Homeostasis short definition. Mechanisms of homeostasis. Homeostasis from a biological and ecological point of view

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

The essence of the concept

Homeostasis is a property of a living organism that allows maintaining important characteristics within acceptable limits. For normal functioning, the constancy of the internal environment and individual indicators is necessary.

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

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

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

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

Definition

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

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

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

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

Characteristics

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

The phenomenon has such features as:

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

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

Application in biology

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

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

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

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

Biologists distinguish between two types of creatures:

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

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

How does a person

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

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

This property affects settings such as:

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

All these parameters affect the state of the person as a whole. The normal course of chemical reactions that contribute to the preservation of life depends on them. Homeostasis allows you to restore the previous performance after any impact, but is not the cause of adaptive reactions. This property is a common characteristic of a large number of processes operating simultaneously.

For blood

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

Thanks to it, individual parts of the body are supplied with oxygen, and an outflow of harmful substances and metabolic products is carried out.

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

This substance must keep the following parameters relatively constant:

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

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

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

Use in medicine

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

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

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

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

Wikipedia

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

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

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

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

Examples

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

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Summing up

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

In contact with

homeostasis(ancient Greek ὁμοιοστάσις from ὅμοιος - 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.

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-update process structural elements organism and restoration of 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, which are characterized by cellular regeneration (bones, loose connective tissue, hematopoietic system, endothelium, mesothelium, mucous membranes of the gastrointestinal tract, respiratory tract and genitourinary 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 in their car are not in a safer position compared to 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 that has a connection with the 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 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 relative constancy chemical composition, osmotic pressure, stability of 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 during 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 is of 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 a stimulus for turning on 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).

So, during 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 the organism provides for the formation of species-specific characteristics not in constant, but in changing environmental conditions, within the limits of the 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, irradiation, 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. The genes responsible for the synthesis of antigens that cause a reaction to the 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 big number 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 the close genetic relationship 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 typical for all levels: protein renewal, constituent parts 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 natural process restoration of body elements 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 original 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, the exchange of 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 bark hemispheres and 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 while maintaining stable birth and death rates.

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 the 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 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 of chemicals known as acids and bases, and their proper balance is essential for the optimal functioning of all organs and body systems. 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 of various organs and tissues are located. 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 somewhat 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 organism functions and interacts with the environment as a single system, the processes underlying various kinds 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 conduction of a nerve impulse (from 0.2 to 180 m/sec). 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 regulated value from the set level is transmitted to the controller through the feedback channels and changes its activity in such a way that the regulated value returns to the initial (optimal) level (Fig. 122). Feedback can be negative(when the controlled value has deviated in a positive direction (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, takes place on different levels organization of biological systems. As an example of their functioning at the molecular level, one can point to 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 for a free life."

Claude Bernard emphasized the difference between the external environment in which organisms live and the internal environment in which their individual cells are located, and understood how important it was for the internal environment to remain 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 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 characteristic of 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 - reproduction of one's own kind - allow one to determine the survival strategy of an 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 is known, living cell represents a mobile, self-regulating system. Its internal organization is supported by active processes aimed at limiting, preventing or eliminating shifts caused by various influences from the environment and the internal environment. The ability to return to the original state after a deviation from a certain average level, caused by one or another "disturbing" factor, is the main property of the cell. A multicellular organism is a holistic organization, the cellular elements of which are specialized to perform various functions. Interaction within the body is carried out by complex regulatory, coordinating and correlating mechanisms with 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. 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 nervous 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, temperature fluctuations in the internal parts of the body at the most abrupt changes ambient temperatures 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 point of view 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 questions 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 disturbances in the normal functioning of the body associated with its aging, forced restructuring of biological rhythms, some phenomena of vegetative dystonia, hyper- and hypocompensatory reactivity during stressful and extreme influences, 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 of physicochemical processes can be established in a biological system, 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 this chain reactions 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, as well as a lack of vitamins, 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 physico-chemical 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. High degree of tissue hydration in newborns and children early age determines a significantly higher than in adults, the child's need for water (per unit of 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 impact 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) . This is due to the greater body surface area 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 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.

Previously, it was 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. Great importance in maintaining the total osmotic pressure in the internal environment has 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 of the executive organs (kidneys, lungs) reach their maximum degree of maturity at this age, so severe syndromes or homeostasis diseases 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 is maintained due to 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. 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, cell membrane potential, etc. is maintained.

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 most important prerequisites for the 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. normal function of the respiratory system is the maintenance of a constant level of oxygen and carbon dioxide in the arterial blood with normal vascular resistance in the pulmonary circulation and with the usual expenditure of energy for respiratory work.

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 of the 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 human environment medium, all other cells are isolated from 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 bio chemical reactions, which constitute the essence of metabolism, depend very strongly on temperature. 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. IN normal conditions existence, including during adaptation and activity, there are small deviations of such parameters, 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 lies 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 an illness or a sharp deterioration in living conditions caused by social causes (war, earthquake, etc.), lags significantly behind his 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 the level of functional development, he soon catches up with his peers and in the future does not differ significantly from them. This explains the fact that children who have had a serious illness at an early age often grow up into healthy and proportionately built adults. Homeoresis plays an important role both in the management of ontogenetic development and in the processes of adaptation. 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 information nor energy resources the organism would not 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 must be maintained at a relatively constant level for the well-being of the vast majority of 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 tension of 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, for 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 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 diseases that lead to a violation of water-salt homeostasis, such as cholera, in which a huge amount of water is removed from the body 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 the 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.

American physiologist Walter B. Cannon in 1932 in his book "The Wisdom of the Body" ("Wisdom of the body") proposed this term as a name for "the coordinated physiological processes that maintain most of the stable states of the body." 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. It is 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 - like, for example, the island of Krakatau, 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 has gone through a chain of ecological changes in the years since the eruption, in which new plant and animal species replaced each other, which led to biodiversity and, as a result, a climax community. Ecological succession in Krakatoa took place in several stages. A complete chain of successions leading to a climax is called a preserie. In the 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, whose reproductive success in the conditions of the microenvironment of its specific ecological niche more energy is invested.

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

Such ecosystems form heterarchies in which homeostasis at one level contributes to homeostatic processes at another complex level. For example, the loss of leaves on a mature tropical tree makes room for new growth and enriches the soil. Equally, the tropical tree reduces the access of light to lower levels and helps prevent other species from invading. But the 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 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 general characteristics 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 too low temperature body.
  • Another type of thermogenesis involves the breakdown of fats to release heat.
  • Sweating cools the body through evaporation.
• Chemical regulation
  • The pancreas secretes insulin and glucagon to control blood glucose levels.
  • The lungs take in oxygen and release carbon dioxide.
  • The kidneys excrete urine and regulate the level of water and a number of ions in the body.

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

see also

Categories:

• homeostasis
• open systems
• Physiological processes

Wikimedia Foundation. 2010.

Homeostasis in the classical sense of the word is a physiological concept that denotes the stability of the composition of the internal environment, the constancy of the components of its composition, as well as the balance of the biophysiological functions of any living organism.

The basis of such a biological function as homeostasis is the ability of living organisms and biological systems to resist environmental changes; while organisms use autonomous defense mechanisms.

For the first time this term was used by the physiologist, American W. Kennon at the beginning of the twentieth century.
Any biological object has universal parameters of homeostasis.

Homeostasis of the system and body

The scientific basis for such a phenomenon as homeostasis was formed by the Frenchman C. Bernard - it was a theory about the constant composition of the internal environment in the organisms of living beings. This scientific theory was formulated in the eighties of the eighteenth century and has been widely developed.

So, homeostasis is the result of a complex mechanism of interaction in the field of regulation and coordination, which occurs both in the body as a whole and in its organs, cells, and even at the molecular level.

The concept of homeostasis received an impetus for further development as a result of the use of cybernetics methods in the study of complex biological systems, such as a biocenosis or a population).

Functions of homeostasis

The study of objects with a feedback function has helped scientists learn about the many mechanisms responsible for their stability.

Even in conditions of serious changes, the mechanisms of adaptation (adaptation) do not allow the chemical and physiological properties of the organism to change greatly. It cannot be said that they remain absolutely stable, but serious deviations usually do not occur.

Mechanisms of homeostasis

The mechanism of homeostasis in organisms is most well developed in higher animals. In the organisms of birds and mammals (including humans), the function of homeostasis allows you to maintain the stability of the number of hydrogen ions, regulates the constancy of the chemical composition of the blood, keeps the pressure in the circulatory system and body temperature at about the same level.

There are several ways in which homeostasis affects organ systems and the body as a whole. This can be an effect with the help of hormones, the nervous system, excretory or neuro-humoral systems of the body.

Human homeostasis

For example, the stability of pressure in the arteries is maintained by a regulatory mechanism that works in the manner of chain reactions that the blood organs enter into.

This happens in such a way that the vascular receptors feel the change in the pressure force and transmit a signal about this to the human brain, which sends response impulses to the vascular centers. The consequence of this is an increase or decrease in the tone of the circulatory system (heart and blood vessels).

In addition, the organs of neuro-humoral regulation come into play. As a result of this reaction, the pressure returns to normal.

Ecosystem homeostasis

An example of homeostasis in flora can serve to maintain a constant moisture content of the leaves by opening and closing the stomata.

Homeostasis is also characteristic of communities of living organisms of any degree of complexity; for example, the fact that a relatively stable composition of species and individuals is preserved within the biocenosis is a direct consequence of the action of homeostasis.

Population homeostasis

Such a type of homeostasis as population (its other name is genetic) plays the role of a regulator of the integrity and stability of the genotypic composition of a population in a changing environment.

It acts through the preservation of heterozygosity, as well as by controlling the rhythm and direction of mutational changes.

This type of homeostasis allows the population to maintain the optimal genetic composition, which allows the community of living organisms to maintain maximum viability.

The role of homeostasis in society and ecology

The need to manage complex systems of a social, economic and cultural nature has led to the expansion of the term homeostasis and its application not only to biological, but also to social objects.

The following situation can serve as an example of the work of homeostatic social mechanisms: if there is a lack of knowledge or skills or a professional shortage in society, then through the feedback mechanism this fact makes the community develop and improve itself.

And in the case of an excess number of professionals who are actually not in demand by society, there will be a negative feedback and there will be fewer representatives of unnecessary professions.

Recently, the concept of homeostasis has found wide application in ecology, due to the need to study the state of complex ecological systems and the biosphere as a whole.

In cybernetics, the term homeostasis is used in relation to any mechanism that has the ability to automatically self-regulate.

Links related to homeostasis

Homeostasis on Wikipedia.

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

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Classmates

The concept and characteristics of homeostasis

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

The main characteristics of homeostasis are as follows:

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

Feedback

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

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

negative feedback

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

positive feedback

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

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

What parameters does homeostasis regulate?

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

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

Body temperature

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

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

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

Water-salt balance

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

Blood homeostasis

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

normal pressure

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

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

Ecological homeostasis

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

Biological homeostasis

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

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

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

Besides, Biological homeostasis includes the following subspecies:

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

Other types

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

Maintenance of homeostasis

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

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

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

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

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

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

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

The very idea of ​​homeostasis does not correspond to the concept of stable (non-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 (fluid matrix), according to W. Cannon. The stability of its active reaction (pH), osmotic pressure, ratio of electrolytes (sodium, calcium, chlorine, magnesium, phosphorus), glucose content, number of formed elements, and so on are well known. So, for example, blood pH, as a rule, does not go beyond 7.35-7.47. Even severe disorders of acid-base metabolism with a pathology of acid accumulation in the tissue fluid, for example, in diabetic acidosis, have very little effect on the active reaction of the blood. Despite the fact that the osmotic pressure of blood and tissue fluid is subject to continuous fluctuations due to the constant supply of osmotically active products of interstitial metabolism, it remains 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 (see Water-salt metabolism). 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 nervous 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.

Various researchers explain the mechanisms of a general biological nature that underlie homeostasis in different ways. So, W. Cannon attached special importance to the higher nervous system, L. A. Orbeli considered the adaptive-trophic function of the sympathetic nervous system to be one of the leading factors of homeostasis. The organizing role of the nervous apparatus (the principle of nervism) underlies the well-known ideas about the essence of the principles of homeostasis (I. M. Sechenov, I. P. Pavlov, A. D. Speransky and others). However, neither the dominant principle (A. A. Ukhtomsky), nor the theory of barrier functions (L. S. Stern), nor the general adaptation syndrome (G. Selye), nor the theory of functional systems (P. K. Anokhin), nor the hypothalamic regulation of homeostasis (N. I. Grashchenkov) and many other theories do not 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” and the like appeared 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. Some authors consider the internal environment of the body as a complex chain system with many "active inputs" (internal organs) and individual physiological indicators (blood flow, blood pressure, gas exchange, etc.), the value of each of which is due to the activity of the "inputs".

In practice, researchers and clinicians face the questions 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 disturbances in the normal functioning of the body associated with its aging, forced restructuring of biological rhythms, some phenomena of vegetative dystonia, hyper- and hypocompensatory reactivity under stressful and extreme influences, and so on.

To assess the state of homeostatic mechanisms in fiziol. experiment and in a wedge, practice various dosed functional tests are applied (cold, thermal, adrenaline, insulin, mezaton and others) with definition in blood and urine of a parity of biologically active agents (hormones, mediators, metabolites) and so on.

Biophysical mechanisms of homeostasis

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 it is possible to establish a stationary course of physicochemical processes, that is, homeostasis, in a biological system. 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, as well as a lack of vitamins, and so on.

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

Age features of homeostasis in children. The constancy of the internal environment of the body and the relative stability of physico-chemical 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 (see Water-salt metabolism). 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). Loss of water or its limitation quickly lead to the development of dehydration due to the extracellular sector, that is, 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 impact 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 varies over a wider range (±50 mosm/l) than in adults ±6 mosm/l). This is due to the greater body surface per 1 kg of weight and, consequently, more significant water loss during respiration, as well as 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 or night diseases. Less studied is the ionic regulation of homeostasis, which is closely related to the activity of the kidneys and the nature of nutrition.

Previously, it was 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 (E. Kerpel-Froniusz, 1964).

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. 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 in puberty is also associated with changes in homeostasis. However, the functions of the executive organs (kidneys, lungs) reach their maximum degree of maturity at this age, so severe syndromes or homeostasis diseases 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, pO 2 and pCO 2.

Features of homeostasis in the elderly and senile age

Features of homeostasis in the elderly and senile age. The same level of homeostatic values ​​in different age periods is maintained due to 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. 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, cell membrane potential, and so on are maintained.

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, and others 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 over 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 most important prerequisites for the development of pathological disorders in old age.

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