The mechanism of regulation of homeostasis. The internal environment of the body. Homeostasis, its types. Mechanisms of regulation of homeostasis and vital functions of the body. Levels of neuroendocrine regulation

In biology, it is the maintenance of the constancy of the internal environment of the body.
Homeostasis is based on the body's sensitivity to the deviation of certain parameters (homeostatic constants) from a given value. Limits of permissible fluctuations of the homeostatic parameter ( homeostatic constant) can be wide or narrow. Narrow limits are: body temperature, blood pH, blood glucose. Wide limits are: blood pressure, body weight, the concentration of amino acids in the blood.
Special intraorganism receptors ( interoreceptors) respond to the deviation of homeostatic parameters from the given limits. Such interoreceptors are found inside the thalamus, hypothalamus, in vessels, and in organs. In response to the deviation of the parameters, they trigger restorative homeostatic reactions.

General mechanism of neuroendocrine homeostatic responses for internal regulation of homeostasis

The parameters of the homeostatic constant deviate, interoreceptors are excited, then the corresponding centers of the hypothalamus are excited, they stimulate the release of the corresponding liberins by the hypothalamus. In response to the action of liberins, hormones are released by the pituitary gland, and then, under their action, hormones of other endocrine glands are released. Hormones, released from the endocrine glands into the blood, change the metabolism and the mode of operation of organs and tissues. As a result, the established new mode of operation of organs and tissues shifts the changed parameters towards the previous set value and restores the value of the homeostatic constant. This is the general principle of restoring homeostatic constants when they deviate.

2. In these functional nerve centers, the deviation of these constants from the norm is determined. The deviation of the constants within the given limits is eliminated due to the regulatory capabilities of the functional centers themselves.

3. However, if any homeostatic constant deviates above or below acceptable limits, the functional centers transmit excitation higher: in "need centers" hypothalamus. This is necessary in order to switch from the internal neurohumoral regulation of homeostasis to the external - behavioral.

4. Excitation of one or another need center of the hypothalamus forms the corresponding functional state, which is subjectively experienced as a need for something: food, water, warmth, cold or sex. There is an activating and stimulating psycho-emotional state of dissatisfaction.

5. To organize purposeful behavior, it is necessary to choose only one of the needs as a priority and create a working dominant to satisfy it. It is believed that leading role this is played by the tonsils of the brain (Corpus amygdoloideum). It turns out that on the basis of one of the needs that the hypothalamus forms, the amygdala creates a leading motivation that organizes purposeful behavior to satisfy only this one chosen need.

6. The next stage can be considered the launch of a preparatory behavior, or drive reflex, which should increase the likelihood of launching an executive reflex in response to a trigger stimulus. The drive reflex prompts the body to create a situation in which there will be an increased likelihood of finding an object suitable for satisfying the current need. This may be, for example, moving to a place rich in food, or water, or sexual partners, depending on the leading need. When, in the achieved situation, a specific object is found that is suitable for satisfying this dominant need, then it launches an executive reflex behavior aimed at satisfying the need with the help of this particular object.

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Homeostasis Systems - A detailed educational resource on homeostasis.

In his book The Wisdom of the Body, he proposed the term as a name for "the coordinated physiological processes that maintain the body's most stable states." In the future, this term was extended to the ability to dynamically maintain the constancy of its internal state of any open system. However, the concept of the constancy of the internal environment was formulated as early as 1878 by the French scientist Claude Bernard.

General information

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 internal, structural and functional organization systems helps to maintain 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. Mainly carried out by the liver, insulin and glucagon secreted by the pancreas.

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, two main types are observed feedback to which the system responds:

1. Negative feedback, expressed as a reaction in which the system responds in such a way as to reverse the direction of change. Since the 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 are signaled 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 amplification of 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 - such as the island of Krakatoa, after strong eruption volcano 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, the 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 the constant change of trees, the cycle of nutrients carried out 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 maintaining the internal environment within acceptable limits.

Internal environment 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.

Homeostasis in the human body

Various factors affect the ability of body fluids to support life. Among them are parameters such as temperature, salinity, acidity and the concentration of nutrients - glucose, various ions, oxygen, and waste products - carbon dioxide and urine. Since these parameters affect the chemical reactions that keep an organism alive, there are built-in physiological mechanisms to keep them at the right level.

Homeostasis cannot be considered the cause of the processes of these unconscious adaptations. It should be taken as a general characteristic of many normal processes acting together, and not as their root cause. Moreover, there are many biological phenomena that do not fit this model - for example, anabolism.

Other areas

The concept of "homeostasis" is also used in other areas.

The actuary can talk about risk homeostasis, in which, for example, people who have non-stick brakes on their cars are not in a safer position than those who do not, because these people unconsciously compensate for a safer car by risky driving. This happens because some of the holding mechanisms - such as fear - stop working.

Sociologists and psychologists can talk about stress homeostasis- the desire of a population or individual to remain at a certain stress level, often artificially causing stress if the "natural" level of stress is not enough.

Examples

• thermoregulation
  • Skeletal muscle trembling may begin if too low temperature body.
  • Another type of thermogenesis involves the breakdown of fats to release heat.
  • Sweating cools the body through evaporation.
• Chemical regulation
  • The pancreas secretes insulin and glucagon to control blood glucose levels.
  • The lungs take in oxygen and release carbon dioxide.
  • The kidneys excrete urine and regulate the level of water and a number of ions in the body.

Many of these organs are controlled by hormones from the hypothalamic-pituitary system.

see also

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See what "Homeostasis" is in other dictionaries:

Homeostasis... Spelling Dictionary

homeostasis - General principle self-regulation of living organisms. Perls strongly emphasizes the importance of this concept in his work The Gestalt Approach and Eye Witness to Therapy. Brief explanatory psychological and psychiatric dictionary. Ed. igisheva. 2008 ... Great Psychological Encyclopedia

Homeostasis (from the Greek. similar, identical and state), the property of the body to maintain its parameters and physiological. functions in def. range, based on the stability of the internal. body environment in relation to perturbing influences ... Philosophical Encyclopedia

- (from the Greek homoios the same, similar and Greek stasis immobility, standing), homeostasis, the ability of an organism or system of organisms to maintain a stable (dynamic) balance in changing environmental conditions. Homeostasis in a population Ecological dictionary

Homeostasis (from homeo... and Greek stasis immobility, state), the ability of biol. systems to resist change and remain dynamic. refers to the constancy of the composition and properties. The term "G." proposed by W. Kennon in 1929 to characterize states ... Biological encyclopedic dictionary

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 influences on the body of adverse harmful factors, maintain a steady 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.

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 interactions between organism and 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. Different kinds reactivity is 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 body (constitution) and the influence 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 characteristic of animals with high organization, whose life does not stop even when abrupt changes 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. stable disequilibrium as a unique feature biological system 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 emphasized that the independence of manifestations 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, 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 - amazing ability 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 have become objects of 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, analyzed 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 the 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 fasting - he goes through 3 stages: 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 governing the behavior of animal beings under particularly stressful conditions. The urgent need to find food and shelter prevents him from thinking about concepts such as 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 the dividing one, there is one more important function membranes in homeostasis 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 " vicious circle", well known to pathophysiologists and clinicians (an example of the pathogenesis of chronic inflammation, autoallergpi).

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. Norma is symbol stable disequilibrium of the organism, 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 muscle volume, hypertrophy of the pregnant uterus, bone structure with malocclusion;
   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 purpose, 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" (the title of the book), since every second it maintains the stability of a large organism without the intervention of the mind, opening up scope 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.

Positive feedback contributes to the birth of a child. At the very beginning of labor, uterine contractions are relatively weak and rare. As the intensity increases various processes during childbirth, their strength and frequency gradually increase. However, after the baby is born, the contractions stop immediately.

In our life, various kinds of changes are constantly taking place, including biological ones. Trillions of our cells provide their own vital activity, thereby supporting the normal functioning of the whole organism. To do this, they constantly use the necessary nutrients and oxygen and get rid of waste products. In other words, each cell of the body is, as it were, an island, the population of which extracts what it needs from the surrounding waters and dumps waste into them. These "waters" - extracellular fluid - consist of a component of blood plasma and a thin layer of fluid that bathes each cell. Together, these components form what physiologists call the internal environment of the body.

Since cells get rid of some substances and produce others, the composition of the extracellular fluid is not constant. Such incessant changes are potentially dangerous: without mechanisms that prevent abrupt shifts, imbalances, the cell would die from a lack of necessary substances or from its overflow with waste products.

Equally important to our survival are the mechanisms that compensate for changes in temperature and other environmental factors. In fact, our organ systems are constantly adapting to maintain the necessary chemical balance in the internal environment of the body. This dynamic balance is called homeostasis. Through feedback mechanisms that provide constant updates to the brain and other organs, our body controls changing conditions and adapts to them in order to continue life.

The negative feedback mechanism is involved in the regulation blood pressure. When it rises above normal values, this is recorded by receptors (baroreceptors) located in some vessels and transmit information to the vascular center of the brain. As a result, the heart rate slows down and the arterioles expand. If the receptors detect a pressure drop, these parameters change in the opposite direction.

FEEDBACK MECHANISM

The feedback mechanism is widely used in the management of homeostasis. With its help, control centers such as the brain receive information about various changes and ensure that the body adapts to them.

The regulation of blood sugar levels, heart rate and many other body functions occurs through a negative feedback mechanism. In this case, a change in some indicator, such as blood pressure, leads to the fact that the activity of the whole organism is aimed at returning it to normal. The feedback mechanism is often compared to a home thermostat. The sensor registers the temperature drop below the set level and transmits this information to the control device, which turns on the heating system to achieve the desired temperature level.

Some functions are regulated by a positive feedback mechanism. At the same time, the ongoing processes, as it were, spur themselves on until some other event leads to their termination. An example of positive feedback is the process of labor, which culminates in the birth of a child.

Among the properties inherent in living beings, homeostasis is mentioned. This concept is called the relative constancy characteristic of the organism. It is worth understanding in detail why homeostasis is needed, what it is, and how it manifests itself.

Homeostasis is the property of a living organism that allows it to maintain important characteristics within allowable norms. For normal functioning, the constancy of the internal environment and individual indicators is necessary.

External influence and adverse factors lead to changes that affect general condition. But the body is able to recover on its own, returning its characteristics to optimal performance. This is due to the property in question.

Considering the concept of homeostasis and finding out what it is, it is necessary to determine how this property is implemented. The easiest way to understand this is on the example of cells. Each is a system that is characterized by mobility. Under the influence of certain circumstances, its features may change.

For normal life, a cell must have those properties that are optimal for its existence. If the indicators deviate from the norm, viability decreases. To prevent death, all properties must return to their original state.

This is what homeostasis is all about. It neutralizes any changes that have arisen as a result of exposure to the cell.

Definition

Let's give a definition of what this property of a living organism is. Initially, this term was called the ability to maintain the constancy of the internal environment. Scientists assumed that this process affects only the intercellular fluid, blood and lymph.

It is their constancy that allows you to maintain the body in a stable state. But later it was found that this ability is inherent in any open system.

The definition of homeostasis has changed. Now this is the name of the self-regulation of an open system, which consists in maintaining a dynamic balance through the implementation of coordinated reactions. Thanks to them, the system keeps relatively constant the parameters necessary for normal life.

This term began to be used not only in biology. It has found application in sociology, psychology, medicine and other sciences. Each of them has its own interpretation of this concept, but they have a common essence - constancy.

Characteristics

To understand what exactly is called homeostasis, you should find out what are the characteristics of this process.

The phenomenon has such features as:

1. Striving for balance. All parameters of an open system must be consistent with each other.
2. Identification of opportunities for adaptation. Before the parameters are changed, the system must establish whether it is possible to adapt to the changed living conditions. This happens through analysis.
3. Unpredictability of results. Regulation of indicators does not always lead to positive changes.

The phenomenon under consideration is a complex process, the implementation of which depends on various circumstances. Its flow is due to the properties of an open system and the peculiarities of the conditions of its functioning.

Application in biology

This term is used not only in relation to living beings. It is used in different areas. To better understand what homeostasis is, you need to find out what biologists mean by it, since it is in this area that it is most often used.

This science attributes this property to all beings without exception, regardless of their structure. It is characterized by unicellular and multicellular. In unicellular organisms, it manifests itself in maintaining the constancy of the internal environment.

In organisms with a more complex structure, this feature concerns individual cells, tissues, organs and systems. Among the parameters that should be constant are body temperature, blood composition, enzyme content.

In biology, homeostasis is not only the preservation of constancy, but also the ability of an organism to adapt to changing environmental conditions.

Biologists distinguish between two types of creatures:

1. Conformational, in which organismal indicators are preserved, regardless of conditions. These include warm-blooded animals.
2. Regulatory, reacting to changes in the external environment and adapting to them. These are the amphibians.

With violations in this area, recovery or adaptation is not observed. The body becomes vulnerable and may die.

How does a person

The human body consists of a large number of cells that are interconnected and form tissues, organs, and organ systems. Due to external influences in each system and organ, changes can occur that entail changes throughout the body.

But for normal functioning, the body must retain optimal features. Accordingly, after any impact, he needs to return to his original state. This is due to homeostasis.

This property affects settings such as:

• temperature,
• nutrient content,
• acidity,
• blood composition,
• waste disposal.

All these parameters affect the state of the person as a whole. They depend on the normal course chemical reactions contributing to the preservation of life. Homeostasis allows you to restore the previous performance after any impact, but is not the cause of adaptive reactions. This property is general characteristics a large number processes running at the same time.

For blood

Blood homeostasis is one of the main characteristics that affect the viability of a living being. Blood is its liquid base, as it is found in every tissue and every organ.

Thanks to it, the supply separate parts body with oxygen, and an outflow of harmful substances and metabolic products is produced.

If there are disturbances in the blood, then the performance of these processes worsens, which affects the functioning of organs and systems. All other functions depend on the constancy of its composition.

This substance must keep the following parameters relatively constant:

• acidity level;
• osmotic pressure;
• plasma electrolyte ratio;
• the amount of glucose;
• cellular composition.

Due to the ability to maintain these indicators within the normal range, they do not change even under the influence of pathological processes. Minor fluctuations are inherent in them, and this does not harm. But they rarely exceed normal values.

This is interesting! If violations occur in this area, then the blood parameters do not return to their original position. This indicates the presence serious problems. The body is unable to maintain balance. As a result, there is a risk of complications.

Use in medicine

This concept is widely used in medicine. In this area, its essence is almost analogous to biological meaning. This term in medical science covers compensatory processes and the body's ability to self-regulate.

This concept includes the relationships and interactions of all components involved in the implementation of the regulatory function. It covers metabolic processes, respiration, blood circulation.

The difference in the medical term lies in the fact that science considers homeostasis as an auxiliary factor in treatment. In diseases, bodily functions are impaired due to damage to organs. This affects the whole body. It is possible to restore the activity of the problematic organ with the help of therapy. The considered ability contributes to the increase of its effectiveness. Thanks to the procedures, the body itself directs efforts to eliminate pathological phenomena, trying to restore normal parameters.

In the absence of opportunities for this, the adaptation mechanism is activated, which manifests itself in reducing the load on the damaged organ. This allows you to reduce damage and prevent the active progression of the disease. It can be said that such a concept as homeostasis is considered in medicine from a practical point of view.

Wikipedia

The meaning of any term or the characteristic of any phenomenon is most often learned from Wikipedia. She considers this concept in sufficient detail, but in the simplest sense: she calls it the body's desire for adaptation, development and survival.

This approach is explained by the fact that in the absence of given property it will be difficult for a living being to adapt to changing environmental conditions and develop in the right direction.

And if there are violations in the functioning of the creature, it will simply die, because it will not be able to return to its normal state.

Important! In order for the process to be carried out, it is necessary that all organs and systems work smoothly. This will ensure that all vital parameters remain within normal limits. If separate indicator not amenable to regulation, this indicates problems with the implementation of this process.

Examples

Examples of this phenomenon will help to understand what homeostasis is in the body. One of them is to maintain a constant body temperature. Some changes are inherent in it, but they are minor. A serious increase in temperature is observed only in the presence of diseases. Another example is blood pressure. A significant increase or decrease in indicators occurs with health disorders. In this case, the body seeks to return to normal characteristics.

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Summing up

The studied property is one of the key ones for normal functioning and life preservation, it is the ability to restore optimal indicators of vital parameters. Changes in them can occur under the influence of external influences or pathologies. Thanks to this ability, living beings can resist external factors.