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 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 a relative dynamic constancy, despite changes in the environment and shifts that occur in the process of life 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 in 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, vary 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 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. 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;

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

General mechanism of neuroendocrine homeostatic reactions for internal regulation of homeostasis

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

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

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

4. Excitation of one or another need center of the hypothalamus forms a corresponding functional state, which is subjectively experienced as a need for something: food, water, heat, cold or sex. An activating and stimulating psychoemotional state of dissatisfaction arises.

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

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

Homeostasis Systems - A comprehensive educational resource on homeostasis.

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

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.

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

Homeostasis, its meaning

Homeostasis–it is the maintenance of the relative constancy of the internal environment of the organism. The internal environment of the body, in which all its cells live, is blood, lymph, interstitial fluid.

Any living organism is exposed to the most diverse and changeable environmental factors; in the same time strictly constant conditions are necessary for the course of vital processes in cells. As a result, living organisms have developed various self-regulating systems that allow them to maintain a favorable internal environment, despite changes in external conditions. It is enough to recall all those adaptive reactions that the human body possesses. When we enter a dark room from the street, our eyes, thanks to automatic internal regulation, quickly adapt to a sharp decrease in illumination. Whether you work in the north in winter or sunbathe in the summer on the hot sand of the south - in all cases, your body temperature remains practically constant, changing by no more than a few fractions of a degree.

Another example. The blood pressure in the brain must be kept at a certain level. If it falls, then the person loses consciousness, and with a sharp increase in pressure due to rupture of capillaries, a cerebral hemorrhage may occur (the so-called "blow"). With various changes in the position of the body (vertical, horizontal and even upside down) under the influence of gravity, the blood flow to the head changes; however, despite this, a complex of adaptive reactions maintains blood pressure in the brain at a strictly constant level, favorable for brain cells. All these examples illustrate the body's ability to maintain the constancy of the internal environment with the help of special regulatory mechanisms; maintaining the constancy of the internal environment is called homeostasis.

If any of the homeostatic mechanisms is disturbed, then a change in the conditions of the vital activity of cells can have very serious consequences for the organism as a whole.

Thus, the internal environment of the body is characterized by relative constancy - homeostasis of various indicators, since any changes in it lead to disruption of the functions of cells and tissues of the body, especially highly specialized cells of the central nervous system. These constant indicators of homeostasis include the temperature of internal organs of the body, maintained within 36 - 37 ºС, acid-base balance of blood, characterized by pH = 7.4 - 7.35, osmotic blood pressure (7.6 - 7.8 atm) , the concentration of hemoglobin in the blood 120 - 140 g / l, etc.

The degree of shift in homeostasis indicators with significant fluctuations in environmental conditions or with hard work in most people is very small. For example, a long-term change in blood pH by only 0.1 - 0.2 can be fatal. However, in the general population there are individual individuals who have the ability to tolerate much greater shifts in the indicators of the internal environment. In highly qualified athletes-runners, as a result of a large intake of lactic acid from skeletal muscles into the blood during running at medium and long distances, the pH of the blood can drop to values of 7.0 or even 6.9. Only a few people in the world were able to climb to an altitude of about 8,800 m above sea level (to the summit of Everest) without an oxygen device, i.e. exist and move in conditions of extreme oxygen deficiency in the air and, accordingly, in the tissues of the body. This ability is determined by the innate characteristics of a person - the so-called genetic reaction rate, which, even for fairly constant functional indicators of the body, has wide individual differences.

Topic 4.1. Homeostasis

Homeostasis(from the Greek. homoios- similar, identical and status- immobility) is the ability of living systems to resist changes and maintain the constancy of the composition and properties of biological systems.

The term "homeostasis" was proposed by W. Cannon in 1929 to characterize the states and processes that ensure the stability of the organism. The idea of the existence of physical mechanisms aimed at maintaining the constancy of the internal environment was expressed in the second half of the 19th century by C. Bernard, who considered the stability of physicochemical conditions in the internal environment as the basis for the freedom and independence of living organisms in a continuously changing external environment. The phenomenon of homeostasis is observed at different levels of the organization of biological systems.

General laws of homeostasis. The ability to maintain homeostasis is one of the most important properties of a living system that is in a state of dynamic equilibrium with environmental conditions.

Normalization of physiological parameters is carried out on the basis of the property of irritability. The ability to maintain homeostasis varies from species to species. As organisms become more complex, this ability progresses, making them more independent from fluctuations in external conditions. This is especially evident in higher animals and humans, which have complex nervous, endocrine and immune mechanisms of regulation. The influence of the environment on the human body is mainly not direct, but indirect due to the creation of an artificial environment by it, the success of technology and civilization.

In the systemic mechanisms of homeostasis, the cybernetic principle of negative feedback operates: with any disturbing effect, the activation of nervous and endocrine mechanisms, which are closely interrelated, occurs.

Genetic homeostasis at the molecular genetic, cellular and organismal levels, it is aimed at maintaining a balanced gene system containing all the biological information of the organism. The mechanisms of ontogenetic (organismic) homeostasis are fixed in the historically developed genotype. At the population-species level, genetic homeostasis is the ability of a population to maintain the relative stability and integrity of the hereditary material, which are provided by the processes of reduction division and free crossing of individuals, which contributes to the maintenance of the genetic balance of allele frequencies.

Physiological homeostasis associated with the formation and continuous maintenance of specific physicochemical conditions in the cell. The constancy of the internal environment of multicellular organisms is maintained by the systems of respiration, blood circulation, digestion, excretion and is regulated by the nervous and endocrine systems.

Structural homeostasis is based on the mechanisms of regeneration that ensure morphological constancy and integrity of the biological system at different levels of organization. This is expressed in the restoration of intracellular and organ structures through division and hypertrophy.

Violation of the mechanisms underlying homeostatic processes is considered as a "disease" of homeostasis.

The study of the patterns of human homeostasis is of great importance for the selection of effective and rational methods of treatment for many diseases.

Target. To have an idea of homeostasis as a property of living things, which ensures self-maintenance of the stability of the organism. Know the main types of homeostasis and the mechanisms of its maintenance. To know the basic laws of physiological and reparative regeneration and its stimulating factors, the importance of regeneration for practical medicine. Know the biological essence of transplantation and its practical significance.

Work 2. Genetic homeostasis and its disturbances

Examine and rewrite the table.

The end of the table.

Methods for maintaining genetic homeostasis	Mechanisms of genetic homeostasis disorders	The result of violations of genetic homeostasis
DNA repair	1. Hereditary and non-hereditary damage to the reparative system. 2. Functional failure of the reparative system	Gene mutations
distribution of hereditary material during mitosis	1. Violation of the formation of the fission spindle. 2. Violation of the divergence of chromosomes	1. Chromosomal aberrations. 2. Heteroploidy. 3. Polyploidy
Immunity	1. Hereditary and acquired immunodeficiency. 2. Functional insufficiency of immunity	Preservation of atypical cells, leading to malignant growth, decreased resistance to a foreign agent

Work 3. Mechanisms of repair on the example of post-radiation restoration of DNA structure

The repair or correction of damaged sections of one of the DNA strands is considered as limited replication. The most studied is the process of repair when the DNA chain is damaged by ultraviolet (UV) radiation. In cells, there are several enzyme repair systems that have formed in the course of evolution. Since all organisms have developed and exist under UV irradiation conditions, cells have a separate system of light repair, which is the most studied at the present time. When a DNA molecule is damaged by UV rays, thymidine dimers are formed, i.e. "Stitching" between adjacent thymine nucleotides. These dimers cannot perform the function of a matrix; therefore, they are corrected by light repair enzymes present in cells. Excisional repair restores damaged areas both by UV radiation and other factors. This repair system has several enzymes: repair endonuclease

and exonuclease, DNA polymerase, DNA ligase. Post-replicative repair is incomplete, since it goes around, and the damaged area is not removed from the DNA molecule. Study the mechanisms of repair using the example of photoreactivation, excisional repair, and postreplicative repair (Fig. 1).

Rice. 1. Repair

Work 4. Forms of protection of the biological individuality of the organism

Examine and rewrite the table.

Forms of protection	Biological essence
Nonspecific factors	Natural individual non-specific resistance to foreign agents
Protective barriers organism: skin, epithelium, hematolymphatic, hepatic, hematoencephalic, hematoophthalmic, hemato-testicular, hematofollicular, hematosalvar	Interfere with the penetration of foreign agents into the body and organs
Nonspecific cellular defense (blood and connective tissue cells)	Phagocytosis, encapsulation, formation of cell aggregates, plasma coagulation
Non-specific humoral protection	The action on pathogenic agents of nonspecific substances in the secretions of the skin glands, saliva, lacrimal fluid, gastric and intestinal juice, blood (interferon), etc.
Immunity	Specialized responses of the immune system to genetically foreign agents, living organisms, malignant cells
Constitutional immunity	Genetically predetermined resistance of certain species, populations and individuals to causative agents of certain diseases or agents of molecular nature, due to the mismatch of foreign agents and receptors of cell membranes, the absence of certain substances in the body, without which a foreign agent cannot exist; the presence in the body of enzymes that destroy a foreign agent
Cellular	The appearance of an increased number of T-lymphocytes selectively reacting with this antigen
Humoral	Formation of specific antibodies circulating in the blood to certain antigens

Work 5. The blood-fluid barrier

The salivary glands have the ability to selectively transport substances from the blood to saliva. Some of them are excreted in saliva in a higher concentration, while others in a lower concentration than in blood plasma. The transition of compounds from blood to saliva is carried out in the same way as transport through any histo-hematolic barrier. The high selectivity of the substances transferred from the blood to the saliva makes it possible to isolate the blood-salivary barrier.

Examine the process of saliva secretion in the acinar cells of the salivary gland in Fig. 2.

Rice. 2. Saliva secretion

Job 6. Regeneration

Regeneration is a set of processes that ensure the restoration of biological structures; it is a mechanism for maintaining both structural and physiological homeostasis.

Physiological regeneration carries out the restoration of structures worn out during the normal life of the body. Reparative regeneration- This is the restoration of the structure after injury or after a pathological process. The ability to regenerate

tions differs both in different structures and in different types of living organisms.

Restoration of structural and physiological homeostasis can be achieved by transplanting organs or tissues from one organism to another, i.e. by transplantation.

Fill in the table using the material from the lectures and the textbook.

Work 7. Transplantation as an opportunity to restore structural and physiological homeostasis

Transplantation- replacement of lost or damaged tissues and organs with their own or taken from another organism.

Implantation- organ transplantation from artificial materials.

Study and rewrite the table in your workbook.

Self-study questions

1. Determine the biological essence of homeostasis and name its types.

2. At what levels of organization is homeostasis maintained?

3. What is genetic homeostasis? Expand the mechanisms of its maintenance.

4. What is the biological essence of immunity? 9. What is regeneration? Types of regeneration.

10. At what levels of the structural organization of the body is the regeneration process manifested?

11. What is physiological and reparative regeneration (definition, examples)?

12. What are the types of reparative regeneration?

13. What are the ways of reparative regeneration?

14. What is the material for the regeneration process?

15. How is the process of reparative regeneration carried out in mammals and in humans?

16. How is the regulation of the reparative process carried out?

17. What are the possibilities of stimulating the regenerative capacity of organs and tissues in humans?

18. What is transplantation and what is its significance for medicine?

19. What is isotransplantation and how is it different from allo- and xenotransplantation?

20. What are the problems and prospects of organ transplantation?

21. What are the methods of overcoming tissue incompatibility?

22. What is the phenomenon of tissue tolerance? What are the mechanisms for achieving it?

23. What are the advantages and disadvantages of implantation of artificial materials?

Test tasks

Choose one correct answer.

1. HOMEOSTASIS IS SUPPORTED AT THE POPULATION-SPECIES LEVEL:

1. Structural

2. Genetic

3. Physiological

4. Biochemical

2. PHYSIOLOGICAL REGENERATION PROVIDES:

1. Formation of the lost organ

2. Self-renewal at the tissue level

3. Tissue repair in response to injury

4. Restoration of a part of a lost organ

3. REGENERATION AFTER REMOVAL OF LIVER SHARE

HUMAN WAYS WAY:

1. Compensatory hypertrophy

2. Epimorphosis

3. Morpholaxis

4. Regenerative hypertrophy

4. TISSUE AND ORGAN TRANSPLANTATION FROM DONOR

TO A RECIPIENT OF THE SAME TYPE:

1. Auto- and isotransplantation

2. Allo and homotransplantation

3. Xeno and heterotransplantation

4. Implantation and xenotransplantation

Choose multiple correct answers.

5. NON-SPECIFIC FACTORS OF IMMUNE PROTECTION IN MAMMALS ARE RELATED TO:

1. Barrier functions of the epithelium of the skin and mucous membranes

2. Lysozyme

3. Antibodies

4. Bactericidal properties of gastric and intestinal juice

6. CONSTITUTIONAL IMMUNITY IS CONDITIONED:

1. Phagocytosis

2. Lack of interaction between cell receptors and antigen

3. Antibody formation

4. Enzymes that destroy a foreign agent

7. MAINTENANCE OF GENETIC HOMEOSTASIS AT THE MOLECULAR LEVEL IS DUE TO:

1. Immunity

2. DNA replication

3. DNA repair

4. Mitosis

8. FOR REGENERATIVE HYPERTROPHY CHARACTERISTIC:

1. Restoration of the original mass of the damaged organ

2. Restoring the shape of the damaged organ

3. Increase in the number and size of cells

4. Scar formation at the site of injury

9. IN HUMAN IMMUNE ORGANS ARE:

2. Lymph nodes

3. Peyer's patches

4. Bone marrow

5. Bag of Fabricius

Establish correspondence.

10. TYPES AND METHODS OF REGENERATION:

1. Epimorphosis

2. Heteromorphosis

3. Homomorphosis

4. Endomorphosis

5. Intercalary growth

6. Morpholaxis

7. Somatic embryogenesis

BIOLOGICAL

ESSENCE:

a) Atypical regeneration

b) Growth from the wound surface

c) Compensatory hypertrophy

d) Regeneration of the body from individual cells

e) Regenerative hypertrophy

f) Typical regeneration g) Rearrangement of the rest of the organ

h) Regeneration of through defects

Literature

The main

Biology / Ed. V.N. Yarygin. - M .: Higher school, 2001. -

S. 77-84, 372-383.

A.A. Slyusarev, S.V. Zhukova Biology. - Kiev: High School,

1987 .-- S. 178-211.