physical. - chemical heterogeneities of the organization of its cytoplasm. Division of the interacting substrates by means of membranes is the important principle of the organization of live system and is shown during implementation of protective and adaptive reactions of an organism. So, e.g., the lyseing enzymes (proteases) in an intact cell are put into lysosomes and cannot digest protein. At damage of a cell and according to its lysosomes their membranes burst, enzymes are released and digest a cell, making thereby process, important for an organism — removal of the damaged cells.

Ultraviolet rays, influencing membranes of cells of skin, release enzyme a tyrosinase, under action to-rogo the melaninovy pigment protecting a body from the burning action of sunshine is formed.

In biomembranes with strictly consecutive chains of enzymes which are «built in» in them (e.g., a respiratory chain of mitochondrions, a redox chain of free oxidation in microsomes) «relay» transformation of substrates in living cell is provided. By such way it is reached economical And. an organism to food (the induced synthesis of the enzymes necessary only in this case), And. to toxins and medicines (biotransformation in microsomes), etc.

Opportunities And. live system are limited to degree of reliability of the organization of biomembranes. Even small increase in an ionic prona of a tsayemost of membranes already leads to loss of their ability to accumulate energy.

The important role in regulation of a condition of biomembranes is attributed to antioxidants (see) by which protect lipidic layers of biomembranes from oxidation decomposition.

See also Membranes biological , Permeability .

Adaptation in cybernetics — automatic (without participation of the person) change by cybernetic system of nature of functioning (behavior) for the purpose of achievement of the best result at accidental, unexpected, change of characteristics of the environment. Such systems call adaptive, or the systems of automatic adaptation or search which are self-adapting, self-adjusted, self-training systems. The biological organism corresponds to the cybernetic system including a control system and object of management. This analogy is widely used during the modeling of various functions. E.g., the bionics (see) investigates mechanisms of biological processes for the purpose of designing on their basis of technical devices and solutions of engineering tasks. Attempts to explain the biological phenomena become, using concepts of the theory of management (cybernetics).

The most important types of adaptive systems are systems of automatic search of any size, self-training systems for recognition of images (see), the systems which are automatically developing model with unknown parameters and using this model for management. Systems of automatic search realize the arranged or accidental (trial-and-error method) search of such parameters of the managed object at which some indicator of work of this object reaches optimum size.

Systems of recognition of images imitate ability of many animals and the person to distinguish from each other (to distinguish) similar objects and to classify them. Methods of automatic recognition are implemented by the technical systems capable to study and then without the assistance of «teacher» and «hints» automatically to classify objects. These methods are applied in many branches of science and technicians, including and in medicine. The system of adaptive information processing allowing to differentiate a carcinoma of the stomach from a peptic ulcer was so created.

The adaptive systems intended for definition of characteristics (identification) of objects unitary enterprise of a ravleniye allow to solve problems of management of the complex systems which are as a result of accidental and uncontrollable influences.

Bibliography: Byzov A. L. Processing of visual information in a retina of vertebrata, Vestya. Academy of Sciences of the USSR, No. 7, page 55, 1969. Granite P. An electrophysiologic research of reception, the lane with English, page z і, M., 1957, bibliogr.; Lazarev L. IL Researches on adaptation, M. — L. 1947; Hodorov B. I. Problem of excitability, L., 1969, bibliogr.; N crnst W. Zur Theorie des elektrischcn Rcizen. Pflugere Arch. ges. Physiol., Bd 122, S. 27b, 1908.

Cellular And.— Alexandrov V. Ya. Adaptive changes of stability of cells, the Guide to cytology, under a yard, A.S. Troshina, t. 2, page 608, M. — L., 1966, bibliogr.; Dean A. and Hinshelvukh Page. Mechanisms of automatic adaptation in bacterial cells, the phenomena of adaptation, in book; Regulation of cellular exchange, the lane with English, iod of an edition of S. Ya. Kap-lansky, page 366, M., 1962; Klegg P. of N of Klegg And. Hormones, cells, organism. A role of hormones at mammals, the lane with English, M., 1971; Sevag M. G. and de Coursi S. D. The biochemical processes which are the cornerstone of medicines resistance of microorganisms and biochemical ways of prevention of this stability in book; Funktsionaln. biochemical, kletochp. structures, under the editorship of A. I. Oparin, page 369, M., 1970, bibliogr.; Yabrov A. A. To a question of the mechanism of a cellular stress. Cytology, t. 11, No. 2, page 137, 1969, bibliogr.

Biophysical mechanisms A. — Bauer E. S. Theoretical biology, page 165, M. — L., 1935; P rigozhin. Introduction to thermodynamics of irreversible processes, the lane with English, M., 1960, bibliogr.; Problems of biochemical adaptation, under the editorship of A. A. Pokrovsky, M., 1966, bibliogr.; Physical and chemical bases avtoregul yatsishch in cells, under the editorship of E. B. Burlakov shch O. R. Necklace * page 7, etc., M., 1968. bibliogr.

And. in cybernetics — Gubler E. In, Computing methods of recognition of pathological processes, L., 1970, bibliogr.; Chadeesh B. M. Adaptive models in control systems, M., 1966, bibliogr.; Fitsnev L. N. Management of coordination of movement, M - 1971, bibliogr.; Tsypkin Ya. and. Adaptation and training in automatically * systems, M., 1968, bibliogr.

A. I. Esakov; A. G. Butkovsky (kib.) V. A. Veselovsky (biophysical) Yu. E. Ershikov (biol)

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