Homeostasis in the classical meaning of the word is a physiological concept that denotes the stability of the composition of the internal environment, the constancy of the components of its composition, as well as the balance of the biophysiological functions of any living organism.
The basis of such a biological function as homeostasis is the ability of living organisms and biological systems to withstand environmental changes; In this case, organisms use autonomous defense mechanisms.
This term was first used by the American physiologist W. Cannon at the beginning of the twentieth century.
Any biological object has universal parameters of homeostasis.
Homeostasis of the system and body
The scientific basis for such a phenomenon as homeostasis was formed by the Frenchman C. Bernard - it was a theory about the constant composition of the internal environment in the organisms of living beings. This scientific theory was formulated in the eighties of the eighteenth century and was widely developed.
So, homeostasis is the result of a complex mechanism of interaction in the field of regulation and coordination, which occurs both in the body as a whole and in its organs, cells and even at the molecular level.
The concept of homeostasis received an impetus for additional development as a result of the use of cybernetics methods in the study of complex biological systems, such as biocenosis or population).
Functions of homeostasis
The study of objects with a feedback function has helped scientists learn about the numerous mechanisms responsible for their stability.
Even in conditions of serious changes, adaptation mechanisms do not allow the chemical and physiological properties of the body to change significantly. This is not to say that they remain absolutely stable, but serious deviations usually do not occur.
Mechanisms of homeostasis
The mechanism of homeostasis in higher animals is the most well developed. In the organisms of birds and mammals (including humans), the function of homeostasis allows one to maintain the stability of the number of hydrogen ions, regulates the constancy of the chemical composition of the blood, and keeps the pressure in the circulatory system and body temperature at approximately the same level.
There are several ways in which homeostasis affects organ systems and the body as a whole. This may be influenced by hormones, the nervous system, excretory or neuro-humoral systems of the body.
Human homeostasis
For example, the stability of pressure in the arteries is maintained by a regulatory mechanism that works in the manner of chain reactions in which the blood organs enter.
This happens because the vascular receptors sense a change in pressure and transmit a signal about this to the human brain, which sends response impulses to the vascular centers. The consequence of this is an increase or decrease in the tone of the circulatory system (heart and blood vessels).
In addition, organs of neurohumoral regulation come into play. As a result of this reaction, the pressure returns to normal.
Ecosystem homeostasis
An example of homeostasis in the plant world is the maintenance of constant leaf moisture by opening and closing stomata.
Homeostasis is also characteristic of communities of living organisms of any degree of complexity; for example, the fact that a relatively stable composition of species and individuals is maintained within a biocenosis is a direct consequence of the action of homeostasis.
Population homeostasis
This type of homeostasis, such as population homeostasis (its other name is genetic) plays the role of a regulator of the integrity and stability of the genotypic composition of the population in a changing environment.
It acts through the preservation of heterozygosity, as well as by controlling the rhythm and direction of mutational changes.
This type of homeostasis allows a population to maintain an optimal genetic composition, which allows the community of living organisms to maintain maximum viability.
The role of homeostasis in society and ecology
The need to manage complex systems of a social, economic and cultural nature has led to the expansion of the term homeostasis and its application not only to biological, but also to social objects.
An example of the work of homeostatic social mechanisms is the following situation: if there is a lack of knowledge or skills or professional deficiency in a society, then through a feedback mechanism this fact forces the community to develop and improve itself.
And if there is an excess number of professionals who are not actually in demand by society, negative feedback will occur and there will be fewer representatives of unnecessary professions.
Recently, the concept of homeostasis has found wide application in ecology, due to the need to study the state of complex ecological systems and the biosphere as a whole.
In cybernetics, the term homeostasis is used to refer to any mechanism that has the ability to automatically self-regulate.
Links on the topic of homeostasis
Homeostasis on WikipediaAdmitted
All-Russian educational and methodological center
for continuing medical and pharmaceutical education
Ministry of Health of the Russian Federation
as a textbook for medical students
The main goal that runs through all the chapters of the textbook you are reading, colleague, is to form the idea of illness as a violation of homeostasis.
The ability of the body, despite the fairly frequent pathogenic effects of adverse harmful factors on the body, to maintain a stable state of health has been known since ancient times. Even Hippocrates knew that diseases can be cured by the natural forces of nature “vis medicas nature”. Now this phenomenon of the nature of living organisms is referred to as Homeostasis. Thus, the term homeostasis in its general form means the body’s resistance to harmful environmental influences.
Reactions ensuring homeostasis are aimed at maintaining a stable (constant) nonequilibrium state of the internal environment, i.e. known levels of condition by coordinating complex processes to eliminate or limit the action of harmful factors, to develop or maintain optimal forms of interaction between the body and the environment.
29.1. Reactivity
Changes in reactivity are aimed at counteracting the harmful influence of the environment and are mainly protective (adaptive), i.e. adaptive nature. Homeostasis is maintained at a new level of expression of resistance mechanisms.
Thus, the term reactivity in its general form denotes the mechanism of resistance (resistance) of the organism to harmful environmental influences, i.e. mechanism for maintaining homeostasis.
The general form of reactivity is biological (species) reactivity. It, in turn, is divided into group and individual reactivity.
Biological reactivity - changes in life activity of a protective-adaptive nature that arise under the influence of normal (adequate) environmental irritations for each type of animal. It is genetically fixed and aimed at preserving both the species (humans, birds, fish) as a whole and each individual individually. Charles Darwin: “The evolutionary mechanism of variability is purposeful (teleological) to increase survival.”
Examples: complex reflex activity of bees, seasonal migrations of birds, fish, seasonal changes in the life activity of animals (hibernation of gophers, bears, etc.).
Characterizing the fundamentals of the doctrine of homeostasis, the prominent Russian pathophysiologist I.D. Gorizontov wrote: “The phenomenon of homeostasis is essentially an evolutionarily developed, hereditarily fixed adaptation device of the body to normal environmental conditions.”
Altered reactivity occurs when the body is exposed to pathogenic environmental factors. It is generally characterized by:
- decreased adaptive reactions;
- but at the same time, during illness, an intensification of a number of reactions occurs to protect the body from this harmful factor and from the consequences of the damage caused by it (fever, sweating, increased blood pressure, production of antibodies, inflammation, etc.).
How, from the point of view of the doctrine of homeostasis, should the body behave in cases of exposure to environmental factors that go beyond the “norm”, that is, harmful? Restoration of the normal properties of the internal environment is the result of an increase in functional activity, either short-term (tachycardia, tachypnea, sweating) or long-term, for example, vicarious increase in the activity of the sweat glands in renal failure; (fever, production of killer T-lymphocytes); at the same time, a pathogenic onset can disrupt the coordination of the mechanisms of maintaining the constancy of the internal environment, which will be accompanied by a decrease in the adaptive reactions of the body.
Let us summarize our thoughts: homeostasis is a broader concept than reactivity. Various types of reactivity are a mechanism of homeostasis. This leads to a fundamental conclusion: homeostasis does not only mean maintaining constancy or optimal restoration and adaptation to environmental conditions. The disease itself, in its biological essence, also represents a problem of homeostasis, disruption of its mechanisms and recovery pathways. Disease is disturbed homeostasis.
So, it is advisable to study and know the “reactivity” section from the position of homeostasis. You will read about reactivity in the textbook by A.D. Ado and co-authors, and I will tell you further about homeostasis. At the same time, you must clearly understand that various types of reactivity can maintain homeostasis to certain limits and are the subject of traditional medicine being studied. In changed environmental conditions, the physiological mechanisms of homeostasis fail, environmental diseases arise (cancer, allergies, hereditary pathologies), a threat that can only be prevented from the standpoint of environmental medicine. Its goal is to identify a harmful environmental factor, develop measures for the prevention and treatment of its adverse effects at the population level.
29.2. Homeostasis, its mechanism and significance. Historical foundations of the doctrine of homeostasis
Almost 100 years ago, the outstanding French scientist Claude Bernard first raised the question of the meaning of homeostasis (although the term itself was introduced later by the American scientist W. Cannon). Being an irreconcilable opponent of vitalism (the spiritual impulse in the origin of life), C. Bernard adhered to materialistic views. In his opinion, all manifestations of life are caused by a conflict between the previous forces of the body (constitution) and the influence of the external environment.
Perhaps this is also where the eternity of the problem of “fathers and sons” lies, the conflict between the views, traditions of 25-35 years ago (the youth of fathers) and new views dictated by current life, which are easily absorbed by youth and critically perceived by fathers?
Returning to the concept of C. Bernard. The conflict itself between the constitution and the environment is revealed in the form of two types of phenomena: synthesis and decay. On the basis of these two opposing processes, the adaptation of organisms to environmental conditions or adaptation is created, which is a harmonious relationship between the organism and the environment.
29.2.1. Forms of life according to C. Bernard
K. Bernard believed that the influence of the external environment led to the formation of 3 forms of life:
- Latent - life does not appear outwardly, complete suppression of metabolism (cysts in worms, spores in plants, dry yeast);
- Oscillating - depending on the environment. This is typical for invertebrates and cold-blooded vertebrates (frogs, snakes), some species of warm-blooded animals that enter a state of hibernation (hibernation). At this time, they are little sensitive to oxygen starvation, injury, and infection. Currently, artificial cooling is also used in humans during complex heart operations. A prerequisite for a favorable exit from hibernation is the preliminary accumulation of nutrients in the body;
- Constant or free life - this form of life is characteristic of animals with a high organization, whose life does not stop even with sudden changes in environmental conditions. Therefore, these forms of life are evolutionarily more progressive, and have become dominant on Earth.
29.2.1.1. Two environments of the body
Organs and tissues function in approximately the same way, without significant changes in their level of activity. This happens due to the fact that the internal environment (blood, lymph, intercellular fluid) surrounding the organs and tissues does not change.
K. Bernard wrote that the body creates its own unchangeable environment, despite the changing conditions of the external environment. As a result, the body lives as if in a greenhouse, remaining free and independent.
Thus, every highly organized animal has two environments: external (ecological interactions), in which the organism is located, and internal, in which tissue elements live. To summarize, we can say that homeostasis, i.e. constancy of the internal environment is a condition for a free and independent life.
29.2.1.2. The importance of reserves in the body for homeostasis
The nutrition of the physiological mechanisms of homeostasis is not direct, but is carried out by spending reserves. We can say that we eat not what we just took, but what we ate before (yesterday). Consequently, the food taken must be assimilated, and then the body consumes it. The importance of reserves for homeostasis was later shown in the writings of Cannon. The body has reserves of carbohydrates (glycogen) and fats. Energy is stored in the form of ATP, GTP. The value of these energy reserves is extremely high, because stable disequilibrium as a unique feature of a biological system is possible only under the condition of constant energy costs.
Summing up the results of the work, C. Bernard wrote that in latent life a creature is completely subordinate to the influence of the external environment. In oscillating - it periodically depends on the environment. In constant life, a being appears to be free and its manifestations are formed and directed by internal life processes. However, this concept is not adequate to the independent “life principle” to which vitalists resort to explain the essence of life.
29.3. Further development of the doctrine of homeostasis
C. Bernard especially emphasized that the independence of manifestations of inner life is illusory. On the contrary, in the mechanisms of constant or free life, the relationship between the internal and external environment is the closest and most obvious.
At the same time, C. Bernard, relying on his doctrine of the constancy of the body’s reactions, believed that it was gaining independence from external vicissitudes and did not recognize the teachings of Charles Darwin. It is known that the great Englishman put the influence of the external environment on the body at the forefront of his teaching. The changed organisms, which acquired more advanced adaptation mechanisms, survived and adapted. Others were mercilessly destroyed by nature. The American physiologist Cannon reconciled these two opposing views.
Cannon Williams (1871-1945) is an outstanding physiologist of our century, the founder of the doctrine of homeostasis as self-regulation of the constancy of the internal environment of the body. The influence of this teaching was not limited to physiology and became fundamental for all medicine. The significance of the doctrine of homeostasis for pathophysiology, which studies the theoretical foundations of the disease, makes it necessary to dwell in more detail on this important milestone in the development of medical science. “The miracle of biology is the amazing ability of a living organism to maintain the constancy of its reactions. And this despite the fragility of the components that make it up.”
How did Cannon manage to combine experimental and evolutionary modes of thinking? He managed to do this based on the position of teleology - the expediency of all living things. He put forward the idea that maintaining a constant internal environment makes the body more resistant to changes in the external environment, i.e. preserves the survival of the body. Simply put, the evolutionarily acquired property of homeostasis in higher organisms allows them to quickly adapt to changes in the external environment.
Cannon views the organism as a whole as an active self-regulating system. The main object of self-regulation is the internal environment - blood, lymph, intercellular fluid.
The main mechanism of homeostasis is reactivity. Cannon considered the sympathetic-adrenal system to be the main engine. In the course of historical knowledge of the nature of the body, nervous and humoral factors turned into objects of special analysis. Phenomena that are inseparable in a living organism turned out to be artificially delimited.
29.4. The regulatory role of the nervous and endocrine (SAS, OSA) systems in maintaining the constancy of the internal environment, i.e. homeostasis
Cannon, in his book The Wisdom of the Body, discussed the role of the sympathetic nervous system in homeostasis. He considered the sympathetic department of the nervous system as the main factor in the urgent mobilization of the body's defenses to restore the disturbed balance. We can generally say that the speed of reaction (seconds) for emergency restructuring is ensured precisely by the nervous system.
L.A. Orbeli, our outstanding physiologist, established the adaptive-trophic role of the nervous system, the essence of which is that the sympathetic nervous system changes the functional readiness of organs in accordance with the conditions of existence of the organism. For example, irritation of the sympathetic nervous system restores the performance of tired skeletal muscles. In fact, he laid the foundations of the doctrine of doping. A major role in this case belongs to the reticular formation (network-like formation) of the brain stem - the central section of the SAS.
Hormonal influences are designed for a longer period of restructuring of the body (minutes, hours). Cannon connected “sympathetic” and “adrenal” with a hyphen, designed to reflect the concept of the systemic, unified nature of the functioning of a special, integral mechanism - the SAS, the purpose of which is to ensure homeostasis.
Further development of ideas about the occurrence of disease as a pathology of the body's regulatory systems is associated with the name of the Canadian physiologist Hans Selye, director of the Institute of Experimental Surgery and Medicine in Montreal, the author of one of the greatest discoveries in biology of the 20th century - the phenomenon of stress.
The development of medicine in the 19th century led to the idea that every disease must have its own cause.
For example, the characteristic syndrome of measles or diphtheria can be caused only by a specific organism (microorganism). But there are so few specific signs by which the diagnosis is made.
In contrast, G. Selye formed the concept of “disease syndrome in general.” He came to the idea of this during his student years. Much later, he put into this concept the nonspecificity of the monotonous reaction of the hypothalamus-pituitary-adrenal cortex system, which is noted under the action of any damaging agent.
He called this reaction “general adaptation syndrome” (GAS), aimed at maintaining homeostasis of the body. This is how G. Selye describes his ideas about OSA: “A person had to understand that in all cases when he was faced with a long or unusually difficult task - be it swimming in cold water, lifting heavy stones or fasting - he goes through 3 stages : at first he feels the difficulty, then he gets used to it, and finally he can no longer cope with it. He does not think of it as a general law regulating the behavior of animal beings in particularly stressful conditions. The urgent need to find food and shelter does not allow him. think about concepts like homeostasis (maintaining a constant internal environment) or biological stress."
G. Selye has shown that to various agents: surgical trauma, burns, pain, humiliation, intoxication, life circumstances of a business person, an athlete and many others, the body responds with a stereotypical form of biochemical, functional and structural changes. For a stress response, it is not important whether it is caused by a pleasant or unpleasant agent. The main thing here is the intensity of the demand for the body that the stress agent will create.
The mechanism of this nonspecific reaction is based on the excitation of the hypothalamic-hyphyseal-adrenal cortex system and the SAS. The emerging neuro-endocrine impulses contribute to the launch of the body's defenses. This contributes to a sharp increase in the homeostatic capabilities of the body. G. Selye's long-term studies have shown that in any disease, its specific manifestations are superimposed on nonspecific reactions caused by the hypothalamic-pituitary-adrenal cortex system. This is the reason for the widespread use of steroids in medical practice.
29.5. The role of biomembranes in the mechanisms of maintaining homeostasis
V. Cannon and K. Bernard considered the liquid part of the body, which includes blood, lymph, and interstitial fluid, to be the basis of the internal environment. However, blood does not come into direct contact with tissue cells. As first shown by domestic researcher L.S. Stern, between blood and tissue there are so-called histo-hematic barriers, the basis of which are biological membranes (BBB, hemato-ophthalmic, placental and other barriers).
In addition to the separation function, there is another important function of membranes in homeostasis - this is the receptor function of cell membranes. It plays a crucial role in providing feedback. Feedback means the influence of the output signal on the input - the control part of the system. Negative feedback leads to a decrease in the influence of the input influence on the magnitude of the output signal. For example, an increase in the blood concentration of thyroid hormones T 3 and T 4 leads to a decrease in the level of somatostatin in the hypothalamus and inhibition of the production of thyroid-stimulating hormone in the pituitary gland.
Positive feedback leads to an increase in the effect of the output signal. For example, the transition from acute to chronic inflammation occurs when the conformation and antigenic properties of one’s own proteins change - the formation of autoantigens. The latter cause increased formation of autoantibodies, and the immune conflict supports the inflammatory response. If negative feedback usually helps to restore the initial state, then positive feedback more often leads it away from this state. As a result, correction does not occur, which can cause a “vicious circle”, well known to pathophysiologists and clinicians (an example of the pathogenesis of chronic inflammation, autoallergies).
29.6. Homeostasis and norm
In one of his first works on homeostasis, Cannon reminds us that animals are open systems with many connections to their environment. These connections are made through the respiratory and digestive tracts, the surface of the skin, receptors, neuromuscular organs and bone levers. Environmental changes directly or indirectly affect these systems. However, these effects are usually not accompanied by large deviations from the norm and do not cause serious disturbances in physiological processes due to the fact that automatic regulation limits the fluctuations that occur in the body within the specified “norm” limits.
From the point of view of homeostasis, the most comprehensive definition of “normal” is given. The norm is a symbol for the stable imbalance of the body, its individual organs and tissues in the external environment. It can be seen that this definition takes into account individual characteristics. For example, a steady state may be with a systolic blood pressure of 120 mm Hg. (for one individual this is the norm) and with blood pressure 140 (for another this is also the norm). You can use the analogy of a sail and the rudder of a ship. Is there a normal position for them? No, because the norm is the change that ensures the movement of a given ship. For example, the reactions of the immune system under the influence of the “wind” of antigenic influences (R.V. Petrova).
This relative constancy could be designated by the term equilibration, used in the description of simple physicochemical processes. However, in a complex living organism, in addition to balancing processes, interaction and integrative cooperation of a number of organs and systems are usually included. So, for example, when conditions are created that change the composition of the blood or cause disturbances in respiratory functions (hemorrhage, pneumonia), the brain, nerves, heart, kidneys, lungs, spleen, etc. quickly react. To denote such phenomena, the term “equilibration” is insufficient, because it does not involve a complex and specific coordination process. For its fastest and most stable position, it is necessary to have counter-regulatory systems, the goal of which is the overall stability of the internal environment.
It was for these states and processes that ensure the stability of the body that Cannon proposed the term homeostasis. The word “homeo” does not indicate a fixed identity “the same,” but rather similarity, likeness.
Thus, homeostasis does not mean the simple constancy of the physicochemical properties of the internal environment. This term also includes physiological mechanisms that ensure the stability of living beings (i.e., reactivity processes). Homeostasis is the active self-regulation of the constancy of the internal environment.
29.7. Homeostasis and adaptation
Essentially, the phenomenon of adaptation is based on homeostasis. Those. the body adapts (adapts) to changing environmental conditions using certain homeostasis mechanisms.
Compensation is a hidden pathology revealed by functional load (aortic valve defect is compensated by myocardial hypertrophy. Its clinical manifestations are revealed by increased physical activity).
29.7.1. Types of adaptation
There are short-term and long-term adaptations:
- If there is a short-term departure from normal limits when exposed to environmental conditions, the body responds with a short-term change in functional activity (running causes tachycardia and tachypnea);
- With prolonged or repeated exposure, more permanent or even structural changes may occur:
- increased physical activity and muscle volume, hypertrophy of the pregnant uterus, bone structure due to malocclusion;
- When any organ is damaged, compensation mechanisms are activated. For example, vicarious (replacement, compensatory) connection of other body systems: blood loss causes tachycardia, tachypnea, blood leaving the depot, increased hematopoiesis).
In medical practice, adaptation means exactly that form of adaptation that will be created in the unusual conditions of the organism’s existence. It should be emphasized once again that any type of adaptation will be created on the basis of already existing homeostasis mechanisms.
29.8. Levels of regulation of homeostasis
From the point of view of homeostasis, the body is a self-regulating system. There are 3 levels of regulation:
- The lowest one determines the constancy of physiological constants and has autonomy (maintaining pH, P osm).
- Medium, determines adaptive reactions when the internal environment of the body changes. Regulated by the neuro-endocrine system.
- The highest determines adaptive reactions, conscious behavior in response to changes in the external environment. According to signals from the external world, the vegetative functions and conscious behavior of the body change. It is regulated by the central nervous system and its external part - the cerebral cortex.
I.P. Pavlov wrote: “The cerebral hemispheres are an organ of a living organism that is specialized to constantly carry out more and more perfect balancing of the organism with the external environment.”
The cerebral cortex is evolutionarily the youngest, but at the same time the most complex regulatory organ. This in no way means that the cerebral cortex constantly interferes with all processes of the body. Its goal, its task is to maintain the connection of the organism with the external environment, mainly social relations. This provides higher animals with a leading position in the animal world.
The great merit of the Russian physiologist I.P. Pavlov is the development of methods for studying free behavior and the intellectual sphere of the body. He substantiated the use of the method of conditioned reflexes for this purpose and showed that the conscious activity of the cerebral cortex is largely built on the principle of adaptive conditioned reflexes. I.P. Pavlov transformed the concept of a reflex from a true, automatic one, which underlies homeostasis, to a conditioned reflex, which determines the mechanisms of “vital encounters of the organism with the environment”, the basis of social homeostasis.
It is extremely important to understand that the evolution of animals is dictated not only by the desire to maintain the stability of a nonequilibrium state through homeostasis with true, automatic reflexes, it is continuously associated with the activity of free behavior (non-homeostatic higher nervous activity with conditioned reflexes), maintaining this imbalance as a distinctive feature of living systems.
Homeostasis, maintained automatically due to the activity of the SAS, opens up space for higher forms of nervous activity, freeing up the cerebral cortex for this. Those. Cannon showed that homeostatic mechanisms exist autonomously, independent of the control of consciousness, keeping it free for intellectual activity. Thus, freeing consciousness from the regulation of bodily processes, we, through the cerebral cortex, establish an intellectual relationship with the outside world, analyze experience, engage in science, technology and art, communicate with friends, raise children, express sympathy, etc. “In a word, we behave like human beings,” Cannon wrote.
In relation to this, the body, according to Cannon, turns out to be “wise” (the title of the book), since every second it maintains the stability of a large organism without the intervention of the mind, opening up spaces for free behavior.
Concluding the topic of the role of homeostasis in the study of the physiology of a sick organism, I would like to say that the main direction of your training at senior clinical departments and future medical activities should be the conscious restoration of the patient’s body’s ability to independently maintain homeostasis in an environmentally safe environment.
The body as an open self-regulating system.
A living organism is an open system that has a connection with the environment through the nervous, digestive, respiratory, excretory systems, etc.
In the process of metabolism with food, water, and gas exchange, various chemical compounds enter the body, which undergo changes in the body, enter the structure of the body, but do not remain permanently. Assimilated substances decompose, release energy, and decomposition products are removed into the external environment. The destroyed molecule is replaced by a new one, etc.
The body is an open, dynamic system. In a constantly changing environment, the body maintains a stable state for a certain time.
The concept of homeostasis. General patterns of homeostasis in living systems.
Homeostasis – the property of a living organism to maintain the relative dynamic constancy of its internal environment. Homeostasis is expressed in the relative constancy of the chemical composition, osmotic pressure, and the stability of basic physiological functions. Homeostasis is specific and determined by genotype.
Preservation of the integrity of the individual properties of the organism is one of the most general biological laws. This law is ensured in the vertical series of generations by reproduction mechanisms, and throughout the life of an individual by homeostasis mechanisms.
The phenomenon of homeostasis is an evolutionarily developed, hereditarily fixed adaptive property of the body to normal environmental conditions. However, these conditions may be outside the normal range for a short or long period of time. In such cases, adaptation phenomena are characterized not only by the restoration of the usual properties of the internal environment, but also by short-term changes in function (for example, an increase in the rhythm of cardiac activity and an increase in the frequency of respiratory movements with increased muscle work). Homeostasis reactions can be aimed at:
maintaining known levels of steady state;
elimination or limitation of harmful factors;
development or preservation of optimal forms of interaction between the organism and the environment in the changed conditions of its existence. All these processes determine adaptation.
Therefore, the concept of homeostasis means not only a certain constancy of various physiological constants of the body, but also includes processes of adaptation and coordination of physiological processes that ensure the unity of the body not only normally, but also under changing conditions of its existence.
The main components of homeostasis were identified by C. Bernard, and they can be divided into three groups:
A. Substances that provide cellular needs:
Substances necessary for energy production, growth and recovery - glucose, proteins, fats.
NaCl, Ca and other inorganic substances.
Oxygen.
Internal secretion.
B. Environmental factors affecting cellular activity:
Osmotic pressure.
Temperature.
Hydrogen ion concentration (pH).
B. Mechanisms ensuring structural and functional unity:
Heredity.
Regeneration.
Immunobiological reactivity.
The principle of biological regulation ensures the internal state of the organism (its content), as well as the relationship between the stages of ontogenesis and phylogenesis. This principle has proven to be widespread. During its study, cybernetics arose - the science of purposeful and optimal control of complex processes in living nature, in human society, and industry (Berg I.A., 1962).
A living organism is a complex controlled system where many variables of the external and internal environment interact. Common to all systems is the presence input variables, which, depending on the properties and laws of behavior of the system, are transformed into weekend variables (Fig. 10).
Rice. 10 - General scheme of homeostasis of living systems
Output variables depend on the input and laws of system behavior.
The influence of the output signal on the control part of the system is called feedback , which is of great importance in self-regulation (homeostatic reaction). Distinguish negative Andpositive feedback.
Negative feedback reduces the influence of the input signal on the output value according to the principle: “the more (at the output), the less (at the input).” It helps restore system homeostasis.
At positive feedback, the magnitude of the input signal increases according to the principle: “the more (at the output), the more (at the input).” It enhances the resulting deviation from the initial state, which leads to a disruption of homeostasis.
However, all types of self-regulation operate according to the same principle: self-deviation from the initial state, which serves as an incentive to turn on correction mechanisms. Thus, normal blood pH is 7.32 – 7.45. A pH shift of 0.1 leads to cardiac dysfunction. This principle was described by Anokhin P.K. in 1935 and called the feedback principle, which serves to carry out adaptive reactions.
General principle of the homeostatic response(Anokhin: “Theory of functional systems”):
deviation from the initial level → signal → activation of regulatory mechanisms based on the feedback principle → correction of the change (normalization).
So, during physical work, the concentration of CO 2 in the blood increases → pH shifts to the acidic side → the signal enters the respiratory center of the medulla oblongata → centrifugal nerves conduct an impulse to the intercostal muscles and breathing deepens → CO 2 in the blood decreases, pH is restored.
Mechanisms of regulation of homeostasis at the molecular genetic, cellular, organismal, population-species and biosphere levels.
Regulatory homeostatic mechanisms function at the gene, cellular and system (organismal, population-species and biosphere) levels.
Gene mechanisms homeostasis. All phenomena of homeostasis in the body are genetically determined. Already at the level of primary gene products there is a direct connection - “one structural gene - one polypeptide chain.” Moreover, there is a collinear correspondence between the nucleotide sequence of DNA and the amino acid sequence of the polypeptide chain. The hereditary program for the individual development of an organism provides for the formation of species-specific characteristics not in constant, but in changing environmental conditions, within the limits of a hereditarily determined reaction norm. The double helicity of DNA is essential in the processes of its replication and repair. Both are directly related to ensuring the stability of the functioning of the genetic material.
From a genetic point of view, one can distinguish between elementary and systemic manifestations of homeostasis. Examples of elementary manifestations of homeostasis include: gene control of thirteen blood coagulation factors, gene control of histocompatibility of tissues and organs, allowing transplantation.
The transplanted area is called transplant. The organism from which tissue is taken for transplantation is donor , and who is being transplanted - recipient . The success of transplantation depends on the body's immunological reactions. There are autotransplantation, syngeneic transplantation, allotransplantation and xenotransplantation.
Autotransplantation – tissue transplantation from the same organism. In this case, the proteins (antigens) of the transplant do not differ from those of the recipient. There is no immunological reaction.
Syngeneic transplantation carried out in identical twins who have the same genotype.
Allotransplantation – transplantation of tissues from one individual to another belonging to the same species. The donor and recipient differ in antigens, which is why higher animals experience long-term engraftment of tissues and organs.
Xenotransplantation – the donor and recipient belong to different types of organisms. This type of transplantation is successful in some invertebrates, but in higher animals such transplants do not take root.
During transplantation, the phenomenon is of great importance immunological tolerance (histocompatibility). Suppression of the immune system in the case of tissue transplantation (immunosuppression) is achieved by: suppression of the activity of the immune system, irradiation, administration of antilymphatic serum, adrenal hormones, chemicals - antidepressants (imuran). The main task is to suppress not just immunity, but transplantation immunity.
Transplant immunity determined by the genetic constitution of the donor and recipient. Genes responsible for the synthesis of antigens that cause a reaction to transplanted tissue are called tissue incompatibility genes.
In humans, the main genetic histocompatibility system is the HLA (Human Leukocyte Antigen) system. Antigens are quite fully represented on the surface of leukocytes and are detected using antisera. The structure of the system in humans and animals is the same. A common terminology has been adopted to describe genetic loci and alleles of the HLA system. Antigens are designated: HLA-A 1; HLA-A 2, etc. New antigens that have not been definitively identified are designated W (Work). Antigens of the HLA system are divided into 2 groups: SD and LD (Fig. 11).
Antigens of the SD group are determined by serological methods and are determined by the genes of 3 subloci of the HLA system: HLA-A; HLA-B; HLA-C.
Rice. 11 - HLA is the main genetic system of human histocompatibility
LD - antigens are controlled by the HLA-D sublocus of the sixth chromosome, and are determined by the method of mixed cultures of leukocytes.
Each of the genes that control human HLA antigens has a large number of alleles. Thus, the HLA-A sublocus controls 19 antigens; HLA-B – 20; HLA-C – 5 “working” antigens; HLA-D – 6. Thus, about 50 antigens have already been discovered in humans.
Antigenic polymorphism of the HLA system is the result of the origin of some from others and the close genetic connection between them. Identity of the donor and recipient by HLA antigens is necessary for transplantation. Transplantation of a kidney identical in 4 antigens of the system ensures a survival rate of 70%; 3 – 60%; 2 – 45%; 1 – 25% each.
There are special centers that conduct the selection of donor and recipient for transplantation, for example, in Holland - “Eurotransplant”. Typing based on HLA system antigens is also carried out in the Republic of Belarus.
Cellular mechanisms homeostasis are aimed at restoring tissue cells and organs in the event of a violation of their integrity. The set of processes aimed at restoring destroyed biological structures is called regeneration. This process is characteristic of all levels: renewal of proteins, components of cell organelles, entire organelles and the cells themselves. Restoring organ functions after injury or nerve rupture and wound healing are important for medicine from the point of view of mastering these processes.
Tissues, according to their regenerative ability, are divided into 3 groups:
Tissues and organs that are characterized by cellular regeneration (bones, loose connective tissue, hematopoietic system, endothelium, mesothelium, mucous membranes of the intestinal tract, respiratory tract and genitourinary system.
Tissues and organs that are characterized by cellular and intracellular regeneration (liver, kidneys, lungs, smooth and skeletal muscles, autonomic nervous system, endocrine, pancreas).
Fabrics that are characterized predominantly intracellular regeneration (myocardium) or exclusively intracellular regeneration (central nervous system ganglion cells). It covers the processes of restoration of macromolecules and cellular organelles by assembling elementary structures or by dividing them (mitochondria).
In the process of evolution, 2 types of regeneration were formed physiological and reparative .
Physiological regeneration - This is a natural process of restoration of body elements throughout life. For example, restoration of erythrocytes and leukocytes, replacement of skin epithelium, hair, replacement of milk teeth with permanent ones. These processes are influenced by external and internal factors.
Reparative regeneration – is the restoration of organs and tissues lost due to damage or injury. The process occurs after mechanical injuries, burns, chemical or radiation injuries, as well as as a result of illnesses and surgical operations.
Reparative regeneration is divided into typical (homomorphosis) and atypical (heteromorphosis). In the first case, an organ that was removed or destroyed regenerates, in the second, another develops in the place of the removed organ.
Atypical regeneration more common in invertebrates.
Hormones stimulate regeneration pituitary gland And thyroid gland . There are several methods of regeneration:
Epimorphosis or complete regeneration - restoration of the wound surface, completion of the part to the whole (for example, the regrowth of a tail in a lizard, limbs in a newt).
Morphollaxis – reconstruction of the remaining part of the organ into a whole, only smaller in size. This method is characterized by the reconstruction of a new one from the remains of an old one (for example, restoration of a limb in a cockroach).
Endomorphosis – restoration due to intracellular restructuring of tissue and organ. Due to the increase in the number of cells and their size, the mass of the organ approaches the original one.
In vertebrates, reparative regeneration occurs in the following form:
Full regeneration – restoration of the original tissue after its damage.
Regenerative hypertrophy , characteristic of internal organs. In this case, the wound surface heals with a scar, the removed area does not grow back and the shape of the organ is not restored. The mass of the remaining part of the organ increases due to an increase in the number of cells and their sizes and approaches the original value. This is how the liver, lungs, kidneys, adrenal glands, pancreas, salivary, and thyroid glands regenerate in mammals.
Intracellular compensatory hyperplasia cell ultrastructures. In this case, a scar is formed at the site of damage, and restoration of the original mass occurs due to an increase in the volume of cells, and not their number based on the proliferation (hyperplasia) of intracellular structures (nervous tissue).
Systemic mechanisms are provided by the interaction of regulatory systems: nervous, endocrine and immune .
Nervous regulation carried out and coordinated by the central nervous system. Nerve impulses entering cells and tissues not only cause excitement, but also regulate chemical processes and the exchange of biologically active substances. Currently, more than 50 neurohormones are known. Thus, the hypothalamus produces vasopressin, oxytocin, liberins and statins, which regulate the function of the pituitary gland. Examples of systemic manifestations of homeostasis are maintaining a constant temperature and blood pressure.
From the standpoint of homeostasis and adaptation, the nervous system is the main organizer of all body processes. The basis of adaptation is the balancing of organisms with environmental conditions, according to N.P. Pavlov, reflex processes lie. Between different levels of homeostatic regulation there is a private hierarchical subordination in the system of regulation of internal processes of the body (Fig. 12).
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cerebral cortex and parts of the brain |
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self-regulation based on feedback principle |
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peripheral neuroregulatory processes, local reflexes |
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Cellular and tissue levels of homeostasis |
Rice. 12. - Hierarchical subordination in the system of regulation of internal processes of the body.
The most primary level consists of homeostatic systems at the cellular and tissue levels. Above them are peripheral nervous regulatory processes such as local reflexes. Further in this hierarchy are systems of self-regulation of certain physiological functions with various “feedback” channels. The top of this pyramid is occupied by the cerebral cortex and the brain.
In a complex multicellular organism, both direct and feedback connections are carried out not only by nervous, but also by hormonal (endocrine) mechanisms. Each of the glands included in the endocrine system influences other organs of this system and, in turn, is influenced by the latter.
Endocrine mechanisms homeostasis according to B.M. Zavadsky, this is a mechanism of plus-minus interaction, i.e. balancing the functional activity of the gland with the concentration of the hormone. With a high concentration of the hormone (above normal), the activity of the gland is weakened and vice versa. This effect is carried out through the action of the hormone on the gland that produces it. In a number of glands, regulation is established through the hypothalamus and the anterior pituitary gland, especially during a stress reaction.
Endocrine glands can be divided into two groups according to their relation to the anterior lobe of the pituitary gland. The latter is considered central, and the other endocrine glands are considered peripheral. This division is based on the fact that the anterior lobe of the pituitary gland produces so-called tropic hormones, which activate some peripheral endocrine glands. In turn, the hormones of the peripheral endocrine glands act on the anterior lobe of the pituitary gland, inhibiting the secretion of tropic hormones.
The reactions that ensure homeostasis cannot be limited to any one endocrine gland, but involve all glands to one degree or another. The resulting reaction takes on a chain course and spreads to other effectors. The physiological significance of hormones lies in the regulation of other functions of the body, and therefore the chain nature should be expressed as much as possible.
Constant disturbances in the body's environment contribute to maintaining its homeostasis over a long life. If you create living conditions in which nothing causes significant changes in the internal environment, then the organism will be completely unarmed when it encounters the environment and will soon die.
The combination of nervous and endocrine regulatory mechanisms in the hypothalamus allows for complex homeostatic reactions associated with the regulation of the visceral function of the body. The nervous and endocrine systems are the unifying mechanism of homeostasis.
An example of a general response of nervous and humoral mechanisms is a state of stress that develops under unfavorable living conditions and there is a threat of disruption of homeostasis. Under stress, a change in the state of most systems is observed: muscular, respiratory, cardiovascular, digestive, sensory organs, blood pressure, blood composition. All these changes are a manifestation of individual homeostatic reactions aimed at increasing the body's resistance to unfavorable factors. The rapid mobilization of the body's forces acts as a protective reaction to stress.
With “somatic stress,” the problem of increasing the overall resistance of the body is solved according to the scheme shown in Figure 13.
Rice. 13 - Scheme for increasing the overall resistance of the body during
A biological system of any complexity, from subcellular structures of functional systems and the whole organism, is characterized by the ability to self-organize and self-regulate. The ability to self-organize is manifested by a variety of cells and organs in the presence of a general principle of elementary structure (membranes, organelles, etc.). Self-regulation is ensured by mechanisms inherent in the very essence of living things.
The human body consists of organs that, to perform their functions, are most often combined with others, thereby forming functional systems. For this, structures of any level of complexity, from molecules to the whole organism, require regulatory systems. These systems ensure the interaction of various structures already in a state of physiological rest. They are especially important in an active state when the body interacts with a changing external environment, since any changes require an adequate response from the body. In this case, one of the mandatory conditions for self-organization and self-regulation is the preservation of the constant conditions of the internal environment characteristic of the body, which is denoted by the concept of homeostasis.
Rhythm of physiological functions. Physiological processes of life, even under conditions of complete physiological rest, proceed with varying activity. Their strengthening or weakening occurs under the influence of a complex interaction of exogenous and endogenous factors, which is called “biological rhythms”. Moreover, the periodicity of fluctuations of various functions varies within extremely wide limits, ranging from a period of up to 0.5 hours up to multi-day and even multi-year periods.
Concept of homeostasis
The efficient functioning of biological processes requires certain conditions, most of which must be constant. And the more stable they are, the more reliably the biological system functions. These conditions must first of all include those that help maintain a normal level of metabolism. This requires the supply of initial metabolic ingredients and oxygen, as well as the removal of final metabolites. The efficiency of metabolic processes is ensured by a certain intensity of intracellular processes, determined primarily by the activity of enzymes. At the same time, enzymatic activity also depends on such seemingly external factors as, for example, temperature.
Stability in most conditions is necessary at any structural and functional level, starting from an individual biochemical reaction, cell, and ending with complex functional systems of the body. In real life, these conditions can often be violated. The appearance of changes is reflected in the state of biological objects and the flow of metabolic processes in them. In addition, the more complex the structure of a biological system, the greater deviations from standard conditions it can withstand without significant disruption of vital functions. This is due to the presence in the body of appropriate mechanisms aimed at eliminating the changes that have arisen. For example, the activity of enzymatic processes in a cell decreases by 2-3 times with every 10 °C decrease in temperature. At the same time, warm-blooded animals, due to the presence of thermoregulation mechanisms, maintain a constant internal temperature over a fairly wide range of changes in external temperature. As a result, the stability of this condition for the occurrence of enzymatic reactions at a constant level is maintained. And for example, a person who also has intelligence, having clothes and housing, can exist for a long time at an external temperature significantly below 0 ° C.
In the process of evolution, adaptive reactions were formed aimed at maintaining constant conditions of the organism’s external environment. They exist both at the level of individual biological processes and the entire organism. Each of these conditions is characterized by corresponding parameters. Therefore, systems for regulating the constancy of conditions control the constancy of these parameters. And if these parameters deviate from the norm for some reason, regulatory mechanisms ensure their return to the original level.
The universal property of a living thing to actively maintain the stability of body functions, despite external influences that can disrupt IT, is called homeostasis.
The state of a biological system at any structural and functional level depends on a complex of influences. This complex consists of the interaction of many factors, both external to it and those that are inside or formed as a result of processes occurring in it. The level of exposure to external factors is determined by the corresponding state of the environment: temperature, humidity, illumination, pressure, gas composition, magnetic fields, etc. However, the body can and should maintain the degree of influence of not all external and internal factors at a constant level. Evolution has selected those that are more necessary for the preservation of life, or those for the maintenance of which appropriate mechanisms have been found.
Homeostasis parameter constants They do not have clear constancy. Their deviations from the average level in one direction or another in a kind of “corridor” are also possible. Each parameter has its own limits of maximum possible deviations. They also differ in the time during which the body can withstand a violation of a specific homeostasis parameter without any serious consequences. At the same time, the mere deviation of a parameter beyond the “corridor” can cause the death of the corresponding structure - be it a cell or even an organism as a whole. So, normally the pH of the blood is about 7.4. But it can fluctuate between 6.8-7.8. The human body can withstand the extreme degree of deviation of this parameter without harmful consequences for only a few minutes. Another homeostatic parameter - body temperature - in some infectious diseases can increase to 40 ° C and above and remain at this level for many hours and even days. Thus, some body constants are quite stable - - hard constants others have a wider range of vibrations - plastic constants.
Changes in homeostasis can occur under the influence of any external factors, and can also be of endogenous origin: the intensification of metabolic processes tends to change the parameters of homeostasis. At the same time, activation of regulatory systems easily ensures their return to a stable level. But, if at rest in a healthy person these processes are balanced and the recovery mechanisms function with a reserve of power, then in the event of a sharp change in living conditions, during illnesses they turn on with maximum activity. The improvement of homeostasis regulation systems is also reflected in evolutionary development. Thus, the absence of a system for maintaining a constant body temperature in cold-blooded animals, causing the dependence of life processes on variable external temperature, sharply limited their evolutionary development. However, the presence of such a system in warm-blooded animals ensured their settlement throughout the planet and made such organisms truly free creatures with high evolutionary potential.
In turn, each person has individual functional capabilities of the homeostasis regulation systems themselves. This largely determines the severity of the body’s reaction to any influence, and ultimately affects life expectancy.
Cellular homeostasis . One of the unique parameters of homeostasis is the “genetic purity” of the cell populations of the body. The body's immune system monitors normal cell proliferation. If it is disrupted or the reading of genetic information is impaired, cells appear that are foreign to the given organism. The mentioned system destroys them. We can say that a similar mechanism also combats the entry of foreign cells (bacteria, worms) or their products into the body. And this is also ensured by the immune system (see section C - “Physiological characteristics of leukocytes”).
Mechanisms of homeostasis and their regulation
Systems that control the parameters of homeostasis consist of mechanisms of varying structural complexity: both relatively simple elements and rather complex neurohormonal complexes. Metabolites are considered one of the simplest mechanisms, some of which can locally influence the activity of enzymatic processes and various structural components of cells and tissues. More complex mechanisms (neuroendocrine) that carry out interorgan interaction are activated when simple ones are no longer enough to return the parameter to the required level.
Local autoregulation processes with negative feedback occur in the cell. For example, during intense muscular work, NEP suboxides and metabolic products accumulate in the skeletal muscles through a relative deficiency of 02. They shift the pH of sarcoplasm to the acidic side, which can cause the death of individual structures, the entire cell, or even the organism. When pH decreases, the conformational properties of cytoplasmic proteins and membrane complexes change. The latter causes a change in the pore radius, an increase in the permeability of membranes (partitions) of all subcellular structures, and a disruption of ion gradients.
The role of body fluids in homeostasis. The body's fluids are considered the central link in maintaining homeostasis. For most organs this is blood and lymph, and for the brain it is blood and cerebrospinal fluid (CSF). Blood plays a particularly important role. In addition, the liquid media for a cell are its cytoplasm and intercellular fluid.
Functions of liquid media The maintenance of homeostasis is quite varied. Firstly, liquid media provide metabolic processes with tissues. They not only bring substances necessary for life to cells, but also transport metabolites from them, which otherwise can accumulate in cells in high concentrations.
Secondly, liquid media have their own mechanisms necessary to maintain certain parameters of homeostasis. For example, buffer systems mitigate the shift in acid-base state when acids or bases enter the blood.
thirdly, liquid media take part in the organization of the homeostasis control system. There are also several mechanisms here. Thus, due to the transport of metabolites, distant organs and systems (kidneys, lungs, etc.) are involved in the process of maintaining homeostasis. In addition, metabolites contained in the blood, acting on the structures and receptors of other organs and systems, can trigger complex reflex responses and hormonal mechanisms. For example, thermoreceptors respond to “hot” or “cold” blood and accordingly change the activity of organs involved in the formation and transfer of heat.
Receptors are also located in the walls of blood vessels themselves. They participate in the regulation of the chemical composition of blood, its volume, and pressure. With irritation of vascular receptors, reflexes begin, the effector part of which is the organs and systems of the body. The great importance of blood in maintaining homeostasis became the basis for the formation of a special homeostasis system for many parameters of the blood itself and its volume. To preserve them, there are complex mechanisms that are included in a unified system for regulating the body’s homeostasis.
The above can be clearly illustrated using the example of intense muscle activity. During its execution, metabolic products in the form of lactic, pyruvic, acetoacetic and other acids are released from the muscles into the bloodstream. Acidic metabolites are first neutralized by alkaline blood reserves. In addition, they activate blood circulation and breathing through reflex mechanisms. Connecting these body systems, on the one hand, improves the supply of 02 to the muscles, and therefore reduces the formation of under-oxidized products; on the other hand, it helps to increase the release of CO2 through the lungs, many metabolites through the kidneys, and sweat glands.
The term “homeostasis” comes from the word “homeostasis”, which means “force of stability”. Many people don’t hear about this concept often, or even at all. However, homeostasis is an important part of our lives, harmonizing contradictory conditions among themselves. And this is not just a part of our life, homeostasis is an important function of our body.
If we define the word homeostasis, the meaning of which is the regulation of the most important systems, then this is the ability that coordinates various reactions, allowing us to maintain balance. This concept applies to both individual organisms and entire systems.
In general, homeostasis is often discussed in biology. In order for the body to function properly and perform the necessary actions, it is necessary to maintain a strict balance in it. This is necessary not only for survival, but also so that we can properly adapt to environmental changes and continue to develop.
It is possible to distinguish the types of homeostasis necessary for a full-fledged existence - or, more precisely, the types of situations when this action manifests itself.
- Instability. At this moment, we, namely our inner self, diagnose changes and, based on this, make decisions to adapt to new circumstances.
- Equilibrium. All our internal forces are aimed at maintaining balance.
- Unpredictability. We can often surprise ourselves by taking action we didn't expect.
All these reactions are determined by the fact that every organism on the planet wants to survive. The principle of homeostasis helps us understand the circumstances and make important decisions to maintain balance.
Unexpected decisions
Homeostasis has taken a strong place not only in biology. This term is also actively used in psychology. In psychology, the concept of homeostasis implies our response to external conditions. Nevertheless, this process closely links the adaptation of the body and individual mental adaptation.
As we see, the principle of homeostasis is based on a close connection between physiology and psychology. However, the principle of homeostasis associated with self-regulation cannot explain the sources of change.
The homeostatic process can be called the process of self-regulation. And this whole process occurs on a subconscious level. Our body has needs in many areas, but psychological contacts play an important role. Feeling the need to contact other organisms, a person shows his desire for development. This subconscious desire in turn reflects a homeostatic drive.
Imagine the situation: a group of deer is grazing not far from a sleeping lion. Suddenly the lion wakes up and roars, the fallow deer scatter. Now imagine yourself in the place of the doe. The instinct of self-preservation worked in her - she ran away. She must run very fast to save her life. This is psychological homeostasis.
But some time passes, and the doe begins to lose steam. Even though there might be a lion chasing after her, she would stop because the need to breathe was at the moment more important than the need to run. This is an instinct of the body itself, physiological homeostasis. Thus, the following types of homeostasis can be distinguished:
- Coercive.
- Spontaneous.
The importance of homeostasis is very important for any organism, both psychologically and physically. A person can learn to live in harmony with himself and the environment without following only the urges of instincts. He only needs to correctly see and understand the world around him, as well as sort out his thoughts, placing priorities in the right order. Author: Lyudmila Mukhacheva