Development techniques

Three examples of the regulation of homeostasis in the human body. Homeostasis and its determining factors; the biological significance of homeostasis. The role of the nervous and humoral systems in the regulation of body functions and ensuring its integrity. Medical use

Feedback.

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

Negative feedback, expressed in 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, this allows homeostasis to be maintained.

For example, when concentration carbon dioxide increases in the human body, the lungs receive a signal to increase their activity and exhale more carbon dioxide.

Thermoregulation is another example of negative feedback. When your body temperature rises (or falls) thermoreceptors v skin and hypothalamus register the change by triggering a signal from the brain. This signal, in turn, triggers a response - a decrease in temperature (or increase).

Positive feedback , which is expressed in increasing the change in the variable. It has a destabilizing effect and therefore does not lead to homeostasis. Positive feedback is less common in natural systems but also has its uses.

For example, in the nerves threshold electric potential causes much more to be generated action potential. Clotting blood and events at birth can be cited as other examples of positive feedback.

Resilient systems require 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 - this situation is called "metastability". Such catastrophic changes can occur, for example, with an increase nutrients in rivers with clear water, which leads to a homeostatic state of high eutrophication(overgrowing of the channel algae) and turbidity.

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 in biological system it is possible to establish a steady flow of physicochemical processes, i.e. homeostasis. The main role in the establishment of homeostasis belongs to the cellular membrane systems, which are responsible for bioenergetic processes and regulate the rate of intake and release of substances by cells.

From this point of view, the main causes of the disturbance are non-enzymatic reactions that are unusual for normal life, occurring in the membranes; in most cases, these are chain reactions of oxidation with the participation of free radicals that occur in the phospholipids of cells. These reactions lead to damage structural elements cells and dysfunction of regulation. The factors that cause disruption of homeostasis also include agents that cause radical formation (ionizing radiation, infectious toxins, certain foods, nicotine, as well as a lack of vitamins, etc.).

The factors that stabilize the homeostatic state and function of membranes include bioantioxidants, which inhibit the development of oxidative radical reactions.

Ecological homeostasis.

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

In disturbed ecosystems, or sub-climax biological communities - such as the island of Krakatoa, after a violent volcanic eruption in 1883 - the state of homeostasis of the previous forest climax ecosystem was destroyed, as was all life on this island.

Over the years after the eruption, Krakatoa underwent a chain of ecological changes, in which new species of plants and animals replaced each other, which led to biodiversity and, as a result, a climax community. The ecological succession to Krakatoa was realized in several stages. The complete chain of successions, which led to the climax, is called the succession. In the example of Krakatoa, a climax community formed on this island with eight thousand different species recorded in 1983, one hundred years after the eruption destroyed life on it. The data confirm that the position remains in homeostasis for some time, while the appearance of new species very quickly leads to the rapid disappearance of old ones.

The case of Krakatoa and other disturbed or pristine ecosystems shows that initial colonization by pioneer species is carried out through reproduction strategies based on positive feedback, in which the species spread, producing as many offspring as possible, but with little to 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). When the ecosystem approaches climax, such species are replaced by more complex climax species, which through negative feedback adapt to the specific conditions of their environment. These species are carefully controlled by the potential capacity of the ecosystem and follow a different strategy - the production of smaller offspring, in whose reproductive success more energy is invested in the microenvironment of its specific ecological niche.

Development starts with the pioneer community and ends with the climax community. This climax community is formed when flora and fauna are in balance with the local environment.

Such ecosystems form heterarchies in which homeostasis at one level promotes homeostatic processes at another complex level.

For example, the loss of leaves from a mature tropical tree provides space for new growth and enriches the soil. Equally, a tropical tree reduces the access of light to lower levels and helps prevent invasion by other species. But trees also fall to the ground and the development of the forest depends on the constant change of trees, the cycle of nutrients carried out by bacteria, insects, fungi.

In a similar way, such forests facilitate ecological processes such as the regulation of microclimates or the hydrological cycles of an ecosystem, and several different ecosystems can interact to maintain river drainage homeostasis within a biological region. The variability of bioregions also plays a role in the homeostatic stability of a biological region, or biome.

Biological homeostasis.

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

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.

For 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 range of temperatures.

We are not talking about the fact that conformational organisms do not possess behavioral adaptations that allow them to to some extent regulate the taken parameter. 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 at low temperatures, while warm-blooded animals are almost as active as ever. On the other hand, regulation requires energy. The reason some snakes can only eat once a week is that they expend 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 a 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, acidity, substrate concentration, and the presence of some macro- and microelements.

Homeostasis in the human body.

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

Homeostasis cannot be considered the cause of 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.

Homeostasis, homeostasis (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 the basic physiological functions (blood circulation, respiration, thermoregulation, metabolism and so on) of the human body 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.

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 external and internal environment. The ability to return to the initial state after a deviation from a certain average level caused by this or that "disturbing" factor is the main property of the cell. A multicellular organism is a holistic organization, the cellular elements of which are specialized to perform various functions. Interaction within the body is carried out by complex regulatory, coordinating and correlating mechanisms with

participation of nervous, humoral, metabolic and other factors. Many separate mechanisms regulating intra- and intercellular relationships, in a number of cases, have mutually opposite (antagonistic) effects, balancing each other. This leads to the establishment in the body of a mobile physiological background (physiological balance) and allows the living system to maintain relative dynamic constancy, despite changes in the environment and shifts that occur in the process of vital activity of the body.

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 expedient to combine them under the general name homeostasis. However, back in 1878, K. Bernard wrote that all life processes have only one goal - to maintain the constancy of living conditions in our internal environment. Similar statements are found in the works of many researchers of the 19th and first half of the 20th century. (E. Pfluger, C. Richet, L.A. Fredericq, I.M.Sechenov, I.P. Pavlov, K.M.Bykov and others). The works of L.S. Stern (with co-workers) on 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 taking place in living systems. It is also wrong to contrast homeostasis with rhythmic fluctuations in the internal environment. Homeostasis in a broad sense covers issues of the cyclic and phase course 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 flexible, varying depending on individual age, sex, social, professional and other conditions.

Of particular importance for the vital activity of the organism is the constancy of the composition of the blood - the fluid matrix of the organism, according to W. Kennon. The stability of its active reaction (pH), osmotic pressure, the ratio of electrolytes (sodium, calcium, chlorine, magnesium, phosphorus), glucose content, the 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 sharp disorders of acid-base metabolism with 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 undergoes continuous fluctuations due to the constant supply of osmotically active products of interstitial metabolism, it remains at a certain level and changes only under certain pronounced pathological conditions.

Despite the fact that blood is 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 characteristics, and the normal state of organs depends on the chemical composition, physicochemical, biological and other properties of this microenvironment. Its homeostasis is due to the functional state of the histohematogenous barriers and their permeability in the directions 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 mechanisms of regulation, is the system for ensuring the optimal level of blood pressure. In this case, the upper limit of the level of blood pressure is determined by the functional capabilities of the baroreceptors of the vascular system of the body, and the lower limit is determined by the needs of the body for blood supply.

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

The body as an open self-regulating system.

A living organism is an open system that has a connection with environment through the nervous, digestive, respiratory, excretory systems, etc.

In the process of metabolism with food, water, 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 disintegrate, release energy, decay products are removed into the external environment. The destroyed molecule is replaced by a new one, etc.

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

Homeostasis concept. General laws of homeostasis of living systems.

Homeostasis - the property of a living organism to maintain the relative dynamic constancy of the internal environment. Homeostasis is expressed in the relative constancy of the chemical composition, osmotic pressure, stability of the main physiological functions. Homeostasis is specific and due to 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 row 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 an organism to normal environmental conditions. However, these conditions can be short-term or long-term outside the normal range. In such cases, the phenomena of adaptation are characterized not only by the restoration of the usual properties of the internal environment, but also by short-term changes in function (for example, an increase in the rhythm of cardiac activity and an increase in the frequency of respiratory movements with increased muscular work). Homeostasis responses can be directed to:

maintaining known steady state levels;

elimination or limitation of the action 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 the known constancy of various physiological constants of the organism, but also includes the processes of adaptation and coordination of physiological processes that ensure the unity of the organism not only in normal conditions, but also under changing conditions of its existence.

The main components of homeostasis were identified by K. 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.

Concentration of hydrogen ions (pH).

B. Mechanisms to ensure structural and functional cohesion:

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 ontogeny and phylogeny. This principle has proven to be widespread. When studying it, cybernetics arose - the science of purposeful and optimal control of complex processes in wildlife, in human society, and 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 weekends variables (Fig. 10).

Rice. 10 - General scheme of homeostasis of living systems

Output variables depend on input and system behavior laws.

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

Negative feedback reduces the influence of the input signal by 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 according to the same principle: self-deviation from the initial state, which serves as an incentive to activate correction mechanisms. So, normal blood pH is 7.32 - 7.45. A change in pH by 0.1 leads to impaired cardiac activity. This principle was described by P.K. Anokhin. in 1935 and called the principle of feedback, which serves to implement adaptive reactions.

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

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

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

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

Regulatory homeostatic mechanisms function at the genetic, cellular and systemic (organismal, population-specific and biospheric) levels.

Gene mechanisms homeostasis. All the phenomena of homeostasis of the organism 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 nucleotide sequence of DNA and the sequence of amino acids 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 hereditarily determined reaction rate. Double stranded 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 tissue and organ histocompatibility, which allows transplantation.

The transplanted site is called graft. The organism from which the tissue for transplantation is taken is donor , and which is transplanted - recipient . The success of the transplant depends on the body's immunological responses. Distinguish between autotransplantation, syngeneic transplantation, allotransplantation and xenotransplantation.

Autotransplantation – tissue transplantation from the same organism. In this case, the proteins (antigens) of the graft do not differ from the proteins of the recipient. An immunological reaction does not occur.

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 is successful in some invertebrates, but in higher animals such transplants do not take root.

In transplantation, the phenomenon of immunological tolerance (tissue compatibility). Suppression of immunity in the case of tissue transplantation (immunosuppression) is achieved by: suppression of the activity of the immune system, radiation, the introduction of anti-lymphotic serum, adrenal cortex hormones, chemical drugs - 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 fairly 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 not definitively identified are designated W (Work). The HLA system antigens are divided into 2 groups: SD and LD (Fig. 11).

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

Rice. 11 - HLA main genetic system of human histocompatibility

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

Antigenic polymorphism of the HLA system is the result of the origin of one from the other and a close genetic relationship between them. The identity of the donor and recipient for the HLA antigens is necessary for transplantation. A kidney transplant, which is identical in terms of 4 antigens of the system, provides a survival rate of 70%; 3 - 60%; 2 - 45%; 1 - 25% each.

There are special centers that are leading the selection of a donor and recipient for transplantation, for example, in Holland - "Eurotransplant". HLA antigen typing is also carried out in the Republic of Belarus.

Cellular mechanisms homeostasis are aimed at restoring tissue cells, organs in case of violation of their integrity. The set of processes aimed at restoring destructible biological structures is called regeneration. This process is typical for all levels: the renewal of proteins, component parts of cell organelles, whole organelles and the cells themselves. Restoration of the functions of organs after injury or nerve rupture, 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 by 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 by 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 (cells of the ganglia of the central nervous system). It covers the processes of restoration of macromolecules and cell organelles by assembling elementary structures or by dividing them (mitochondria).

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

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

Reparative regeneration - This is the restoration of organs and tissues lost during 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 subdivided into typical (homomorphosis) and atypical (heteromorphosis). In the first case, an organ that has been removed or destroyed is regenerated, in the second, another one develops in place of the removed organ.

Atypical regeneration more common in invertebrates.

Regeneration is stimulated by hormones pituitary gland and thyroid gland . There are several ways to regenerate:

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

Morfollaxis - 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 remains of the old (for example, the restoration of a limb in a cockroach).

Endomorphosis - restoration 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 original.

In vertebrates, reparative regeneration takes place in the following form:

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

Regenerative hypertrophy characteristic of the 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 the 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 are regenerated.

Intracellular compensatory hyperplasia ultrastructures of the cell. 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 excitement, but also regulate chemical processes, the exchange of biologically active substances. More than 50 neurohormones are currently known. So, in the hypothalamus, vasopressin, oxytocin, liberins and statins are produced, which regulate the function of the pituitary gland. Examples of systemic manifestations of homeostasis are the maintenance of constancy of temperature and 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, there are reflex processes. Between different levels of homeostatic regulation, there is a particular hierarchical subordination in the system of regulation of internal processes of the body (Fig. 12).

cerebral cortex and parts of the brain

self-regulation based on feedback

peripheral neuro-regulatory processes, local reflexes

Cellular and tissue level of homeostasis

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

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

In a complex multicellular organism, both direct and reverse connections are carried out not only by nervous, but also by hormonal (endocrine) mechanisms. Each of the glands, which is part of the endocrine system, influences 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. At a high concentration of the hormone (above the norm), the activity of the gland is weakened and vice versa. This effect is carried out by the action of the hormone on the gland producing it. In a number of glands, regulation is established through the hypothalamus and the anterior pituitary gland, especially during a stress reaction.

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

The reactions that provide homeostasis cannot be limited to any one endocrine gland, but captures to one degree or another all the glands. The resulting reaction takes on 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 disturbances in the body's environment contribute to the preservation of its homeostasis for a long life. If you create such living conditions in which nothing causes significant changes in the internal environment, then the body will be completely unarmed when it encounters the environment and soon dies.

The combination of nervous and endocrine regulation mechanisms in the hypothalamus makes it possible to carry out complex homeostatic reactions associated with the regulation of the visceral function of the body. The nervous and endocrine systems are the unifying mechanisms of homeostasis.

An example of a common response of nervous and humoral mechanisms is the state of stress, which develops under unfavorable living conditions and the threat of disruption of homeostasis arises. Under stress, there is a change in the state of most systems: muscle, 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 defensive reaction to stress.

In case of "somatic stress", the task of increasing the general resistance of the organism is solved according to the scheme shown in Figure 13.

Rice. 13 - Scheme of increasing the general resistance of the body with

In his book, The Wisdom of the Body, he coined the term as a name for "the coordinated physiological processes that support most 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 idea of the constancy of the internal environment was formulated back in 1878 by the French scientist Claude Bernard.

General information

The term homeostasis is most commonly used in biology. For multicellular organisms to exist, it is necessary to maintain the constancy of the internal environment. Many ecologists are convinced that this principle applies to the external environment as well. 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 changes in the environment and evolve.

Homeostasis properties

Homeostatic systems have the following properties:

Instability systems: tests how it is best to adapt.
Striving for balance: the entire internal, structural and functional organization of systems contributes to maintaining balance.
Unpredictability: the resulting effect of a particular action can often differ from what is expected.

Regulation of the amount of micronutrients and water in the body - osmoregulation. It is carried out in the kidneys.
Removal of metabolic waste - excretion. It is carried out by exocrine organs - kidneys, lungs, sweat glands and gastrointestinal tract.
Regulation of body temperature. Lowering the temperature through sweating, various 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. In many organisms, endogenous changes are observed 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.

Homeostasis mechanisms: feedback

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

Negative feedback, expressed in 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, this allows homeostasis to be maintained.
- For example, when the concentration of carbon dioxide in the human body increases, the lungs receive a signal to increase their activity and exhale more carbon dioxide.
- Thermoregulation is another example of negative feedback. When body temperature rises (or falls), thermoreceptors in the skin and hypothalamus register a change, triggering a signal from the brain. This signal, in turn, triggers a response - a decrease in temperature (or increase).
Positive feedback, which is expressed in increasing the change in the variable. It has a destabilizing effect and therefore does not lead to homeostasis. Positive feedback is less common in natural systems, but it also has its uses.
- For example, in nerves, a threshold electrical potential causes a much larger action potential to be generated. Blood clotting and birth events are other examples of positive feedback.

Resilient systems require 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 - this situation is 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 (overgrowth of the channel with algae) and turbidity.

Ecological homeostasis

In disturbed ecosystems, or sub-climax biological communities, such as the island of Krakatoa, after a violent volcanic eruption, the state of homeostasis of the previous forest climax ecosystem was destroyed, like all life on this island. Over the years after the eruption, Krakatoa underwent a chain of ecological changes, in which new species of plants and animals replaced each other, which led to biodiversity and, as a result, a climax community. The ecological succession to Krakatoa was realized in several stages. The complete chain of successions, which led to the climax, is called the succession. In the example of Krakatoa, a climax community formed on this island with eight thousand different species recorded in, one hundred years after the eruption destroyed life on it. The data confirm that the position remains in homeostasis for some time, while the appearance of new species very quickly leads to the rapid disappearance of old ones.

Development starts with the pioneer community and ends with the climax community. This climax community is formed when flora and fauna are in balance with the local environment.

Such ecosystems form heterarchies in which homeostasis at one level promotes homeostatic processes at another complex level. For example, the loss of leaves from a mature tropical tree creates space for new growth and enriches the soil. Equally, a tropical tree reduces the access of light to lower levels and helps prevent invasion by other species. But trees also fall to the ground and the development of the forest depends on the constant change of trees, the cycle of nutrients carried out by bacteria, insects, fungi. In a similar way, such forests facilitate ecological processes, such as the regulation of microclimates or the hydrological cycles of an ecosystem, and several different ecosystems can interact to maintain river drainage homeostasis within a biological region. The variability of bioregions also plays a role in the homeostatic stability of a biological region, or biome.

Biological homeostasis

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

Homeostasis in the human body

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

Other areas

Homeostasis is also used in other fields.

The actuary can talk about risk homeostasis, in which, for example, people who have anti-jamming brakes on their car are not in a safer position than those who do not have them, because these people unconsciously compensate for a safer car with risky driving. This is because some of the restraining mechanisms - for example, fear - cease to work.

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

Examples of

Thermoregulation
- Skeletal muscle tremors may occur if the body temperature is too low.
- Another type of thermogenesis involves the breakdown of fats to produce heat.
- Sweating cools the body through evaporation.
Chemical regulation
- The pancreas secretes insulin and glucagon to control blood glucose levels.
- The lungs receive oxygen, emit 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 the hormones of the hypothalamic-pituitary system.