From Big Medical Encyclopedia

FUNCTION in physiology (Latin functio execution, commission) — the form of activity characteristic of live structure at the cellular, fabric, organ and system levels, and also at the level of a complete organism.

The main F. live structure at any level the constant metabolism and energy is (see), about the Crimea such manifestations of life activity as growth, development, reproduction, food, breath, the movement are connected (see the Movements, Breath, Reproduction, Growth). In the high-differentiated cells of an organism implementation specific physiological F. it is provided with specialized cytoplasmatic and membrane structures (see the Cell). Nair., the structure of a membrane of excitable cells provides a possibility of generation and carrying out impulses of excitement (see Excitability, In ozbuzhde-ny, Nervous impulse.); muscle cells due to availability of ak-tomiozinovy threads have ability to be reduced, making mechanical work (see Muscular contraction); the erythrocytes containing hemoglobin transport with tokokhm blood oxygen and carbon dioxide gas (see Blood). Function of a cell is connected with structural changes, to-rye are, as a rule, reversible. Updating of structures of a cell is provided with a metabolism, including the synthesis of protein regulated by the genetic device. Increase physiological F. cells causes in them activation of synthesis nucleinic to - t and specific proteins. Preservation raised F. for a long time can lead to the subsequent oppression of synthesis of protein and decrease in concentration of DNA in cells. Similar two-phase reaction is inherent in cells of various fabrics, napr, to cells of a liver, kidneys, etc. For implementation of a cell by structures specific F. (reduction, secretion, and a rovedeniye of excitement), and also inflow of energy in the form of ATP is necessary for synthesis nucleinic to - t and a squirrel, edges it is formed in the course of oxidizing and substrate phosphorylation (see biological oxidation, Phosphorylation). As intensity carried out F. depends on amount of the arriving energy, functionality of live structure in many respects is defined by the speed of the processes proceeding in it (see Lability).

The functional spetsializiro-vannost of cellular structures and feature of an obkhmen of substances define specialized F. fabrics and separate bodies. E.g., sokratitelny F. to muscular tissue (see Muscles) it is provided with specific mechanisms of interaction of threads of actin and a myosin in muscle fibers, and T. secretory glands (see Secretion) it is connected with mechanisms of synthesis of active agents in specialized secretory cells. Physiological F. various human organs and animals depend on their structural organization. So, hemodynamic F. hearts it is carried out not only due to reduction of muscle fibers of a wall of ventricles and auricles, but also thanks to existence of the valve device providing the directed movement of blood (see the Hemodynamics). Secretory F. kidneys it is caused not only by mechanisms of passive filtering, but also the active reabsorption of these or those substances provided with a rotary counter-current flow system of tubules (see the Water salt metabolism, Kidneys).

Long increase physiological F. any body inevitably leads to increase of its weight, a cut it can be caused not only by increase in quantity of the functioning cells of body, but also growth of each cell (see. Compensatory processes).

Possible limits of fluctuations of functional activity of body are genetically programmed in cells of this specialized fabric. Endogenous level of activity is set and regulated by the special intracellular mechanism which received the name of a pacemaker (see). Participation of pacemakers in processes of an erythrogenesis (see the Hemopoiesis), in regulation of frequency of reduction of heart and respiratory movements in the first days after the birth is established. At the same time T. body it cannot be connected with any one endogenous process, it always reflects set of biophysical, biochemical and morphological changes. Besides, increase or reduction F. can occur at the regulating influence from c. N of page

(see Neyrogu moral regulation), and also under the influence of biologically active agents coming to fluid mediums of an organism — hormones, mediators, metabolites (see. Humoral regulation).

System F. are considered, as a rule, within anatomic associations (the alimentary system, respiratory system, the blood circulatory system sight, hearing, etc.)*. However for maintenance defined fiziol. indicators (e.g., the osmotic pressure, temperature of blood, etc.) on a fixed level various bodies in the anatomic relation can combine in functional systems (see). Association F. various bodies it is carried out on the basis of neyrogu-moral regulation therefore changes F. one cells, fabrics and bodies cause reorganization of activity of other cells, fabrics and bodies. Similar interaction excludes a possibility of mechanical transfer of the consistent patterns of functioning of the isolated bodies determined in an experiment on a complete organism.

The major F. at the level of a complete organism preservation of constancy of internal environment is (see the Homeostasis). In the conditions of influence of various factors of a natural or artificial origin (climate change, structure and properties of food, a lack or excess of oxygen of air, zero gravity) the organism at the expense of mechanisms of adaptation (see Adaptation, Adaptation) aims to keep the integrity.

Stability physiological F. in an organism of the adult it is very relative. Quickly reaching the maximum level, physiological F. with approach of the period of a maturity begin to lose the intensity gradually. With age there is a natural reduction of minute volume of heart, in parallel with it the ABP and peripheric resistance raises systolic (see the Old age, aging). Nevertheless such homeostatic indicators as quantity of uniform elements of blood, a sugar content in blood, acid-base equilibrium (see), are rather stable and keep under various living conditions of an organism, practically without changing with age.

It is possible to note also nek-ry sexual features physiological F. Except distinctions in specific sexual functions, the level of standard metabolism (see), the vital capacity of lungs (see), the minute volume of lung ventilation (see), the heart rate, minute volume of heart (see Blood circulation) at women is about 10 — 20% lower, than at men.

In a phylogenetic row, various organisms carry out identical F. (e.g., hemodynamic F. hearts, T. breath, secretory F.). However specific features F. hl are connected. obr. with degree of adaptedness of organisms to specific conditions of existence.

Disturbances F. can be shown in weakening of activity of body or tissue (hypofunction), in inadequate reaction of live structure to action of irritants (dysfunction). At influence of superstrong or pathogenic irritants strengthening of activity of any body or systems (hyperfunction) is possible, a cut is considered or as protective and adaptive reaction or as pathological.

See also Physiology.

Bibliography: Anokhin P. K. Sketches

on physiology of functional systems, M., 1975; Biology of aging, under the editorship of V. V. Frolkis, etc., L., 1982; M e e r-with about N F. 3. Plastic ensuring functions of an organism, M., 1967; Fundamentals

of physiology of functional systems, under the editorship of K. V. Sudakov, M., 1983; The System organization of physiological functions, under the editorship of V. V. Parin, M., 1969; Comparative zoophysiology, under the editorship of L. Prosser, the lane with English, t. 1 — 3, M., 1977 — 1978; The Person, Medicobiological data, the lane with English, M., 1977.

Yu. A. Fadeyev.