From Big Medical Encyclopedia

FEED-BACK — impact of results of functioning of any system (exit of system) on the nature of functioning of this system. In systems with O. page control is exercised by registration of a deviation of an indicator of process from its set (desirable) value. The principle O. of page was widely adopted at the methodological and mathematical description biol, systems and the phenomena at all levels of the organization of life.

Need of maintenance of a certain law of change of the managed parameters always demands O. of page. Existence reduces it influence of changes of parameters of system on work of system in general, provides stabilization, stability of system, improves transient phenomenons in it, provides increase in a noise stability because of reduction of influence of hindrances (uncontrollable external influences).

Irrespective of the nature all systems (or elements) having stable characteristics possess O. page E.g., in systems of organizational management of O.'s analog page it is possible to consider control and the accounting of execution. In such systems it is always possible to find a closed circuit of influences. Studying biol, objects allows to allocate a large number of various systems with a closed circuit of influence — systems of attemperation of a body, a sugar content in blood etc. (see. Biological system, autoregulyation of biological systems ).

Distinguish positive and negative O. of page. Communication of an exit of system with its entrance through an intensifying link with a positive intensification coefficient — a positive feed-back, with negative strengthening — a negative feed-back. Positive O. of page raises an overal coefficient of strengthening and provides a possibility of management of considerable energy flows (capacities), spending small energy resources. Negative O. of page improves stability of system, i.e. property of system to be returned to an initial state after cancellation of external indignation. The requirement of stability — one of the main requirements for control systems since stability defines, as a rule, operability of all system. For biol, systems, e.g., one of the purposes of regulation consists in ensuring life activity of an organism in certain limits. In such systems at the strong revolting influences the deviation of this or that fiziol, (biochemical) parameter from norm from the outside is possible. Negative O.'s presence by the village provides a possibility of return of these or those values fiziol, (biochemical) parameters in limits of norm as information on the actual change of adjustable size allows to reveal a mismatch and to recover compliance of the valid and necessary values of adjustable parameter.

O.'s action by the village in biol, the system can consider on an example homeostasis (see), or sets of systems of the regulyation in an organism supporting its stable state. An analog of homeostatic regulation is the scheme of automatic control on a deviation from the setting signal. Broader idea of a homeostasis corresponds to a look about existence in an organism of set of chains of negative O. of page at the different levels, to-rye mutually influence at each other though in usual conditions have considerable autonomy. In an organism mechanisms O. of page are imposed one on another, duplicate each other. At the same time they can be divided into several groups, napr, on time constants — to divide into high-speed nervous mechanisms, slower humoral etc. Therefore for the analysis of similar systems it is also possible to use idea of several layers of O. of the page included in the same system.

The theory of systems with O. page is well developed for systems of automatic control by technical (artificial) objects (see. Automatic equipment ). Results and methods of a research and creation of similar objects are suitable for studying of a course of these or those processes in live organisms.

See also Bioelectric management , Regulation (in biological systems) .

Bibliography: Novoseltsev V. N. Theory of management and biosystem, page 80, M., 1978; The Theory of systems and biology, the lane with English, under the editorship of V. I. Krinsky, page 7, M., 1971.

O. I. Aven.