Barrier functions. Barrier function What is the barrier role of the liver

BARRIER FUNCTIONS- functions carried out by special physiological mechanisms (barriers) to protect the body or its individual parts from environmental changes and maintain the relative constancy of the composition, physico-chemical and biological properties of the internal environment (blood, lymph, tissue fluid) necessary for the normal functioning of organs and tissues ). Like all other adaptive properties of the organism, the barrier functions developed in the process of evolution. As multicellular organisms became more complex, differentiated and improved, barrier functions were improved that regulate the metabolism between the organism and the environment, as well as help protect the cells of organs and tissues from contact with damaging agents, foreign substances, poisons, toxins, products of impaired metabolism, viruses, etc. d.

Conventionally, barriers are distinguished between external and internal. External barriers include: 1) the skin, which protects the animal body from physical and chemical changes in the environment and takes part in thermoregulation. The skin barrier prevents the penetration of bacteria, toxins, poisons into the body and helps to remove some metabolic products from it; 2) breathing apparatus, which, in addition to its main function of gas exchange, retains various harmful substances in the atmosphere; 3) the digestive apparatus, through which the necessary nutrients are supplied. In it they undergo corresponding changes, lose their antigenic properties, becoming suitable for assimilation and use by living systems; 4) the liver, which neutralizes a number of toxic compounds foreign to the body, received with food or formed in the intestinal cavity; 5) kidneys, which regulate the constancy of the blood composition and free it from the end products of metabolism. Many authors also include the reticuloendothelial system, which is involved in the neutralization of foreign and pathogenic agents, as external barriers.

Internal barriers regulate the supply of necessary energy resources from the blood to organs and tissues and the timely outflow of cellular metabolic products (purification, clearance), which ensures the constancy of the composition, physico-chemical and biological properties of the tissue (extracellular) fluid and their preservation at a certain optimal level. At the same time, they prevent the entry of foreign and toxic substances from the blood into organs and tissues.

The founder of the doctrine of barrier functions is JI. S. Stern, who for the first time at the International Physiological Congress in Boston (1929) suggested that there are differentiated protective-regulatory devices between blood and tissue fluid, which she called histo-hematic barriers. Each organ, according to L.S. Stern, has its own adequate environment (direct nutrient medium or microenvironment), since blood does not come into contact with the cells of organs. The functional characteristics of individual barriers are determined by the physiological and morphological features of the corresponding organs and tissues. A feature of each histo-hematic barrier is its selective (selective) permeability, that is, the ability to pass some substances and retain others.

In the literature, internal barriers have received various names: tissue, hemato-parenchymal (A. A. Bogomolets and N. D. Strazhesko), histiocytic, vascular tissue (A. V. Lebedinsky), biological, physiological, etc. However, the most the term "histohematic barriers" is common, although it does not reflect their leading role in the exchange between the general internal environment (blood) and the microenvironment of organs and tissues. The study of barrier functions is not limited to the problem of biological membranes. It is much wider, although one of the mechanisms that determine the functional state of the barriers is the permeability of membranes (see Permeability).

Towards histo-hematological barriers all barrier formations between blood and organs can be included without exception. Some authors recognize the existence of specialized barriers that are particularly important for the life of the body. These usually include the more thoroughly studied blood-brain barrier (between the blood and the central nervous system), the blood-ophthalmic barrier (between the blood and the aqueous humor of the eye), the blood-labyrinth barrier (between the blood and the endolymph of the labyrinth), the barrier between the blood and the genitals. glands. Histo-hematic barriers also include barriers between blood and body fluids (cerebrospinal fluid, lymph, pleural, synovial fluids). They are called hemato-CSF, hemato-lymphatic, hemato-pleural, hemato-synovial barriers. The placental barrier (between mother and fetus), although not a histo-hematological barrier, performs an extremely important function of protecting the developing fetus (see Placenta).

The structure of histo-hematological barriers is determined to a large extent by the structure of the organ into which they belong. It differs in some specific features in various organs and tissues and varies depending on their morphological and physiological characteristics. The main structural element of histo-hematological barriers are blood capillaries. It has been established that the endothelium of capillaries in different organs has characteristic morphological features. The shape of the nucleus, the structure of its shell, the structure and amount of chromatin, endothelial cells of various organs differ significantly from each other. The extremely variable features of endothelial cells that develop during ontogenesis are the morphological basis for the selective permeability of histo-hematological barriers. Differences in the mechanisms of barrier functions are reflected in the structural features of the main substance (non-cellular formations that fill the spaces between cells) that can be impregnated with silver. The main substance forms membranes that envelop macromolecules of fibrillar protein, formed in the form of protofibrils, which make up the supporting framework of fibrous structures.

Directly under the endothelium is the basement membrane of the capillaries, which contains a large amount of neutral mucopolysaccharides. The basement membrane, the main amorphous substance and fibers make up the barrier mechanism, in which the main reactive and labile link, according to some researchers, is the main substance. A. A. Bogomolets attached great importance to the barrier function of connective tissue, which also has the properties of a depot from which the body draws the nutrients necessary for the activity of cellular elements.

According to modern concepts, the system of histo-hematological barriers also includes intracellular barriers. Electron microscopy has made it possible to penetrate into the submicroscopic organization of the cell and thus approach the study of these barriers. The barrier mechanisms of the cell consist of the same type of three-layer lipoprotein membranes, which are the main structural elements of the mitochondria, the channel system, the endoplasmic reticulum, the Golgi apparatus and the cell wall. The presence of a cytoplasmic membrane makes it possible, to a certain extent, to understand the selectivity of the permeability of histo-hematic barriers (electron transfer, energy transformation, enzymatic cleavage, transport of ions and metabolites, the kinetics of some biosynthetic processes).

Studies have shown that the chemical composition, physicochemical and biological properties of the immediate nutrient medium of organs (tissue fluid) are due to: 1) the intake of substances from the blood, which depends on the resistance of the histo-hematic barrier of this organ in the direction of blood -> tissues; 2) absorption and use of the constituent parts of the tissue fluid by cells and non-cellular elements in the process of interstitial exchange; 3) the entry of products of cellular and tissue metabolism (metabolites) into the tissue fluid; 4) removal of metabolites from the tissue fluid, that is, their transition from the immediate nutrient medium of the organ into the blood through the histo-hematic barrier of this organ (tissue -> blood).

The histo-hematic barrier of an organ determines the functional state of the latter, its activity, and ability to resist harmful influences. The significance of the barrier lies in delaying the transition of one or another foreign substance from the blood and tissue (protective function) and in regulating the composition and properties of the immediate nutrient medium of the organ, that is, creating optimal conditions for the life of its cellular and non-cellular elements (regulatory function), which is especially important for the whole organism and its individual parts. Carrying out a regulatory function, histo-hematological barriers contribute to the preservation of organ and cellular homeostasis.

The functional state of each histo-hematological barrier is characterized by a mathematical value that reflects the ratio of the concentration of a particular substance in the organ and in the blood. This value is called the permeability coefficient. However, in fact, it corresponds to the distribution of the test substance between tissues and blood, since its content in the tissue depends not only on the flow from the blood into the tissues or from the tissue into the blood, but also on the intensity of cell metabolism. The functional state of histo-hematological barriers cannot be characterized by its permeability alone and, therefore, the permeability coefficient is more correctly considered as a distribution coefficient. The functional state of histo-hematological barriers is determined not only by their permeability or resistance (resistance) to foreign or chemicals inherent to the body. compounds, but mainly physiological activity, that is, the ability to create and maintain the most favorable conditions for the normal functioning of organs, tissues and the body as a whole.

Depending on the activity of the histo-hematological barriers, their resistance (or permeability) to certain substances may increase or decrease, which leads to an increase or decrease in the distribution coefficients. So, for example, with a significant increase in the concentration of one or another substance in the blood, its content in the organ may not change or may increase slightly. In this case, the distribution coefficient decreases, which is an indicator of the high activity of the corresponding histo-hematological barrier and at the same time a decrease in its permeability. In other cases, the content of the substance in the organ increases at a constant or low concentration in the blood. An increased distribution coefficient in this case indicates a decrease in the activity of the barrier and at the same time its high permeability.

The functioning of histo-hematological barriers explains all phenomena that prevent, reduce, slow down and even facilitate the entry of substances into organs and tissues and the removal of interstitial metabolic products from them. Numerous physical, chemical and morphological concepts proposed to explain the selective permeability of histo-hematological barriers do not solve the problem of barrier functions. Barrier functions are based on the mechanisms of dialysis, ultrafiltration, osmosis, as well as changes in electrical properties, lipid solubility, tissue affinity or metabolic activity of cellular elements. Barriers actively select from the blood substances necessary for the vital functions of organs and tissues and remove metabolic products from their microenvironment.

One of the mechanisms of barrier functions is the active transport of certain electrolytes across membranes. It has been established that the transition of biologically active substances (metabolites, mediators, enzymes, hormones) through histo-hematological barriers depends not only on the size of molecules, the size of pores in membranes, electrical charge, solubility in lipids, but mainly on the needs of the organ, nervous and humoral influences, hemodynamics (blood flow speed), microcirculation, area of ​​open and reserve capillaries, the presence or absence of functional and morphological disorders. The presence of metabolic structures in them, that is, tissue elements capable of neutralizing, destroying or binding substances contained in the blood, is important for the condition of the barriers. Thus, histo-hematological barriers can be considered as a self-regulating system, representing one of the links in the complex neuro-humoral-hormonal regulatory apparatus that ensures a state of homeostasis (see).

Histo-hematological barriers control the timely entry into the immediate nutrient medium of organs and tissues of adequate humoral information about the state of regulatory metabolic systems in various parts of the body. Penetrating through the histo-hematonic barrier into the organ, biologically active substances exert their effect on effector cells and specific chemoreceptors, which leads to the occurrence of both local and widespread (general) physiological and biochemical reactions. An example is the effect of substances that penetrate from the blood into the formation of the central nervous system, which are different in their structure, chemical composition and functions, through the blood-brain barrier (see). The existence of an active biological membrane between the blood and eye fluids, which regulates the composition of intraocular fluids, has been proven. This biological membrane was given the name blood-ophthalmic barrier (see).

In some cases, the mechanisms for regulating functions are insufficient, and the biologically active substances accumulated in the blood penetrate, for example, into various nervous structures usually protected by the blood-brain barrier, causing effects that differ from the usual ones. In this case, the compensatory acting system is strengthened (for example, the sympathetic system during the accumulation of parasympathomimetic substances in the blood and vice versa), which is of utmost importance for the restoration of disturbed homeostasis.

Physiological and biochemical processes occurring in both a healthy and sick body, the state of an organ, its trophism, regulation of functions, the relationship between individual organs and physiological systems are closely related to the state of histo-hematological barriers. Violation of the resistance of barriers to various foreign substances and products of impaired metabolism circulating in the blood can in many cases be the cause of a pathological process in individual organs and in the entire organism. Insensitivity or immunity, as well as the affinity or ability of an organ to capture certain chemicals, bacteria, toxins, depends to one degree or another on the state of the corresponding histo-hematological barrier, since a mandatory prerequisite for a direct effect on cellular elements is the penetration of the active principle into the microenvironment of the organ .

A decrease in the resistance of the corresponding histo-hematological barrier makes the organ more susceptible, and an increase in it - less sensitive to chemical compounds formed during the metabolic process or introduced into the body for experimental or therapeutic purposes.

Assessing the state of individual histo-hematological barriers in an experiment or clinic requires a comprehensive study of tissue fluid, which is practically impossible at the current level of knowledge. Therefore, a large number of different methods have been proposed that allow, to a certain extent, both in laboratory experiments and when examining patients in clinical practice, to assess the state of a particular histo-hematological barrier. The most common experimental methods remain the classical methods of introducing dyes (colloidal, semi-colloidal, crystalline), ink, some complex chemical compounds and radioisotope indicators into the blood, followed by determination of their concentration and distribution in organs and tissues, proposed for the study of tissue permeability. For this purpose, methods of light, intravital (vital), luminescent and electron microscopy, microcombustion, determination of radioactivity, etc. are used. Both in experiment and in the clinic, methods are used for comparative study of the composition of the fluid flowing to the organ (arterial) and flowing from it (arterial). venous) blood. To judge the protective and regulatory functions of barriers between blood and body fluids (lymph, cerebrospinal, pleural, synovial fluids), a quantitative determination of substances inherent to the body or introduced from outside in the blood and corresponding fluids is carried out.

To assess the state of the histo-hematological barriers in the direction of the crawl tissue, the test substance is usually injected into the tissue (intradermally, subcutaneously, intramuscularly) and the rate of its absorption is determined or, when radioisotope tracers are introduced, the half-life time is determined.

To assess the barrier functions of the whole organism, the test substance is administered intravenously and its release from the blood is examined for a certain time or, with the introduction of radioisotope tracers, the half-life is examined.

The great plasticity of histo-hematological barriers, their lability and adaptability to constantly changing conditions of the external and internal environment play an important role in the life of the body. Barrier functions vary depending on age, gender, nervous, humoral and hormonal relationships in the body, the tone and reactivity of the autonomic nervous system, and numerous external and internal influences. Studies by a number of authors have shown that the functional state of the histo-hematological barriers of various organs can selectively change under the influence of various factors on the body (changes in sleep and wakefulness, fasting, fatigue, traumatic lesions, exposure to ionizing radiation, etc.).

Certain biologically active substances contained in the blood and tissues or introduced externally (for example, acetylcholine, histamine, kinins, especially bradykinin, some enzymes, primarily hyaluronidase) in physiological concentrations reduce the resistance of histo-hematological barriers and thereby increase the transfer of substances from blood into organs and tissues. Catecholamines, calcium salts, and vitamin P have the opposite effect. In pathological conditions of the body, barrier functions are often rearranged, and the resistance of histo-hematic barriers increases or decreases. In some cases, this restructuring enhances, in others it weakens the course of the disease. A decrease in the resistance of histo-hematological barriers makes organs more susceptible to poisons and infections, and according to some data, increases tumor growth. On the contrary, increasing resistance can in certain cases be protective or compensatory in nature. Considering that in most cases, histo-hematological barriers prevent the entry into organs of drugs and antibodies administered for therapeutic purposes, the problem of regulating the functional state of barriers is of great importance for the clinic. It has been established that irradiation (general or local) with different parts of the light spectrum (infrared and ultraviolet), exposure to ultrashort, high-frequency waves, x-rays, ultrasound, ultra-high frequency electromagnetic fields, as well as the introduction into the body of certain hormones (for example, cortisone), psychotropic substances , vitamins, etc. reduces the resistance of histo-hematological barriers. All these methods can be used in clinical practice to purposefully change the state of barrier functions. An artificial decrease in the resistance of a particular histohematological barrier through various physical or pharmacological effects can increase or expand the effect of drugs that do not penetrate the microenvironment of the organ, while increasing resistance serves the purpose of prevention against infections, intoxications, tumor growth, etc. B In certain cases, to directly affect the affected organ, a chemical compound, drugs, medicinal serums are introduced bypassing the barrier (for example, into the cerebrospinal fluid, pleural and synovial cavities, etc.) or into the artery feeding the organ.

Bibliography: Histo-blood barriers, ed. L. S. Stern, M., 1961; Kassil G. N. Blood-brain barrier, M., 1963; Problems of histo-hematological barriers, ed. JI. S. Stern, M., 1965; Development and regulation of histo-hematological barriers, ed. L. S. Stern, M., 1967; Structure and function of histo-blood barriers, ed. Ya. A. Rosina, M., 1971; Physiology and pathology of histo-hematological barriers, ed. JI. S. Stern, M., 1968; Stern L. S. Direct nutrient medium of organs and tissues, M., 1960; G e 1 1 h o g n E. et R e g n i e g J. La perteoalyShyo en phy-siologie et en pathologie g6n6rale, P., 1936.

Since ancient times, humanity has suffered from contagious diseases.

The most severe of them - plague, smallpox - often spread massively, causing widespread pestilence. History holds memories of terrible times when prosperous cities turned into vast cemeteries.

While observing the spread of infectious diseases, people could not help but notice that not every person was susceptible to the disease. Very often, those who were ill did not become infected again, even in close contact with the sick. It is well known, for example, that many children do not get sick with diphtheria, whooping cough, or mumps, although they were in close contact with their sick peers.

Nowadays, hardly anyone will dispute the fact that the development of an infectious disease is caused not only by microorganisms. The state of the body’s protective barriers also plays a significant role.

What is it - the body's protective barriers? What factors reduce their activity and thereby increase the risk of the disease? Are there ways to increase these protective barriers?

There are specific and nonspecific protective barriers. Without diminishing the role of specific immunological reactions of the body, we will talk about nonspecific protective factors.

The skin and mucous membranes are the first to be attacked by microbes. They can rightly be called the body's front line of defense. The skin and mucous membranes are covered with a continuously renewed layer of epithelial cells - a dense invisible shell. They are primarily a mechanical obstacle that prevents microbes from penetrating deep into the body.

This by no means exhausts the protective role of the skin and mucous membranes. Our skin itself is capable of “dealing” with bacteria that have fallen on it. This property is known in medicine as the bactericidal function of the skin. On a dry, dense stratum corneum, the proliferation of microbes is difficult. The acidic reaction of the skin surface is also unfavorable for most microorganisms; they are also affected by the fatty acids contained in the skin. Many researchers have studied the fate of microbes on human skin. Thus, the English scientist Colbrok, having moistened his finger with a broth culture of streptococcus (the causative agent of purulent infections), found on it after 3 minutes 30,000,000 of these bacteria, after an hour - 1,722,000, and after 2 hours - only 7,000.

Interestingly, healthy, clean skin has the ability to destroy microorganisms more quickly. Experiments have shown that on unwashed hands, the number of microbes applied to the skin not only does not decrease, but slowly increases. At the same time, microorganisms placed on the skin of clean hands disappear very quickly. Thus, during the washing process, the skin is mechanically freed from microbes, and moreover, its self-sterilizing ability is enhanced. This is why it is so important to strictly follow hygiene rules. This is a sure and reliable means of strengthening our first protective barrier.

However, researchers have found that the sterilizing property of the skin manifests itself mainly in relation to those types of microbes that come into contact with it relatively rarely. This effect is insignificant against microbes - the usual inhabitants of the skin.

Is it possible to enhance the bactericidal function of the skin? Scientists answer: yes, it is possible. Sun rays, especially the ultraviolet part of the spectrum, air baths, water procedures - all these factors, if used skillfully and wisely, increasing the body's resistance to various influences, significantly strengthen the protective properties of the skin.

You may have noticed more than once how quickly and easily abrasions and small wounds in the mouth heal. If the wound surface, formed, for example, after tooth extraction, was located in any other part of the body, in the vicinity of so many microbes that are in the mouth, infection would be inevitable. What's the matter? What increases the protective potential of mucous membranes? Lysozyme. This is a special substance that has a detrimental effect on microorganisms. It is named lysozyme for its ability to dissolve and lyse bacteria.

The content of lysozyme on the mucous membranes of the eyes, nasal cavity, and respiratory tract does not remain unchanged. For example, its level in saliva decreases in some diseases of the oral cavity. Interesting data were obtained in the laboratory of the Department of Microbiology of the Chelyabinsk Medical Institute. It turned out that non-smoking people have twice the level of lysozyme in their saliva than smokers.

Despite the fact that the skin and mucous membranes are a significant obstacle to the path of microbes, these barriers are not always reliable enough. Their integrity can be broken, and then the microorganisms penetrate into the tissues. In the vast majority of cases, an inflammatory process develops.

I. I. Mechnikov was the first to show that inflammation is a protective reaction of the body that prevents the further spread of pathogenic microbes. The inflammatory reaction is based on the ability of various cells of the body to capture and digest microorganisms, that is, to phagocytose them.

Phagocytosis is a very sensitive reaction, which reflects not only the body’s readiness to fight pathogens, but also its general reactivity, that is, the ability to respond to external influences.

Our laboratory has long studied the effect of regular physical training on phagocytosis. A direct relationship was found between the general condition of the body and its immunobiological reactivity, which was determined by the level of phagocytosis. Observations have shown that in people who are not sufficiently trained, phagocytosis is lower than in athletes who train regularly. Based on the level of the body’s phagocytic reaction, determined on the eve of the competition, one could even judge the athlete’s degree of fitness.

So, inflammation and phagocytosis are a powerful barrier to microbes. However, if there are too many microbes or they have high pathogenic properties, they pass through this barrier. Then the body’s lymphatic system and, above all, the lymph nodes, become involved in the fight against them.

If panaritium (inflammation of the tissues of the finger) is not treated in time, you may notice how thin red threads appear under the skin of the palmar surface of the forearm, which over time lengthen in the direction of the ulnar fossa. These threads are nothing more than inflamed lymphatic capillaries into which microbes have penetrated. Through these capillaries, pathogenic microorganisms move towards the lymph nodes - elbow, axillary, popliteal, inguinal. There are such nodes in the lungs, intestines, in the pharyngeal cavity, in the neck, etc. Performing a barrier function, lymph nodes trap bacteria, which often die in them.

The participation of lymph nodes in protecting the body from infection can be proven by the following experience. If you take two groups of mice and inject one of them with microbes into the palmar surface of the front paw, then within 30 minutes the microbes will appear in the blood of these mice. In mice that were infected through the palmar surface of the hind paw, bacteria appear in the blood only after 3 hours and in much smaller quantities. What's the matter? It turns out that mice have only one lymph node on the front leg - the axillary one, while on the back leg there are two: the popliteal and inguinal. Microorganisms introduced into the hind paw of an experimental animal had to pass through two lymphatic barriers, which contributed to their retention for a longer period.

When the protective role of the lymph nodes is insufficient, bacteria enter directly into the blood. Researchers have long drawn attention to the fact that if experimental animals are injected with a certain dose of microbes, then after a while they disappear from the body. At first it was assumed that microorganisms were removed by excretory organs, for example, the kidneys. Later it was found that a significant role is played by the ability of cells to absorb microbes that enter the body, and then kill and dissolve them. In addition, the disappearance of microbes is directly related to the presence in the body, mainly in the blood, of a number of so-called humoral substances that have a detrimental effect on microorganisms.

What substances kill and dissolve bacteria? A lot of them. This includes lysozyme (we have already talked about it above), and alexin, and properdin, and leukins, which are formed during the death of leukocytes, and antibodies. The most powerful of these factors are alexin and lysozyme.

Aleksin was discovered in the blood by the German scientist Buchner back in 1899. He introduced a known amount of bacteria into test tubes with fresh blood serum. At various intervals, he sown these mixtures on plates with a nutrient medium. The cups were kept in a thermostat for a strictly defined period, and then the number of microorganism colonies grown on them was counted. It turned out that the later the mixture was sown from the test tube, the smaller it was. Scientists came to the conclusion that the serum contains a special substance that has a detrimental effect on microorganisms. This substance is called alexin.

Observations on donors in which the levels of alexin, lysozyme and other natural protective factors of the body were studied at different times of the day and in different seasons of the year gave a lot of interesting things. It has been established that in autumn and winter the activity of lysozyme and alexin is lower compared to spring and summer. Even during the day, the level of these protective factors varies, as a rule, within significant limits. Their minimum number is noted in the morning and evening, and the maximum in the afternoon.

The level of alexin and lysozyme is reduced in pregnant women, as well as in various diseases. Many reflections are suggested by the fact that in the blood of people suffering from chronic alcoholism, as well as in smokers, lysozyme is two times less than it should be according to the norm.

In the animal world, huge and diverse, adaptation to new conditions of existence is constantly taking place. Microbes entering our body do not always cause disease. And the fact that infection is not yet equivalent to a disease is possible only due to the extraordinary flexibility of the body’s protective and adaptive systems. In order to preserve this most valuable quality, this ability to quickly respond to any changes in the environment, to the introduction of various microbes dangerous to us, the body should be trained and hardened. We must never forget about this main condition, which in many cases determines the body’s resistance to various harmful factors.

- Professor L. Y. Ebert

The liver is the largest gland in our body and one of the most important organs, without which a person cannot live. Located in the right part of the abdominal cavity, it has a lobular structure and acts as a kind of filter in the human body, which passes blood through itself, purifying it and neutralizing it. It performs many vital functions, regulates the functioning of other organs and systems, and the barrier role of the liver is of key importance in the life of the human body.

The role of the liver in our body is difficult to overestimate. After all, the largest gland of the digestive system, which is often called the “second heart of man,” performs dozens of different functions, including:

• Digestive function. The liver is an integral part of the digestive system. It is in this vital human organ that bile is produced, which enters the duodenum through the sphincter of Oddi and is excreted from the body. During the day, the human liver is capable of secreting up to 1.5 liters of bile, which, in turn, takes an active part in the digestive processes.
• Barrier (protective) function. This is one of the most important tasks of the liver. Being a kind of filter in the human body, it takes an active part in the deactivation and neutralization of toxic substances that come from the outside. In addition, it is in the cells of this organ that the processing of toxic substances (phenol, indole, etc.) occurs, which are formed as a result of the work of the intestinal microflora.
• Metabolic function. The liver takes an active part in the metabolism of proteins, fats, carbohydrates and vitamins. It is capable of producing reserve protein, converting glycogen into glucose, breaking down a number of hormones, and also synthesizing vitamins A and B12.
• Hematopoietic function. The liver is a “blood depot”. It is the main source of enrichment and the main reservoir of blood; it is in it that substances that are necessary for normal blood clotting are produced.

In addition, the liver regulates the level of glucose and enzymes in the blood, synthesizes growth hormones (especially at the stage of embryonic development), and maintains the normal balance of proteins, fats, carbohydrates, immunoglobulins and enzymes in the blood.

What is the barrier role of the liver?

Every hour, tens of liters of blood pass through the liver, which must be purified. That is why the barrier role of a vital organ in the human body is to perform the following tasks:

• neutralization of toxic substances that enter the human body along with food, medications or alcohol;
• ingestion and neutralization of bacteria;
• binding of poisons and ammonia that enter the liver as a result of the work of intestinal microflora;
• destruction of heavy metals;
• removal of breakdown products of proteins and other substances from the body.

The liver performs its barrier function in two stages. At the first stage, which is called “quarantine,” the degree of harmfulness of toxic substances and the method of their neutralization are determined. For example, alcohol is converted into acetic acid, and ammonia into urea.

Interestingly, the liver can convert even some toxic substances into products beneficial to the body.

At the second stage, harmful and toxic substances are removed from the body. Toxic compounds that the liver cannot convert into safe and useful products are either excreted through bile or enter the kidneys and are excreted from the body through urine.

Location of the liver in the human body

When is liver barrier function impaired?

The protective function of the liver plays a key role in the human body. However, sometimes it happens that under the influence of negative factors, the largest gland of the digestive system fails, and its barrier function is impaired.

The most common causes of barrier dysfunction are:

• the influence of chemical, radioactive and toxic substances on the human body;
• alcohol abuse;
• the use of certain medications that have an extremely strong hepatotoxic effect;
• obesity and lack of physical activity;
• poor nutrition;
• virus attack;
• diseases (hepatitis, fibrosis, cirrhosis, hepatosis, etc.).

Liver damage from medications is one of the most common side effects, and symptoms may appear as long as 3 months after you stop taking the medication.

Violation of the protective function is expressed in a decrease in the number and activity of hepatocytes, which break down, transform and remove toxic substances from the human body.

As a result, there is a disruption in the excretion of bile, digestion processes in the intestines, and a malfunction of the stomach and other organs of the digestive system.

How to determine that the liver barrier function is impaired?

It is very difficult to diagnose a violation of the barrier role of the liver in the early stages, since this organ is devoid of pain receptors. However, since the liver and its functions are closely related to other human organs, already in the early stages of a violation of the protective function, the following extrahepatic symptoms may appear:

• loss of appetite;
• indigestion (heartburn, nausea, vomiting);
• fast fatiguability;
• sleep disorder;
• itchy skin.

It is extremely difficult to detect liver barrier dysfunction in the early stages.

More characteristic symptoms of impaired protective function of the largest gland of the digestive system appear only in the later stages. As a rule, at this stage the patient begins to worry about:

• sharp, nagging or aching pain in the right hypochondrium;
• yellowing or pallor of the skin;
• regular attacks of nausea and vomiting;
• the appearance of red spots on the palms;
• specific odor from the mouth;
• hair loss and sexual dysfunction.

If these symptoms appear, urgent medical attention and consultation with a hepatologist are required.

How to restore liver barrier function?

To improve and restore the barrier function of the liver, it is first necessary to eliminate the negative factors that provoked its impairment. After the unfavorable factors have been eliminated, to restore the protective functions of the largest gland in our body, liver cells and enzymes, hepatologists recommend:

Use of hepatoprotective drugs

Hepatoprotectors are drugs that stimulate and restore liver cells, and also help normalize its basic functions.

In medicine, there are several groups of hepatoprotectors:

• herbal preparations (Gepabene, Karsil, Silibor, Legalon);
• preparations of animal origin (Hepatosan, Sirepar);
• preparations containing phospholipids (Essentiale, Essliver Forte, Phosphonciale);
• preparations that contain amino acids and their derivatives (Heptral, Hepa-Merz, Hepasol).

Contrary to the popular belief that hepatoprotective drugs are absolutely safe and harmless to the human body and can be taken uncontrolled, hepatologists argue that when interacting with other drugs, these drugs can have a hepatotoxic effect. Therefore, you can choose and take hepatoprotective drugs only on the recommendation of your doctor.

Maintaining proper nutrition and diet

Quick snacks, unbalanced nutrition, excessive consumption of unhealthy foods, preservatives and processed foods - all this often becomes the main cause of disruption of basic liver functions. Therefore, maintaining proper nutrition and diet is the main condition on the path to restoring the normal functioning and protective function of a vital organ in the human body.

First of all, we are talking about eliminating harmful foods from the diet - fatty, spicy and fried foods, smoked meats, herbs, marinades, coffee, spices.

However, proper nutrition and diet do not mean fasting. Nutritionists note that in this case we are talking about a healthy diet, which should be based on healthy foods such as vegetables, berries and fruits, cottage cheese and dairy products, lean meats, as well as steamed dishes.

To restore normal liver function and its barrier function, sometimes it is enough to exclude harmful foods from your diet and adhere to proper nutrition

Rejection of bad habits

Smoking and alcohol are the worst enemies of our liver. Regular consumption of alcoholic beverages and smoking reduce its ability to neutralize poisons and toxic substances, lead to damage to the cells and tissues of the organ and often become the main cause of liver failure. In addition, the listed bad habits very often provoke the development of many diseases, including alcoholic hepatosis, diabetes and cirrhosis.

Therefore, a healthy lifestyle is a necessary condition for maintaining and preserving the basic functions of the liver.

Thus, the liver is not only an organ that performs dozens of different functions, it is a powerful barrier in our body that protects it from the harmful effects of both external and internal factors. By daily converting toxic substances, the liver regulates the functioning of other organs and systems in the human body. However, the potential of the liver is not unlimited, so this vital organ must be protected and not subjected to testing in order to maintain its health into old age.

Barrier functions

physiological mechanisms (barriers) that ensure the protection of the body and its individual parts from environmental changes and the preservation of the constancy of composition, physicochemical and biological properties of the internal environment (blood, lymph, tissue fluid) necessary for their normal functioning.

Conventionally, external and internal barriers are distinguished. External barriers include the skin, respiratory and digestive organs, as well as the mucous membranes of the mouth, nose, and genitals. protects against mechanical, radiation and chemical influences, prevents the penetration of microorganisms and toxic substances into it, and promotes the removal of certain metabolic products. In the respiratory organs, in addition to the exchange of gases, the inhaled air is purified from dust and finely dispersed harmful substances. Throughout the digestive tract, specific processing of nutrients entering it is carried out, removing products not used by the body, as well as gases formed in the intestines during fermentation. The liver neutralizes foreign toxic compounds that come from food or are formed during the digestion process. Due to the function of the kidneys, the constancy of the blood composition and the removal of metabolic end products from the body are ensured.

Internal barriers regulate the flow of substances necessary for their activity from the blood into organs and tissues and the timely removal of the final products of cellular metabolism, ensuring the constancy of the optimal composition of tissue (extracellular) fluid. At the same time, they prevent the entry of foreign and toxic substances from the blood into organs and tissues.

Internal barriers have received various names: tissue, hematoparenchymal, vascular-tissue, etc. The most widely used term is “”. A feature of the histohematic barrier is its selective nature, i.e. the ability to pass some substances and retain others. Specialized barriers are of particular importance for the functioning of the body. These include the blood-brain barrier (between the blood and the central nervous system), (between the blood and intraocular fluid), (between the blood and the endolymph of the labyrinth), the barrier between the blood and the gonads. Histohematic barriers also include barriers between blood and body fluids (cerebrospinal fluid, lymph, pleural and synovial fluids) - the so-called hematocerebrospinal fluid, hematolymphatic, hematopleural, hematosynovial barriers. And has barrier properties that protect the developing one.

The main structural elements of histohematic barriers are blood vessels, which include a large amount of neutral mucopolysaccharides, basic amorphous substance, fibers, etc. The structure of histohematic barriers is determined to a large extent by the structural features of the organ and varies depending on the morphological and physiological characteristics of the organ and tissue.

At the heart of B. f. The processes of dialysis, ultrafiltration, osmosis, as well as changes in electrical properties, lipid solubility, tissue affinity or metabolic activity of cellular elements lie. Important importance in the function of some histohematic barriers is attached to the enzyme barrier, for example, in the walls of the microvessels of the brain and the surrounding connective tissue stroma () - a high level of enzymes was found - carbonic anhydrase, DOPA decarboxylase, etc. These, breaking down some biologically active substances, prevent their penetration into brain.

The functional state of the histohematic barrier is determined by the ratio of the concentrations of a particular substance in the organ and the blood washing it. This value is called the permeability coefficient, or distribution coefficient.

B. f. vary depending on age, gender, nervous, humoral and hormonal relationships in the body, the tone of the autonomic nervous system, and numerous external and internal influences. In particular, exposure to ionizing radiation on the body causes a decrease in the protective function of histohematic barriers, and the degree of decrease and reversibility of functional changes depend on the magnitude of the absorbed dose. The permeability of histohematic barriers is also affected by mechanical and thermal influences. A selective change in the permeability of cell membranes of histohematic barriers was noted when psychotropic drugs and ethanol were introduced into the body.

Various pathological conditions can impair the permeability of histohematological barriers. for example, with meningoencephalitis, the permeability of the blood-brain barrier sharply increases, which causes various kinds of violations of the integrity of surrounding tissues. Histohematic barriers can be changed in a targeted manner, which is used in the clinic (for example, to increase the effectiveness of chemotherapy drugs).

Bibliography: Bradbury M. The concept of the blood-brain barrier, . from English, M., 1983; and pathology of histohematic barriers, ed. L.S. Stern, M., 1968; Human Physiology, ed. R. Schmidt and G. Tevs. per. from English, vol. 2, M., 1985.

1. Small medical encyclopedia. - M.: Medical encyclopedia. 1991-96 2. First aid. - M.: Great Russian Encyclopedia. 1994 3. Encyclopedic Dictionary of Medical Terms. - M.: Soviet Encyclopedia. - 1982-1984.

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Barrier functions are a set of biochemical and physicochemical processes on the cell membrane that regulate the flow of various substances from the surrounding intercellular fluid into the cell.

Barrier functions ensure the constancy of the internal environment of the body, which in higher animals and humans consists of blood and lymph. Barrier functions are carried out by so-called histo-hematic barriers. They perform two main functions: 1) regulation of the physico-chemical constancy and qualitative biological characteristics of the intercellular fluid; 2) protection of cells of various organs and tissues from the effects of harmful substances that penetrate the body. Among the histo-blood barriers, the most important and studied is the blood-brain barrier. It regulates the flow of vital substances from the blood into the nervous tissue and cerebrospinal fluid and protects it from the penetration of foreign substances.

Barrier functions - the state and activity of special physiological mechanisms - barriers; the main function of which is to maintain the relative constancy of the composition and properties of the internal environment of the body (blood and tissue fluid). Conventionally, barriers are distinguished between external (skin, mucous membranes, respiratory, digestive and excretory apparatus) and internal (according to the terminology of different authors: histo-hematic, hemato-parenchymatous, histiocytic, tissue), located between the blood and the tissue (intercellular) fluid of organs and tissues . Through internal barriers, substances necessary to nourish cells selectively enter the tissue fluid and products of cellular metabolism are excreted.

Each organ has its own specialized barrier, the functional characteristics of which are determined by the morphological and physiological characteristics of this organ. Barriers regulate the metabolism between blood and tissue elements (regulatory function) and protect organs from the entry of foreign substances artificially introduced into the body, as well as toxic metabolic products formed during certain pathological conditions of the body (protective function). The sensitivity of organs and tissues to bacteria, poisons and toxins largely depends on barrier functions. The manifestation of the protective function of barriers explains the uneven distribution of various chemical and biologically active substances introduced into the blood and the lack of effect when treated with certain medications.

The state of any organ, its trophism and the influence that other organs and physiological systems have on it are in close connection with barrier mechanisms. An increase in the permeability of the corresponding barriers makes any organ more susceptible, and its decrease makes it less sensitive, less susceptible to substances circulating in the blood or introduced into it for one or another experimental or therapeutic purpose.

A decrease in the resistance of individual barriers to various pathogenic agents in the blood can cause disease in a particular organ. Under the influence of various factors (physiological, physical, chemical, infectious, etc.), the permeability of barriers changes - it increases in some cases and decreases in others. This property of barriers can be used for targeted effects on individual organs or the entire body. The greater plasticity of barrier mechanisms, their adaptability to external and internal environmental conditions are important for the normal existence of the body, maintaining a certain level of physiological functions, protection from infections, intoxications, functional and organic disorders.

The anatomical substrate of internal barriers is mainly the endothelium of capillaries and precapillaries, the structure of which varies in different organs. The physiological activity of barriers depends both on the permeability of the vascular wall and on the diverse neuro-endocrine-humoral influences that regulate the relationship between the body and its environment, on the one hand, and between blood and tissue fluid, on the other.

The problem of the barrier function is widely developed in the USSR (works by L. S. Stern et al., A. A. Bogomolets, N. D. Strazhesko, B. N. Mogilnitsky, A. I. Smirnova-Zamkova, G. N. Kassil, N.N. Zaiko, Ya.L. Rapoport, etc.). A number of methods have been proposed for studying barrier functions (introduction of various dyes, intravital microscopy, microcombustion, radioisotope indication, electron microscopy, etc.). In most cases, to judge the barrier function, the method of quantitative determination of an indicator introduced into the blood in organs and tissues is used, which is not always a specific indicator of the functional state of barriers, and in many cases depends on the intensity of interstitial metabolism.

Among the internal barriers, the blood-brain barrier has been studied in most detail - a physiological mechanism that regulates the metabolism between the blood and the central nervous system, as well as protects the brain and spinal cord from foreign substances introduced into the blood, or from products of disrupted tissue metabolism formed in the body itself. A new branch of science is the study of intracellular barriers, begun in Soviet and foreign laboratories.

Blood-ophthalmic barrier. The fluid of the anterior chamber of the eye differs significantly in composition from blood plasma: protein, enzymes and antibodies are absent or contained in small quantities in the chamber fluid. With regard to electrolytes, the difference in their concentration in the chamber humor and in the blood cannot be explained by simple filtration or dialysis. Analysis of data on the penetration of various substances into eye fluids, as well as studies using radioactive isotopes, lead to the conclusion that between the blood and eye fluids there is an active regulatory and protective biological membrane (blood-ophthalmic barrier), which performs a barrier function.

Histological studies give reason to believe that the anatomical substrate of the blood-ophthalmic barrier is the vascular endothelium, which has very active properties. The trigeminal nerve, as well as the autonomic nervous system, have a noticeable influence on the function of the blood-ophthalmic barrier. The possibility of a conditioned reflex change in the permeability of blood vessels in the anterior segment of the eyeball indicates the existence of control over the function of the blood-ophthalmic barrier by the cerebral cortex.