Homeostasis is a process that takes place independently in the body and is aimed at stabilizing the state of human systems when internal conditions (changes in temperature, pressure) or external conditions (changes in climate, time zone) change. This name was proposed by the American physiologist Cannon. Subsequently, homeostasis began to be called the ability of any system (including the environment) to maintain its internal constancy.

The concept and characteristics of homeostasis

Wikipedia characterizes this term as the desire to survive, adapt and develop. In order for homeostasis to be correct, the coordinated work of all organs and systems is needed. In this case, all parameters in a person will be normal. If some parameter is not regulated in the body, this indicates a violation of homeostasis.

The main characteristics of homeostasis are as follows:

  • analysis of the possibilities of adapting the system to new conditions;
  • the desire to maintain balance;
  • the impossibility of predicting the results of the regulation of indicators in advance.

Feedback

Feedback is the actual mechanism of action of homeostasis. Thus the body reacts to any changes. The body functions continuously throughout a person's life. However individual systems should have time to rest and recover. During this period, the work of individual organs slows down or stops altogether. This process is called feedback. Its example is a break in the work of the stomach, when food does not enter it. Such a break in digestion provides a stop in the production of acid due to the action of hormones and nerve impulses.

There are two types of this mechanism, which will be described next.

negative feedback

This type of mechanism is based on the fact that the body reacts to changes, trying to direct them to opposite side. That is, it strives again for stability. For example, if carbon dioxide accumulates in the body, the lungs begin to work more actively, breathing quickens, due to which excess carbon dioxide is removed. And also it is thanks to the negative feedback that thermoregulation is carried out, due to which the body avoids overheating or hypothermia.

positive feedback

This mechanism is directly opposite to the previous one. In the case of its action, the change in the variable is only amplified by the mechanism, which brings the organism out of equilibrium. This is a rather rare and less desirable process. An example of this is the presence of electrical potential in nerves., which instead of decreasing the action, leads to its increase.

However, thanks to this mechanism, development and transition to new states occur, which means that it is also necessary for life.

What are the parameters of homeostasis?

Despite the fact that the body is constantly trying to maintain the values ​​of parameters important for life, they are not always stable. Body temperature will still change within a small range, as will heart rate or blood pressure. The task of homeostasis is to maintain this range of values, as well as help in the functioning of the body.

Examples of homeostasis are the excretion of waste products from the human body, carried out by the kidneys, sweat glands, gastrointestinal tract, as well as the dependence of metabolism on diet. A little more about the adjustable parameters will be discussed later.

Body temperature

The clearest and simplest example of homeostasis is the maintenance of normal body temperature. Overheating of the body can be avoided by sweating. normal temperature is a range of 36 to 37 degrees Celsius. An increase in these values ​​\u200b\u200bcan be triggered by inflammatory processes, hormonal and metabolic disorders, or any diseases.

The part of the brain called the hypothalamus is responsible for controlling body temperature in the body. Failure signals are sent there. temperature regime, which can also be expressed in rapid breathing, an increase in the amount of sugar, an unhealthy acceleration of metabolism. All this leads to lethargy, a decrease in the activity of the organs, after which the systems begin to take measures to regulate temperature indicators. A simple example The body's thermoregulatory response is sweating..

It is worth noting that this process also works with an excessive decrease in body temperature. So the body can warm itself due to the breakdown of fats, in which heat is released.

Water-salt balance

Water is necessary for the body, and everyone knows this well. There is even a norm of daily fluid intake, in the amount of 2 liters. In fact, each organism needs its own amount of water, and for some it may exceed the average value, while for others it may not reach it. However, no matter how much water a person drinks, the body will not accumulate all the excess fluid. Water will be kept for required level , while all the excess will be removed from the body due to osmoregulation carried out by the kidneys.

Blood homeostasis

In the same way, the amount of sugar, namely glucose, which is an important element of the blood, is regulated. A person cannot be completely healthy if the sugar level is far from normal. This indicator is regulated by the functioning of the pancreas and liver. In the case when the glucose level exceeds the norm, the pancreas acts, in which insulin and glucagon are produced. If the amount of sugar becomes too low, glycogen from the blood is processed into it with the help of the liver.

normal pressure

Homeostasis is also responsible for normal pressure blood in the body. If it is broken, signals about this will come from the heart to the brain. The brain reacts to the problem and, with the help of impulses, helps the heart to reduce high pressure.

The definition of homeostasis characterizes not only the correct functioning of the systems of one organism, but can also apply to entire populations. Depending on this, there are types of homeostasis described below.

Ecological homeostasis

This type is present in the provided necessary conditions community life. It arises through the action of a positive feedback mechanism, when organisms that begin to inhabit an ecosystem multiply rapidly, thereby increasing their numbers. But such a rapid settlement can lead to an even faster destruction of a new species in the event of an epidemic or a change in conditions to less favorable ones. So organisms need to adapt and stabilize, which is due to negative feedback. Thus, the number of inhabitants decreases, but they become more adapted.

Biological homeostasis

This type is just typical for individuals whose body strives to maintain internal balance, in particular, by regulating the composition and amount of blood, intercellular substance and other fluids necessary for the normal functioning of the body. At the same time, homeostasis does not always oblige to keep the parameters constant, sometimes it is achieved by adapting and adapting the body to changing conditions. Due to this difference, organisms are divided into two types:

  • conformational - those who strive to preserve values ​​(for example, warm-blooded animals, whose body temperature should be more or less constant);
  • regulatory, which adapt (cold-blooded, having a different temperature depending on the conditions).

At the same time, the homeostasis of each of the organisms is aimed at compensating for the costs. If warm-blooded animals do not change their lifestyle when the ambient temperature drops, then cold-blooded animals become lethargic and passive so as not to waste energy.

Besides, Biological homeostasis includes the following subspecies:

  • cellular homeostasis is aimed at changing the structure of the cytoplasm and the activity of enzymes, as well as the regeneration of tissues and organs;
  • homeostasis in the body is ensured by regulating temperature indicators, the concentration of substances necessary for life, and the removal of waste.

Other types

In addition to use in biology and medicine, the term has found application in other areas.

Maintenance of homeostasis

Homeostasis is maintained due to the presence in the body of so-called sensors that send impulses to the brain containing information about pressure and body temperature, water-salt balance, blood composition and other parameters important for normal life. As soon as some values ​​begin to deviate from the norm, a signal about this enters the brain, and the body begins to regulate its performance.

This complex adjustment mechanism incredibly important to life. The normal state of a person is maintained with the correct ratio of chemicals and elements in the body. Acids and alkalis are necessary for the stable functioning of the digestive system and other organs.

Calcium is a very important structural material, without the right amount of which a person will not have healthy bones and teeth. Oxygen is essential for breathing.

Toxins can interfere with the smooth functioning of the body. But so that health is not harmed, they are excreted due to the work of the urinary system.

Homeostasis works without any human effort. If the body is healthy, the body will self-regulate all processes. If people are hot, the blood vessels dilate, which is expressed in reddening of the skin. If it's cold - there is a shiver. Thanks to such responses of the body to stimuli, human health is maintained at the right level.

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    The term "homeostasis" is most commonly used in biology. For multicellular organisms to exist, it is necessary to maintain the constancy of the internal environment. Many ecologists are convinced that this principle also applies to the external environment. If the system is unable to restore its balance, it may eventually cease to function.

    Complex systems - for example, the human body - must have homeostasis in order to maintain stability and exist. These systems not only have to strive to survive, they also have to adapt to environmental changes and evolve.

    properties of homeostasis

    Homeostatic systems have the following properties:

    • instability system: tests how it can best adapt.
    • Striving for balance: all the internal, structural and functional organization of systems contributes to maintaining balance.
    • unpredictability: The resultant effect of a certain action can often be different from what was expected.
    • Regulation of the amount of micronutrients and water in the body - osmoregulation. Carried out in the kidneys.
    • Removal of waste products of the metabolic process - isolation. It is carried out by exocrine organs - kidneys, lungs, sweat glands and gastrointestinal tract.
    • Body temperature regulation. Lowering the temperature through sweating, a variety of thermoregulatory reactions.
    • Regulation of blood glucose levels. It is mainly carried out by the liver, insulin and glucagon secreted by the pancreas.
    • Regulation of the level of basic metabolism depending on the diet.

    It is important to note that although the body is in balance, its physiological state can be dynamic. Many organisms exhibit endogenous changes in the form of circadian, ultradian, and infradian rhythms. So, even while in homeostasis, body temperature, blood pressure, heart rate and most metabolic indicators are not always at a constant level, but change over time.

    Mechanisms of homeostasis: feedback

    When there is a change in variables, there are two main types of feedback that the system responds to:

    1. Negative feedback, expressed in a reaction in which the system responds in such a way as to change the direction of change to the opposite. Because Feedback serves to maintain the constancy of the system, it allows you to maintain homeostasis.
      • For example, when the concentration of carbon dioxide in the human body increases, the lungs receive a signal to increase their activity and exhale more carbon dioxide.
      • Thermoregulation is another example of negative feedback. When body temperature rises (or falls), thermoreceptors in the skin and hypothalamus register the change, triggering a signal from the brain. This signal, in turn, causes a response - a decrease in temperature (or increase).
    2. Positive feedback, which is expressed as an increase in the change in a variable. It has a destabilizing effect, so it does not lead to homeostasis. Positive feedback is less common in natural systems, but also has its uses.
      • For example, in nerves, a threshold electrical potential causes the generation of a much larger action potential. Blood clotting and birth events are other examples of positive feedback.

    Stable systems need combinations of both types of feedback. While negative feedback allows you to return to a homeostatic state, positive feedback is used to move to a completely new (and quite possibly less desirable) state of homeostasis, a situation called "metastability". Such catastrophic changes can occur, for example, with an increase in nutrients in rivers with clear water, which leads to a homeostatic state of high eutrophication (algae overgrowth of the channel) and turbidity.

    Ecological homeostasis

    In disturbed ecosystems, or sub-climax biological communities - like, for example, the island of Krakatau, after a strong volcanic eruption in - the state of homeostasis of the previous forest climax ecosystem was destroyed, like all life on this island. Krakatoa has gone through a chain of ecological changes in the years since the eruption, in which new plant and animal species replaced each other, which led to biodiversity and, as a result, a climax community. Ecological succession in Krakatoa took place in several stages. A complete chain of successions leading to a climax is called a preserie. In the example of Krakatau, this island developed a climax community with eight thousand different species recorded in , a hundred years after the eruption destroyed life on it. The data confirm that the position is maintained in homeostasis for some time, while the emergence of new species very quickly leads to the rapid disappearance of old ones.

    The case of Krakatoa and other disturbed or intact ecosystems shows that the initial colonization by pioneer species occurs through positive feedback reproduction strategies in which the species disperse, producing as many offspring as possible, but with little or no investment in the success of each individual. . In such species, there is a rapid development and an equally rapid collapse (for example, through an epidemic). As an ecosystem approaches climax, such species are replaced by more complex climax species that adapt through negative feedback to the specific conditions of their environment. These species are carefully controlled by the potential capacity of the ecosystem and follow a different strategy - the production of smaller offspring, in the reproductive success of which in the conditions of the microenvironment of its specific ecological niche, more energy is invested.

    Development begins with the pioneer community and ends with the climax community. This climax community is formed when flora and fauna come into balance with the local environment.

    Such ecosystems form heterarchies, in which homeostasis at one level contributes to homeostatic processes at another complex level. For example, the loss of leaves on a mature tropical tree makes room for new growth and enriches the soil. Equally tropical tree reduces the access of light to lower levels and helps prevent invasion by other species. But trees also fall to the ground and the development of the forest depends on permanent shift trees, nutrient cycling by bacteria, insects, fungi. Similarly, such forests contribute to ecological processes, such as the regulation of microclimates or ecosystem hydrological cycles, and several different ecosystems may interact to maintain river drainage homeostasis within a biological region. The variability of bioregions also plays a role in the homeostatic stability of a biological region, or biome.

    Biological homeostasis

    Homeostasis acts as a fundamental characteristic of living organisms and is understood as the maintenance internal environment within acceptable limits.

    The internal environment of the body includes body fluids - blood plasma, lymph, intercellular substance and cerebrospinal fluid. Maintaining the stability of these fluids is vital for organisms, while its absence leads to damage to the genetic material.

    With regard to any parameter, organisms are divided into conformational and regulatory. Regulatory organisms keep the parameter at a constant level, regardless of what happens in the environment. conformational organisms allow environment define a parameter. For example, warm-blooded animals maintain a constant body temperature, while cold-blooded animals exhibit a wide temperature range.

    We are not talking about the fact that conformational organisms do not have behavioral adaptations that allow them to regulate the given parameter to some extent. Reptiles, for example, often sit on heated rocks in the morning to raise their body temperature.

    The advantage of homeostatic regulation is that it allows the body to function more efficiently. For example, cold-blooded animals tend to become lethargic in cold temperatures, while warm-blooded animals are almost as active as ever. On the other hand, regulation requires energy. The reason why some snakes can only eat once a week is that they use much less energy to maintain homeostasis than mammals.

    Cellular homeostasis

    Regulation of the chemical activity of the cell is achieved through a number of processes, among which special meaning has a change in the structure of the cytoplasm itself, as well as the structure and activity of enzymes. Autoregulation depends on

    admitted
    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 goes through all the chapters of the textbook you read, colleague, is to form an idea of ​​the disease as a violation of homeostasis.

    The ability of the body, despite the fairly frequent pathogenic effects on the body of adverse harmful factors, to maintain steady state 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.

    The reactions that ensure homeostasis are aimed at maintaining a stable (constant) non-equilibrium state of the internal environment, i.e. known levels of state by coordinating complex processes to eliminate or limit the action of harmful factors, to develop or maintain optimal forms of interaction between the organism and the environment.

    29.1. Reactivity

    Changes in reactivity are aimed at counteracting the harmful effects of the environment and are mainly protective (adaptive), i.e. adaptive character. At the same time, homeostasis is maintained at a new level of manifestation of resistance mechanisms.

    Thus, the term reactivity in a general form means the mechanism of resistance (resistance) of an 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 the vital activity of a protective and adaptive nature, which arise under the influence of the usual (adequate) environmental stimuli for each type of animal. It is genetically fixed and is aimed at preserving both the species (human, bird, fish) as a whole, and each individual individually. C. 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 of animals (hibernation of gophers, bears, etc.).

    Giving a description of the fundamentals of the doctrine of homeostasis, a prominent domestic 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 under the action of pathogenic environmental factors on the body. It is generally characterized by:

    1. decrease in adaptive reactions;
    2. but at the same time, during the disease, there is also an increase in a number of reactions 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? The 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, a vicarious increase in the activity of the sweat glands in kidney failure; (fever, production of T-lymphocytes-killers); at the same time, the pathogenic principle can disrupt the coordination of the mechanisms for maintaining the constancy of the internal environment, which will be accompanied by a decrease in the body's adaptive reactions.

    Let's summarize our thoughts: homeostasis is a broader concept than reactivity. Various types of reactivity are the mechanism of homeostasis. This leads to a fundamental conclusion: homeostasis means not only the preservation of constancy or optimal recovery and adaptation to environmental conditions. The disease itself, in its biological essence, is also a problem of homeostasis, a violation of its mechanisms and ways of recovery. Disease is a disturbed homeostasis.

    So, it is advisable to study and know the "reactivity" section from the standpoint of homeostasis. You will read about reactivity in the textbook by A.D. Ado et al., 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 study of traditional medicine. Under changed environmental conditions, the physiological mechanisms of homeostasis cannot cope, environmental diseases arise (cancer, allergies, hereditary pathologies), the threat can only be prevented from the standpoint of environmental medicine. Its purpose is the identification of a harmful environmental factor, the development of 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. Kennon). Being an implacable opponent of vitalism (a spiritual first impulse in the origin of life), K. Bernard adhered to materialistic views. In his opinion, all manifestations of life are due to the conflict between the previous forces of the organism (the constitution) and the influence of the external environment.

    Maybe this is also the eternity of the problem of "fathers and children", the conflict between the views, traditions of 25-35 years ago (the youth of the fathers) and new views dictated by current life, which are easily absorbed by youth and critically perceived by fathers?

    Returning to the concept of K. Bernard. The very conflict between the constitution and the environment is revealed in the form of phenomena of two types: synthesis and decay. On the basis of these two opposite 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 K. Bernard

    K. Bernard believed that the impact of the external environment led to the formation of 3 forms of life:

    1. Latent - life does not appear outwardly, complete suppression of metabolism (cysts in worms, spores in plants, dry yeast);
    2. Oscillating - dependent on the environment. This is typical for invertebrates and cold-blooded vertebrates (frogs, snakes), some types of warm-blooded, falling into a state of hibernation (hibernation). At this time, they are not very sensitive to oxygen starvation, trauma, and infection. Currently, artificial cooling is also caused in humans during complex heart operations. A prerequisite for a favorable exit from hibernation is the preliminary accumulation of nutrients in the body;
    3. Permanent or free life - this form of life is typical for 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. The two environments of the body

    Organs and tissues function in approximately the same way, without a significant change in their level of activity. This happens due to the fact that the internal environment (blood, lymph, intercellular fluid) surrounding organs and tissues does not change.

    K. Bernard wrote that the body creates its own unchanging environment, despite the changing environmental conditions. As a result, the body lives as if in a greenhouse, remaining free and independent.

    Thus, each highly organized animal has two environments: external (ecological interactions), in which the organism is located, and internal, in which tissue elements live. Summarizing, we can say that homeostasis, i.e. the 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 do not eat what we just took, but what we ate before (yesterday). Therefore, 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. In the body there are reserves of carbohydrates (glycogen), fats. Energy is stored in the form of ATP, GTP. The value of these energy reserves is extremely high, because. sustainable 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, K. Bernard wrote that in latent life the being is entirely subject to the influence of the external environment. In oscillating - it periodically depends on the environment. In permanent life the being seems to be free and its manifestations are formed and directed by the inner life processes. However, this concept is not adequate to the independent "life principle" that vitalists resort to to explain the essence of life.

    29.3. Further development of the doctrine of homeostasis

    K. 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 relationships between the internal and external environment are the closest and most obvious.

    At the same time, K. Bernard, relying on his doctrine of the constancy of the body's reactions, believed that it acquires 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 head of his teaching. Changed organisms, having acquired more advanced mechanisms of adaptability, survived and adapted. Others were mercilessly destroyed by nature. These two opposing views were reconciled by the American physiologist Cannon.

    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 doctrine was not limited to physiology and became fundamental to all medicine. The significance of the doctrine of homeostasis for pathophysiology, which studies theoretical basis diseases, 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 is despite the fragility of the components that make it up."

    How did Cannon manage to combine experimental and evolutionary ways of thinking? He managed to do this, proceeding from the positions of teleology - the expediency of all living things. He put forward the idea that maintaining the constancy of the internal environment makes the body more resistant to changes in the external environment, i.e. maintains the survival of the organism. Simply put, the evolutionarily acquired property of homeostasis in higher organisms allows them to quickly adapt to changes in the external environment.

    Cannon sees 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 motor. In the course of historical knowledge of the nature of the organism, the nervous and humoral factors turned into objects special analysis. Phenomena that are inseparable in a living organism turned out to be artificially demarcated.

    29.4. The regulatory role of the nervous and endocrine (SAS, OAS) 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 disturbed balance. In general, it can be said that the speed of reaction (sec) for emergency restructuring is provided precisely by the nervous system.

    L.A. Orbeli, our outstanding physiologist, established the adaptive-trophic role of the nervous system, the essence of which lies in the fact that the sympathetic nervous system changes the functional readiness of organs in accordance with the conditions of the organism's existence. For example, irritation of the sympathetic nervous system restores the working capacity of tired skeletal muscles. In fact, he laid the foundations of the doctrine of doping. A large role in this belongs to the reticular formation (network formation) of the brain stem - the central section of the SAS.

    Hormonal influences are designed for a longer time of body restructuring (minutes, hours). Cannon connected "sympathetic" and "adrenal" with a hyphen, designed to reflect the concept of a systemic single nature of the functioning of a special, integral mechanism - SAS, the purpose of which is to ensure homeostasis.

    Further development of ideas about the origin of the 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 notion that every disease must have its own cause.

    For example, the characteristic syndrome of measles or diphtheria may be due only to a specific organism (microorganism). But there are so few specific signs by which a diagnosis is made.

    In contrast, G. Selye formed the concept of "disease syndrome in general." He came to the idea of ​​this in his student years. Much later, he invested in this concept the nonspecificity of the monotonous reaction of the hypothalamus-hypophansis-adrenal cortex system, which is noted under the action of any damaging agent.

    This reaction was called by him "general adaptation syndrome" (GAS), aimed at maintaining the body's homeostasis. Here is how G. Selye describes his ideas about OAS: "A person had to understand that in all cases when he was faced with a long or unusually difficult task - whether it was swimming in cold water, lifting heavy stones or starvation - 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 especially 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 showed that the body responds to various agents: surgical trauma, burns, pain, humiliation, intoxication, life circumstances of a business person, athlete and many others with a stereotyped form of biochemical, functional and structural changes. For a stress reaction, it is immaterial whether it is caused by a pleasant or unpleasant agent. The main thing here is the intensity of the demand for the body, which will create a stress agent.

    The mechanism of this non-specific reaction is based on the excitation of the hypothalamus-hyophysis-adrenal cortex and 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 non-specific reactions caused by the hypothalamus-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 to be the basis of the internal environment, which includes blood, lymph, and interstitial fluid. However, blood does not come into direct contact with tissue cells. As shown for the first time by Russian researcher L.S. Stern, between blood and tissue there are so-called histo-hematic barriers, which are based on biological membranes (BBB, hemato-ophthalmic, placental, and other barriers).

    In addition to separating, there is another important function of membranes in homeostasis - this is the receptor function of cell membranes. It plays a crucial role in the implementation of 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 action on the value of the output signal. For example, an increase in the concentration of thyroid hormones T 3 and T 4 in the blood 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 action of the output signal. For example, the transition of acute inflammation to chronic occurs when the conformation and antigenic properties of its own proteins change - the formation of autoantigens. The latter cause an increase in the formation of autoantibodies, and the immune conflict supports the inflammatory response. If negative feedback usually contributes to the restoration of the initial state, then positive feedback more often leads it away from this state. As a result, there is no correction, which can cause the emergence of a "vicious circle" well known to pathophysiologists and clinicians (an example of the pathogenesis of chronic inflammation, autoallergy).

    29.6. homeostasis and norm

    In one of his early works on homeostasis, Cannon recalls that animal beings are open systems with many connections to their environment. These connections are carried out through the respiratory and digestive tracts, the surface of the skin, receptors, neuromuscular organs and bone levers. Changes in the environment 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 "normal" limits.

    From the point of view of homeostasis, the most capacious definition of "norm" is given. The norm is a symbol for a 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, steady state may be at systolic blood pressure equal to 120 mm Hg. (for one individual this is the norm) and at BP 140 (for another this is also the norm). You can use the analogy with the sail and rudder of a ship. Is there a normal position for them? No, because norm is a 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 denoted by the term equilibration, which is used in the description of simple physical and chemical processes. However, in a complex living organism, in addition to balancing processes, interaction, integrative cooperation of a number of organs and systems is usually included. So, for example, when conditions are created that change the composition of the blood or cause violations of respiratory functions (hemorrhage, pneumonia), the brain, nerves, heart, kidneys, lungs, spleen, etc. quickly react. To designate such phenomena, the term "balancing" is insufficient, because it does not include a complex and specific coordination process. For its fastest and most stable position, the presence of counter-regulatory systems is necessary, the purpose 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 point to a fixed identity "the same", but to similarity, likeness.

    Thus, homeostasis does not mean mere constancy physical and chemical properties 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

    In essence, the phenomenon of adaptation is based on the basis of homeostasis. Those. the body adapts (adapts) to changing environmental conditions, using certain mechanisms of homeostasis.

    Compensation is a latent pathology revealed by functional load (aortic valve defect is compensated by myocardial hypertrophy. Its clinical manifestations are revealed by increased physical load).

    29.7.1. Types of adaptation

    Distinguish between short-term and long-term adaptation:

    1. With a short-term departure from the norm when exposed to environmental conditions, the body responds with a short-term change in functional activity (running causes tachycardia and tachypnea);
    2. With prolonged or repeated exposure, more permanent or even structural changes may occur:
      1. increased exercise stress and volume of muscles, hypertrophy of the pregnant uterus, structures bone tissue with an incorrect bite;
      2. 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 exit from the depot, increased hematopoiesis).

    In medical practice, adaptation means exactly the form of adaptation that will be created in the unusual conditions of the organism's existence. It should be emphasized again that any kind of adaptation will be created on the basis of already existing mechanisms of homeostasis.

    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:

    1. The lowest one determines the constancy of physiological constants and has autonomy (maintaining pH, P osm).
    2. Medium, determines adaptive reactions when the internal environment of the body changes. Regulated by the neuro-endocrine system.
    3. Higher, determines adaptive reactions, conscious behavior in case of changes in the external environment. According to the signals of the external world, the vegetative functions and conscious behavior of the organism change. It is regulated by the central nervous system and its external department - the cerebral cortex.

    IP Pavlov wrote: "The large hemispheres are an organ of a living organism, which 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 in all body processes. Its goal, its task is to maintain the connection of the organism with the external environment, mainly social relations. This provides the higher animals with a leading position in the animal kingdom.

    The great merit of the Russian physiologist I.P. Pavlov is the development of methods for studying free behavior, 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 based on the principle of adaptive conditioned reflexes. IP Pavlov carried out the transformation of the concept of a reflex from a true, automatic, underlying homeostasis, to a conditional reflex, which determines the mechanisms of "life 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 non-equilibrium state due to homeostasis with true, automatic reflexes, it is continuously associated with the activity of free behavior (non-homeostatic higher nervous activity with conditioned reflexes) that maintains this disequilibrium as a hallmark of living systems.

    Homeostasis, maintained automatically due to the activity of the SAS, opens up scope for higher forms of nervous activity, releasing the cerebral cortex for this. Those. Cannon showed that homeostatic mechanisms exist autonomously, independent of mind control, 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" (title of the book), since it maintains stability every second. 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 diseased organism, I want to say that the main direction of your training at the clinical departments of senior courses and future medical activity should be the conscious restoration of the patient's body's ability to independently maintain homeostasis in an environmentally safe environment.

    Homeostasis, homeostasis (homeostasis; Greek homoios similar, the same + stasis state, immobility), is the relative dynamic constancy of the internal environment (blood, lymph, tissue fluid) and the stability of basic physiological functions (blood circulation, respiration, thermoregulation, metabolism and etc.) of the human and animal organisms. Regulatory mechanisms that maintain the physiological state or properties of cells, organs and systems of the whole organism at an optimal level are called homeostatic.

    As you know, a living cell is a mobile, self-regulating system. Its internal organization is supported by active processes aimed at limiting, preventing or eliminating shifts caused by various influences from the environment and the internal environment. The ability to return to the original state after a deviation from a certain average level, caused by one or another "disturbing" factor, is the main property of the cell. A multicellular organism is a holistic organization, the cellular elements of which are specialized to perform various functions. Interaction within the body is carried out by complex regulatory, coordinating and correlating mechanisms with

    participation of nervous, humoral, metabolic and other factors. Many individual mechanisms that regulate intra- and intercellular relationships, in some cases, have mutually opposite (antagonistic) effects that balance each other. This leads to the establishment of a mobile physiological background (physiological balance) in the body and allows the living system to maintain relative dynamic constancy, despite changes in the environment and shifts that occur during the life of the organism.

    The term "homeostasis" was proposed in 1929 by the physiologist W. Cannon, who believed that the physiological processes that maintain stability in the body are so complex and diverse that it is advisable to combine them under common name homeostasis. However, back in 1878, K. Bernard wrote that all life processes have only one goal - to maintain the constancy of living conditions in our internal environment. Similar statements are found in the works of many researchers of the 19th and the first half of the 20th century. (E. Pfluger, S. Richet, L.A. Fredericq, I.M. Sechenov, I.P. Pavlov, K.M. Bykov and others). Great importance to study the problem of homeostasis, the works of L.S. Stern (with collaborators), devoted to the role of barrier functions that regulate the composition and properties of the microenvironment of organs and tissues.

    The very concept of homeostasis does not correspond to the concept of a stable (non-fluctuating) balance in the body - the principle of balance is not applicable to

    complex physiological and biochemical

    processes in living systems. It is also wrong to oppose homeostasis to rhythmic fluctuations in the internal environment. Homeostasis in a broad sense covers the issues of cyclic and phase flow of reactions, compensation, regulation and self-regulation of physiological functions, the dynamics of the interdependence of nervous, humoral and other components of the regulatory process. The boundaries of homeostasis can be rigid and plastic, vary depending on individual age, gender, social, professional and other conditions.

    Of particular importance for the life of the organism is the constancy of the composition of the blood - the liquid basis of the body (fluid matrix), according to W. Cannon. The stability of its active reaction (pH), osmotic pressure, ratio of electrolytes (sodium, calcium, chlorine, magnesium, phosphorus), glucose content, number of formed elements, and so on are well known. So, for example, blood pH, as a rule, does not go beyond 7.35-7.47. Even severe disorders of acid-base metabolism with a pathology of acid accumulation in the tissue fluid, for example, in diabetic acidosis, have very little effect on the active reaction of the blood. Despite the fact that the osmotic pressure of blood and tissue fluid is subject to continuous fluctuations due to the constant supply of osmotically active products of interstitial metabolism, it remains certain level and changes only in some severe pathological conditions.

    Despite the fact that blood represents the general internal environment of the body, the cells of organs and tissues do not directly come into contact with it.

    In multicellular organisms, each organ has its own internal environment (microenvironment) corresponding to its structural and functional features, and the normal state of organs depends on chemical composition, physicochemical, biological and other properties of this microenvironment. Its homeostasis is determined by the functional state of histohematic barriers and their permeability in the directions of blood→tissue fluid, tissue fluid→blood.

    especially importance has a constancy of the internal environment for the activity of the central nervous system: even minor chemical and physico-chemical shifts that occur in the cerebrospinal fluid, glia and pericellular spaces can cause a sharp disruption in the course of life processes in individual neurons or in their ensembles. A complex homeostatic system, including various neurohumoral, biochemical, hemodynamic and other regulatory mechanisms, is the system for ensuring the optimal level of blood pressure. At the same time, the upper limit of the level of blood pressure is determined by the functionality of baroreceptors. vascular system body, and the lower limit - the body's needs for blood supply.

    The most perfect homeostatic mechanisms in the body of higher animals and humans include the processes of thermoregulation;

    Homeostasis is the ability human body adapt to changing conditions of the external and internal environment. Stable work of homeostasis processes guarantees a person a comfortable state of health in any situation, maintaining the constancy of vital signs of the body.

    Homeostasis from a biological and ecological point of view

    In homeostasis apply to any multicellular organisms. At the same time, ecologists often pay attention to the balance of the external environment. It is believed that this is the homeostasis of the ecosystem, which is also subject to change and is constantly rebuilt for further existence.

    If the balance in any system is disturbed and it is not able to restore it, then this leads to a complete cessation of functioning.

    Man is no exception, homeostatic mechanisms play essential role in daily life, and the permissible degree of change in the main indicators of the human body is very small. With unusual fluctuations in the external or internal environment, a malfunction in homeostasis can lead to fatal consequences.

    What is homeostasis and its types

    Every day a person is exposed to various environmental factors, but in order for the basic biological processes in the body to continue to work stably, their conditions must not change. It is in maintaining this stability that the main role of homeostasis lies.

    It is customary to distinguish three main types:

    1. Genetic.
    2. Physiological.
    3. Structural (regenerative or cellular).

    For a full-fledged existence, a person needs the work of all three types of homeostasis in a complex, if one of them fails, this leads to unpleasant consequences for health. Well-coordinated work of processes will allow you to ignore or endure the most common changes with minimal inconvenience and feel confident.

    This type of homeostasis is the ability to maintain a single genotype within one population. At the molecular-cellular level, a single genetic system is maintained, which carries a certain set of hereditary information.

    The mechanism allows individuals to interbreed, while maintaining the balance and uniformity of a conditionally closed group of people (population).

    Physiological homeostasis

    This type homeostasis is responsible for maintaining the main vital signs in an optimal state:

    The immune, endocrine and nervous systems are responsible for its proper functioning. In the event of an unexpected failure in the operation of one of the systems, this immediately affects the well-being of the whole organism, leads to a weakening of protective functions and the development of diseases.

    Cellular homeostasis (structural)

    This species is also called "regeneration", which probably best describes the functional features.

    The main forces of such homeostasis are aimed at restoring and healing damaged cells. internal organs human body. It is these mechanisms that, when working properly, allow the body to recover from illness or injury.

    The main mechanisms of homeostasis develop and evolve together with a person, better adapting to changes in the external environment.

    Functions of homeostasis

    In order to correctly understand the functions and properties of homeostasis, it is best to consider its action on specific examples.

    So, for example, when playing sports, human breathing and pulse quicken, which indicates the body's desire to maintain internal balance under changed environmental conditions.

    When moving to a country with a climate that is significantly different from the usual, for some time you can feel unwell. Depending on the general health of a person, the mechanisms of homeostasis allow you to adapt to new living conditions. For some, acclimatization is not felt and the internal balance quickly adjusts, someone has to wait a bit before the body adjusts its performance.

    In conditions of elevated temperature, a person becomes hot and sweating begins. This phenomenon is considered direct evidence of the functioning of self-regulation mechanisms.

    In many ways, the work of the main homeostatic functions depends on heredity, the genetic material transmitted from the older generation of the family.

    Based on the examples given, it is clearly possible to trace the main functions:

    • Energy.
    • Adaptive.
    • Reproductive.

    It is important to pay attention to the fact that in old age, as well as in infancy, the stable work of homeostasis requires special attention, due to the fact that the reaction of the main regulatory systems during these periods of life is slow.

    properties of homeostasis

    Knowing about the basic functions of self-regulation, it is also useful to understand what properties it has. Homeostasis is a complex interrelation of processes and reactions. Among the properties of homeostasis are:

    • Instability.
    • Striving for balance.
    • Unpredictability.

    Mechanisms are in constant change, testing conditions to choose best option adaptations to them. This is the property of instability.

    Balance is the main goal and property of any organism, it constantly strives for it, both structurally and functionally.

    In some cases, the reaction of the body to changes in the external or internal environment can become unexpected, lead to restructuring of vital important systems. The unpredictability of homeostasis can cause some discomfort, which does not indicate a further detrimental effect on the state of the body.

    How to improve the functioning of the mechanisms of the homeostatic system

    From the point of view of medicine, any disease is evidence of a malfunction in homeostasis. External and internal threats constantly affect the body, and only coherence in the work of the main systems will help to cope with them.

    The weakening of the immune system does not happen for no reason. modern medicine has a wide range of tools that can help a person maintain their health, regardless of what caused the failure.

    Changing weather conditions, stressful situations, injuries - all this can lead to the development of diseases of varying severity.

    In order for the functions of homeostasis to work correctly and as quickly as possible, it is necessary to monitor the general state of your health. To do this, you can consult a doctor for an examination to determine your vulnerabilities and choose a set of therapy to eliminate them. Regular diagnostics will help to better control the basic processes of life.

    In this case, it is important to independently follow simple recommendations:

    • Avoid stressful situations to protect nervous system from constant overvoltage.
    • Monitor your diet, do not overload yourself with heavy foods, avoid mindless starvation, which will allow digestive system easier to do your job.
    • Choose suitable vitamin complexes to reduce the impact of seasonal weather changes.

    A vigilant attitude towards one's own health will help the homeostatic processes to respond in a timely and correct manner to any changes.