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

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

properties of homeostasis

Homeostatic systems have the following properties:

• instability system: tests how it can best adapt.
• Striving for balance: all the internal, structural and functional organization of systems contributes to maintaining balance.
• unpredictability: The resultant effect of a certain action can often be different from what was expected.

• Regulation of the amount of micronutrients and water in the body - osmoregulation. Carried out in the kidneys.
• Removal of waste products of the metabolic process - isolation. It is carried out by exocrine organs - kidneys, lungs, sweat glands and gastrointestinal tract.
• Body temperature regulation. Lowering the temperature through sweating, a variety of thermoregulatory reactions.
• Regulation of blood glucose levels. Mainly carried out by the liver, insulin and glucagon secreted by the pancreas.
• Regulation of the level of basic metabolism depending on the diet.

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

Mechanisms of homeostasis: feedback

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

1. Negative feedback, expressed 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 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 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 (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 the chain in the years since the eruption environmental change, in which new species of plants and animals succeeded each other, which led to biological diversity 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 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 - producing 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 the tropical tree reduces the access of light to the lower levels and helps to prevent the invasion of 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 regulation of microclimates or hydrological cycles of an ecosystem, and several different ecosystems may interact to maintain homeostasis of river drainage 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.

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

3) tissues, which are characterized mainly or exclusively by intracellular regeneration (myocardium and ganglion cells of the central nervous system)

In the process of evolution, 2 types of regeneration were formed: physiological and reparative.

Homeostasis in the human body

Various factors affect the ability of body fluids to sustain 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 required 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.

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An excerpt characterizing Homeostasis

At half past six, Napoleon rode on horseback to the village of Shevardin.
It began to dawn, the sky cleared, only one cloud lay in the east. Abandoned fires burned out in the faint morning light.
To the right, a thick lone cannon shot rang out, swept and froze in the general silence. Several minutes passed. There was a second, third shot, the air shook; the fourth and fifth resounded close and solemnly somewhere to the right.
The first shots had not yet finished ringing before others rang out, again and again, merging and interrupting one another.
Napoleon rode up with his retinue to the Shevardinsky redoubt and dismounted from his horse. The game started.

Returning from Prince Andrei to Gorki, Pierre, having ordered the bereator to prepare the horses and wake him up early in the morning, immediately fell asleep behind the partition, in the corner that Boris gave him.
When Pierre woke up completely the next morning, there was no one in the hut. Glass rattled in the small windows. The Rector stood pushing him aside.
“Your excellency, your excellency, your excellency ...” the bereytor said stubbornly, without looking at Pierre and, apparently, having lost hope of waking him up, shaking him by the shoulder.
- What? Began? Is it time? Pierre spoke, waking up.
“If you please, hear the firing,” said the bereytor, a retired soldier, “already all the gentlemen have risen, the brightest ones themselves have long passed.
Pierre hastily dressed and ran out onto the porch. Outside it was clear, fresh, dewy and cheerful. The sun, having just escaped from behind the cloud that obscured it, splashed up to half of its rays, broken by a cloud, through the roofs of the opposite street, onto the dew-covered dust of the road, onto the walls of houses, on the windows of the fence and on Pierre's horses standing by the hut. The rumble of cannons was heard more clearly in the yard. An adjutant with a Cossack roared down the street.
- It's time, Count, it's time! shouted the adjutant.
Ordering to lead the horse behind him, Pierre went down the street to the mound, from which he had looked at the battlefield yesterday. There was a crowd of military men on this mound, and the French dialect of the staff was heard, and Kutuzov's gray-haired head was visible with his white cap with a red band and a gray-haired nape sunk into his shoulders. Kutuzov looked through the pipe ahead along the high road.
Entering the steps of the entrance to the mound, Pierre looked ahead of him and froze in admiration before the beauty of the spectacle. It was the same panorama that he had admired yesterday from this mound; but now the whole area was covered with troops and the smoke of shots, and the slanting rays of the bright sun, rising behind, to the left of Pierre, threw on her in the clear morning air a piercing light with a golden and pink hue and dark, long shadows. The distant forests that complete the panorama, as if carved from some kind of precious yellow-green stone, could be seen with their curved line of peaks on the horizon, and between them, behind Valuev, the big Smolensk road cut through, all covered with troops. Closer, golden fields and copses gleamed. Everywhere - in front, on the right and on the left - troops were visible. All this was lively, majestic and unexpected; but what struck Pierre most of all was the view of the battlefield itself, Borodino and the hollow above Kolochaya on both sides of it.
Above Kolochaya, in Borodino and on both sides of it, especially to the left, where the Voyna flows into Kolocha in the swampy banks, there was that fog that melts, blurs and shines through when the bright sun comes out and magically colors and outlines everything seen through it. This fog was joined by the smoke of shots, and through this fog and smoke lightnings of morning light shone everywhere - now over the water, then over the dew, then over the bayonets of the troops crowding along the banks and in Borodino. Through this fog one could see the white church, in some places the roofs of Borodin's huts, in some places solid masses of soldiers, in some places green boxes, cannons. And it all moved, or seemed to move, because the mist and smoke stretched all over this space. Both in this locality of the lower parts near Borodino, covered with fog, and outside it, higher and especially to the left along the entire line, through the forests, through the fields, in the lower parts, on the tops of the elevations, were constantly born of themselves, out of nothing, cannon, then lonely, now lumpy, now rare, now frequent clouds of smoke, which, swelling, growing, swirling, merging, were visible throughout this space.
These gunshot smokes and, strange to say, their sounds produced the main beauty of the spectacle.
Puff! - suddenly one could see round, dense smoke playing with purple, gray and milky white colors, and boom! - the sound of this smoke was heard in a second.
"Poof poof" - two smokes rose, pushing and merging; and "boom boom" - confirmed the sounds that the eye saw.
Pierre looked back at the first smoke that he had left in a rounded dense ball, and already in its place were balls of smoke stretching to the side, and poof ... (with a stop) poof poof - three more, four more, and for each, with the same constellations, boom ... boom boom boom - answered beautiful, solid, true sounds. It seemed that these smokes were running, that they were standing, and forests, fields and shiny bayonets were running past them. On the left side, over the fields and bushes, these large smokes with their solemn echoes were constantly born, and closer still, along the lower levels and forests, small smokes of guns, which did not have time to round off, flared up and gave their small echoes in the same way. Fuck ta ta tah - the guns crackled, although often, but incorrectly and poorly in comparison with gun shots.
Pierre wanted to be where these smokes were, these shiny bayonets and cannons, this movement, these sounds. He looked back at Kutuzov and at his retinue in order to check his impression with others. Everyone was exactly the same as he was, and, as it seemed to him, they looked forward to the battlefield with the same feeling. On all faces shone now that latent heat(chaleur latente) a feeling that Pierre noticed yesterday and which he fully understood after his conversation with Prince Andrei.
“Go, my dear, go, Christ is with you,” said Kutuzov, without taking his eyes off the battlefield, to the general standing next to him.
Having listened to the order, this general walked past Pierre, to the exit from the mound.
- To the crossing! - the general said coldly and sternly in response to the question of one of the staff, where he was going. “And I, and I,” thought Pierre and went in the direction of the general.
The general mounted a horse, which was given to him by a Cossack. Pierre went up to his bereytor, who was holding the horses. Asking which one was quieter, Pierre mounted the horse, grabbed the mane, pressed the heels of his twisted legs against the horse’s stomach, and, feeling that his glasses were falling off and that he was unable to take his hands off the mane and reins, he galloped after the general, arousing the smiles of the staff, from the barrow looking at him.

The general, behind whom Pierre rode, went downhill, turned sharply to the left, and Pierre, losing sight of him, jumped into the ranks of the infantry soldiers walking ahead of him. He tried to get out of them first to the right, then to the left; but everywhere there were soldiers, with equally preoccupied faces, busy with some invisible, but obviously important business. Everyone was looking with the same dissatisfied questioning look at this fat man in a white hat, for some unknown reason, trampling them with his horse.
- Why does he ride in the middle of the battalion! one shouted at him. Another pushed his horse with the butt, and Pierre, clinging to the pommel and barely holding the shy horse, jumped forward the soldier, where it was more spacious.
There was a bridge ahead of him, and other soldiers were standing by the bridge, firing. Pierre rode up to them. Without knowing it himself, Pierre drove to the bridge over the Kolocha, which was between Gorki and Borodino and which, in the first action of the battle (taking Borodino), was attacked by the French. Pierre saw that there was a bridge ahead of him, and that on both sides of the bridge and in the meadow, in those rows of hay that he noticed yesterday, soldiers were doing something in the smoke; but, in spite of the incessant shooting that took place in this place, he did not think that this was the battlefield. He did not hear the sounds of bullets squealing from all sides, and the shells flying over him, did not see the enemy who was on the other side of the river, and for a long time did not see the dead and wounded, although many fell not far from him. With a smile that never left his face, he looked around him.
- What does this one drive in front of the line? Someone shouted at him again.
“Take the left, take the right,” they shouted to him. Pierre took to the right and unexpectedly moved in with the adjutant of General Raevsky, whom he knew. This adjutant looked angrily at Pierre, obviously intending to shout at him too, but, recognizing him, nodded his head to him.
– How are you here? he said and rode on.
Pierre, feeling out of place and idle, afraid to interfere with someone again, galloped after the adjutant.
- It's here, right? May I come with you? he asked.
“Now, now,” the adjutant answered and, jumping up to the fat colonel who was standing in the meadow, handed him something and then turned to Pierre.
“Why did you come here, Count?” he told him with a smile. Are you all curious?
“Yes, yes,” said Pierre. But the adjutant, turning his horse, rode on.
“Here, thank God,” said the adjutant, “but on Bagration’s left flank there is a terrible fire going on.
– Really? Pierre asked. – Where is it?
- Yes, let's go with me to the mound, you can see from us. And it’s still tolerable with us on the battery, ”said the adjutant. - Well, are you going?
“Yes, I am with you,” said Pierre, looking around him and looking for his bereator with his eyes. Here, only for the first time, Pierre saw the wounded, wandering on foot and carried on a stretcher. On the same meadow with fragrant rows of hay through which he had passed yesterday, across the rows, awkwardly turning his head, lay motionless one soldier with a fallen shako. Why didn't they bring it up? - Pierre began; but, seeing the stern face of the adjutant, who looked back in the same direction, he fell silent.
Pierre did not find his bereytor and, together with the adjutant, rode down the hollow to the Raevsky barrow. Pierre's horse lagged behind the adjutant and shook him evenly.
- You, apparently, are not used to riding, count? the adjutant asked.
“No, nothing, but she jumps a lot,” Pierre said in bewilderment.
- Eh! .. yes, she was wounded, - said the adjutant, - right front, above the knee. Bullet must be. Congratulations, Count,” he said, “le bapteme de feu [baptism by fire].
Passing through the smoke along the sixth corps, behind the artillery, which, moved forward, fired, deafening with its shots, they arrived at a small forest. The forest was cool, quiet and smelled of autumn. Pierre and the adjutant dismounted from their horses and walked up the mountain.
Is the general here? asked the adjutant, approaching the mound.
“We were just now, let’s go here,” they answered him, pointing to the right.
The adjutant looked back at Pierre, as if not knowing what to do with him now.
"Don't worry," said Pierre. - I'll go to the mound, can I?
- Yes, go, everything is visible from there and not so dangerous. And I'll pick you up.
Pierre went to the battery, and the adjutant rode on. They did not see each other again, and much later Pierre learned that this adjutant's arm had been torn off that day.
The barrow that Pierre entered was that famous one (later known by the Russians under the name of the kurgan battery, or Raevsky battery, and by the French under the name la grande redoute, la fatale redoute, la redoute du center [large redoubt, fatal redoubt, central redoubt ] a place around which tens of thousands of people were laid and which the French considered the most important point of the position.
This redoubt consisted of a mound, on which ditches were dug on three sides. In a place dug in by ditches stood ten firing cannons protruding through the openings of the ramparts.
Cannons stood in line with the mound on both sides, also firing incessantly. A little behind the cannons were infantry troops. Entering this mound, Pierre never thought that this place dug in with small ditches, on which several cannons stood and fired, was the most important place in the battle.
Pierre, on the contrary, it seemed that this place (precisely because he was on it) was one of the most insignificant places of the battle.
Entering the mound, Pierre sat down at the end of the ditch surrounding the battery, and with an unconsciously joyful smile looked at what was happening around him. Occasionally, Pierre would get up with the same smile and, trying not to interfere with the soldiers loading and rolling the guns, who constantly ran past him with bags and charges, walked around the battery. The cannons from this battery continuously fired one after another, deafening with their sounds and covering the whole neighborhood with gunpowder smoke.
In contrast to the eerie feeling between the infantry soldiers of the covering, here, on the battery, where a small number of people engaged in business are white limited, separated from others by a ditch, here one felt the same and common to all, as if family animation.
The appearance of the non-military figure of Pierre in a white hat first struck these people unpleasantly. The soldiers, passing by him, looked with surprise and even fear at his figure. The senior artillery officer, a tall, pockmarked man with long legs, as if in order to look at the action of the extreme gun, approached Pierre and looked at him curiously.
A young, round-faced officer, still a perfect child, obviously just released from the corps, disposing of the two guns entrusted to him very diligently, turned sternly to Pierre.
“Sir, let me ask you out of the way,” he said to him, “it’s not allowed here.
The soldiers shook their heads disapprovingly, looking at Pierre. But when everyone was convinced that this man in a white hat not only did nothing wrong, but either sat quietly on the slope of the rampart, or with a timid smile, courteously avoiding the soldiers, walked along the battery under the shots as calmly as along the boulevard, then little by little, a feeling of unfriendly bewilderment towards him began to turn into affectionate and playful participation, similar to that which soldiers have for their animals: dogs, roosters, goats, and in general animals living with military teams. These soldiers immediately mentally accepted Pierre into their family, appropriated and gave him a nickname. “Our master” they called him and they affectionately laughed about him among themselves.
One core blew up the ground a stone's throw from Pierre. He, cleaning the earth sprinkled with a cannonball from his dress, looked around him with a smile.
- And how are you not afraid, master, really! - the red-faced broad soldier turned to Pierre, baring his strong white teeth.
– Are you afraid? Pierre asked.
– But how? answered the soldier. “Because she won’t have mercy. She slams, so the guts out. You can't help but be afraid," he said, laughing.
Several soldiers with cheerful and affectionate faces stopped near Pierre. They did not seem to expect him to speak like everyone else, and this discovery delighted them.
“Our business is soldiery. But the sir, so amazing. That's the barin!
- In places! - shouted a young officer at the soldiers gathered around Pierre. This young officer, apparently, performed his position for the first or second time, and therefore treated both the soldiers and the commander with particular distinctness and uniformity.

homeostasis(ancient Greek ὁμοιοστάσις from ὅμοιος - the same, similar and στάσις - standing, immobility) - self-regulation, the ability of an open system to maintain its constancy internal state through coordinated responses aimed at maintaining dynamic balance. The desire of the system to reproduce itself, to restore the lost balance, to overcome the resistance of the external environment. Population homeostasis is the ability of a population to maintain a certain number of its individuals for a long time.

General information

properties of homeostasis

• instability
• Striving for balance
• unpredictability

• Regulation of the level of basic metabolism depending on the diet.

Main article: Feedback

Ecological homeostasis

Biological homeostasis

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 temperature, the degree of acidity, the concentration of the substrate, the presence of certain macro- and microelements. Cellular mechanisms of homeostasis are aimed at restoring naturally dead cells of tissues or organs in case of violation of their integrity.

Regeneration-the process of updating the structural elements of the body and restoring their number after damage, aimed at providing the necessary functional activity

Depending on the regenerative response, tissues and organs of mammals can be divided into 3 groups:

1) tissues and organs that are characterized by cellular regeneration (bones, loose connective tissue, hematopoietic system, endothelium, mesothelium, mucous membranes of the gastrointestinal tract, respiratory tract and urinary system)

2) tissues and organs that are characterized by cellular and intracellular regeneration (liver, kidneys, lungs, smooth and skeletal muscles, autonomic nervous system, pancreas, endocrine system)

3) tissues, which are characterized mainly or exclusively by intracellular regeneration (myocardium and ganglion cells of the central nervous system)

In the process of evolution, 2 types of regeneration were formed: physiological and reparative.

Other areas

The actuary can talk about risk homeostasis in which, for example, people who have an anti-lock braking system installed in their car are not in a safer position than those who do not have it installed, 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.

stress homeostasis

Examples

• thermoregulation
  • Skeletal muscle trembling may begin if the body temperature is too low.
• Chemical regulation

Sources

1. O.-Ya.L.Bekish. Medical biology. - Minsk: Urajay, 2000. - 520 p. - ISBN 985-04-0336-5.

Topic № 13. Homeostasis, mechanisms of its regulation.

The body as an open self-regulating system.

A living organism is an open system connected with environment through the nervous, digestive, respiratory, excretory systems, etc.

In the process of metabolism with food, water, during gas exchange, various chemical compounds enter the body, which undergo changes in the body, enter the structure of the body, but do not remain permanently. Assimilated substances decompose, release energy, decay products are removed into the external environment. The destroyed molecule is replaced by a new one, and so on.

The body is an open, dynamic system. In a constantly changing environment, the body maintains a stable state for a certain time.

The concept of homeostasis. General patterns of homeostasis of living systems.

homeostasis - the property of a living organism to maintain a relative dynamic constancy of the internal environment. Homeostasis is expressed in the relative constancy of the chemical composition, osmotic pressure, stability of the basic physiological functions. Homeostasis is specific and determined by the genotype.

The preservation of the integrity of the individual properties of an organism is one of the most general biological laws. This law is provided in the vertical series of generations by the mechanisms of reproduction, and throughout the life of the individual - by the mechanisms of homeostasis.

The phenomenon of homeostasis is an evolutionarily developed, hereditarily fixed adaptive property of the body to normal environmental conditions. However, these conditions can be short-term or long-term outside the normal range. In such cases, the phenomena of adaptation are characterized not only by the restoration of the usual properties of the internal environment, but also by short-term changes in function (for example, an increase in the rhythm of cardiac activity and an increase in the frequency of respiratory movements with increased muscular work). Homeostasis reactions can be directed to:

maintaining known steady state levels;

elimination or limitation of harmful factors;

development or preservation of optimal forms of interaction between the organism and the environment in the changed conditions of its existence. All these processes determine adaptation.

Therefore, the concept of homeostasis means not only a certain constancy of various physiological constants of the body, but also includes the processes of adaptation and coordination of physiological processes that ensure the unity of the body not only in the norm, but also under changing conditions of its existence.

The main components of homeostasis were defined by C. Bernard, and they can be divided into three groups:

A. Substances that provide cellular needs:

Substances necessary for the formation of energy, for growth and recovery - glucose, proteins, fats.

NaCl, Ca and other inorganic substances.

Oxygen.

internal secretion.

B. Environmental factors affecting cellular activity:

osmotic pressure.

Temperature.

Hydrogen ion concentration (pH).

B. Mechanisms that ensure structural and functional unity:

Heredity.

Regeneration.

immunobiological reactivity.

The principle of biological regulation ensures the internal state of the organism (its content), as well as the relationship between the stages of ontogenesis and phylogenesis. This principle has become widespread. When studying it, cybernetics arose - the science of purposeful and optimal control of complex processes in wildlife, in human society, industry (Berg I.A., 1962).

A living organism is a complex controlled system where many variables of the external and internal environment interact. Common to all systems is the presence input variables, which, depending on the properties and laws of the system's behavior, are transformed into weekend variables (Fig. 10).

Rice. 10 - General scheme of homeostasis of living systems

The output variables depend on the input variables and the laws of the system behavior.

The influence of the output signal on the control part of the system is called feedback , which has great importance in self-regulation (homeostatic reaction). Distinguish negative andpositive feedback.

negative feedback reduces the influence of the input signal on the value of the output according to the principle: "the more (at the output), the less (at the input)". It helps to restore the homeostasis of the system.

At positive feedback, the value of the input signal increases according to the principle: "the more (at the output), the more (at the input)". It enhances the resulting deviation from the initial state, which leads to a violation of homeostasis.

However, all types of self-regulation operate on the same principle: self-deviation from the initial state, which serves as an incentive to turn on the correction mechanisms. So, normal blood pH is 7.32 - 7.45. A shift in pH by 0.1 leads to a violation of cardiac activity. This principle was described by Anokhin P.K. in 1935 and called the feedback principle, which serves to implement adaptive reactions.

General principle of homeostatic response(Anokhin: "Theory of functional systems"):

deviation from the initial level → signal → activation of regulatory mechanisms based on the feedback principle → correction of changes (normalization).

Yes, at physical work the concentration of CO 2 in the blood increases → pH shifts to the acid side → the signal enters the respiratory center of the medulla oblongata → centrifugal nerves conduct an impulse to the intercostal muscles and breathing deepens → a decrease in CO 2 in the blood, pH is restored.

Mechanisms of regulation of homeostasis at the molecular-genetic, cellular, organismal, population-species and biospheric levels.

Regulatory homeostatic mechanisms function at the gene, cellular and systemic (organismic, population-species and biospheric) levels.

Gene mechanisms homeostasis. All phenomena of body homeostasis are genetically determined. Already at the level of primary gene products there is a direct connection - "one structural gene - one polypeptide chain". Moreover, there is a collinear correspondence between the DNA nucleotide sequence and the amino acid sequence of the polypeptide chain. The hereditary program of the individual development of an organism provides for the formation of species-specific characteristics not in constant, but in changing environmental conditions, within the limits of a hereditarily determined norm of reaction. The double helix of DNA is essential in the processes of its replication and repair. Both are directly related to ensuring the stability of the functioning of the genetic material.

From a genetic point of view, one can distinguish between elementary and systemic manifestations of homeostasis. Examples of elementary manifestations of homeostasis are: gene control of thirteen blood coagulation factors, gene control of histocompatibility of tissues and organs, which allows transplantation.

The transplanted area is called transplant. The organism from which tissue is taken for transplantation is donor , and to whom they transplant - recipient . The success of transplantation depends on the immunological reactions of the body. There are autotransplantation, syngeneic transplantation, allotransplantation and xenotransplantation.

Autotransplantation – transplantation of tissues in the same organism. In this case, the proteins (antigens) of the transplant do not differ from the proteins of the recipient. There is no immunological reaction.

Syngeneic transplant carried out in identical twins with the same genotype.

allotransplantation – transplantation of tissues from one individual to another belonging to the same species. The donor and recipient differ in antigens, therefore, in higher animals, long-term engraftment of tissues and organs is observed.

Xenotransplantation Donor and recipient belong to different types of organisms. This type of transplantation succeeds in some invertebrates, but such transplants do not take root in higher animals.

In transplantation, the phenomenon is of great importance immunological tolerance (tissue compatibility). Suppression of immunity in the case of tissue transplantation (immunosuppression) is achieved by: suppression of the activity of the immune system, radiation, administration of antilymphotic serum, hormones of the adrenal cortex, chemical preparations - antidepressants (imuran). The main task is to suppress not just immunity, but transplant immunity.

transplant immunity determined by the genetic constitution of the donor and recipient. Genes responsible for the synthesis of antigens causing a reaction on transplanted tissue are called tissue incompatibility genes.

In humans, the main genetic system of histocompatibility is the HLA (Human Leukocyte Antigen) system. Antigens are sufficiently well represented on the surface of leukocytes and are determined using antisera. The plan of the structure of the system in humans and animals is the same. A unified terminology has been adopted to describe the genetic loci and alleles of the HLA system. Antigens are designated: HLA-A 1 ; HLA-A 2 etc. New antigens that have not been finally identified are designated - W (Work). Antigens of the HLA system are divided into 2 groups: SD and LD (Fig. 11).

Antigens of the SD group are determined by serological methods and are determined by the genes of 3 subloci of the HLA system: HLA-A; HLA-B; HLA-C.

Rice. 11 - HLA main human histocompatibility genetic system

LD - antigens are controlled by the HLA-D sublocus of the sixth chromosome, and are determined by the method of mixed cultures of leukocytes.

Each of the genes that control HLA - human antigens, has a large number of alleles. So the HLA-A sublocus controls 19 antigens; HLA-B - 20; HLA-C - 5 "working" antigens; HLA-D - 6. Thus, about 50 antigens have already been found in humans.

The antigenic polymorphism of the HLA system is the result of the origin of one from the other and close genetic connection between them. The identity of the donor and recipient according to the antigens of the HLA system is necessary for transplantation. Transplantation of a kidney identical in 4 antigens of the system provides survival by 70%; 3 - 60%; 2 - 45%; 1 - 25%.

There are special centers that conduct the selection of a donor and recipient for transplantation, for example, in the Netherlands - "Eurotransplant". Typing by antigens of the HLA system is also carried out in the Republic of Belarus.

Cellular mechanisms homeostasis are aimed at restoring the cells of tissues, organs in case of violation of their integrity. The totality of processes aimed at restoring destructible biological structures is called regeneration. Such a process is characteristic of all levels: renewal of proteins, components of cell organelles, whole organelles and the cells themselves. Restoration of organ functions after an injury or rupture of a nerve, wound healing is important for medicine in terms of mastering these processes.

Tissues, according to their regenerative capacity, are divided into 3 groups:

Tissues and organs that are characterized cellular regeneration (bones, loose connective tissue, hematopoietic system, endothelium, mesothelium, mucous membranes of the intestinal tract, respiratory tract and genitourinary system.

Tissues and organs that are characterized cellular and intracellular regeneration (liver, kidneys, lungs, smooth and skeletal muscles, autonomic nervous system, endocrine, pancreas).

Fabrics that are predominantly intracellular regeneration (myocardium) or exclusively intracellular regeneration (ganglion cells of the central nervous system). It covers the processes of restoration of macromolecules and cell organelles by assembling elementary structures or by their division (mitochondria).

In the process of evolution, 2 types of regeneration were formed physiological and reparative .

Physiological regeneration - This is a natural process of restoring the elements of the body throughout life. For example, the restoration of erythrocytes and leukocytes, the change of the epithelium of the skin, hair, the replacement of milk teeth with permanent ones. These processes are influenced by external and internal factors.

Reparative regeneration is the restoration of organs and tissues lost due to damage or injury. The process occurs after mechanical injuries, burns, chemical or radiation injuries, as well as as a result of diseases and surgical operations.

Reparative regeneration is divided into typical (homomorphosis) and atypical (heteromorphosis). In the first case, it regenerates an organ that was removed or destroyed, in the second, another organ develops in place of the removed organ.

Atypical regeneration more common in invertebrates.

Hormones stimulate regeneration pituitary gland and thyroid gland . There are several ways to regenerate:

Epimorphosis or complete regeneration - restoration of the wound surface, completion of the part to the whole (for example, the growth of a tail in a lizard, limbs in a newt).

Morphollaxis - restructuring of the remaining part of the organ to the whole, only smaller. This method is characterized by the restructuring of the new from the remnants of the old (for example, the restoration of a limb in a cockroach).

Endomorphosis - recovery due to intracellular restructuring of tissue and organ. Due to the increase in the number of cells and their size, the mass of the organ approaches the initial one.

In vertebrates, reparative regeneration occurs in the following form:

Complete regeneration - restoration of the original tissue after its damage.

Regenerative hypertrophy characteristic of internal organs. In this case, the wound surface heals with a scar, the removed area does not grow back and the shape of the organ is not restored. The mass of the remaining part of the organ increases due to an increase in the number of cells and their size and approaches the original value. So in mammals, the liver, lungs, kidneys, adrenal glands, pancreas, salivary, thyroid glands regenerate.

Intracellular compensatory hyperplasia cell ultrastructures. In this case, a scar is formed at the site of damage, and the restoration of the initial mass occurs due to an increase in the volume of cells, and not their number, based on the growth (hyperplasia) of intracellular structures (nervous tissue).

Systemic mechanisms are provided by the interaction of regulatory systems: nervous, endocrine and immune .

Nervous regulation carried out and coordinated by the central nervous system. Nerve impulses, entering cells and tissues, cause not only excitation, but also regulate chemical processes, exchange biologically active substances. Currently, more than 50 neurohormones are known. So, in the hypothalamus, vasopressin, oxytocin, liberins and statins are produced that regulate the function of the pituitary gland. Examples of systemic manifestations of homeostasis are the maintenance of a constant temperature, blood pressure.

From the standpoint of homeostasis and adaptation, the nervous system is the main organizer of all body processes. At the heart of adaptation, balancing organisms with environmental conditions, according to N.P. Pavlov, are reflex processes. Between different levels of homeostatic regulation there is a private hierarchical subordination in the system of regulation of the internal processes of the body (Fig. 12).

hemispheric cortex and parts of the brain

feedback self-regulation

peripheral neuro-regulatory processes, local reflexes

Cellular and tissue levels of homeostasis

Rice. 12. - Hierarchical subordination in the system of regulation of the internal processes of the organism.

The most primary level is the homeostatic systems of the cellular and tissue levels. Above them are peripheral nervous regulatory processes such as local reflexes. Further in this hierarchy are the systems of self-regulation of certain physiological functions with various channels of "feedback". The top of this pyramid is occupied by the cerebral cortex and the brain.

In a complex multicellular organism, both direct and feedback connections are carried out not only by nervous, but also by hormonal (endocrine) mechanisms. Each of the glands that make up the endocrine system affects the other organs of this system and, in turn, is influenced by the latter.

Endocrine mechanisms homeostasis according to B.M. Zavadsky, this is a mechanism of plus or minus interaction, i.e. balancing the functional activity of the gland with the concentration of the hormone. With a high concentration of the hormone (above normal), the activity of the gland is weakened and vice versa. This effect is carried out by the action of the hormone on the gland that produces it. In a number of glands, regulation is established through the hypothalamus and the anterior pituitary gland, especially during a stress response.

Endocrine glands can be divided into two groups in relation to their relation to the anterior pituitary gland. The latter is considered central, and the other endocrine glands are considered peripheral. This division is based on the fact that the anterior pituitary gland produces the so-called tropic hormones, which activate certain peripheral endocrine glands. In turn, the hormones of the peripheral endocrine glands act on the anterior pituitary gland, inhibiting the secretion of tropic hormones.

The reactions that provide homeostasis cannot be limited to any one endocrine gland, but captures all glands to one degree or another. The resulting reaction acquires a chain flow and spreads to other effectors. The physiological significance of hormones lies in the regulation of other body functions, and therefore the chain character should be expressed as much as possible.

Constant violations of the body's environment contribute to the preservation of its homeostasis during a long life. If you create such conditions of life under which nothing causes significant changes in the internal environment, then the organism will be completely unarmed when it encounters the environment and will soon die.

The combination of nervous and endocrine mechanisms of regulation in the hypothalamus allows for complex homeostatic reactions associated with the regulation of the visceral function of the body. The nervous and endocrine systems are the unifying mechanism of homeostasis.

An example of a general response of nervous and humoral mechanisms is a state of stress that develops under adverse living conditions and there is a threat of homeostasis disturbance. Under stress, there is a change in the state of most systems: muscular, respiratory, cardiovascular, digestive, sensory organs, blood pressure, blood composition. All these changes are a manifestation of individual homeostatic reactions aimed at increasing the body's resistance to adverse factors. The rapid mobilization of the body's forces acts as a protective reaction to a state of stress.

With "somatic stress" the task of increasing the overall resistance of the organism is solved according to the scheme shown in Figure 13.

Rice. 13 - Scheme of increasing the overall resistance of the body when

Homeostasis - what is it? The concept of homeostasis

Homeostasis is a self-regulating process in which all biological systems strive to maintain stability during the period of adaptation to certain conditions that are optimal for survival. Any system, being in dynamic equilibrium, strives to achieve a stable state that resists external factors and stimuli.

The concept of homeostasis

All body systems must work together to maintain proper homeostasis within the body. Homeostasis is the regulation of body temperature, water content, and carbon dioxide levels. For example, diabetes mellitus is a condition in which the body cannot regulate blood glucose levels.

Homeostasis is a term that is used both to describe the existence of organisms in an ecosystem and to describe the successful functioning of cells within an organism. Organisms and populations can maintain homeostasis under conditions of maintenance stable level fertility and mortality.

Feedback

Feedback is a process that occurs when the body's systems need to be slowed down or completely stopped. When a person eats, food enters the stomach and digestion begins. In between meals, the stomach should not work. The digestive system works with a series of hormones and nerve impulses to stop and start acid production in the stomach.

Another example of negative feedback can be observed in the case of an increase in body temperature. The regulation of homeostasis is manifested by sweating, a protective reaction of the body to overheating. In this way, the rise in temperature is stopped and the problem of overheating is neutralized. In case of hypothermia, the body also provides for a number of measures taken in order to warm up.

Maintaining internal balance

Homeostasis can be defined as a property of an organism or system that helps it to maintain given parameters within the normal range of values. This is the key to life, and the wrong balance in maintaining homeostasis can lead to diseases such as hypertension and diabetes.

Homeostasis is a key element in understanding how the human body works. Such a formal definition characterizes a system that regulates its internal environment and seeks to maintain the stability and regularity of all processes occurring in the body.

Homeostatic regulation: body temperature

Body temperature control in humans is a good example of homeostasis in a biological system. When a person is healthy, their body temperature fluctuates around + 37°C, but various factors can affect this value, including hormones, metabolic rate, and various diseases that cause fever.

In the body, temperature regulation is controlled in a part of the brain called the hypothalamus. Through the bloodstream to the brain, temperature signals are received, as well as the analysis of the results of data on the frequency of respiration, blood sugar and metabolism. The loss of heat in the human body also contributes to reduced activity.

Water-salt balance

No matter how much water a person drinks, the body does not swell like a balloon, and the human body does not shrink like raisins if you drink very little. Probably, someone once thought about it at least once. One way or another, the body knows how much fluid needs to be stored to maintain the desired level.

The concentration of salt and glucose (sugar) in the body is maintained at a constant level (in the absence of negative factors), the amount of blood in the body is about 5 liters.

Blood sugar regulation

Glucose is a type of sugar found in the blood. The human body must maintain proper glucose levels in order for a person to remain healthy. When glucose levels get too high, the pancreas releases the hormone insulin.

If the blood glucose level drops too low, the liver converts the glycogen in the blood, thereby raising the sugar level. When pathogenic bacteria or viruses enter the body, it begins to fight the infection before pathogenic elements can lead to any health problems.

Pressure under control

Maintaining healthy blood pressure is also an example of homeostasis. The heart can sense changes in blood pressure and send signals to the brain for processing. Next, the brain sends a signal back to the heart with instructions on how to respond correctly. If the blood pressure is too high, it must be lowered.

How is homeostasis achieved?

How does the human body regulate all systems and organs and compensate for the ongoing changes in the environment? This is due to the presence of many natural sensors that control temperature, blood salt composition, blood pressure and many other parameters. These detectors send signals to the brain, to the main control center, in case some values ​​deviate from the norm. After that, compensatory measures are launched to restore the normal state.

Maintaining homeostasis is incredibly important for the body. The human body contains a certain amount chemical substances, known as acids and alkalis, their correct balance is essential for the optimal functioning of all organs and systems of the body. The level of calcium in the blood must be maintained at the proper level. Because breathing is involuntary, the nervous system provides the body with much-needed oxygen. When toxins enter your bloodstream, they disrupt the body's homeostasis. The human body responds to this disturbance with the help of the urinary system.

It is important to emphasize that the body's homeostasis works automatically if the system functions normally. For example, a reaction to heat - the skin turns red, because its small blood vessels automatically dilate. Trembling is a response to being cold. Thus, homeostasis is not a set of organs, but the synthesis and balance of bodily functions. Together, this allows you to maintain the entire body in a stable state.

9.4. The concept of homeostasis. General patterns of homeostasis of living systems

Despite the fact that a living organism is an open system that exchanges matter and energy with the environment and exists in unity with it, it retains itself in time and space as a separate biological unit, retains its structure (morphology), behavioral reactions, specific physical -chemical conditions in cells, tissue fluid. The ability of living systems to withstand changes and maintain the dynamic constancy of composition and properties is called homeostasis. The term "homeostasis" was proposed by W. Cannon in 1929. However, the idea of ​​the existence of physiological mechanisms that ensure the maintenance of the constancy of the internal environment of organisms was expressed in the second half of the 19th century by C. Bernard.

Homeostasis has improved in the course of evolution. Multicellular organisms have an internal environment in which cells are located various bodies and fabrics. Then specialized organ systems (circulation, nutrition, respiration, excretion, etc.) were formed, which are involved in ensuring homeostasis at all levels of organization (molecular, subcellular, cellular, tissue, organ and organism). The most perfect mechanisms of homeostasis were formed in mammals, which contributed to a significant expansion of the possibilities of their adaptation to the environment. Mechanisms and types of homeostasis evolved in the process of long-term evolution, being fixed genetically. The appearance in the body of alien genetic information, which is often introduced by bacteria, viruses, cells of other organisms, as well as its own mutated cells, can significantly disrupt the body's homeostasis. As a protection against alien genetic information, the penetration of which into the body and its subsequent implementation would lead to poisoning with toxins (foreign proteins), such a type of homeostasis arose as genetic homeostasis, which ensures the genetic constancy of the internal environment of the body. It is based on immunological mechanisms, including non-specific and specific protection of the body's own integrity and individuality. Non-specific mechanisms underlie innate, constitutional, species immunity, as well as individual nonspecific resistance. These include the barrier function of the skin and mucous membranes, the bactericidal action of the secretion of sweat and sebaceous glands, the bactericidal properties of the contents of the stomach and intestines, lysozyme secretion of the salivary and lacrimal glands. If the organisms penetrate into the internal environment, they are eliminated during the inflammatory reaction, which is accompanied by enhanced phagocytosis, as well as the virusostatic effect of interferon (a protein with a molecular weight of 25,000 - 110,000).

Specific immunological mechanisms form the basis of acquired immunity, carried out by the immune system, which recognizes, processes and eliminates foreign antigens. Humoral immunity is carried out through the formation of antibodies circulating in the blood. The basis of cellular immunity is the formation of T-lymphocytes, the appearance of long-lived T- and B-lymphocytes of "immunological memory", the occurrence of allergies (hypersensitivity to a specific antigen). In humans, protective reactions come into effect only at the 2nd week of life, reach their highest activity by the age of 10, decrease slightly from 10 to 20 years, remain approximately at the same level from 20 to 40 years, then gradually fade away.

Immunological defense mechanisms are a serious obstacle in organ transplantation, causing graft resorption. The most successful are currently the results of autotransplantation (transplantation of tissues within the body) and allotransplantation between identical twins. They are much less successful in interspecies transplantation (heterotransplantation or xenotransplantation).

Another type of homeostasis is biochemical homeostasis helps to maintain the constancy of the chemical composition of the liquid extracellular (internal) environment of the body (blood, lymph, tissue fluid), as well as the constancy of the chemical composition of the cytoplasm and plasmolemma of cells. Physiological homeostasis ensures the constancy of the processes of vital activity of the body. Thanks to him, isoosmia (the constancy of the content of osmotically active substances), isothermia (maintenance of the body temperature of birds and mammals within certain limits), etc., have arisen and are being improved. Structural homeostasis ensures the constancy of the structure (morphological organization) at all levels (molecular, subcellular, cellular, etc.) of the organization of the living.

Population homeostasis ensures the constancy of the number of individuals in the population. Biocenotic homeostasis contributes to the constancy of the species composition and number of individuals in biocenoses.

Due to the fact that the body functions and interacts with the environment as a single system, the processes underlying various types of homeostatic reactions are closely interconnected with each other. Separate homeostatic mechanisms are combined and implemented in a holistic adaptive reaction of the body as a whole. Such association is carried out due to the activity (function) of regulatory integrating systems (nervous, endocrine, immune). The most rapid changes in the state of the regulated object are provided by the nervous system, which is associated with the speed of the processes of occurrence and conduct nerve impulse(from 0.2 to 180 m/s). The regulatory function of the endocrine system is carried out more slowly, as it is limited by the rate of release of hormones by the glands and their transfer in the bloodstream. However, the effect of hormones accumulating in it on a regulated object (organ) is much longer than with nervous regulation.

The body is a self-regulating living system. Due to the presence of homeostatic mechanisms, the body is a complex self-regulating system. The principles of existence and development of such systems are studied by cybernetics, while those of living systems are studied by biological cybernetics.

Self-regulation of biological systems is based on the principle of direct and feedback.

Information about the deviation of the controlled value from the set level is transmitted to the controller through the feedback channels and changes its activity in such a way that the controlled value returns to the initial (optimal) level (Fig. 122). Feedback can be negative(when the controlled variable deviates in positive side(the synthesis of a substance, for example, has increased excessively)) and put-

Rice. 122. Scheme of direct and feedback in a living organism:

P - regulator (nerve center, endocrine gland); RO - regulated object (cell, tissue, organ); 1 – optimal functional activity of RO; 2 - reduced functional activity of RO with positive feedback; 3 - increased functional activity of RO with negative feedback

body(when the controlled value has deviated in the negative direction (the substance is synthesized in insufficient quantity)). This mechanism, as well as more complex combinations of several mechanisms, take place at different levels of organization of biological systems. As an example of their operation on molecular level you can specify the inhibition of a key enzyme with excessive formation of the final product or the repression of enzyme synthesis. At the cellular level, the mechanisms of direct and feedback provide hormonal regulation and optimal density (number) of the cell population. A manifestation of direct and feedback at the level of the body is the regulation of blood glucose. In a living organism, the mechanisms of automatic regulation and control (studied by biocybernetics) are especially complex. The degree of their complexity contributes to an increase in the level of "reliability" and stability of living systems in relation to environmental changes.

The mechanisms of homeostasis are duplicated at different levels. This in nature realizes the principle of multi-loop regulation of systems. The main circuits are represented by cellular and tissue homeostatic mechanisms. They have a high degree of automatism. The main role in the control of cellular and tissue homeostatic mechanisms belongs to genetic factors, local reflex influences, chemical and contact interactions between cells.

The mechanisms of homeostasis undergo significant changes throughout human ontogenesis. Only 2 weeks after birth

Rice. 123. Options for loss and recovery in the body

biological defense reactions come into play (cells are formed that provide cellular and humoral immunity), and their effectiveness continues to increase by the age of 10. During this period, the mechanisms of protection against alien genetic information are improved, and the maturity of the nervous and endocrine regulatory systems also increases. The mechanisms of homeostasis reach the greatest reliability in adulthood, by the end of the period of development and growth of the organism (19-24 years). The aging of the body is accompanied by a decrease in the effectiveness of the mechanisms of genetic, structural, physiological homeostasis, a weakening of the regulatory influences of the nervous and endocrine systems.

5. Homeostasis.

An organism can be defined as a physicochemical system that exists in the environment in a stationary state. It is this ability of living systems to maintain a stationary state in a continuously changing environment that determines their survival. To ensure a steady state, all organisms - from the morphologically simplest to the most complex - have developed a variety of anatomical, physiological and behavioral adaptations that serve the same purpose - to maintain the constancy of the internal environment.

For the first time, the idea that the constancy of the internal environment provides optimal conditions for the life and reproduction of organisms was expressed in 1857 by the French physiologist Claude Bernard. Throughout his scientific activity Claude Bernard was struck by the ability of organisms to regulate and maintain within fairly narrow limits such physiological parameters as body temperature or water content. He summarized this idea of ​​self-regulation as the basis of physiological stability in the form of the classic statement: “The constancy of the internal environment is a prerequisite free life».

Claude Bernard emphasized the distinction between the external environment in which organisms live and the internal environment in which their individual cells reside, and understood the importance of keeping the internal environment unchanged. For example, mammals are able to maintain body temperature despite fluctuations in ambient temperature. If it gets too cold, the animal may move to a warmer or more sheltered place, and if this is not possible, self-regulatory mechanisms come into play that increase body temperature and prevent heat loss. The adaptive significance of this lies in the fact that the organism as a whole functions more efficiently, since the cells of which it is composed are located in optimal conditions. Self-regulation systems operate not only at the level of the organism, but also at the level of cells. An organism is the sum of its constituent cells, and the optimal functioning of the organism as a whole depends on the optimal functioning of its constituent parts. Any self-organizing system maintains the constancy of its composition - qualitative and quantitative. This phenomenon is called homeostasis, and it is common to most biological and social systems. The term homeostasis was introduced in 1932 by the American physiologist Walter Cannon.

homeostasis(Greek homoios - similar, the same; stasis-state, immobility) - the relative dynamic constancy of the internal environment (blood, lymph, tissue fluid) and the stability of basic physiological functions (blood circulation, respiration, thermoregulation, metabolism, etc. ) of humans and animals. Regulatory mechanisms that maintain the physiological state or properties of cells, organs and systems of the whole organism at an optimal level are called homeostatic. Historically and genetically, the concept of homeostasis has biological and biomedical prerequisites. There it is correlated as a final process, a period of life with a separate isolated organism or a human individual as a purely biological phenomenon. The finiteness of existence and the need to fulfill one's destiny - reproductions of one's own kind - allow one to determine a survival strategy individual organism through the concept of "preservation". "Preservation of structural and functional stability" is the essence of any homeostasis, controlled by a homeostat or self-regulating.

As you know, a living cell is a mobile, self-regulating system. Its internal organization is maintained active processes aimed at limiting, preventing or eliminating shifts caused by various influences from the environment and the internal environment. The ability to return to the original state after a deviation from a certain average level, caused by one or another "disturbing" factor, is the main property of the cell. A multicellular organism is a holistic organization, the cellular elements of which are specialized to perform various functions. Interaction within the body is carried out by complex regulatory, coordinating and correlating mechanisms with the participation of nervous, humoral, metabolic and other factors. Many individual mechanisms that regulate intra- and intercellular relationships, in some cases, have mutually opposite effects that balance each other. This leads to the establishment of a mobile physiological background (physiological balance) in the body and allows the living system to maintain relative dynamic constancy, despite changes in the environment and shifts that occur during the life of the organism.

As studies show, the methods of regulation existing in living organisms have many features in common with regulatory devices in non-living systems, such as machines. In both cases, stability is achieved through a certain form of management.

The very concept of homeostasis does not correspond to the concept of stable (not fluctuating) balance in the body - the principle of balance is not applicable to complex physiological and biochemical processes occurring in living systems. It is also wrong to oppose homeostasis to rhythmic fluctuations in the internal environment. Homeostasis in a broad sense covers the issues of cyclic and phase flow of reactions, compensation, regulation and self-regulation of physiological functions, the dynamics of the interdependence of nervous, humoral and other components of the regulatory process. The boundaries of homeostasis can be rigid and plastic, vary depending on individual age, gender, social, professional and other conditions.

Of particular importance for the life of the organism is the constancy of the composition of the blood - the liquid basis of the body (fluidmatrix), according to W. Cannon. The stability of its active reaction (pH), osmotic pressure, ratio of electrolytes (sodium, calcium, chlorine, magnesium, phosphorus), glucose content, number of formed elements, etc. is well known. For example, blood pH, as a rule, does not beyond 7.35-7.47. Even severe disorders of acid-base metabolism with a pathological accumulation of acids in the tissue fluid, for example, in diabetic acidosis, have very little effect on the active reaction of the blood. Despite the fact that the osmotic pressure of blood and tissue fluid is subject to continuous fluctuations due to the constant supply of osmotically active products of interstitial metabolism, it remains at a certain level and changes only in some severe pathological conditions. Maintaining a constant osmotic pressure is of paramount importance for water metabolism and maintaining ionic balance in the body. The greatest constancy is the concentration of sodium ions in the internal environment. The content of other electrolytes also fluctuates within narrow limits. The presence of a large number of osmoreceptors in tissues and organs, including in the central nerve formations(hypothalamus, hippocampus), and a coordinated system of regulators of water metabolism and ionic composition allows the body to quickly eliminate shifts in the osmotic blood pressure that occur, for example, when water is introduced into the body.

Despite the fact that blood represents the general internal environment of the body, the cells of organs and tissues do not directly come into contact with it. In multicellular organisms, each organ has its own internal environment (microenvironment) corresponding to its structural and functional features, and the normal state of organs depends on the chemical composition, physicochemical, biological and other properties of this microenvironment. Its homeostasis is determined by the functional state of histohematic barriers and their permeability in the directions of blood - tissue fluid; tissue fluid - blood.

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

The most perfect homeostatic mechanisms in the body of higher animals and humans include the processes of thermoregulation; in homoiothermic animals, fluctuations in temperature in the internal parts of the body during the most dramatic changes in temperature in the environment do not exceed tenths of a degree.

The organizing role of the nervous apparatus (the principle of nervism) underlies the well-known ideas about the essence of the principles of homeostasis. However, neither the dominant principle, nor the theory of barrier functions, nor the general adaptation syndrome, nor the theory of functional systems, nor the hypothalamic regulation of homeostasis, and many other theories can completely solve the problem of homeostasis.

In some cases, the concept of homeostasis is not quite rightly used to explain isolated physiological states, processes, and even social phenomena. This is how the terms “immunological”, “electrolyte”, “systemic”, “molecular”, “physico-chemical”, “genetic homeostasis”, etc., appear in the literature. Attempts have been made to reduce the problem of homeostasis to the principle of self-regulation. An example of solving the problem of homeostasis from the standpoint of cybernetics is Ashby's attempt (W.R. Ashby, 1948) to design a self-regulating device that simulates the ability of living organisms to maintain the level of certain quantities within physiologically acceptable limits.

In practice, researchers and clinicians face the issues of assessing the adaptive (adaptive) or compensatory capabilities of the body, their regulation, strengthening and mobilization, predicting the body's response to disturbing influences. Some states of vegetative instability, caused by insufficiency, excess or inadequacy of regulatory mechanisms, are considered as “diseases of homeostasis”. With a certain conventionality, they can include functional disorders of the normal activity of the body associated with its aging, forced restructuring biological rhythms, some phenomena of vegetative dystonia, hyper- and hypocompensatory reactivity during stressful and extreme exposure etc.

To assess the state of homeostatic mechanisms in a physiological experiment and in clinical practice, various dosed functional tests are used (cold, thermal, adrenaline, insulin, mezaton, etc.) with the determination of the ratio of biologically active substances (hormones, mediators, metabolites) in blood and urine, etc. .d.

Biophysical mechanisms of homeostasis.

From the point of view of chemical biophysics, homeostasis is a state in which all processes responsible for energy transformations in the body are in dynamic equilibrium. This state is the most stable and corresponds to the physiological optimum. In accordance with the concepts of thermodynamics, an organism and a cell can exist and adapt to such environmental conditions under which a stationary flow can be established in a biological system. physical and chemical processes, i.e. homeostasis. The main role in establishing homeostasis belongs primarily to cellular membrane systems, which are responsible for bioenergetic processes and regulate the rate of entry and release of substances by cells.

From these positions, the main causes of the disturbance are non-enzymatic reactions that are unusual for normal life activity, occurring in membranes; in most cases, these are chain reactions of oxidation involving free radicals that occur in cell phospholipids. These reactions lead to damage to the structural elements of cells and disruption of the regulatory function. Factors that cause homeostasis disorders also include agents that cause radical formation, - ionizing radiation, infectious toxins, certain foods, nicotine, and vitamin deficiencies, etc.

One of the main factors stabilizing the homeostatic state and functions of membranes are bioantioxidants, which inhibit the development of oxidative radical reactions.

Age features of homeostasis in children.

The constancy of the internal environment of the body and the relative stability of physicochemical parameters in childhood are provided with a pronounced predominance of anabolic metabolic processes over catabolic ones. This is an indispensable condition for growth and distinguishes the child's body from the body of adults, in which the intensity of metabolic processes is in a state of dynamic equilibrium. In this regard, the neuroendocrine regulation of the homeostasis of the child's body is more intense than in adults. Each age period is characterized by specific features of homeostasis mechanisms and their regulation. Therefore, in children much more often than in adults, there are severe violations of homeostasis, often life-threatening. These disorders are most often associated with the immaturity of the homeostatic functions of the kidneys, with disorders of the functions of the gastrointestinal tract or respiratory function of the lungs.

The growth of the child, expressed in an increase in the mass of his cells, is accompanied by distinct changes in the distribution of fluid in the body. The absolute increase in the volume of extracellular fluid lags behind the rate of overall weight gain, so the relative volume of the internal environment, expressed as a percentage of body weight, decreases with age. This dependence is especially pronounced in the first year after birth. In older children, the rate of change in the relative volume of extracellular fluid decreases. The system for regulating the constancy of the volume of liquid (volume regulation) provides compensation for deviations in the water balance within fairly narrow limits. A high degree of tissue hydration in newborns and young children determines a significantly higher need for water than in adults (per unit body weight). Losses of water or its limitation quickly lead to the development of dehydration due to the extracellular sector, i.e., the internal environment. At the same time, the kidneys - the main executive organs in the system of volume regulation - do not provide water savings. The limiting factor of regulation is the immaturity of the tubular system of the kidneys. The most important feature of the neuroendocrine control of homeostasis in newborns and young children is the relatively high secretion and renal excretion of aldosterone, which has a direct effect on the state of tissue hydration and the function of the renal tubules.

Regulation of the osmotic pressure of blood plasma and extracellular fluid in children is also limited. The osmolarity of the internal environment fluctuates over a wider range ( 50 mosm/l) , than adults

( 6 mosm/l) . It's connected with larger body surface per 1 kg weight and, consequently, with more significant losses of water during respiration, as well as with the immaturity of the renal mechanisms of urine concentration in children. Homeostasis disorders, manifested by hyperosmosis, are especially common in children during the neonatal period and the first months of life; at older ages, hypoosmosis begins to predominate, associated mainly with gastrointestinal disease or kidney disease. Less studied is the ionic regulation of homeostasis, which is closely related to the activity of the kidneys and the nature of nutrition.

It was previously believed that the main factor determining the value of the osmotic pressure of the extracellular fluid is the concentration of sodium, but more recent studies have shown that there is no close correlation between the sodium content in the blood plasma and the value of the total osmotic pressure in pathology. The exception is plasmatic hypertension. Therefore, homeostatic therapy by administering glucose-salt solutions requires monitoring not only the sodium content in serum or plasma, but also changes in the total osmolarity of the extracellular fluid. Of great importance in maintaining the total osmotic pressure in the internal environment is the concentration of sugar and urea. The content of these osmotically active substances and their effect on water-salt metabolism can increase sharply in many pathological conditions. Therefore, for any violations of homeostasis, it is necessary to determine the concentration of sugar and urea. In view of the foregoing, in children of early age, in violation of the water-salt and protein regimes, a state of latent hyper- or hypoosmosis, hyperazotemia may develop.

An important indicator characterizing homeostasis in children is the concentration of hydrogen ions in the blood and extracellular fluid. In the antenatal and early postnatal periods, the regulation of acid-base balance is closely related to the degree of blood oxygen saturation, which is explained by the relative predominance of anaerobic glycolysis in bioenergetic processes. Moreover, even moderate hypoxia in the fetus is accompanied by the accumulation of lactic acid in its tissues. In addition, the immaturity of the acidogenetic function of the kidneys creates the prerequisites for the development of "physiological" acidosis (a shift in the acid-base balance in the body towards a relative increase in the number of acid anions.). In connection with the peculiarities of homeostasis in newborns, disorders often occur that stand on the verge between physiological and pathological.

The restructuring of the neuroendocrine system during puberty (puberty) is also associated with changes in homeostasis. However, the functions executive bodies(kidneys, lungs) reach the maximum degree of maturity at this age, so severe syndromes or diseases of homeostasis are rare, but more often we are talking about compensated changes in metabolism, which can only be detected by a biochemical blood test. In the clinic, to characterize homeostasis in children, it is necessary to examine the following indicators: hematocrit, total osmotic pressure, sodium, potassium, sugar, bicarbonates and urea in the blood, as well as blood pH, p0 2 and pCO 2.

Features of homeostasis in the elderly and senile age.

The same level of homeostatic values ​​in different age periods supported by various shifts in the systems of their regulation. For example, the constancy of blood pressure at a young age is maintained due to a higher cardiac output and low total peripheral vascular resistance, and in the elderly and senile - due to a higher total peripheral resistance and a decrease in cardiac output. During the aging of the body, the constancy of the most important physiological functions is maintained in conditions of decreasing reliability and reducing the possible range of physiological changes in homeostasis. The preservation of relative homeostasis with significant structural, metabolic and functional changes is achieved by the fact that at the same time not only extinction, disturbance and degradation occurs, but also the development of specific adaptive mechanisms. Due to this, a constant level of sugar in the blood, blood pH, osmotic pressure, membrane potential cells, etc.

Changes in the mechanisms of neurohumoral regulation, an increase in the sensitivity of tissues to the action of hormones and mediators against the background of a weakening of nervous influences, are essential in maintaining homeostasis during the aging process.

With the aging of the body, the work of the heart, pulmonary ventilation, gas exchange, renal functions, secretion of the digestive glands, the function of the endocrine glands, metabolism, etc., change significantly. These changes can be characterized as homeoresis - a regular trajectory (dynamics) of changes in the intensity of metabolism and physiological functions with age in time. The value of the course of age-related changes is very important for characterizing the aging process of a person, determining his biological age.

In the elderly and senile age, the general potential of adaptive mechanisms decreases. Therefore, in old age, with increased loads, stress and other situations, the likelihood of disruption of adaptive mechanisms and homeostasis disturbances increase. Such a decrease in the reliability of homeostasis mechanisms is one of the essential prerequisites development of pathological disorders in old age.

Thus, homeostasis is an integral concept, functionally and morphologically uniting cardiovascular system, respiratory system, renal system, water-electrolyte metabolism, acid-base balance.

Main purpose of cardio-vascular system – supply and distribution of blood in all pools of microcirculation. The amount of blood ejected by the heart in 1 minute is the minute volume. However, the function of the cardiovascular system is not just to maintain a given minute volume and its distribution among the pools, but to change the minute volume in accordance with the dynamics of tissue needs in different situations.

The main task of the blood is the transport of oxygen. Many surgical patients experience an acute drop in minute volume, which impairs oxygen delivery to tissues and can lead to cell, organ, and even whole-body death. Therefore, the assessment of the function of the cardiovascular system should take into account not only the minute volume, but also the supply of oxygen to the tissues and their need for it.

Main purpose respiratory system - ensuring adequate gas exchange between the body and the environment at a constantly changing rate of metabolic processes. The normal function of the respiratory system is to maintain a constant level of oxygen and carbon dioxide in the arterial blood with normal vascular resistance in the pulmonary circulation and with ordinary cost energy for breathing.

This system is closely connected with other systems, and primarily with the cardiovascular system. The function of the respiratory system includes ventilation, pulmonary circulation, diffusion of gases across the alveolar-capillary membrane, transport of gases by the blood, and tissue respiration.

Functions renal system : The kidneys are the main organ designed to maintain the constancy of the physicochemical conditions in the body. The main of their functions is excretory. It includes: regulation of water and electrolyte balance, maintenance of acid-base balance and removal of metabolic products of proteins and fats from the body.

Functions water and electrolyte metabolism : water in the body plays a transport role, filling cells, interstitial (intermediate) and vascular spaces, is a solvent of salts, colloids and crystalloids and takes part in biochemical reactions. All biochemical fluids are electrolytes, since salts and colloids dissolved in water are in a dissociated state. It is impossible to list all the functions of electrolytes, but the main ones are: maintaining osmotic pressure, maintaining the reaction of the internal environment, participating in biochemical reactions.

Main purpose acid-base balance It consists in maintaining the constancy of the pH of the liquid media of the body as the basis for normal biochemical reactions and, consequently, life. Metabolism occurs with the indispensable participation of enzymatic systems, the activity of which closely depends on the chemical reaction of the electrolyte. Together with water-electrolyte metabolism, acid-base balance plays a decisive role in the ordering of biochemical reactions. Buffer systems and many physiological systems of the body take part in the regulation of acid-base balance.

homeostasis

Homeostasis, homeoresis, homeomorphosis - characteristics of the state of the body. The system essence of the organism is manifested primarily in its ability to self-regulate in continuously changing environmental conditions. Since all organs and tissues of the body consist of cells, each of which is a relatively independent organism, the state of the internal environment human body is of great importance for its normal functioning. For the human body - a land creature - the environment is the atmosphere and the biosphere, while it interacts to a certain extent with the lithosphere, hydrosphere and noosphere. At the same time, most of the cells of the human body are immersed in a liquid medium, which is represented by blood, lymph and intercellular fluid. Only integumentary tissues directly interact with the human environment, all other cells are isolated from the outside world, which allows the body to largely standardize the conditions for their existence. In particular, the ability to maintain a constant body temperature of about 37 ° C ensures the stability of metabolic processes, since all the biochemical reactions that make up the essence of metabolism are very temperature dependent. It is equally important to maintain a constant tension of oxygen, carbon dioxide, concentration of various ions, etc. in the liquid media of the body. Under normal conditions of existence, including during adaptation and activity, small deviations of such parameters occur, but they are quickly eliminated, the internal environment of the body returns to a stable norm. Great French physiologist of the 19th century. Claude Bernard said: "The constancy of the internal environment is a prerequisite for a free life." The physiological mechanisms that ensure the maintenance of the constancy of the internal environment are called homeostatic, and the phenomenon itself, which reflects the body's ability to self-regulate the internal environment, is called homeostasis. This term was introduced in 1932 by W. Cannon, one of those physiologists of the 20th century, who, along with N.A. Bernstein, P.K. Anokhin and N. Wiener, stood at the origins of the science of control - cybernetics. The term "homeostasis" is used not only in physiological, but also in cybernetic research, since it is precisely the maintenance of the constancy of any characteristics of a complex system that is main goal any management.

Another remarkable researcher, K. Waddington, drew attention to the fact that the body is able to maintain not only the stability of its internal state, but also the relative constancy of dynamic characteristics, i.e., the flow of processes over time. This phenomenon, by analogy with homeostasis, was called homeoresis. It is of particular importance for a growing and developing organism and consists in the fact that the organism is able to maintain (within certain limits, of course) the "channel of development" in the course of its dynamic transformations. In particular, if a child, due to illness or a sharp deterioration in living conditions caused by social reasons(war, earthquake, etc.), lags significantly behind its normally developing peers, this does not mean that such a lag is fatal and irreversible. If the period of adverse events ends and the child receives adequate conditions for development, then both in terms of growth and level functional development he soon catches up with his peers and in the future does not differ significantly from them. This explains the fact that those transferred to early age severe illness, children often grow up into healthy and proportionately built adults. Homeoresis plays a crucial role both in the management ontogenetic development and in adaptation processes. Meanwhile, the physiological mechanisms of homeoresis are still insufficiently studied.

The third form of self-regulation of body constancy is homeomorphosis - the ability to maintain the invariance of the form. This characteristic is more characteristic of an adult organism, since growth and development are incompatible with the invariance of form. Nevertheless, if we consider short periods of time, especially during periods of growth inhibition, then in children it is possible to detect the ability to homeomorphosis. We are talking about the fact that in the body there is a continuous change of generations of its constituent cells. Cells do not live long (the only exception is nerve cells): the normal lifespan of body cells is weeks or months. Nevertheless, each new generation of cells almost exactly repeats the shape, size, arrangement and, accordingly, the functional properties of the previous generation. Special physiological mechanisms prevent significant changes in body weight in conditions of starvation or overeating. In particular, during starvation, the digestibility of nutrients increases sharply, and during overeating, on the contrary, most of the proteins, fats and carbohydrates that come with food are "burned" without any benefit to the body. It has been proven (N.A. Smirnova) that in an adult, sharp and significant changes in body weight (mainly due to the amount of fat) in any direction are sure signs of a breakdown in adaptation, overstrain and indicate a functional dysfunction of the body. The child's body becomes especially sensitive to external influences during periods of the most rapid growth. Violation of homeomorphosis is the same unfavorable sign as violations of homeostasis and homeoresis.

The concept of biological constants. The body is a complex of a huge number of a wide variety of substances. In the process of vital activity of body cells, the concentration of these substances can change significantly, which means a change in the internal environment. It would be unthinkable if the control systems of the body were forced to monitor the concentration of all these substances, i.e. have a lot of sensors (receptors), continuously analyze the current state, make management decisions and monitor their effectiveness. Neither the information nor the energy resources of the body would be enough for such a regime of control of all parameters. Therefore, the body is limited to monitoring a relatively small number of the most significant indicators that need to be maintained at a relatively constant level for the sake of well-being. absolute majority body cells. These most rigidly homeostatic parameters thus turn into "biological constants", and their invariance is ensured by sometimes quite significant fluctuations of other parameters that do not belong to the category of homeostatic ones. Thus, the levels of hormones involved in the regulation of homeostasis can change tenfold in the blood, depending on the state of the internal environment and the impact of external factors. At the same time, homeostatic parameters change only by 10-20%.

The most important biological constants. Among the most important biological constants, for the maintenance of which at a relatively unchanged level, various physiological systems of the body are responsible, we should mention body temperature, blood glucose level, content of H+ ions in body fluids, partial voltage oxygen and carbon dioxide in tissues.

Disease as a symptom or consequence of homeostasis disorders. Almost all human diseases are associated with a violation of homeostasis. So, for example, in many infectious diseases, as well as in the case of inflammatory processes, temperature homeostasis is sharply disturbed in the body: fever (fever), sometimes life-threatening, occurs. The reason for such a violation of homeostasis may lie both in the features of the neuroendocrine reaction, and in violations of the activity of peripheral tissues. In this case, the manifestation of the disease - fever- is a consequence of a violation of homeostasis.

Usually, feverish conditions are accompanied by acidosis - a violation of the acid-base balance and a shift in the reaction of body fluids to the acid side. Acidosis is also characteristic of all diseases associated with the deterioration of the cardiovascular and respiratory systems(diseases of the heart and blood vessels, inflammatory and allergic lesions of the bronchopulmonary system, etc.). Often, acidosis accompanies the first hours of a newborn's life, especially if normal breathing did not begin immediately after birth. To eliminate this condition, the newborn is placed in a special chamber with a high oxygen content. Metabolic acidosis with heavy muscular exertion can occur in people of any age and manifests itself in shortness of breath and increased sweating, as well as painful sensations in the muscles. After completion of work, the state of acidosis can persist from several minutes to 2-3 days, depending on the degree of fatigue, fitness and the effectiveness of homeostatic mechanisms.

Very dangerous are diseases that lead to a violation of water-salt homeostasis, for example, cholera, in which great amount water and tissues lose their functional properties. Many kidney diseases also lead to a violation of water-salt homeostasis. As a result of some of these diseases, alkalosis can develop - an excessive increase in the concentration of alkaline substances in the blood and an increase in pH (shift to the alkaline side).

In some cases, minor but long-term disturbances in homeostasis can cause the development of certain diseases. So, there is evidence that excessive consumption of sugar and other sources of carbohydrates that disrupt glucose homeostasis leads to damage to the pancreas, as a result, a person develops diabetes. Also dangerous is the excessive consumption of table and other mineral salts, hot spices, etc., which increase the load on the excretory system. Kidneys May not cope with the abundance of substances that need to be removed from the body, resulting in a violation of water-salt homeostasis. One of its manifestations is edema - the accumulation of fluid in the soft tissues of the body. The cause of edema usually lies either in the insufficiency of the cardiovascular system, or in violations of the kidneys and, as a result, mineral metabolism.

Homeostasis is:

homeostasis

homeostasis(ancient Greek ὁμοιοστάσις from ὁμοιος - the same, similar and στάσις - standing, immobility) - self-regulation, the ability of an open system to maintain the constancy of its internal state through coordinated reactions aimed at maintaining dynamic balance. The desire of the system to reproduce itself, to restore the lost balance, to overcome the resistance of the external environment.

Population homeostasis is the ability of a population to maintain a certain number of its individuals for a long time.

The American physiologist Walter B. Cannon proposed the term in 1932 in his book The Wisdom of the Body as a name for "the coordinated physiological processes that maintain the body's most stable states." Later, 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 often used in biology. For multicellular organisms to exist, it is necessary to maintain the constancy of the internal environment. Many ecologists are convinced that this principle also applies to the external environment. If the system is unable to restore its balance, it may eventually cease to function.

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

properties of homeostasis

Homeostatic systems have the following properties:

• instability system: tests how it can best adapt.
• Striving for balance: all the internal, structural and functional organization of systems contributes to maintaining balance.
• unpredictability: The resultant effect of a certain action can often be different from what was expected.

Examples of homeostasis in mammals:

• 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. Carried out by exocrine organs - kidneys, lungs, sweat glands and the 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.

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

Main article: Feedback

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

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 increase in the change in a variable. It has a destabilizing effect, so it does not lead to homeostasis. Positive feedback is less common in natural systems, but also has its uses.
   • For example, in nerves, a threshold electrical potential causes the generation of a much larger action potential. Blood clotting and birth events are other examples of positive feedback.

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

Ecological homeostasis

Ecological homeostasis is observed in climax communities with the highest possible biodiversity under favorable environmental conditions.

In disturbed ecosystems, or sub-climax biological communities - such as the island of Krakatoa, after a strong volcanic eruption in 1883 - the state of homeostasis of the previous forest climax ecosystem was destroyed, like all life on this island. Krakatoa went through a chain of ecological changes in the years following the eruption, in which new plant and animal species succeeded 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 Krakatoa example, this island developed a climax community with 8,000 different species recorded in 1983, a hundred years after the eruption wiped out 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 microenvironment of its specific ecological niche is invested more energy.

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 other species from invading. 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

Further information: Acid-base balance

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

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

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

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

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

Cellular homeostasis

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 temperature, the degree of acidity, the concentration of the substrate, the presence of certain macro- and microelements.

Homeostasis in the human body

Further information: Acid-base balance See also: Blood buffer systems

Various factors affect the ability of body fluids to sustain life. These include 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 the body alive, there are built-in physiological mechanisms to keep them at the required 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 the 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 the body temperature is too low.
  • 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

Categories:

• homeostasis
• open systems
• Physiological processes

Wikimedia Foundation. 2010.

Homeostasis (Greek homoios - the same, similar, stasis - stability, balance) is a set of coordinated reactions that maintain or restore the constancy of the internal environment of the body. In the middle of the nineteenth century, the French physiologist Claude Bernard introduced the concept of the internal environment, which he considered as a collection of body fluids. This concept was expanded by the American physiologist Walter Cannon, who meant by the internal environment the totality of fluids (blood, lymph, tissue fluid) that are involved in metabolism and maintaining homeostasis. The human body adapts to constantly changing environmental conditions, but the internal environment remains constant and its indicators fluctuate within very narrow limits. Therefore, a person can live in various environmental conditions. Some physiological parameters are regulated especially carefully and finely, for example, body temperature, blood pressure, glucose, gases, salts, calcium ions in the blood, acid-base balance, blood volume, its osmotic pressure, appetite, and many others. Regulation is carried out according to the principle of negative feedback between the receptors f , which detect changes in the indicated indicators and control systems. So, a decrease in one of the parameters is captured by the corresponding receptor, from which impulses are sent to one or another structure of the brain, at the command of which the autonomic nervous system turns on complex mechanisms balancing out the changes. The brain uses two main systems to maintain homeostasis: autonomic and endocrine. Recall that main function autonomic nervous system is the preservation of the constancy of the internal environment of the body, which is carried out due to a change in the activity of the sympathetic and parasympathetic parts of the autonomic nervous system. The latter, in turn, is controlled by the hypothalamus, and the hypothalamus by the cerebral cortex. The endocrine system regulates the function of all organs and systems through hormones. Moreover, the endocrine system itself is under the control of the hypothalamus and pituitary gland. Homeostasis (Greek homoios - the same and stasis - state, immobility)

As our understanding of normal, and even more pathological, physiology became more complex, this concept was refined as homeokinesis, i.e. mobile equilibrium, the balance of constantly changing processes. The body is woven from millions of "homeokinesics". This huge living galaxy determines the functional status of all organs and cells that are bound by regulatory peptides. Like the world economic and financial system - many firms, industries, factories, banks, stock exchanges, markets, shops ... And between them - "convertible currency" - neuropeptides. All body cells constantly synthesize and maintain a certain, functionally necessary, level of regulatory peptides. But when deviations from "stationarity" occur, their biosynthesis (in the body as a whole or in its individual "loci") either increases or weakens. Such fluctuations occur constantly when it comes to adaptive reactions (getting used to new conditions), performance of work (physical or emotional actions), the state of pre-illness - when the body "turns on" increased protection against functional imbalance. The classic case of maintaining balance is the regulation of blood pressure. There are groups of peptides between which there is constant competition - to increase / decrease pressure. In order to run, climb a mountain, bathe in a sauna, perform on stage, and finally think, a functionally sufficient increase in blood pressure is necessary. But as soon as the work is over, the regulators come into action, ensuring the “calming” of the heart and normal pressure in the vessels. Vasoactive peptides constantly interact to "allow" to increase the pressure to such and such a level (no more, otherwise the vascular system will go "peddling"; a well-known and bitter example is a stroke) and so that after the completion of physiologically necessary work

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. The key idea of ​​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 when studying the physiological properties of these elements, it is necessary to consider the conditions for 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 general physiology University of Paris, since 1868 - an employee of the Museum of 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 studies of C. Bernard are devoted to the physiology of the nervous system, digestion and blood circulation. The merits of the scientist in the development of experimental physiology are great. He conducted classical studies on the anatomy and physiology of the gastrointestinal tract, the role of the pancreas, carbohydrate metabolism, the functions of digestive juices, discovered the formation of glycogen in the liver, studied the innervation of blood vessels, the vasoconstrictive effect of sympathetic nerves, etc. One of the creators of the doctrine of homeostasis, introduced 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 the existing forces of the body (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 a 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, C. Bernard is still in the second half 19th century gave a 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 rather 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 of the Academy of Sciences of the USSR (since 1942). Main scientific work 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). He considered the human body as a 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: it denotes the most probable state of an 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 are constantly taking place, ensuring 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 indicators 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, the concentration of glucose and mineral salts in the blood plasma, pressure in the vessels - fluctuate within very narrow limits near certain average values ​​- physiological constants. Maintaining these constants in the body is required condition 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.). At the present stage of development of knowledge about homeostasis, this classification has been 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 violations 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 are devoted to the study of the chemical foundations of 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 drugs 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 individual parts of the body (organs and tissues) differentiate and develop, each organ, each tissue must create and develop its own immediate nutrient medium, the composition and properties of which must correspond to the structural and functional features of this organ. 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 the barriers contributes to the preservation of homeostasis and the known specificity of the internal environment necessary for the normal function of a particular 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 of the own environment of the organ and cell. 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, this concept is still 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. at the 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 of 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 USSR AMS. Laureate of the 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 a general pattern of the 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.

Analysis of the definitions available in the biological and reference literature, made it possible to single out the most important aspects of this concept and formulate a general definition: homeostasis is a state of relative dynamic equilibrium of the system, supported by self-regulation mechanisms. 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 ensure regulation and self-regulation at different levels of the organization of living matter was described by G.N. Kassil. There are the following levels of 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 neural 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 as 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 is the individual development of the organism from the formation of a germ cell to death or the 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, an integral part of the body's adaptive mechanism. 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 the 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 associated, on the one hand, with the fight for the purity of the genetic code and the prevention of various diseases, and on the other hand, with maintaining the liquid state of 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 "switching 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) the general mechanism for switching 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 is occupied by 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 to and from the cell, changing its permeability, takes part in the regulation of the electrolyte composition of the cell, and functions as biological "pumps".

Homeostats and technical models of homeostatic processes

In recent decades, the problem of homeostasis has been 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. In this phrase, there is an indication of the need for both direct and feedback relationships that underlie 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 a problem of controlling the flows of substances and energy that an open system exchanges with the environment.

The first attempt to model homeostasis and establish possible mechanisms for controlling it 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 practical development organized control systems, revealed some cybernetic analogies between a living system and complex production.

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

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. Russian scientists I.P. Razenkov and L.S. Stern.

The accumulated colossal factual material describing various manifestations of homeostasis in living, technical, social, 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.

Modern 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 for stabilizing the composition of incoming substances, liquids and gases and the release of end products of metabolism - stage 3. Thus, temperature, water content and the concentration of electrolytes, oxygen and carbon dioxide, and the amount of nutrients are maintained at a relatively constant level. and excreted metabolic products.

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 properties;
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 are some examples of topics that can be studied using the materials of the article. "Organs. Organ systems, the organism as a whole. "Nervous and humoral regulation 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".

In the organism of higher animals, adaptations have been developed that counteract many influences of the external environment, providing relatively constant conditions for the existence of cells. It has essential for the life of the whole organism. We illustrate this with examples. The cells of the body of warm-blooded animals, that is, animals with a constant body temperature, function normally only within narrow temperature limits (in humans, within 36-38 °). A temperature shift beyond these limits leads to disruption of cell activity. At the same time, the body of warm-blooded animals can normally exist with much wider fluctuations in the temperature of the external environment. For example, a polar bear can live at temperatures of -70° and +20-30°. This is due to the fact that in the whole organism its heat exchange with the environment is regulated, i.e., heat generation (the intensity of chemical processes occurring with the release of heat) and heat transfer. So, at a low ambient temperature, heat generation increases, and heat transfer decreases. Therefore, with fluctuations in external temperature (within certain limits), the constancy of body temperature is maintained.

The functions of body cells are normal only with a relative constancy of osmotic pressure, due to the constancy of the content of electrolytes and water in the cells. Changes in osmotic pressure - its decrease or increase - lead to sharp violations of the functions and structure of cells. The organism as a whole can exist for some time both with excessive intake and with deprivation of water, and with large and small amounts of salts in food. This is due to the presence in the body of adaptations that contribute to maintaining
constancy of the amount of water and electrolytes in the body. In the case of excess water intake, significant amounts of it are quickly excreted from the body by the excretory organs (kidneys, sweat glands, skin), and with a lack of water, it is retained in the body. In the same way, the excretory organs regulate the content of electrolytes in the body: they quickly remove excess amounts of them or keep them in the body fluids with insufficient intake of salts.

The concentration of individual electrolytes in the blood and tissue fluid, on the one hand, and in the protoplasm of cells, on the other, is different. The blood and tissue fluid contain more sodium ions, and the protoplasm of cells contains more potassium ions. The difference in the concentration of ions inside the cell and outside it is achieved by a special mechanism that keeps potassium ions inside the cell and does not allow sodium ions to accumulate in the cell. This mechanism, the nature of which is not yet clear, is called the sodium-potassium pump and is associated with the process of cell metabolism.

Body cells are very sensitive to shifts in the concentration of hydrogen ions. A change in the concentration of these ions in one direction or another sharply disrupts the vital activity of cells. The internal environment of the body is characterized by a constant concentration of hydrogen ions, which depends on the presence of so-called buffer systems in the blood and tissue fluid (p. 48) and on the activity of the excretory organs. With an increase in the content of acids or alkalis in the blood, they are quickly excreted from the body and in this way the constancy of the concentration of hydrogen ions in the internal environment is maintained.

Cells, especially nerve cells, are very sensitive to changes in blood sugar, an important nutrient. Therefore, the constancy of the sugar content in the blood is of great importance for the life process. It is achieved by the fact that with an increase in blood sugar levels in the liver and muscles, a polysaccharide, glycogen, deposited in the cells, is synthesized from it, and with a decrease in blood sugar levels, glycogen is broken down in the liver and muscles and grape sugar is released into the blood.

The constancy of the chemical composition and physicochemical properties of the internal environment is important feature higher animal organisms. To designate this constancy, W. Cannon proposed a term that has become widespread - homeostasis. The expression of homeostasis is the presence of a number of biological constants, i.e., stable quantitative indicators that characterize the normal state of the body. Such constant values ​​are: body temperature, osmotic pressure of blood and tissue fluid, the content of sodium, potassium, calcium, chlorine and phosphorus ions, as well as proteins and sugar, the concentration of hydrogen ions and a number of others.

Noting the constancy of the composition, physicochemical and biological properties of the internal environment, it should be emphasized that it is not absolute, but relative and dynamic. This constancy is achieved by the continuously performed work of a number of organs and tissues, as a result of which the shifts in the composition and physicochemical properties of the internal environment that occur under the influence of changes in the external environment and as a result of the vital activity of the organism are leveled.

Role various organs and their systems in maintaining homeostasis is different. Thus, the digestive system ensures the flow of nutrients into the blood in the form in which they can be used by the cells of the body. The circulatory system carries out the continuous movement of blood and the transport of various substances in the body, as a result of which nutrients, oxygen and various chemical compounds formed in the body itself enter the cells, and the decay products, including carbon dioxide, released by the cells are transferred to the organs that remove them from the body. The respiratory organs provide oxygen to the blood and remove carbon dioxide from the body. The liver and a number of other organs carry out a significant number of chemical transformations - the synthesis and breakdown of many chemical compounds that are important in the life of cells. Excretory organs - kidneys, lungs, sweat glands, skin - remove end products of decay from the body organic matter and maintain the constancy of the content of water and electrolytes in the blood, and consequently, in the tissue fluid and in the cells of the body.

plays an important role in maintaining homeostasis nervous system. Sensitively reacting to various changes in the external or internal environment, it regulates the activity of organs and systems in such a way that shifts and disturbances that occur or could occur in the body are prevented and leveled.

Thanks to the development of adaptations that ensure the relative constancy of the internal environment of the body, its cells are less susceptible to the changing influences of the external environment. According to Cl. Bernard, "the constancy of the internal environment is a condition for a free and independent life."

Homeostasis has certain limits. When the body stays, especially for a long time, in conditions that differ significantly from those to which it is adapted, homeostasis is disturbed and shifts incompatible with normal life can occur. So, with a significant change in external temperature in the direction of both its increase and decrease, the body temperature may rise or fall and overheating or cooling of the body may occur, leading to death. Similarly, with a significant restriction of the intake of water and salts into the body or a complete deprivation of these substances, the relative constancy of the composition and physico-chemical properties of the internal environment is disturbed after a while and life stops.

High level homeostasis occurs only at certain stages of species and individual development. The lower animals do not have sufficiently developed adaptations to mitigate or eliminate the influences of changes in the external environment. So, for example, the relative constancy of body temperature (homeothermia) is maintained only in warm-blooded animals. In the so-called cold-blooded animals, the body temperature is close to the temperature of the external environment and represents a variable value (poikilothermia). A newborn animal does not have such a constancy of body temperature, composition and properties of the internal environment, as in an adult organism.

Even small violations of homeostasis lead to pathology, and therefore the determination of relatively constant physiological parameters, such as body temperature, blood pressure, composition, physicochemical and biological properties of blood, etc., is of great diagnostic value.