Homeostasis is any self-regulating process by which biological systems strive to maintain internal stability by adapting to optimal conditions for survival. If homeostasis is successful, then life goes on; otherwise, disaster or death will occur. The achieved stability is in fact a dynamic equilibrium in which continuous changes occur, but relatively homogeneous conditions prevail.

Features and role of homeostasis

Any system in dynamic equilibrium desires to reach a steady state, a balance that opposes external changes. When such a system is disturbed, the built-in regulatory devices react to deviations in order to establish a new balance. Such a process is one of the elements of feedback control. Examples of homeostatic regulation are all processes of integration and coordination of functions mediated by electrical circuits and nervous or hormonal systems.

Another example of homeostatic regulation in mechanical system is the action of the regulator room temperature or thermostat. The heart of the thermostat is a bimetallic strip that reacts to temperature changes by shutting down or breaking electrical circuit. When the room cools down, the circuit is completed and the heating is turned on, and the temperature rises. At the set level, the circuit is interrupted, the oven stops and the temperature drops.

However, biological systems, which are of great complexity, have regulators that are difficult to compare with mechanical devices.

As noted earlier, the term homeostasis refers to the maintenance of the internal environment of the body within narrow and tightly controlled limits. The main functions important for maintaining homeostasis are fluid and electrolyte balance, acid regulation, thermoregulation, and metabolic control.

Body temperature control in humans is considered great example homeostasis in a biological system. The normal human body temperature is around 37°C, but various factors can affect this, including hormones, metabolic rate, and illnesses that lead to excessively high or low temperatures. Body temperature regulation is controlled by an area of ​​the brain called the hypothalamus.

Feedback about body temperature is carried through the bloodstream to the brain and results in compensatory adjustments in breathing rate, blood sugar levels, and metabolic rate. Heat loss in humans is mediated by reduced activity, sweating, and heat transfer mechanisms that allow more blood to circulate near the surface of the skin.

Heat loss is reduced through insulation, reduced circulation on the skin, and cultural changes such as the use of clothing, housing, and third-party heat sources. The range between high and low levels of body temperature constitutes the homeostatic plateau - the "normal" range that sustains life. As either of the two extremes is approached, corrective action (via negative feedback) brings the system back into the normal range.

The concept of homeostasis also applies to environmental conditions. First proposed by the American ecologist Robert MacArthur in 1955, the idea that homeostasis is the product of a combination of biodiversity and the many ecological interactions that occur between species.

Such an assumption was considered a concept that could help explain the sustainability of an ecological system, that is, its persistence as a specific type of ecosystem over time. Since then, the concept has changed somewhat, and included the non-living component of the ecosystem. The term has been used by many ecologists to describe the reciprocity that occurs between the living and non-living components of an ecosystem to maintain the status quo.

The Gaia hypothesis is a model of the Earth proposed by the English scientist James Lovelock, which considers various living and non-living components as components of a larger system or single organism, suggesting that the collective efforts of individual organisms contribute to homeostasis at the planetary level.

Cellular homeostasis

Depend on the environment of the body to stay alive and function properly. Homeostasis maintains the body's environment under control and maintains favorable conditions for cellular processes. Without the right body conditions, certain processes (eg osmosis) and proteins (eg enzymes) will not function properly.

Why is homeostasis important for cells? Living cells depend on movement chemical substances Around them. Chemicals such as oxygen, carbon dioxide, and dissolved food need to be transported in and out of cells. This is carried out by the processes of diffusion and osmosis, which depend on the balance of water and salt in the body, which are maintained by homeostasis.

Cells depend on enzymes to speed up many of the chemical reactions that keep cells alive and functioning. These enzymes work best at certain temperatures and so again homeostasis is vital for cells as it maintains a constant body temperature.

Examples and mechanisms of homeostasis

Here are some basic examples of homeostasis in the human body, as well as the mechanisms that support them:

Body temperature

The most common example of homeostasis in humans is the regulation of body temperature. The normal body temperature, as we wrote above, is 37 ° C. The temperature is higher or lower normal indicators can cause serious complications.

Muscle failure occurs at a temperature of 28 ° C. At 33 ° C, loss of consciousness occurs. At a temperature of 42 ° C, the central nervous system begins to collapse. Death occurs at 44°C. The body controls temperature by producing or releasing excess heat.

Glucose concentration

Glucose concentration refers to the amount of glucose (blood sugar) present in the bloodstream. The body uses glucose as an energy source, but too much or too little can cause serious complications. Some hormones regulate the concentration of glucose in the blood. Insulin lowers the concentration of glucose, while cortisol, glucagon and catecholamines increase it.

Calcium levels

Bones and teeth contain approximately 99% of the calcium in the body, while the remaining 1% circulates in the blood. Too much or too little calcium in the blood has negative consequences. If blood calcium levels drop too low, the parathyroid glands activate their calcium-sensing receptors and release parathyroid hormone.

PTH signals to the bones that it needs to release calcium in order to increase its concentration in the bloodstream. If the calcium level increases too much, thyroid releases calcitonin and fixes excess calcium in the bones, thereby reducing the amount of calcium in the blood.

Liquid volume

The body must maintain a constant internal environment, which means it needs to regulate fluid loss or replenishment. Hormones help regulate this balance by causing excretion or fluid retention. If the body does not have enough fluid, antidiuretic hormone signals the kidneys to conserve fluid and reduces urine output. If the body contains too much fluid, it suppresses aldosterone and signals to produce more urine.

Homeostasis is the ability human body adapt to changing conditions of the external and internal environment. The stable operation of homeostasis processes guarantees a person a comfortable state of health in any situation, maintaining the constancy of vitality. important indicators organism.

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 main biological processes in the body continued to work stably, their conditions should 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 backfire for good 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 optimal condition main vital signs:

• body temperature.
• Blood pressure.
• Digestive stability.

For him correct work the immune, endocrine and nervous systems respond. In the event of an unforeseen 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 in order to choose the best option for adapting 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 general condition 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 the nervous system from constant overexertion.
• Watch your diet, do not overload yourself with heavy foods, avoid mindless starvation, which will allow the digestive system to more easily cope with its work.
• 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.

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 in the opposite direction. 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. carbon dioxide. 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 parameters does homeostasis regulate?

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. The normal temperature range is 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 of 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 remain at the 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 the normal blood pressure 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 species is present in a community provided with the necessary living conditions. 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 characteristic of individual 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 different temperature depending on 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 mechanism adjustments 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 essential for stable operation 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.

violate well-coordinated work organism can get into it toxins. 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 body responses to stimuli, human health is maintained at 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 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. 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, it physiological state may 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. 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 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 (algal overgrowth) and turbidity.

  Ecological homeostasis

  In disturbed ecosystems, or subclimax biological communities - like, for example, the island of Krakatoa, 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. Complete chain The succession that leads to the climax is called a preserie. In the Krakatau example, a climax community formed on this island with eight thousand various kinds, registered 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. AT equally tropical tree reduces light access 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.

  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 the environment to determine the parameter. For example, warm-blooded animals maintain a constant body temperature, while cold-blooded animals show wide range temperatures.

  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 when low temperatures, while warm-blooded ones 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

  The regulation of the chemical activity of the cell is achieved through a number of processes, among which the change in the structure of the cytoplasm itself, as well as the structure and activity of enzymes, is of particular importance. Autoregulation depends on

  The history of the development of the doctrine of homeostasis

  K. Bernard and his role in the development of the doctrine of the internal environment

  For the first time, homeostatic processes in the body as processes that ensure the constancy of its internal environment were considered by the French naturalist and physiologist C. Bernard in mid-nineteenth in. The term itself homeostasis was proposed by the American physiologist W. Kennon only in 1929.

  In the development of the doctrine of homeostasis, the leading role was played by the idea of ​​C. Bernard that for a living organism there are “actually, two environments: one external environment in which the organism is placed, the other internal environment in which tissue elements live.” In 1878, the scientist formulates the concept of the constancy of the composition and properties of the internal environment. key idea This concept was the idea that the internal environment is not only blood, but also all the plasma and blastoma fluids that come from it. “The internal environment,” wrote K. Bernard, “... is formed from all the constituent parts of the blood - nitrogenous and nitrogen-free, protein, fibrin, sugar, fat, etc., ... with the exception of blood globules, which are already independent organic elements.”

  The internal environment includes only the liquid components of the body, which wash all the elements of tissues, i.e. blood plasma, lymph and tissue fluid. K. Bernard considered the attribute of the internal environment to be “in direct contact with the anatomical elements of a living being”. He noted that while studying physiological properties these elements, it is necessary to consider the conditions of their manifestation and their dependence on the environment.

  Claude Bernard (1813-1878) The largest French physiologist, pathologist, naturalist. In 1839 he graduated from the University of Paris. In 1854–1868 headed the Department of General Physiology of the University of Paris, since 1868 - an employee of the Museum natural history. Member of the Paris Academy (since 1854), its vice-president (1868) and president (1869), foreign corresponding member of the St. Petersburg Academy of Sciences (since 1860). Scientific research K. Bernard devoted to the physiology of the nervous system, digestion and circulation. The merits of the scientist in the development of experimental physiology are great. He conducted classical studies on anatomy and physiology gastrointestinal tract, the role of the pancreas, carbohydrate metabolism, the functions of digestive juices, discovered the formation of glycogen in the liver, studied innervation blood vessels, vasoconstrictor action of sympathetic nerves, etc. One of the creators of the doctrine of homeostasis, introduced the concept of the internal environment of the body. Laid the foundations of pharmacology and toxicology. He showed the commonality and unity of a number of vital phenomena in animals and plants.

  The scientist rightly believed that the manifestations of life are due to the conflict between existing forces organism (constitution) and the influence of the external environment. The vital conflict in the body manifests itself in the form of two opposite and dialectically related phenomena: synthesis and decay. As a result of these processes, the body adapts, or adapts, to environmental conditions.

  An analysis of the works of K. Bernard allows us to conclude that all physiological mechanisms, no matter how different they may be, serve to maintain the constancy of living conditions in the internal environment. “The constancy of the internal environment is the condition of a free, independent life. This is achieved through a process that maintains in the internal environment all the conditions necessary for the life of the elements. The constancy of the environment presupposes such a perfection of the organism, in which external variables would be compensated and balanced at every moment. For liquid medium the main conditions for its constant maintenance were determined: the presence of water, oxygen, nutrients and a certain temperature.

  The independence of life from the external environment, which K. Bernard spoke about, is very relative. The internal environment is closely related to the external one. Moreover, it retained many properties of the primary environment in which life once originated. Living beings, as it were, closed the sea water into a system of blood vessels and turned the constantly fluctuating external environment into an internal environment, the constancy of which is protected by special physiological mechanisms.

  The main function of the internal environment is to bring "organic elements into relation with each other and with the external environment." K. Bernard explained that there is a constant exchange of substances between the internal environment and the cells of the body due to their qualitative and quantitative differences inside and outside the cells. The internal environment is created by the organism itself, and the constancy of its composition is maintained by the organs of digestion, respiration, excretion, etc., the main function of which is to "prepare a common nutrient fluid" for the cells of the body. The activity of these organs is regulated by the nervous system and with the help of "specially produced substances." This "consists an uninterrupted circle of mutual influences that form life harmony."

  Thus, in the second half of the 19th century, K. Bernard gave the correct scientific definition of the internal environment of the body, singled out its elements, described the composition, properties, evolutionary origin and emphasized its importance in ensuring the vital activity of the organism.

  The doctrine of homeostasis by W. Kennon

  Unlike K. Bernard, whose conclusions were based on broad biological generalizations, W. Kennon came to the conclusion about the importance of the constancy of the internal environment of the body by another method: on the basis of experimental physiological studies. The scientist drew attention to the fact that the life of an animal and a person, despite the fairly frequent adverse effects, proceeds normally for many years.

  American physiologist. Born in Prairie-du-Chine (Wisconsin), in 1896 he graduated from Harvard University. In 1906–1942 - professor of physiology at Harvard high school, foreign Honorary Member Academy of Sciences of the USSR (since 1942). The main scientific works are devoted to the physiology of the nervous system. He discovered the role of adrenaline as a sympathetic transmitter and formulated the concept of the sympathetic-adrenal system. He discovered that when sympathetic nerve fibers are stimulated, sympathin is released in their endings - a substance that is similar in its action to adrenaline. One of the creators of the doctrine of homeostasis, which he outlined in his work "The Wisdom of the Body" (1932). Viewed the human body as self-regulating system with the leading role of the autonomic nervous system.

  W. Kennon noted that the constant conditions maintained in the body could be called balance. However, this word has already been completely fixed certain value: they denote the most probable state isolated system in which all known forces are mutually balanced, therefore, in equilibrium state the parameters of the system do not depend on time, and there are no flows of matter or energy in the system. In the body, complex coordinated physiological processes, which ensure the stability of its states. An example is the coordinated activity of the brain, nerves, heart, lungs, kidneys, spleen and other internal organs and systems. Therefore, W. Kennon proposed a special designation for such states - homeostasis. This word does not at all imply something frozen and motionless. It means a condition that can change, but still remain relatively constant.

  Term homeostasis formed from two Greek words: homoios similar, similar and stasis- standing still. In interpreting this term, W. Kennon emphasized that the word stasis implies not only a stable state, but also a condition leading to this phenomenon, and the word homoios indicates the similarity and similarity of phenomena.

  The concept of homeostasis, according to W. Kennon, also includes physiological mechanisms that ensure the stability of living beings. This special stability is not characterized by the stability of the processes, on the contrary, they are dynamic and constantly changing, however, under the conditions of the "norm" the fluctuations of physiological parameters are rather severely limited.

  Later, W. Kennon showed that all metabolic processes and the main conditions under which the most important vital functions of the body are performed - body temperature, glucose concentration and mineral salts in blood plasma, pressure in the vessels, - fluctuate within very narrow limits near some average values ​​- physiological constants. Maintaining these constants in the body is a prerequisite for existence.

  W. Kennon singled out and classified main components of homeostasis. He referred to them materials that provide cellular needs(materials necessary for growth, repair and reproduction - glucose, proteins, fats; water; chlorides of sodium, potassium and other salts; oxygen; regulatory compounds), and physical and chemical factors that affect cellular activity (osmotic pressure, temperature, concentration of hydrogen ions, etc.). On the present stage development of knowledge about homeostasis, this classification was replenished mechanisms that ensure the structural constancy of the internal environment of the body and structural and functional integrity the whole organism. These include:

  a) heredity;
  b) regeneration and reparation;
  c) immunobiological reactivity.

  conditions automatic maintaining homeostasis, according to W. Kennon, are:

  – a flawlessly functioning alarm system that notifies the central and peripheral regulatory devices of any changes that threaten homeostasis;
  - the presence of corrective devices that take effect in a timely manner and delay the onset of these changes.

  E.Pfluger, Sh.Richet, I.M. Sechenov, L. Frederick, D. Haldane and other researchers who worked at the turn of the 19th–20th centuries also approached the idea of ​​the existence of physiological mechanisms that ensure the stability of the organism, and used their own terminology. However, the term homeostasis, proposed by W. Kennon to characterize the states and processes that create such an ability.

  For the biological sciences, in understanding homeostasis according to W. Kennon, it is valuable that living organisms are considered as open systems that have many connections with the environment. These connections are carried out through the respiratory and digestive organs, surface receptors, nervous and muscular systems and others. Changes in the environment directly or indirectly affect these systems, causing appropriate changes in them. However, these effects are usually not accompanied by large deviations from the norm and do not cause serious disturbances in physiological processes.

  Contribution of L.S. Stern in the development of ideas about homeostasis

  Russian physiologist, Academician of the Academy of Sciences of the USSR (since 1939). Born in Libava (Lithuania). In 1903 she graduated from the University of Geneva and worked there until 1925. In 1925–1948 - Professor of the 2nd Moscow medical institute and at the same time director of the Institute of Physiology of the USSR Academy of Sciences. From 1954 to 1968 she was in charge of the department of physiology at the Institute of Biophysics of the USSR Academy of Sciences. Works by L.S. Stern devoted to the study chemical bases physiological processes occurring in various parts of the central nervous system. She studied the role of catalysts in the process of biological oxidation, proposed a method for introducing medicinal substances into the cerebrospinal fluid in the treatment of certain diseases.

  Simultaneously with W. Cannon in 1929 in Russia, the Russian physiologist L.S. Stern. “Unlike the simplest, in more complex multicellular organisms, the exchange with the environment takes place through the so-called environment, from which individual tissues and organs draw the material they need and into which they secrete the products of their metabolism. ... As the differentiation and development of individual parts of the body (organs and tissues) should be created and developed for each organ, for each tissue, its own immediate nutrient medium, the composition and properties of which must correspond to the structural and functional features of this body. This immediate nourishing, or intimate, environment must have a certain constancy to ensure the normal functioning of the washed organ. ... The immediate nutrient medium of individual organs and tissues is intercellular or tissue fluid.

  L.S. Stern established the importance for the normal activity of organs and tissues of the constancy of the composition and properties of not only blood, but also tissue fluid. She showed the existence of histohematic barriers- physiological barriers separating blood and tissues. These formations, in her opinion, consist of capillary endothelium, basement membrane, connective tissue, cell lipoprotein membranes. The selective permeability of barriers contributes to the preservation of homeostasis and the known specificity of the internal environment necessary for normal function specific organ or tissue. Proposed and well substantiated by L.S. Stern's theory of barrier mechanisms is a fundamentally new contribution to the study of the internal environment.

  Histohematic , or vascular tissue , barrier - this is, in essence, a physiological mechanism that determines the relative constancy of the composition and properties own environment organ and cells. It performs two important functions: regulatory and protective, i.e. ensures the regulation of the composition and properties of the own environment of the organ and cell and protects it from the intake of substances from the blood that are alien to this organ or the whole organism.

  Histohematic barriers are present in almost all organs and have the appropriate names: hematoencephalic, hematoophthalmic, hematolabyrinthic, hematoliquor, hematolymphatic, hematopulmonary and hematopleural, hematorenal, as well as the blood-gonadal barrier (for example, hematotesticular), etc.

  Modern concepts of homeostasis

  The idea of ​​homeostasis turned out to be very fruitful, and throughout the 20th century. it was developed by many domestic and foreign scientists. However, until now this concept in biological science does not have a clear terminological definition. In scientific and educational literature one can meet either the equivalence of the terms "internal environment" and "homeostasis", or a different interpretation of the concept of "homeostasis".

  Russian physiologist, academician of the USSR Academy of Sciences (1966), full member of the USSR Academy of Medical Sciences (1945). Graduated from the Leningrad Institute of Medical Knowledge. Since 1921, he worked at the Institute of the Brain under the direction of V.M. Bekhterev, in 1922–1930. in Military Medical Academy in the laboratory of I.P. Pavlova. In 1930–1934 Professor of the Department of Physiology of the Gorky Medical Institute. In 1934–1944 - head of the department of the All-Union Institute experimental medicine in Moscow. In 1944–1955 worked at the Institute of Physiology of the USSR Academy of Medical Sciences (since 1946 - director). Since 1950 - Head of the Neurophysiological Laboratory of the USSR Academy of Medical Sciences, and then head of the Department of Neurophysiology of the Institute of Normal and Pathological Physiology of the USSR Academy of Medical Sciences. Laureate Lenin Prize(1972). The main works are devoted to the study of the activity of the body and especially the brain on the basis of the theory of functional systems developed by him. The application of this theory to the evolution of functions made it possible for P.K. Anokhin to formulate the concept of systemogenesis as general pattern evolutionary process.

  The internal environment of the body called the whole set of circulating body fluids: blood, lymph, intercellular (tissue) fluid, washing cells and structural tissues, involved in metabolism, chemical and physical transformations. The components of the internal environment also include the intracellular fluid (cytosol), considering that it is directly the environment in which the main reactions of cellular metabolism take place. The volume of the cytoplasm in the body of an adult is about 30 liters, the volume of the intercellular fluid is about 10 liters, and the volume of blood and lymph occupying the intravascular space is 4–5 liters.

  In some cases, the term "homeostasis" is used to refer to the constancy of the internal environment and the body's ability to provide it. Homeostasis is a relative dynamic, fluctuating within strictly defined boundaries, the constancy of the internal environment and the stability (stability) of the basic physiological functions of the body. In other cases, homeostasis is understood as physiological processes or control systems that regulate, coordinate and correct the vital activity of the body in order to maintain a stable state.

  Thus, the definition of the concept of homeostasis is approached from two sides. On the one hand, homeostasis is seen as a quantitative and qualitative constancy of physicochemical and biological parameters. On the other hand, homeostasis is defined as a set of mechanisms that maintain the constancy of the internal environment of the body.

  An analysis of the definitions available in the biological and reference literature made it possible to identify the most important aspects this concept and formulate general definition: homeostasis - a state of relative dynamic equilibrium of the system, maintained by the mechanisms of self-regulation. This definition not only includes knowledge of the relativity of the constancy of the internal environment, but also demonstrates the importance of the homeostatic mechanisms of biological systems that ensure this constancy.

  The vital functions of the body include homeostatic mechanisms of a very different nature and action: nervous, humoral-hormonal, barrier, controlling and maintaining the constancy of the internal environment and acting at different levels.

  The principle of operation of homeostatic mechanisms

  The principle of operation of homeostatic mechanisms that provide regulation and self-regulation on different levels organization of living matter, described by G.N. Kassil. Allocate next levels regulation:

  1) submolecular;
  2) molecular;
  3) subcellular;
  4) cellular;
  5) liquid (internal environment, humoral-hormonal-ionic relationships, barrier functions, immunity);
  6) tissue;
  7) nervous (central and peripheral nervous mechanisms, neurohumoral-hormonal-barrier complex);
  8) organismic;
  9) population (populations of cells, multicellular organisms).

  The elementary homeostatic level of biological systems should be considered organismic. Within its boundaries, a number of others are distinguished: cytogenetic, somatic, ontogenetic and functional (physiological) homeostasis, somatic genostasis.

  Cytogenetic homeostasis how morphological and functional adaptability expresses the continuous restructuring of organisms in accordance with the conditions of existence. Directly or indirectly, the functions of such a mechanism are performed by the hereditary apparatus of the cell (genes).

  Somatic homeostasis- the direction of the total shifts in the functional activity of the body to establish the most optimal relationship with the environment.

  Ontogenetic homeostasis- This individual development organism from the formation of a germ cell to death or cessation of existence in its former quality.

  Under functional homeostasis understand the optimal physiological activity of various organs, systems and the whole organism in specific environmental conditions. In turn, it includes: metabolic, respiratory, digestive, excretory, regulatory (providing an optimal level of neurohumoral regulation under given conditions) and psychological homeostasis.

  Somatic genostasis is a control over the genetic constancy of the somatic cells that make up the individual organism.

  It is possible to distinguish circulatory, motor, sensory, psychomotor, psychological and even informational homeostasis, which ensures the optimal response of the body to incoming information. Separately, a pathological level is distinguished - diseases of homeostasis, i.e. disruption of homeostatic mechanisms and regulatory systems.

  

  Hemostasis as an adaptive mechanism

  Hemostasis is a vital complex of complex interrelated processes, integral part adaptive mechanism of the body. Due to the special role of blood in maintaining the basic parameters of the body, it is isolated in independent view homeostatic reactions.

  The main component of hemostasis is a complex system adaptive mechanisms that ensure the fluidity of blood in the vessels and its coagulation in violation of their integrity. However, hemostasis not only maintains the liquid state of blood in the vessels, the resistance of the walls of the vessels and stops bleeding, but also affects hemodynamics and vascular permeability, participates in wound healing, in the development of inflammatory and immune reactions, and is related to nonspecific resistance of the organism.

  The hemostasis system is in functional interaction with the immune system. These two systems form a single humoral defense mechanism, the functions of which are connected, on the one hand, with the struggle for purity. genetic code and the prevention of various diseases, and on the other hand, with the preservation of the liquid state of the blood in the circulatory bed and stopping bleeding in case of violation of the integrity of the vessels. Their functional activity is regulated by the nervous and endocrine systems.

  The presence of common mechanisms for "turning on" the body's defense systems - immune, coagulation, fibrinolytic, etc. - allows us to consider them as a single structurally and functionally defined system.

  Its features are: 1) the cascade principle of sequential inclusion and activation of factors until the formation of final physiologically active substances: thrombin, plasmin, kinins; 2) the possibility of activation of these systems in any part of the vascular bed; 3) general mechanism turning on systems; 4) feedback in the mechanism of interaction of these systems; 5) the existence of common inhibitors.

  Ensuring the reliability of the functioning of the hemostasis system, as well as other biological systems, is carried out in accordance with the general principle of reliability. This means that the reliability of the system is achieved by redundancy of control elements and their dynamic interaction, duplication of functions or interchangeability of control elements with a perfect quick return to the previous state, the ability for dynamic self-organization and the search for stable states.

  

  Fluid circulation between cellular and tissue spaces, as well as blood and lymphatic vessels

  Cellular homeostasis

  The most important place in self-regulation and preservation of homeostasis, occupies cellular homeostasis. It is also called cell autoregulation.

  Neither the hormonal nor the nervous systems are fundamentally capable of coping with the task of maintaining the constancy of the composition of the cytoplasm of an individual cell. Each cell of a multicellular organism has its own mechanism of autoregulation of processes in the cytoplasm.

  The leading place in this regulation belongs to the outer cytoplasmic membrane. It ensures the transmission of chemical signals into and out of the cell, changing its permeability, takes part in the regulation of the electrolyte composition of the cell, and performs the function of biological "pumps".

  Homeostats and technical models of homeostatic processes

  AT recent decades the problem of homeostasis began to be considered from the standpoint of cybernetics - the science of purposeful and optimal control of complex processes. Biological systems such as cells, brains, organisms, populations, ecosystems operate according to the same laws.

  Ludwig von Bertalanffy (1901–1972) Austrian theoretical biologist, creator of the "general systems theory". From 1949 he worked in the USA and Canada. Approaching biological objects as organized dynamic systems, Bertalanffy gave a detailed analysis of the contradictions between mechanism and vitalism, the emergence and development of ideas about the integrity of the organism and, on the basis of the latter, the formation of systemic concepts in biology. Bertalanffy is responsible for a number of attempts to apply an "organismic" approach (i.e., an approach from the point of view of integrity) in the study of tissue respiration and the relationship between metabolism and growth in animals. Proposed scientist method The analysis of open equifinal (aiming at a goal) systems made it possible to widely use the ideas of thermodynamics, cybernetics, and physical chemistry in biology. His ideas have found application in medicine, psychiatry and other applied disciplines. Being one of the pioneers of the system approach, the scientist put forward the first generalized system concept in modern science, the tasks of which are to develop a mathematical apparatus for describing different types of systems, to establish the isomorphism of laws in various fields of knowledge and to search for means of integrating science (“ General theory systems", 1968). These tasks, however, have been realized only in relation to certain types of open biological systems.

  The founder of the theory of control in living objects is N. Wiener. The basis of his ideas is the principle of self-regulation - automatic maintenance of constancy or change according to the required law of the regulated parameter. However, long before N. Wiener and W. Kennon, the idea of ​​automatic control was expressed by I.M. Sechenov: “... in the animal body, regulators can only be automatic, i.e. be put into action by changed conditions in the state or course of the machine (organism) and develop activities by which these irregularities are eliminated. This phrase indicates the need for both direct and feedback underlying self-regulation.

  The idea of ​​self-regulation in biological systems was deepened and developed by L. Bertalanffy, who understood a biological system as “an ordered set of interconnected elements”. He also considered the general biophysical mechanism of homeostasis in the context of open systems. Based on the theoretical ideas of L. Bertalanffy in biology, a new direction has developed, called systems approach. The views of L. Bertalanffy were shared by V.N. Novoseltsev, who presented the problem of homeostasis as the task of controlling the flows of matter and energy, which open system exchanges with the environment.

  The first attempt to model homeostasis and establish possible mechanisms management belongs to W.R. Ashby. He designed an artificial self-regulating device called "homeostat". Homeostat U.R. Ashby was a system of potentiometric circuits and reproduced only the functional aspects of the phenomenon. This model could not adequately reflect the essence of the processes underlying homeostasis.

  The next step in the development of homeostatics was made by S. Beer, who pointed out two new fundamental points: the hierarchical principle of building homeostatic systems for managing complex objects and the principle of survivability. S. Beer tried to apply certain homeostatic principles in the practical development of organized control systems, revealed some cybernetic analogies between a living system and complex production.

  A qualitatively new stage in the development of this direction came after the creation of a formal homeostat model by Yu.M. Gorsky. His views were formed under the influence of the scientific ideas of G. Selye, who argued that “... if it is possible to include contradictions in models reflecting the work of living systems, and even at the same time to understand why nature, creating living things, went this way, this will be a new breakthrough into the secrets of the living with a great practical output.

  Physiological homeostasis

  Physiological homeostasis is maintained by the autonomic and somatic nervous system, a complex of humoral-hormonal and ionic mechanisms that make up the physico-chemical system of the body, as well as behavior, in which the role of both hereditary forms and acquired individual experience is great.

  The idea of ​​the leading role of the autonomic nervous system, especially its sympathoadrenal department, was developed in the works of E. Gelgorn, B.R. Hess, W. Kennon, L.A. Orbeli, A.G. Ginetsinsky and others. The organizing role of the nervous apparatus (the principle of nervism) underlies the Russian physiological school of I.P. Pavlova, I.M. Sechenov, A.D. Speransky.

  Humoral-hormonal theories (the principle of humoralism) were developed abroad in the works of G. Dale, O. Levy, G. Selye, C. Sherrington and others. great attention Russian scientists I.P. Razenkov and L.S. Stern.

  accumulated colossal factual material, which describes various manifestations of homeostasis in living, technical, social, and ecological systems, requires study and consideration from a unified methodological standpoint. The unifying theory that was able to combine all the diverse approaches to understanding the mechanisms and manifestations of homeostasis was functional systems theory created by P.K. Anokhin. In his views, the scientist was based on N. Wiener's ideas about self-organizing systems.

  

  Contemporary scientific knowledge about the homeostasis of the whole organism is based on understanding it as a friendly and coordinated self-regulating activity of various functional systems, characterized by quantitative and qualitative changes in their parameters during physiological, physical and chemical processes.

  The mechanism for maintaining homeostasis resembles a pendulum (scales). First of all, the cytoplasm of the cell should have a constant composition - homeostasis of the 1st stage (see diagram). This is provided by the mechanisms of homeostasis of the 2nd stage - circulating fluids, the internal environment. In turn, their homeostasis is associated with vegetative systems stabilization of the composition of incoming substances, liquids and gases and the release of end products of metabolism - stage 3. Thus, the temperature, water content and concentrations of electrolytes, oxygen and carbon dioxide, the amount of nutrients and excreted metabolic products are maintained at a relatively constant level.

  The fourth step in maintaining homeostasis is behavior. In addition to expedient reactions, it includes emotions, motivations, memory, and thinking. The fourth stage actively interacts with the previous one, builds on it and influences it. In animals, behavior is expressed in the choice of food, feeding grounds, nesting sites, daily and seasonal migrations, etc., the essence of which is the desire for peace, the restoration of disturbed balance.

  So homeostasis is:

  1) the state of the internal environment and its property;
  2) a set of reactions and processes that maintain the constancy of the internal environment;
  3) the ability of the organism to resist changes in the environment;
  4) the condition for the existence, freedom and independence of life: “The constancy of the internal environment is the condition for a free life” (K. Bernard).

  Since the concept of homeostasis is a key one in biology, it should be mentioned when studying all school courses: “Botany”, “Zoology”, “ General biology”, “Ecology”. But, of course, the main attention should be paid to the disclosure of this concept in the course “Man and his health”. Here sample topics, in the study of which the materials of the article can be used. "Organs. Organ systems, the organism as a whole. "Nervous and humoral regulation of functions in the body". “The internal environment of the body. Blood, lymph, tissue fluid. Composition and properties of blood. "Circulation". "Breath". Metabolism as the main function of the body. "Isolation". "Thermoregulation".