BIOLOGICAL SYSTEM

From Big Medical Encyclopedia

BIOLOGICAL SYSTEM — set of functionally connected elements forming a complete biological object. Difficulty of more complete definition of B. of page is connected with the fact that this concept shall reflect the main properties of objectively existing spatio-temporal structure having the open nature of interaction with the environment and having high degree of specificity, complexity and organization.

Same biol, an object can act both as complete B. as page, and as its subsystem or an element. An example biol, the object considered as B. by page is the organism; at suborganismic level as B. cells, fabrics, bodies, systems of bodies (e.g., system of a respiratory organs, digestion, etc.), and at the nadorganizmenny level — populations, ecosystems, biogeocenoses, the biosphere can be considered by page. For the last type B. of page the special term «biological macrosystems» is sometimes used.

B. villages have high resistance to external indignations; at influence of factors of the environment in them there are processes directed to reduction of effect of these indignations. The B. page keeps the specificity in the changing conditions of the environment and in certain limits provides a homeostasis of internal environment.

B. pages are open circuits, i.e. in the course of life activity they exchange substance and energy with Wednesday. Such exchange is reasonablly adjustable, managed; it is directed to obtaining free energy from the environment and its use for implementation biol, functions of system. Therefore for understanding of the processes proceeding in B. of page it is necessary to analyze work of two main components it parts — power and information.

Power a component B. of page it is connected with processes of receiving, accumulation, transfer and use of energy. These processes provide a possibility of retention of structure, growth, the movement and performance of all specific functions B. of page. The second part B. of page is connected with management of power processes and realizes perception, storage, processing and use of information. Pages define management information mechanisms in B. what power processes and to what intensity happen in it.

Various power and management information processes are characteristic of various types B. of page, but in any B. components are closely connected by page both among themselves and play an essential role in maintenance of its existence, jointly providing preservation of a stationary nonequilibrium state of all subsystems and the most complete B. to page. Such processes are most well studied at organismic and suborganismic level and in a little smaller degree — on nadorganizmenny.

Management information mechanisms B. of page not only provide stabilization and preservation of power part B. of page, but in some cases participate in its education. So, at B.'s self-reproduction by the village of organisms genetic management creates both power to a component, and system of management information mechanisms fiziol, level.

Power a component of biological system represents set of its elements transforming substance and energy in the course of life activity. The analysis power components B. of page is connected with a research of structure and function of the bodies and fabrics providing their energy balance, and at the level of nadorganizmenny educations — with studying of flows of substance and energy in biocommunities and the biosphere.

Complexity and specificity biol, structures and the processes which are implemented in them causes a number of deep distinctions between B.'s power of page and power of the inorganic world. Key feature of B. of page in this sense is its open character. Thermodynamics (see) B. the page significantly differs from classical. The concept of an equilibrium state, fundamental to classical thermodynamics, is replaced with idea of a stationary nonequilibrium state of system, and the second beginning of thermodynamics (the principle of increase of entropy) receives the fresh wording in the form of Prigozhin's theorem: speed of increase of entropy in system aims at the minimum value, the corresponding dynamic equilibrium.

Studying power components B. of page is one of tasks bio-energetics (see) — the science which is on a joint of biophysics, biochemistry and molecular biology.

Management information a component of biological system exerts the regulating impact on processes in power a component at all possible levels of the organization — from molecular to complete. In complete B. pages can work genetic, ecological, evolutionary and fiziol, regulators, are characteristic of each of which the time frames and the specific mechanisms biol, managements. So, at the level of a complete organism the conducting and integrating role in management processes and coordination of functions is played by mechanisms of c. N of page. At the same time at other levels into the forefront other mechanisms of regulation act (e.g., at suborganismic level — specific Neuro and humoral and autoregulyatorny mechanisms).

For implementation of function of management in B. page obligatory is impact on controlled process (or the size, a variable) at least two antagonistic factors (or processes) from which one increases or activates this element, and another — reduces or suppresses it. The reactions of any metabolic process going in the direct and opposite direction, exciting and brake neurons, flexor muscles and extensor muscles etc. can be such antagonists.

However, as a rule, in B. page managing function for nek-ry this process is carried out not just by two antagonistic factors, and the whole group of managing mechanisms, each of which has the regulating effect on the managed process in the limited range of change of external conditions and in a nek-swarm of limited area of activity of B. of page. So, e.g., the heat balance of an organism is supported by the fact that the contribution to maintenance of standard temperature is made by two types of the regulating mechanisms — the processes directed to calorification (chemical thermal control), and the processes directed to dispersion of heat (physical. thermal control). In general interaction of these two antagonistic factors leads to the fact that at any change of conditions of the environment and operating conditions of an organism the system moves to a stationary state, at Krom total heat production at all processes is equal in an organism to total dispersion of heat. However each of two main antagonistic factors represents result of activity of a number of the regulatory processes which are turning on mechanisms of a shiver, vascular reactions, sweating, phosphorylation, and also behavioural reactions (a pose, muscular activity).

Existence of a set of the regulatory mechanisms duplicating each other and functioning in parallel or replacing one with another in various conditions of the environment explains a possibility of existence of B. of page with rather broad range of external conditions and defines flexibility and reliability of management information system B. of page.

Studying of cybernetic processes in management information a component B. of page is a task biol, and the medical cybernetics investigating the general patterns of management and regulation in the live systems which are in continuous difficult interaction with Wednesday.

Fundamental methodological reception of a research B. of page is the principle of system organization, according to Krom any biol, an object represents B. of page, capable to regulation both internal ratios between the subsystems, and ratios of a complete object with Wednesday. Studying biol, objects in such methodological framework represents systems analysis of biological systems.

At systems analysis biol, an object is presented in B.'s form of page — sets of functionally connected elements realizing power and information processes in system. Set of essential bonds between these elements B. of page defines its structure. One of the most important properties of complex systems in general and B. of page in particular is hierarchy of a structure, i.e. consecutive inclusion of systems of low level in systems of more high level. A row of hierarchically coordinated systems forms the sequence of structural levels B. of page.

B.'s consideration by the village at various hierarchical levels and transition from one level to another, more difficult, is not necessarily connected with complication of structure of B. of page and, therefore, with complication of its analysis. This results from the fact that along with emergence of the new characteristics not inherent to the sum of subsystems of the previous level, a number of signs of these subsystems is insignificant now. The number of levels of consideration of B. of page and a possibility of a partition of B. of page on elementary components are limited.

The lowest level B. of page is the system of the macromolecules capable to discrete reproduction, the highest — the biosphere, the cut can be considered elements biogeocenoses. Between these levels it is possible to allocate several intermediate — cellular, organismal, population, biogeotsenotichesky.

It is possible to tell that systems analysis represents an antithesis to the known cybernetic representation biol, objects in the form of «a black box». If at a research of system as «black box» the scientist is interested only in entrances (entrance processes or sizes) and exits of system, and the research objective consists in definition of patterns of transformation of entrances to exits without penetration into internal processes and mechanisms of system, then at systems approach a main goal of the researcher is opening of internal structure of B. of page, understanding of the processes which are implemented in this structure.

A standard method of a research B. of page at systems approach is modeling of its structure and patterns of behavior. At B.'s modeling by the village its power and management information components are considered jointly as uniform complete system, safety and functioning of metabolic system are supported and go to a cut mechanisms of regulation (see below Autoregulyation in biological system). For mathematical modeling of managing processes in B. of page special value has use of a mathematical and conceptual framework of cybernetics.

In cybernetic system existence of regulation (management) means that it can be presented in the form of two interacting blocks — subject to regulation and the regulator. The regulator on channels of a feedforward through the corresponding set of effectors transfers managing impacts to subject to regulation. Information on a condition of an object is perceived by receptors and on channels feed-back (see) it is transferred to the regulator (scheme).

Methodologically reasonable should consider such division of structure of B. of page into an object and the regulator, at Krom power and metabolic processes create an object in system of regulation, and management information processes contact the block of the regulator. However specific B.' representation by the village in the form of such block diagram is not always possible as in complex live systems the regulator and subject to regulation are structurally and functionally divided not always, and elements B. of page often combine in themselves property of both the regulator, and subject to regulation.

In B. of page there are two main types of management processes: management as a feedforward (e.g., management according to the set program — synthesis of protein on a matrix of DNA) and management by the principle of a feed-back. The page special value has the last appearance of management for B.

In simple cases when influence of any one factor on one controlled variable is modelled, allocate two types of feed-backs — positive and negative. A positive feed-back increases influence of a factor on an output variable, negative — reduces. Simpler form of the description of a negative feed-back — a negative feed-back on a deviation when the signal in a chain of a feed-back arises at a deviation of an adjustable signal from nek-ry «desirable» level gained distribution in literature on B.'s modeling of page. In difficult B. of page, however, the specific regulating mechanisms and processes at the same time participate in management of a set of the adjustable processes connected among themselves and therefore more difficult models developed in the theory of automatic control (the theory of multicoherent systems, the theory of sensitivity, the theory of invariancy) begin to be applied to difficult B.' analysis of page recently.

The concept «biological system» is widely used in such sections of cybernetics as cybernetics biological and cybernetics medical (see). Aiming to understand the nature live, scientists aimed to find in an organism and others biol, objects what can be investigated separately, aimed to allocate in them separate systems and processes. Studying biol, objects as B. of page taking into account the main interrelations of their structures and elements became the purpose of these sections of cybernetics. In particular, a number of sections of medical cybernetics relies on idea of an organism as about B. of page. So, development of mathematical methods of the analysis of data of comprehensive examination of the patient, development of methods of mathematical modeling on the COMPUTER of activity of its interconnected functional systems, use of the automated machine methods for assessment of a condition of the patient represent perspective areas in which systems analysis can find direct application in clinical practice. Systems analysis of functions of an organism as B. the page will allow to compare and integrate indications of numerous devices, to estimate the general orientation of processes in an organism of the patient during big operations, at the postoperative and rehabilitation period.

Are of particular importance of work on a research B. of page at the level of an organism in medical cybernetics in connection with development of the latest methods of life support using cardiopulmonary bypasses, an artificial respiration, artificial heart. Effective use of these means leads to increase of requirements imposed to quantitative methods in anesthesiology and resuscitation as at the disposal of doctors there is a wide choice of means and methods for recovery of the vital functions of the patient.

See also System .

Autoregulyation in biological system

Autoregulyation in biological system — process of natural change or maintenance on a fixed level certain regulated biol, sizes — such as, e.g., blood pressure, body temperature, mitotic activity of cells of fabrics, position of extremities and all body in space etc. In many cases is obvious that these functions are carried out corresponding biol, systems independently, without the external regulating influence. Therefore in such cases simpler term «regulation» instead of the term «auto-regulation» or other synonyms of this term is usually used.

Distinguish the following two philosophy of an autoregulyation: regulation on a deviation of adjustable size and regulation on indignation.

The systems based on the first principle are capable to define a difference between the set and actual value of adjustable size. This difference is used by the regulator for elaboration of the regulating impact on an object, a cut reduces a deviation of the actual value of adjustable size from a preset value.

If the set value of adjustable size does not change in time, then the autoreguliruyushchy system represents the stabilizer, i.e. the system maintaining constancy of value of adjustable size. If the set value of adjustable size changes in time under a certain law, then the autoreguliruyushchy system carries out «tracking» time history of the set value of adjustable size and supports the minimum difference between the set value and the current (actual) value of adjustable size.

Distinctiveness of the systems based on the principle of regulation on a deviation of the adjustable size (fig. 1) is existence at them feed-back (see), with the help a cut the regulator obtains information on the current actual value of adjustable size. A feed-back together with direct impact of the regulator on an object forms a closed path (a contour of regulation, a contour of a feed-back, a loop of a feed-back). Therefore the systems based on the principle of regulation on a deviation are often called loop systems of regulation.

The deviation of adjustable size from a preset value caused by external indignation is weakened in loop systems since the regulator by means of a feed-back develops such impact on an object, a cut results in effect, on a sign to opposite initial indignation. Such feed-back is called a negative feed-back.

Specific B.' representation by the village with automatic control in the form of the uniform flowchart perhaps not always. Quite often the regulator and subject to regulation are combined in one biol, structure or a functional unit.

by Fig. 1. Examples of the biological systems of automatic control based on the principle of regulation on a deviation: and — oppression of key E1 enzyme the end product of Sn (is specified by an arrow with a dotted line) which is formed of initial S0 substrate through a number of the intermediate S1, S2 forms... Sn; E2, E3... En — the enzymes catalyzing intermediate reactions; the arrow with a dot-dash line showed action on enzyme of the substances M capable to activate or oppress enzyme; — repression of synthesis of E1, E2 enzymes... En an end product of Sn (it is specified by a dotted arrow); Sn oppresses synthesis of the corresponding information RNA (IRNK), interfering with receipt of necessary information for synthesis of the enzymes catalyzing intermediate reactions (E1. E2... En); in — regulation of density of cell population in a metaphyte. (Trunk) cells, undifferentiated, capable to division, make the differentiated cells rendering oppressing (direct or indirect) action on mitotic activity of stem cells. The hormones capable to strengthen or, on the contrary, to weaken oppression of stem cells, define the set value of adjustable size — the population density of the differentiated cells.

In particular, oppression of activity of enzymes end products (oppression of enzymes by the principle of a feed-back, retroinhibition of enzymes, allosteric oppression by end products) consists that activity of the enzyme which is taking part in synthesis of this end product decreases in process of increase in concentration of this product (fig. 1, a). Such oppression usually is allosteric by the nature, i.e. the oppressing end product has no sterichesky (structural) looking alike substrate and joins a molecule of enzyme in the specific site, or the center other than the catalytic center. Such accession involves conformational reorganization of a molecule of enzyme and loss (partial or full) activities of the catalytic center (see. Conformation ). This negative feedback mechanism leads to stabilization of concentration of an end product: at change of speed of consumption of an end product over a wide range of its concentration changes only in rather narrow limits.

The mechanism of oppression of enzymes end products is very eurysynusic. This type of regulation controls practically all major links of cellular metabolism both one-celled, and metaphytes. E.g., key reactions of cellular metabolism (glycolysis and oxidizing phosphorylation) are oppressed by high concentration of an end product — ATP. Accumulation of cations, sugars, amino acids, nucleotides, lipids and other vital substances in a cell leads to oppression of the enzymes which are taking part in active membrane transport and (or) in biosynthesis of these substances.

Oppression, or repression, synthesis of enzymes end products represents much more inertial negative feedback mechanism in comparison with the mechanism of oppression of activity of enzymes. It joins when the mechanism of oppression of activity of enzymes is not able to prevent accumulation of this end product in a cell as a result of surplus of a product in the environment or falloff of speed of its consumption. In such cases the end product can cause repression of the site of DNA bearing hereditary information on primary structure of the enzymes synthesizing this product (fig. 1, b).

Combined action of a large number of the negative feedback mechanisms controlling activity and speed of synthesis of enzymes allows not only to stabilize intracellular concentration of many vital connections, but also to economically spend initial substrates and energy for synthesis of these connections.

In the organization of metaphytes an extremely important role is played by a nadkletochny negative feedback mechanism, controlling mitotic activity of cells of normal fabrics. This mechanism carries the name of contact oppression of cellular division (a synonym: oppression of a cellular cycle, contact regulation of cellular division, oppression of cellular division, density dependent, regulation by density etc.) also it is shown that mitotic activity of normal somatic cells depends on density of cell population, in a cut they grow. The somatic cell at normal fiziol, conditions is usually not capable to share and make the amoeboid movements if it contacts to the next cells surrounding it from all directions. The elimination of these contacts (full, and sometimes only partial) caused by removal or death of the next cells causes bystry recovery of ability to the active movements and division. Contact oppression has specific character and plays an important role in morphogenetic processes (see. Morphogenesis ).

Contact oppression, apparently, is a special case of regulation of mitotic activity of cells of fabrics of a metaphyte. The flowchart of such regulation, in a cut plays a major role the oppressing action of the differentiated cells (direct or indirect) on mitotic activity of not differentiated (trunk) cells, is shown in the figure 1, century. A typical example of such scheme of an autoregulyation is regulation of number of blood cells.

The systems based on the principles of regulation on indignation use indignation for elaboration of the nek-ry compensating impact on an object to prevent change of adjustable size. As the actual value of adjustable size in such systems does not make impact on the regulator, in them there is no closed path of regulation characteristic of systems with a negative feed-back (regulation on a deviation). This circumstance makes almost impossible full compensation of indignation that leads to change of adjustable size aside, opposite to that, in to-ruyu this size in the absence of the regulator changes.

Under some conditions the compensating influence can cause even a bigger deviation of adjustable size, than uncompensated indignation.

Fig. 2. Examples of the biological systems of automatic control based on the principle of compensation of indignation of adjustable size: and — activation of Ek enzyme by the predecessor of S0 substrate; — induction of synthesis of E1, E2 enzymes... En initial S0 substrate; in — compensation of the accelerated intake of glucose from intestines in a blood channel.

The most widely studied and most widespread mechanisms of an autoregulyation of compensation type at molecular level are mechanisms by means of which initial substrates have the activating effect on the enzymes which are taking part or in utilization of these substrates (substrate activation, the advancing activation, activation by predecessors of substrate), or on the speed of synthesis of such enzymes (induction of enzymes, induction of synthesis of enzymes, substrate induction of enzymes).

Operation of the mechanism of activation of enzyme by the predecessor of substrate can be explained by means of the scheme submitted in the figure 2, and.

On the scheme reaction sequence is shown, initial S0 substrate turns into a cut through a number of intermediate forms (S1, S2... etc.) in the Sn connection utilized by various reactions. This connection serves as substrate for the Ek enzyme sensitive to the activating effect of initial S0 substrate (it is shown by a dashed line). Change of speed of formation of initial V0 substrate affects as external indignation concentration of Sn: at increase in V0 this concentration also increases. However activation of Ek enzyme by means of S0 allows to compensate the strengthened formation of Sn from S0 due to increase in outflow of Sn in the reaction catalyzed by this enzyme. At invariable activity of the enzymes utilizing Sn and at certain ratios of parameters of system of reactions almost full compensation of the indignation caused by change of V0 is possible: concentration of Sn can remain almost invariable at change of V0 over a wide range.

The simplest form of regulation of activity of enzymes of compensation type is allosteric activation of enzymes substrates.

Molecules of substrates activators join the regulatory centers on a molecule of enzyme that causes such change of its conformation, a cut promotes increase in catalytic activity of an active center.

Induction of synthesis of enzymes substrates (fig. 2, b) represents an inertial analog of the mechanism of substrate activation of enzymes.

The essence of the phenomenon consists that substrates can cause derepression of synthesis of the enzymes participating in utilization of these substrates. Induction of synthesis of enzymes is one of universal mechanisms of adaptation of cells to the changing environmental conditions. Quite often natural selection which leads eventually to emergence of the cells capable to synthesize new enzymes is involved in this process. As a typical example of such grade of the autoregulyation using natural selection adaptation of bacteria to antibiotics and insects to insecticides can serve. In particular, at the insects treated during many generations to action of an insecticide of DDT ability to synthesize new enzyme — to DDT-dekhlorgidraz, the inactivating this insecticide was developed.

As example of an autoregulyation of compensation type on fiziol, level regulation of level of glucose can serve in blood a pancreas (fig. 2, c). Increase in intake of glucose from intestines stimulates formation of insulin with a pancreas which stimulates deposition of glucose in the form of a glycogen and fats in a liver, muscles and fatty tissue. This strengthened outflow of glucose in the depositing fabrics compensates the strengthened inflow of glucose from intestines. Similar compensation mechanisms are traced in regulation of secretory activity of all closed glands and in immune responses of an organism. Compensation mechanisms of an autoregulyation are a basis of very many behavioural reactions controlled by c. N of page, are also shown usually in the form of reflex elimination of an irritant.

Fig. 3. The combined systems of automatic control: and — the flowchart of the combined system of automatic control (the regulator I reacts to indignation, the regulator II — on a deviation from a preset value); — simple biochemical system of an autoregulyation of the combined action. Oppression of Et enzyme a product of S represents a negative feedback mechanism, and activation of E2 enzyme substrate S — the compensation mechanism. Operation of both mechanisms is directed to stabilization of level of the substance S used by consumers; in — the combined multicircuit system of level control of glucose in blood. On the scheme two contours are presented: a negative feed-back (dotted line) and the compensating communication (dot-dash line).

The combined systems of an autoregulyation. In the majority the B. pages represent the combined systems of an autoregulyation. Such systems have in the structure both negative feedback mechanisms, and mechanisms of compensation of indignation (fig. 3, a). From the point of view of the theory of automatic control such combined systems are capable to provide almost ideal isolation of an adjustable object from external indignations. In the figure 3, the scheme of the typical combined biochemical system of the autoregulyation containing a negative feed-back (oppression of enzyme its product of S) and compensation communication is provided (activation of E2 enzyme its substrate S). Operation of both mechanisms is directed to stabilization of level of the substance S used by the consumer.

All the major промежуточны© connections of cellular metabolism are controlled by similar combinations of the regulating bonds. E.g., hexosemonophosphates oppress the education in the reactions catalyzed by enzymes a hexokinase, a glucokinase, fruktokinazy and glikogenfosforilazy, and activate the utilization in the reactions catalyzed by enzymes glyukozo-6-fosfatdegidrogenazoy, fosfofruktokinazy and glikogensintetazy. Level and other connections is similarly regulated in cells (e.g., AMF, atsetil-KOA, many intermediat of a tricarbonic acid cycle, the majority of amino acids).

The principle of the combined auto-regulation widely is used also on more high levels biol, the organizations. In the figure 3, in the flowchart of neurohumoral regulation of level of glucose is provided in blood. On the scheme three autoreguliruyushchy mechanisms are presented. Two of them represent the negative feed-backs joining at lowering of the level of glucose. Both of these mechanisms lead to activation of formation of glucose in a liver from the glycogen of a liver and a lactate, amino acids and glycerides transported in a liver from muscles and fatty tissue. The third, compensating mechanism turns on at increase in level of glucose in blood. Operation of this mechanism comes down to activation of deposition of glucose in various fabrics. Except the mechanisms specified on the scheme, there are some more neurohumoral mechanisms controlling the level of glucose. Among such mechanisms the large role in regulation of level of glucose is played by the mechanism of increase in level of glucose which is becoming isolated through a chain: a hypothalamus —> a hypophysis —> AKTG —> a medulla of adrenal glands —> adrenaline —> activation of phosphorylase of a liver —> increase in glucose of blood by the principle of a negative feed-back.

In total B. page of an autoregulirovaniye have a certain inertance, because of a cut bystry (e.g., spasmodic) indignation of an adjustable object cannot be instantly compensated by the regulator and therefore adjustable size manages to deviate (sometimes quite strongly) a preset value before the regulator works as appropriate. The process of achievement by the adjustable size of the set stationary value caused by single indignation of an adjustable object is called transient phenomenon.

Autoregulyation generating the autonomous movements in biological systems. Fundamental property of live systems is their ability to different types autonomous (not depending on external indignations) changes biol, sizes in time and space. All types endogenous biol, rhythms, all forms of the mechanical movement, generation and carrying out nervous impulses, processing of information in a nervous system etc. — all this directly or indirectly is result of functioning of special mechanisms of an autoregulyation — generators of autonomous movements.

The self-movement of any system volunteers and supported by instability of an equilibrium or stationary state of system. Therefore idiosyncrasy of generators of autonomous movements is existence at them the special mechanism providing such instability — a so-called positive feed-back. Positive feed-back develops such impact on an adjustable object, a cut matches on a sign an initial deviation of adjustable size from stationary value according to what the condition of systems with a positive feed-back under certain conditions is unstable. As much as small indignation of adjustable size caused by external influence or inevitable fluctuations (i.e. spontaneous fluctuations) in the system, leads to progressively accruing deviation of adjustable size from a reference value. The deviation proceeds until the system does not reach new, already stable stationary state. Can be this new stationary state or a condition of rest, in Krom variables do not change in time, or a self-oscillatory state, in Krom variables fluctuate in time with a constant amplitude.

Typical positive feedback mechanism at molecular level is the autocatalysis (see). Very many links of cellular metabolism have autocatalytic character. E.g., it is necessary for synthesis of ATP that ATP was already present at catalytic quantities in cells. «Start» of phosphorylation of ADF glycoclastic system requires availability of ATP which serves as a cofactor of the first two stages. A positive feed-back controls activity of such enzymes as phosphorylase — key enzyme of a glycogenolysis, glutamatdegidrogenez — key enzyme of a nitrogen metabolism.

Reproduction of viruses, one-celled and metaphytes in the absence of the factors constraining reproduction also has autocatalytic character.

Rice 4. Plurality of stationary states in biological system with a positive feed-back: and — the system with a positive feed-back consisting of a source of substance P and the consumer of this substance. Substance P is formed by a source with a speed of V (p) and also it is utilized by the consumer with a speed of V (p) p . The dot-dash line showed a positive feed-back — P activating action on a source; — the graphic representation of interaction of a source and the consumer. As the speed of formation of a product is described by a S-shaped curve, interaction of a source and the consumer generates three alternative stationary states presented on graphics by points of intersection of the curves describing dependence of speeds and on concentration of P (fat curves of V (p) and and V (p) p . To each stationary state (points 1, 2 and 3) there corresponds the value to concentration of P (concentration [P] 1, [R] 2 and [R] 3) and the value of stationary speed of V = V (p) and = V (p) p (V1, V2 and V3 values). The dotted line showed dependence of speed of V (p) and from concentration of P in the absence of a positive feed-back.

Plurality of alternative stationary states in biological system. The simplest form of the autonomous movement is switching of system from one stationary state in another. Similar switching can be studied on the example of system with the positive feed-back shown in the figure 4, and. This system consists of a source and the consumer of any product (R). Formation of P is regulated by a positive feed-back. Speed of education by P source [V (p) and ] increases with increase in concentration of River. If speed of utilization by P consumer [V (p) p ] grows with increase in concentration of P (fig. 4, b), in system a source — the consumer there can be three alternative stationary states which are characterized by three various values of concentration of P and three various values of speeds and V (p) p . In the drawing stationary states are presented by points of intersection of the schedules representing dependence of speeds of V (p) and and V (p) p from concentration of P (point 1, 2 and 3). In each such point the condition is satisfied:

i.e. concentration of P does not change t over time.

Fig. 5. The changes of concentration of substance P in time of t caused by instability of the stationary state 2 passing into a stable state 1.

At small deviations of concentration of P in both parties from stationary values [P] 1 and [R] 3 a difference of speeds — V (p) and - V (p) p compensates these deviations so that concentration of P accepts former stationary value again. However at as much as small deviation of concentration of P from stationary value [P]2 a difference of speeds of V (p) and - V (p) p due to action of a positive feed-back leads to a further deviation of concentration of P from value [P]2 aside, matching an initial deviation. So, at small increase [R] in comparison with [P]2 a difference of V (p) and - V (p) p it is positive, and [R] begins to increase over time — in system the autonomous movement leading to switching of system from an unstable stationary state (fig. 5,2) in a stable state (fig. 5,7) begins. At a small deviation [R] towards reduction in comparison with stationary value [P]2 a difference of speeds of V (p) and - V (p) p <0, and it leads to further reduction of concentration of P until it does not accept new steady value [P]1 (a curve 2).

Fig. 6. The critical phenomena and a hysteresis in system with a positive feed-back: and — system with a positive feed-back, in which the speed of formation of a product P source of V (p) and depends on concentration of substrate S • V (p) p — speed of utilization by P consumer; — interaction of a source and the consumer at several fixed values of concentration of S (values of concentration of S are specified on graphics in conventional units). Points of intersection of curves of V (p) and and curve of V (p) p represent stationary states of system about fight. The number of stationary states changes with change of concentration of S; in — dependence of stationary speed of V = V (p) and = V (p) p = from concentration of substrate S. Shooters showed the directions of autonomous movements at achievement of concentration of S of one of two critical values — at [S] = the 4th transition from a point and in a point in, at [S] = the 2nd transition from a point with in a point of d.

Changes of the parameters determining the speed of a source of V (p) and and the speed of the consumer is V (p) p , can displace stationary states — to change stationary values of speeds and concentration of River. At achievement of some critical (threshold) values there can be new stationary states, and the system switches from one stationary state in another. If the speed of a source is V (p) and depends on concentration of substrate S, from to-rogo the product of P is formed (fig. 6, a), that change of concentration of S changes a relative positioning of stationary points (fig. 6, b) where the family of curves of V is presented (p) and the fixed values of concentration of substrate S constructed at five, and a curve of V (p) p . At small concentration of S, i.e. 0< =< [S] 2, in system exists only one stationary state. This state is steady, as well as a state 1 in the figure 4, and is characterized by low stationary values of concentration of P and speeds of V (p) and and V (p) p . At high concentration of S — >([S] 4) — in system also exists one stationary state, a cut, as well as a state 3 (fig. 4, b), steadily, but is characterized by high stationary values of variables. At average values of concentration of S — (<2 [S]< 4) — in system there are three stationary states, similar to states 1, 2 and 3 (fig. 4, b). Unstable transient stationary state [midpoint of crossing of a curve of V (p) p constructed for [S] = 3, from a curve of V (p) and (fig. 6, b)] with increase in concentration approaches an upper stable stationary state, and at reduction of concentration of S — the lower stable stationary state. There are two critical values of concentration of S ([S] — 2 and [S] = 4) at which the unstable stationary point merges with steady upper (at [S] = 2) or lower (at [S] = 4) a stationary point therefore stability of these points is lost, and the system makes the autonomous movement — switches in one of steady stationary points. In the figure 6, in dependence of stationary speed of V = is shown V (p) and = V (p) p from concentration of substrate. This dependence has hysteresis character: direct and return transitions of system from one stable stationary state in another (are shown in the drawing by shooters) are made at various critical values of concentration by S and different ways. Thanks to this property the system is neekvifinalny: depending on initial conditions it can appear in one of two stable alternative stationary states. Thus, the system is capable vaguely long to store a trace (to remember) such changes in the environment which are capable to lead to change of its stationary states. Capacity of memory of the considered system is minimum and equal to 1 bit. However the large number of the similar neekvifinalny systems functioning in big B. of page can form a basis to high-capacity memory. The systems having two stable stationary states are often called triggers with two stable states (sometimes simply triggers) or bistable systems.

Self-oscillations. If in system (fig. 6, a) all substrate turns into a product P, then speed of consumption of a product (V (s) p ) equals speeds of its education (V (p) p ), and therefore dependence of V (s) p from [S] has just the same appearance (fig. 6, b), as well as dependence of V on [S] in the figure 6, century. Hysteresis dependence on concentration of S can be the cause of one of the most important types of the autonomous movements — self-oscillations (autonomous fluctuations).

Fig. 7. Self-oscillations in system with a positive feed-back: and — the system with a positive feed-back consisting of a source of substrate S, the consumer of the substrate which is a source of a product P and the consumer of a product R. Produkt of P activates own education. Speeds of formation of S and P are designated through V (s) and and V (p) and , and speeds of utilization — through V (s) p and V (p) p  ; — interaction of a source and the consumer of substrate S. The S-shaped curve represents dependence of speed of V (s) p from concentration of S, and straight line of V (s) and — dependence of speed on concentration of S. Crossing of a curve of V (s) p from a straight line of V (s) and (a point about) represents a stationary point of system. The closed path of b, with, oh, a, d represents a limit cycle on which the system makes the autonomous cyclic movement; in — self-oscillations of speed of V (s) p in time of t. Letters noted the values of speed corresponding to points of the limit cycle shown in the figure 7, at the left.


Self-oscillations arise if substrate is formed a nek-eye by a source (fig. 7, a) with such speed (V (s) and ), that the stationary state of system determined by two conditions

it is unstable. At the hysteresis nature of dependence of V (s) p from concentration S stationary state (a point About in fig. 7, b) is unstable if values of speed of a source of V (s) and match unstable values of speed of V (s) p . If a stationary state is unstable, then at the slightest deviation of concentration of S or P from stationary values the system begins the autonomous movement to one of steady branches of a curve of V (s) p (the movement O — >b' or About — >d' in fig. 7, b). At the time of achievement of a steady branch (a point of b' or a point of d') in system the quasi-stationary state is established, in Krom the condition (3), but not a condition is met (2). This quasi-stationary state is characterized by slow drift of system along a steady branch of a curve of V (s) p towards one of extrema of this curve (the movement b' —> with or d' —> and). At the time of achievement of the extreme point (with or a) the system «breaks» in the bystry movement (with —> d or and —> b) towards other steady branch. After achievement of a steady branch the movement is sharply slowed down again and again slow drift begins (d —> and or b —> c). Thus, hysteresis of dependence of V (s) p from concentration S and instability of a stationary state lead to the autonomous movement of system on a closed circuit (on a cycle and —> b —> with —> d — >and). Such cycle is called a limit cycle of system. At the movement of system on a limit cycle all its variables periodically change. In the figure 7, in autonomous fluctuations (self-oscillations) of speed of V are shown (s) p in time of t.

Except a positive feed-back, there is a big variety of the mechanisms of an autoregulyation capable to cause instability of stationary states of B. of page and by that to form a basis for generation of various forms of autonomous Movements. In particular, systems with a negative feed-back under certain conditions can also lose stability and to be a source of self-oscillations. Such systems the excessive inertance of a feedback mechanism and too big sensitivity of the regulator to a signal of a feed-back leading to the fact that the regulating influence of big amplitude is developed by the regulator with big delay that causes strong reregulation — a deviation of adjustable size aside, opposite to initial indignation is the main reason for loss of stability. This secondary deviation of adjustable size leads in turn to elaboration of the new regulating influence, a cut because of delay causes reregulation again, but already opposite sign, etc. Such «roving» of system of an autoregulyation with a negative feed-back under certain conditions can have self-oscillatory character.

Self-oscillatory processes are observed at all levels of the organization of living matter. Fluctuations of concentration of reactants can arise in separate enzymatic reactions, polyfermental systems, membrane transport, muscular contraction, mitotic activity of cells of various fabrics, electric activity of a cerebral cortex etc. The self-oscillations generated by various B. page form a basis to the temporary organization (i.e. a certain order of functioning in time) to B. of page. Self-oscillations play very important role in processes of coding, transfer and transformation of information in a nervous system. E.g., the majority of receptor cells is the self-oscillatory systems coding information on the measured parameters of the environment (intensity of light, temperature, pressure, concentration of various substances etc.) in the form of self-oscillations of membrane potential of the corresponding amplitude and frequency.

Fig. 8. Generation of an impulse of a standard form in system with a positive feed-back: and — dependence of speed of consumption of substrate V (s) and and speeds of formation of substrate source of V (s) and from concentration of substrate S; — change of speed of consumption of substrate V (s) p during t0, caused by short-term superthreshold increase in speed of a source of V (s) and in timepoint of t0. Duration of exciting action of increase in V (s) and it is shown by a piece under the schedule. The dot-dash line showed a critical level of V (s) and , which exceeding leads to generation by system of an impulse of a standard form. Change of V is shown to a fat dotted curve (s) p , caused by short-term subthreshold increase in V (s) and , which duration is specified by short fat line under the schedule. Stationary value V (s) p it is shown to a dotted straight line.

Generation of a single impulse of a standard form. If the stationary point of the system shown in the figure 7, and, is located on a steady branch of a curve of V (s) p near one of extrema as it is shown in the figure 8, and, that such state is characterized by relative stability. At small indignations the system reverts to the original state. However at big, superthreshold indignations the system temporarily loses stability and makes the single autonomous cyclic movement (and —> b —> with —> d —> oh, fig. 8, a) which is coming to the end with return to a reference stationary state. As a result of such cycle the system generates a single impulse (fig. 8, b), amplitude and duration to-rogo almost do not depend on amplitude and duration of superthreshold indignation. Such behavior of the «everything or nothing» type (see. «Everything or nothing», the law) the page, in particular for the biological membranes capable to be excited under the influence of a superthreshold incentive is characteristic of many B.

Switching from one stationary state in another, generation of single impulses of a standard form and generation of self-oscillations are elementary forms of autonomous movements. Interaction of elementary movements with each other in B. of the pages containing a large number of various generators of autonomous movements generates irregular shapes of movements. B.'s example of page generating such irregular shapes of movements is the nervous system.

Pathology as disturbance of normal functioning of systems of an autoregulyation

All types of B. of page of an autoregulyation are capable to perform the normal functions of a homeostasis or generation of autonomous movements only in certain criteria ranges. Indignations of the environment and processes of internal development (in particular, aging) an organism can cause the changes of internal environment which are not compensated by homeostatic mechanisms. Under the influence of such unindemnifiable changes there are shifts of stationary states of various systems of an autoregulyation. These shifts, reaching rejection limits, cause loss of stability of stationary states and switching of systems in new stationary states and generation of new types of autonomous movements by them. New stationary states and the autonomous movements can be incompatible with normal functioning of an organism, and then in an organism morbid condition develops.

Reliability of systems of an autoregulyation. B. pages of auto-regulation are characterized by special forms of the organization, thanking the Crimea exclusively high reliability of functioning of such systems is reached (see. Reliability ). Feature of reliability of B. of page in comparison with technical is high reliability of all system in general at rather low reliability of the elements entering it (cells, organellas, etc.). The most important lines of this organization are: 1) plurality (duplication) of the regulating bonds controlling the same function; 2) plurality and relative autonomy in parallel the functioning elements; 3) repeated reservation, deposition of reserve nutrients and energy sources; 4) substitution or recovery of elements and bonds, out of service; 5) ability to self-cleaning from alien elements; 6) protection against overloads and ability to adapt to frequent overloads.



Bibliography: Apter M. Kibernetika and development, the lane with English, M., 1970; B Ηχο in with to and y M. JI. and Vishnevsky A. A. Cybernetic systems in medicine, M., 1971, bibliogr.; A. A ravens. Bases of the theory of automatic control, the p. 3, M. — L., 1970, bibliogr.; Novoseltsev V. N. Homeostasis of control systems, Automatic equipment and telemechanics, No. 12, page 118, 1973, bibliogr.; Uoterment. The theory of systems and biology, in book: The theory of systems and biology, the lane with English, under the editorship of V. I. Krinsky, page 7, M., 1971, bibliogr.; Shumakov V. I., etc. Modeling of physiological systems of an organism, M., 1971.

Autoregulyation in B. of page. — Klegg P. and Klegg And. Hormones, cells, an organism, the lane with English, M., 1971, bibliogr.; Oscillatory processes in biological and chemical systems, under the editorship of G. M. Frank, M., 1967, bibliogr.; M it about. and Sh and to about F. The general conclusions, teleonomichesky mechanisms in processes of cellular exchange, in book: Regulyatorn. mechanisms of a cell, the lane with English, under the editorship of I. B. Zbarsky, page 477, M., 1964, bibliogr.; Selkov E. E. Issledovaniye of the mechanism of glycoclastic fluctuations, in book: Matemat. models biol, systems, under the editorship of G. M. Frank, page 5, M., 1971, bibliogr.; T and with and to and And. Nervous excitement, the lane with English, M., 1971, bibliogr.; Trinkaus D. From cells to bodies, the lane with English, M., 1972, bibliogr.; X and - a fleece And. and Spigelmans. Auto-catalytic synthesis of virus RNA, in book: Enzymes and synthesis of biopolymers, the lane with English, under the editorship of. I. M. Warsaw, page 90, M., 1967; Stadtman E. R. Allosteric regulation of enzyme activity, Advanc. Enzymol., v. 28, p. 41, 1966, bibliogr.; it, Mechanism of enzyme regulation in metabolism, in book: Enzymes, ed. by P. D. Boyer, v. 1, p. 397, N. Y., 1970.

Century of H. Novoseltsev; E. E. Selkov (biophysical.).

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