Blood osmotic pressure. Functional system for maintaining constant osmotic pressure. Blood Increased osmotic pressure

Blood volume - the total amount of blood in the body of an adult is on average 6 - 8% of body weight, which corresponds to 5 - 6 liters. An increase in total blood volume is called hypervolemia, a decrease is called hypovolemia. The relative density of blood - 1.050 - 1.060 depends mainly on the number of red blood cells. The relative density of blood plasma is 1.025 - 1.034, determined by the concentration of proteins. The viscosity of blood is 5 conventional units, plasma - 1.7 - 2.2 conventional units, if the viscosity of water is taken as 1. It is determined by the presence of red blood cells in the blood and in to a lesser extent of plasma proteins.

Osmotic pressure of blood is the force with which a solvent passes through a semi-permeable membrane from a less to a more concentrated solution. The osmotic pressure of the blood is calculated using the cryoscopic method by determining the freezing point of the blood (depression), which for it is 0.56 - 0.58 C. The osmotic pressure of the blood is on average 7.6 atm. It is caused by osmotically active substances dissolved in it, mainly inorganic electrolytes, and to a much lesser extent proteins. About 60% of the osmotic pressure is created by sodium salts (NaCl).

Osmotic pressure determines the distribution of water between tissues and cells. The functions of body cells can only be carried out with relative stability of osmotic pressure. If red blood cells are placed in a saline solution that has the same osmotic pressure as blood, they do not change their volume. This solution is called isotonic or physiological. This may be a 0.85% sodium chloride solution. In a solution whose osmotic pressure is higher than the osmotic pressure of blood, red blood cells shrink as water leaves them into the solution. In a solution with a lower osmotic pressure than blood pressure, red blood cells swell as a result of the transfer of water from the solution into the cell. Solutions with a higher osmotic pressure than blood pressure are called hypertonic, and those with a lower pressure are called hypotonic.

Blood oncotic pressure is part of the osmotic pressure created by plasma proteins. It is equal to 0.03 - 0.04 atm, or 25 - 30 mm Hg. Oncotic pressure is mainly caused by albumin. Due to their small size and high hydrophilicity, they have a pronounced ability to attract water, due to which it is retained in the vascular bed. When the oncotic pressure of the blood decreases, water escapes from the vessels into the interstitial space, which leads to tissue edema.

Acid-base status of blood (ABS). The active blood reaction is determined by the ratio of hydrogen and hydroxyl ions. To determine the active blood reaction, the pH value is used - the concentration of hydrogen ions, which is expressed as the negative decimal logarithm of the molar concentration of hydrogen ions. Normal pH is 7.36 (weakly basic reaction); arterial blood – 7.4; venous – 7.35. Under various physiological conditions, blood pH can vary from 7.3 to 7.5. The active blood reaction is a rigid constant that ensures enzymatic activity. The extreme limits of blood pH compatible with life are 7.0 – 7.8. A shift in the reaction to the acidic side is called acidosis, which is caused by an increase in hydrogen ions in the blood. A shift in the blood reaction to the alkaline side is called alkalosis. This is due to an increase in the concentration of hydroxyl ions OH and a decrease in the concentration of hydrogen ions.

There are 4 buffer systems in the blood: bicarbonate BS, phosphate BS, hemoglobin BS, protein and plasma BS. All BS create an alkaline reserve in the blood, which is relatively constant in the body.

Blood osmotic pressure (BOP) is the level of force that circulates the solvent (for our body this is water) through the membrane of red blood cells.

Level maintenance occurs on the basis of movement from solutions that are less concentrated to those where the concentration of water is greater.

This interaction is the exchange of water between the blood and tissues of the human body. Ions, glucose, proteins, and other useful elements concentrated in the blood.

Normal osmotic pressure is 7.6 atm., or 300 mOsmol, which is equal to 760 mmHg.

Osmol is the concentration of one mole of non-electrolyte dissolved per liter of water. Osmotic concentration in the blood is determined precisely by measuring them.

What is the UEC?

Surrounding cells with a membrane is inherent in both tissues and blood elements; water easily passes through it and dissolved substances practically do not penetrate. Therefore, a deviation in osmotic pressure indicators can lead to an increase in the red blood cell, and its loss of water and deformation.

For red blood cells and most tissues, it is detrimental to increase the consumption of salts in the body, which settle on the walls of blood vessels and narrow the passages of blood vessels.

This pressure is always at approximately the same level and is regulated by receptors, localized in the hypothalamus, blood vessels and tissues.

Their common name is osmoreceptors; they are the ones who maintain the TDC indicator at the required level.

One of the most stable blood parameters is the plasma osmotic concentration, which maintains normal levels of blood osmotic pressure, with the help of hormones and body signals - a feeling of thirst.

What are the normal ODC indicators?

Normal indicators of osmotic pressure are indicators of cryoscopic examination not exceeding 7.6 atm. The analysis determines the point at which the blood freezes. Normal freezing values ​​for a solution for humans are 0.56-0.58 degrees Celsius, which is equivalent to 760 mm Hg.

A separate type of ODC is created by plasma proteins. Also, the osmotic pressure of plasma proteins is called oncotic pressure. This pressure is several times lower than the pressure created in the plasma by salts, since proteins have high levels of molecular weight.

In relation to other osmotic elements, their presence is insignificant, although they are found in the blood in large quantities.

It affects the overall indicators of the UEC, but in a small ratio(one point two hundred and twentieth part) to the general indicators.

This is equivalent to 0.04 atm., or 30 mmHg. For indicators of blood osmotic pressure, their quantitative factor and mobility are more important than the mass of dissolved particles.

The described pressure counteracts the strong movement of solvent from the blood into the tissues, and affects the transfer of water from the tissues to the vessels. This is why tissue swelling progresses, as a result of a decrease in protein concentration in the plasma.

The nonelectrolyte contains a lower osmotic concentration than the electrolyte. This is noted because. That electrolyte molecules dissolve ions, which leads to an increase in the concentration of active particles that characterize the osmotic concentration.

What influences deviations in osmotic pressure?

Reflex changes in the activity of the excretory organs entail irritation of osmoreceptors. When they become inflamed, they remove from the body excess water and salts that have entered the blood.

An important role here is played by the skin, the tissues of which feed on excess water from the blood or return it to the blood, with an increase in osmotic pressure.

The indicators of normal BDC are influenced by the quantitative saturation of the blood with electrolytes and non-electrolytes that are dissolved in the blood plasma.

At least sixty percent is ionized potassium chloride. Isotonic solutions are solutions in which the TDC level is close to the plasma level.

When this value increases, the composition is called hypertonic, and when it decreases, it is called hypotonic.

If the normal osmotic pressure deviates from the norm, cell damage is provoked. In order to restore osmotic pressure in the blood, solutions can be injected orally, which are selected depending on the disease that provokes deviations of the BDC from the norm.

Among them:

• Hypotonic concentrated solution. When used in the correct dosage, it cleanses wounds of pus and helps reduce the size of allergic swelling. But with the wrong doses, it provokes rapid filling of cells with solution, which leads to their rapid rupture;
• Hypertonic solution. By introducing this solution into the blood, they promote improved excretion of water cells into the vascular system;
• Dilution of drugs in isotonic solution. The drugs are stirred in this solution at normal ODC values. Sodium chloride is the most commonly mixed drug.

The daily maintenance of normal BDC levels is monitored by the sweat glands and kidneys. They prevent the effects of products that remain after metabolism on the body by creating protective shells.

That is why the osmotic pressure of the blood almost always fluctuates at the same level. A sharp increase in its indicators is possible with active physical activity. But even in this case, the body itself quickly stabilizes the indicators.

Interaction of erythrocytes with solutions depending on their osmotic pressure.

What happens when there are deviations?

With an increase in blood osmotic pressure, water cells move from red blood cells into the plasma, as a result of which the cells become deformed and lose their functionality. When the concentration of osmoles decreases, the saturation of the cell with water increases, which leads to an increase in its size and deformation of the membrane, which is called hemolysis.

Hemolysis is characterized by the fact that during it the most numerous blood cells - red cells, also called erythrocytes - are deformed, then hemoglobin protein enters the plasma, subsequently making it transparent.

Hemolysis is divided into the following types:

Type of hemolysis	Characteristic
Osmotic	Progresses with the decline of the UDC. Leads to an increase in red blood cells, followed by deformation of their membrane, and the release of hemoglobin
Mechanical	This type of hemolysis occurs due to a strong mechanical effect on the blood. As an example, when a test tube with blood is shaken vigorously
Biological	Progresses under the influence of immune hemolysis, blood transfusions that do not match the blood group, and with bites of certain types of snakes
Thermal	Develops when blood is thawed or frozen
Chemical	Progresses under the influence of substances that deform the protein membrane of red cells. Alcoholic drinks, essential oils, chloroform, benzene and others can affect this

In research, both clinical and scientific, osmotic hemolysis is used to determine the quality indicators of red cells (red cell osmotic resistance method), as well as the resistance of red cell membranes to deformation in solution.

Does diet affect blood osmotic pressure?

Maintaining proper nutrition with a balanced diet of foods helps in the prevention of many diseases.

A high concentration of salt consumed leads to sodium deposition on the walls of blood vessels. They become narrower, which disrupts normal blood circulation and fluid removal, increases blood pressure, and provokes swelling.

Drinking less than one and a half liters of clean drinking water per day leads to an imbalance in water balance.

This, in turn, leads to increased blood viscosity due to insufficient solvent.

This creates a feeling of thirst, which, when satisfied, the body resumes the normal functionality of the body.

By what methods is it determined?

The TDC indicator is measured using an osmometer - a device for measuring the total concentration of blood, cryoscopic method, active substances (osmolarity) in blood fluids, urine and aqueous solutions.

Osmometer

Determination of blood osmotic pressure is done in most cases using the cryoscopic method - studying solutions, where the basis is the lowering of the freezing point of the solution compared to the temperature at which a pure solvent freezes.

This method determines depression, or the decline in the level at which the blood freezes. The higher the osmotic pressure, the higher the concentration of dissolved particles in the blood. It follows from this that the higher the ODC level, the lower the temperature at which the solution freezes.

Within normal limits, the indicators range from 7.5 to 8 atm.

Also important is the oncotic pressure indicator, and if it fluctuates below normal, it may indicate kidney or liver pathologies, or prolonged hunger strike.

The osmotic pressure indicator is an important factor in the body, and indicates the normal circulation of the solvent (water) in the human body.

In a broad sense, the concept of “physicochemical properties” of an organism includes the entire set of components of the internal environment, their connections with each other, with the cellular contents and with the external environment. In relation to the objectives of this monograph, it seemed appropriate to select physicochemical parameters of the internal environment that are of vital importance, well “homeostasis” and at the same time relatively fully studied from the point of view of specific physiological mechanisms that ensure the preservation of their homeostatic boundaries. The gas composition, acid-base state and osmotic properties of blood were selected as such parameters. Essentially, the body does not have separate isolated systems for homeostasis of these parameters of the internal environment.

Osmotic homeostasis

Along with the acid-base balance, one of the most strictly homeostasis parameters of the internal environment of the body is the osmotic pressure of the blood.

The magnitude of osmotic pressure, as is known, depends on the concentration of the solution and its temperature, but does not depend on either the nature of the solute or the nature of the solvent. The unit of osmotic pressure is the pascal (Pa). Pascal is the pressure caused by a force of 1 N, uniformly distributed over a surface area of ​​1 m2. 1 atm = 760 mm Hg. Art. 10 5 Pa = 100 kPa (kilopascal) = 0.1 MPa (megapascal). For a more accurate conversion: 1 atm = 101325 Pa, 1 mm Hg. Art. = 133.322 Pa.

Blood plasma, which is a complex solution containing various molecules of non-electrolytes (urea, glucose, etc.), ions (Na +, K +, C1 -, HCO - 3, etc.) and micelles (protein), has an osmotic pressure equal to the sum of the osmotic pressures of the ingredients it contains. In table Figure 21 shows the concentrations of the main plasma components and the osmotic pressure created.

Table 21. Concentration of the main plasma components and the osmotic pressure they create
Main components of plasma	Molar concentration, mmol/l	Molecular mass	Osmotic pressure, kPa
Na+	142	23	3,25
C1 -	103	35,5	2,32
NSO - 3	27	61	0,61
K+	5,0	39	0,11
Ca 2+	2,5	40	0,06
PO 3- 4	1,0	95	0,02
Glucose	5,5	180	0,13
Protein	0,8	Between 70,000 and 400,000	0,02
Note. Other plasma components (urea, uric acid, cholesterol, fats, SO 2-4, etc.) account for approximately 0.34-0.45 kPa. The total osmotic pressure of plasma is 6.8-7.0 kPa.

As can be seen from table. 21, the osmotic pressure of plasma is determined mainly by the ions Na +, C1 -, HCO - 3 and K +, since their molar concentration is relatively high, while the molecular weight is insignificant. The osmotic pressure caused by high molecular weight colloidal substances is called oncotic pressure. Despite the significant protein content in plasma, its share in creating the total osmotic pressure of plasma is small, since the molar concentration of proteins is very low due to their very large molecular weight. In this regard, albumins (concentration 42 g/l, molecular weight 70,000) create an oncotic pressure of 0.6 mosmol, and globulins and fibrinogen, whose molecular weight is even higher, create an oncotic pressure of 0.2 mosmol.

The constancy of the electrolyte composition and osmotic properties of the extracellular and intracellular sectors is in close relationship with the body's water balance. Water makes up 65-70% of body weight (40-50 l), of which 5% (3.5 l) is in the intravascular sector, 15% (10-12 l) is in the interstitial sector and 45-50% (30-35 l) - to the intracellular space. The overall balance of water in the body is determined, on the one hand, by the intake of alimentary water (2-3 l) and the formation of endogenous water (200-300 ml), and on the other hand, by its release through the kidneys (600-1600 ml), respiratory tract and skin (800-1200 ml) and with feces (50-200 ml) (Bogolyubov V.M., 1968).

In maintaining water-salt (osmotic) homeostasis, it is customary to distinguish three parts: the intake of water and salts into the body, their redistribution between extra- and intracellular sectors, and their release into the external environment. The basis for the integration of the activities of these links are neuroendocrine regulatory functions. The behavioral sphere plays a damping role between the external and internal environments, helping autonomic regulation to ensure the constancy of the internal environment.

The leading role in maintaining osmotic homeostasis is played by sodium ions, which account for more than 90% of extracellular cations. To maintain normal osmotic pressure, even a small sodium deficiency cannot be replaced by any other cations, since such a replacement would be expressed in a sharp increase in the concentration of these cations in the extracellular fluid, which would inevitably result in severe disorders of the body's vital functions. Another main component that ensures osmotic homeostasis is water. A change in the volume of the liquid part of the blood, even while maintaining a normal sodium balance, can significantly affect osmotic homeostasis. The intake of water and sodium into the body is one of the main links in the water-salt homeostasis system. Thirst is an evolutionarily developed reaction that ensures an adequate (under conditions of normal functioning of the body) supply of water to the body. The feeling of thirst usually occurs due to either dehydration, or an increased intake of salts into the body or insufficient excretion. Currently, there is no single view on the mechanism of the feeling of thirst. One of the first ideas about the mechanism of this phenomenon is based on the fact that the initial factor of thirst is the drying of the mucous membrane of the oral cavity and pharynx, which occurs with an increase in the evaporation of water from these surfaces or with a decrease in the secretion of saliva. The correctness of this “dry mouth” theory has been confirmed by experiments with ligation of the salivary ducts, removal of the salivary glands, and anesthesia of the oral cavity and pharynx.

Proponents of general theories of thirst believe that this feeling arises as a result of general dehydration of the body, leading either to thickening of the blood or to dehydration of cells. This point of view is based on the discovery of osmoreceptors in the subcutaneous region and other areas of the body (Ginetsinsky A. G., 1964; Verney E. V., 1947). It is believed that osmoreceptors, when excited, form a feeling of thirst and cause appropriate behavioral reactions aimed at searching for and absorbing water (Anokhin P.K., 1962). Thirst quenching is ensured by the integration of reflex and humoral mechanisms, and the cessation of the drinking reaction, i.e., the “primary saturation” of the body is a reflex act associated with the effect on the extero- and interoreceptors of the digestive tract, and the final restoration of water comfort is ensured by the humoral route (Zhuravlev I N., 1954).

Recently, data have been obtained on the role of the renin-agiotensin system in the formation of thirst. Receptors were found in the subcutaneous region, irritation of which by angiotensin II leads to thirst (Fitzimos J., 1971). Angiotensin apparently increases the sensitivity of osmoreceptors in the subthalamic region to the action of sodium (Andersson B., 1973). The formation of the sensation of thirst occurs not only at the level of the subcutaneous region, but also in the limbic system of the forebrain, which is connected with the subcutaneous region into a single nerve ring.

The problem of thirst is inextricably linked with the problem of specific salt appetites, which play an important role in maintaining osmotic homeostasis. It has been shown that the regulation of thirst is determined mainly by the state of the extracellular sector, and salt appetite - by the state of the intracellular sector (Arkind M.V. et al. 1962; Arkind M.V. et al., 1968). However, it is possible that the feeling of thirst can be caused by cell dehydration alone.

Currently, the large role of behavioral reactions in maintaining osmotic homeostasis is known. Thus, in experiments on dogs exposed to overheating, it was found that animals instinctively choose to drink from the offered salt solutions the one whose salts are not enough in the body. During periods of overheating, dogs preferred a solution of potassium chloride rather than sodium chloride. After the cessation of overheating, the appetite for potassium decreased and the appetite for sodium increased. It was found that the nature of appetite depends on the concentration of potassium and sodium salts in the blood. Preliminary administration of potassium chloride prevented an increase in potassium appetite due to overheating. If the animal received sodium chloride before the experiment, after the cessation of overheating, the sodium appetite characteristic of this period disappeared (Arkind M.V., Ugolev A.M., 1965). At the same time, it has been shown that there is no strict parallelism between changes in the concentration of potassium and sodium in the blood, on the one hand, and water and salt appetite, on the other. Thus, in experiments with strophanthin, which inhibits the potassium-sodium pump and consequently leads to an increase in sodium content in the cell and a decrease in its extracellular concentration (changes of the opposite nature were noted for potassium), sodium appetite sharply decreased and potassium appetite increased. These experiments indicate the dependence of salt appetite not so much on the overall balance of salts in the body, but on the ratio of cations in the extra- and intracellular sectors. The nature of salt appetite is determined mainly by the level of intracellular salt concentration. This conclusion is confirmed by experiments with aldosterone, which enhances the removal of sodium from cells and the entry of potassium into them. Under these conditions, sodium appetite increases, and potassium appetite decreases (Ugolev A.M., Roshchina G.M., 1965; Roshchina G.M., 1966).

The central mechanisms of regulation of specific salt appetites have not been sufficiently studied at present. There is evidence confirming the existence of structures in the subcutaneous region, the destruction of which changes salt appetite. For example, destruction of the ventromedial nuclei of the subtubercular region leads to a decrease in sodium appetite, and destruction of the lateral regions causes a loss of preference for sodium chloride solutions to water. When the central zones are damaged, the appetite for sodium chloride sharply increases. Thus, there is reason to talk about the presence of central mechanisms for regulating sodium appetite.

It is known that shifts in the normal sodium equilibrium cause corresponding, precisely coordinated changes in the intake and excretion of sodium chloride. For example, bloodletting, infusion of fluids into the blood, dehydration, etc. naturally change natriuresis, which increases with increasing volume of circulating blood and decreases with decreasing volume. This effect has a twofold explanation. According to one point of view, a decrease in the amount of sodium released is a reaction to a decrease in the volume of circulating blood; according to another, the same effect is a consequence of a decrease in the volume of interstitial fluid, which, during hypovolemia, passes into the vascular bed. Hence, one could assume a dual localization of receptive fields that “monitor” the level of sodium in the blood. Tissue localization is supported by experiments with intravenous administration of protein (Goodyer A.V.N. et al., 1949), in which a decrease in the volume of interstitial fluid, due to its passage into the bloodstream, caused a decrease in natriuresis. The introduction of saline solutions into the blood, regardless of whether they were iso-, hyper- or hypotonic, led to an increase in sodium excretion. This fact is explained by the fact that saline solutions that do not contain colloids are not retained in the vessels and pass into the interstitial space, increasing the volume of fluid located there. This leads to a weakening of the stimuli that ensure the activation of sodium retention mechanisms in the body. Increasing the intravascular volume by introducing an iso-oncotic solution into the blood does not change natriuresis, which can be explained by the preservation of the volume of interstitial fluid under the conditions of this experiment.

There is reason to believe that the regulation of natriuresis is carried out not only by signals from tissue receptors. Their intravascular localization is just as likely. In particular, it has been established that stretching of the right atrium causes a natriuretic effect (Kappagoda S. T. et al., 1978). It has also been shown that stretching the right atrium prevents a decrease in sodium excretion by the kidneys against the background of bleeding. These data allow us to assume the presence in the right atrium of receptor formations that are directly related to the regulation of sodium excretion by the kidneys. There are also assumptions about the localization of receptors that signal shifts in the concentration of osmotically active substances in the blood in the left atrium (Mitrakova O.K., 1971). Similar receptor zones were found at the site of the thyroid-carotid branch; compression of the common carotid arteries caused a decrease in sodium excretion in the urine. This effect disappeared against the background of preliminary denervation of the vascular walls. Similar receptors were found in the vascular bed of the pancreas (Inchina V.I. et al., 1964).

All reflexes that affect natriuresis equally and unambiguously affect diuresis. The localization of both receptors is almost the same. Most of the currently known volume receptor formations are located in the same place where baroreceptor zones are found. As most researchers believe, volume receptors are not different in nature from baroreceptors, and the different effects of excitation of both are explained by the arrival of impulses to different centers. This indicates a very close relationship between the mechanisms regulating water-salt homeostasis and blood circulation (see diagram and Fig. 40). This connection, initially discovered at the level of the afferent link, now extends to effector formations. In particular, after the work of F. Gross (1958), who suggested the aldosterone-stimulating function of renin, and based on the hypothesis of juxtaglomerular control of circulating blood volume, there were grounds to consider the kidneys not only an effector link in the system of water-salt homeostasis, but also a source of information about changes in volume blood.

The volume receptor apparatus can obviously regulate not only the volume of fluid, but also indirectly the osmotic pressure of the internal environment. At the same time, it is logical to assume that there must be a special osmoregulatory mechanism. The existence of receptors sensitive to changes in osmotic pressure was shown in the laboratory of K. M. Bykov (Borshchevskaya E. A., 1945). However, fundamental research into the problem of osmoregulation belongs to E.V. Verney (1947, 1957).

According to E.V. Verney, the only zone capable of perceiving changes in the osmotic pressure of the internal environment of the body is a small area of ​​nervous tissue in the region of the supraoptic nucleus. Several dozen special types of hollow neurons were discovered here, excited when the osmotic pressure of the interstitial fluid surrounding them changes. The operation of this osmoregulatory mechanism is based on the principle of an osmometer. The central localization of osmoreceptors was later confirmed by other researchers.

The activity of osmosensitive receptor formations affects the amount of hormone of the posterior lobe of the pituitary gland entering the blood, which determines the regulation of diuresis and indirectly osmotic pressure.

A great contribution to the further development of the theory of osmoregulation was made by the work of A. G. Ginetsinsky and co-workers, who showed that Verney's osmoreceptors represent only the central part of a large number of osmoreflexes that are activated as a result of excitation of peripheral osmoreceptors localized in many organs and tissues of the body. It has now been shown that osmoreceptors are localized in the liver, lungs, spleen, pancreas, kidneys and some muscles. Irritation of these osmoreceptors by hypertonic solutions introduced into the bloodstream has an unambiguous effect - a decrease in diuresis occurs (Velikanova L.K., 1962; Inchina V.I., Finkinshtein Ya.D., 1964).

The delay in the release of water in these experiments was determined by changes in the osmotic pressure of the blood, and not by the chemical nature of osmotically active substances. This gave the authors reason to consider the effects obtained as osmoregulatory reflexes caused by irritation of osmoreceptors.

As a result of modern research, the existence of sodium chemoreceptors has been established in the liver, spleen, skeletal muscles, the region of the third ventricle of the brain, and lungs (Kuzmina B. L., 1964; Finkinshtein Ya. D., 1966; Natochin Yu. V., 1976; Eriksson L. et al., 1971; Passo S. S. et al., 1973). Thus, the afferent link of the osmotic homeostatic system is apparently represented by receptors of a different nature: general osmoreceptors, specific sodium chemoreceptors, extra- and intravascular volume receptors. It is believed that under normal conditions these receptors act unidirectionally and only under pathological conditions is discoordination of their function possible.

The main role in maintaining osmotic homeostasis belongs to three systemic mechanisms: adenopituitary, adrenal and renin-angiotensin. Experiments proving the participation of neurohypophyseal hormones in osmoregulation made it possible to construct a scheme for influencing the function of the kidneys, which are considered the only organ capable of ensuring the constancy of osmotic homeostasis in animals and humans (Natochin Yu. V., 1976). The central link is the supraoptic nucleus of the anterior subcutaneous region, in which neurosecretion is synthesized, which is then converted into vasopressin and oxytocin. The function of this nucleus is influenced by afferent impulses from the receptor zones of blood vessels and interstitial space. Vasopressin is able to change the tubular reabsorption of “osmotically free” water. With hypervolemia, the release of vasopressin decreases, which weakens reabsorption; hypovolemia leads through a vasopressive mechanism to increased reabsorption.

The regulation of natriuresis itself is carried out mainly by changing the tubular reabsorption of sodium, which in turn is controlled by aldosterone. According to the hypothesis of G. L. Farrell (1958), the center for the regulation of aldosterone secretion is located in the midbrain, in the area of ​​the Sylvian aqueduct. This center consists of two zones, one of which is the anterior one, located closer to the posterior subcutaneous region, has the ability to neurosecretion, and the other, the posterior one, has an inhibitory effect on this neurosecretion. The secreted hormone enters the pineal gland, where it accumulates, and then into the blood. This hormone is called adrenoglomerulotrophin (AGTG) and, according to the hypothesis of G. L. Farrel, it is a link between the central nervous system and the glomerular zone of the adrenal cortex.

There is also evidence of the effect on the secretion of aldosterone by the hormone of the anterior pituitary gland - ACTH (Singer B. et al., 1955). There is convincing evidence that the regulation of aldosterone secretion is carried out by the renin-angiotensin system (Carpenter S. S. et al., 1961). Apparently, there are several options for turning on the renin-aldosterone mechanism: by directly changing blood pressure in the vas afferens region; by reflex influence from volume receptors through sympathetic nerves on the tone of the vas afferens and, finally, through changes in the sodium content in the fluid entering the lumen of the distal tubule.

Sodium reabsorption is also under direct nervous control. The endings of adrenergic nerves are found on the basement membranes of the proximal and distal tubules, stimulation of which increases sodium reabsorption in the absence of changes in renal blood flow and glomerular filtration (Di Bona G. F., 1977, 1978).

Until recently, it was generally accepted that the formation of osmotically concentrated urine occurs as a result of the extraction of salt-free water from the isosmotic plasma of the tubular fluid. According to N. W. Smith (1951, 1956), the process of diluting and concentrating urine occurs in stages. In the proximal tubules of the nephron, water is reabsorbed due to the osmotic gradient created by the epithelium during the transfer of osmotically active substances from the lumen of the tubule into the blood. At the level of the thin segment of the loop of Henle, osmotic equalization of the composition of the tubular fluid and blood occurs. According to the proposal of N. W. Smith, the reabsorption of water in the proximal tubules and the thin segment of the loop is usually called obligate, since it is not regulated by special mechanisms. The distal part of the nephron provides “facultative”, regulated reabsorption. It is at this level that active reabsorption of water against the osmotic gradient occurs. Subsequently, it was proven that active reabsorption of sodium against a concentration gradient is also possible in the proximal tubule (Windhager E. E. et al., 1961; Hugh J. S. et al., 1978). The peculiarity of proximal reabsorption is that sodium is absorbed with an osmotically equivalent amount of water and the contents of the tubule always remain isosmotic to the blood plasma. At the same time, the wall of the proximal tubule has low permeability to water compared to the glomerular membrane. In the proximal tubule, a direct relationship was found between glomerular filtration rate and reabsorption.

From a quantitative point of view, sodium reabsorption in the distal part of the neuron was approximately 5 times less than in the proximal part. It has been established that in the distal segment of the nephron, sodium is reabsorbed against a very high concentration gradient.

Regulation of sodium reabsorption in renal tubular cells is carried out in at least two ways. Vasopressin increases the permeability of cell membranes by stimulating adenyl cyclase, under the influence of which cAMP is formed from ATP, activating intracellular processes (Handler J. S., Orloff J., 1971). Aldosterone is able to regulate active sodium transport by stimulating de novo protein synthesis. It is believed that under the influence of aldosterone, two types of proteins are synthesized, one of which increases the permeability to sodium of the apical membrane of renal tubular cells, the other activates the sodium pump (Janacek K. et al., 1971; Wiederhol M. et al., 1974).

Sodium transport under the influence of aldosterone is closely related to the activity of tricarboxylic acid cycle enzymes, during the conversion of which the energy necessary for this process is released. Aldosterone has the most pronounced effect on sodium reabsorption compared to other currently known hormones. However, regulation of sodium excretion can be carried out without changing aldosterone production. In particular, an increase in natriuresis due to the intake of moderate amounts of sodium chloride occurs without the participation of the aldosterone mechanism (Levinky N. G., 1966). Intrarenal non-aldosterone mechanisms for the regulation of natriuresis have been established (Zeyssac R. R., 1967).

Thus, in the homeostatic system, the kidneys perform both executive and receptor functions.

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Human health and well-being depend on the balance of water and salts, as well as normal blood supply to organs. A balanced, normalized exchange of water from one structure of the body to another (osmosis) is the basis of a healthy lifestyle, as well as a means of preventing a number of serious diseases (obesity, vegetative-vascular dystonia, systolic hypertension, heart disease) and a weapon in the fight for beauty and youth.

It is very important to maintain the balance of water and salts in the human body.

Nutritionists and doctors talk a lot about controlling and maintaining water balance, but do not delve into the origins of the process, the dependencies within the system, the definition of structure and connections. As a result, people remain illiterate in this matter.

The concept of osmotic and oncotic pressure

Osmosis is the process of transfer of liquid from a solution with a lower concentration (hypotonic) to an adjacent one with a higher concentration (hypertonic). Such a transition is possible only under appropriate conditions: with the “neighborhood” of liquids and with the separation of a permeable (semi-permeable) partition. At the same time, they exert a certain pressure on each other, which in medicine is usually called osmotic.

In the human body, each biological fluid is just such a solution (for example, lymph, tissue fluid). And cell walls are “barriers”.

One of the most important indicators of the state of the body, the content of salts and minerals in the blood is osmotic pressure

Blood osmotic pressure is an important vital indicator, reflecting the concentration of its constituent elements (salts and minerals, sugars, proteins). It is also a measurable quantity that determines the force with which water is redistributed into tissues and organs (or vice versa).

It has been scientifically determined that this force corresponds to the pressure in saline solution. This is what doctors call sodium chloride solution with a concentration of 0.9%, one of the main functions of which is plasma replacement and hydration, which helps combat dehydration, exhaustion in case of large blood losses, and it also protects red blood cells from destruction when drugs are administered. That is, relative to blood it is isotonic (equal).

Oncotic blood pressure is a component (0.5%) of osmosis, whose value (necessary for the normal functioning of the body) ranges from 0.03 atm to 0.04 atm. Reflects the force with which proteins (in particular albumins) act on neighboring substances. Proteins are heavier, but their number and mobility are inferior to salt particles. Therefore, oncotic pressure is much less than osmotic pressure, but this does not reduce its importance, which is to maintain the transition of water and prevent reabsorption.

No less important is such an indicator as oncotic blood pressure

An analysis of the plasma structure shown in the table helps to imagine their relationship and the significance of each.

Regulatory and metabolic systems (urinary, lymphatic, respiratory, digestive) are responsible for maintaining a constant composition. But this process begins with signals sent by the hypothalamus, which responds to irritation of osmoreceptors (nerve endings in the cells of blood vessels).

The level of this pressure directly depends on the functioning of the hypothalamus

For proper functioning and viability of the body, blood pressure must correspond to cellular, tissue and lymphatic pressure. When the body systems work properly and harmoniously, its value remains constant.

It can increase sharply during physical activity, but quickly returns to normal.

How is osmotic pressure measured and its importance?

Osmotic pressure is measured in two ways. The choice is made depending on the current situation.

Cryoscopic method

It is based on the dependence of the temperature at which a solution freezes (depression) on the concentration of substances in it. The saturated ones have lower depression than the diluted ones. For human blood at normal pressure (7.5 - 8 atm), this value ranges from -0.56 °C to -0.58 °C.

To measure blood pressure in this case, a special device is used - an osmometer.

Osmometer measurement

This is a special device that consists of two vessels with a dividing partition that has partial patency. Blood is placed in one of them, covered with a lid with a measuring scale, in the other - a hypertonic, hypotonic or isotonic solution. The level of the water column in the tube is an indicator of the osmotic value.

For the life of the body, the osmotic pressure of blood plasma is the foundation. It provides tissues with the necessary nutrients, monitors the healthy and proper functioning of systems, and determines the movement of water. In case of its excess, red blood cells increase in size, their membrane bursts (osmotic hemolysis), while in case of deficiency, the opposite process occurs - drying out. The work of each level (cellular, molecular) is based on this process. All cells of the body are semi-permeable membranes. Fluctuations caused by improper water circulation lead to swelling or dehydration of cells and, as a result, organs.

Oncotic pressure of blood plasma is indispensable in the treatment of serious inflammations, infections, and suppurations. Growing at the very location of the bacteria (due to the destruction of proteins and an increase in the number of particles), it provokes the expulsion of pus from the wound.

Remember that osmotic pressure affects the entire body as a whole.

Another important role is its influence on the functioning and lifespan of each cell. Proteins responsible for oncotic pressure are important for blood coagulation and viscosity, maintaining the pH environment, and protecting red blood cells from sticking together. They also provide synthesis and transport of nutrients.

What affects osmosis rates

Osmotic pressure indicators can change for various reasons:

• Concentration of non-electrolytes and electrolytes (mineral salts) dissolved in plasma. This dependence is directly proportional. A high particle content provokes an increase in pressure, as well as vice versa. The main component is ionized sodium chloride (60%). However, osmotic pressure does not depend on the chemical composition. The normal concentration of salt cations and anions is 0.9%.
• Number and mobility of particles (salts). An extracellular environment with insufficient concentration will accept water, and an environment with excess concentration will release it.
• Oncotic pressure of plasma and serum, which plays a major role in retaining water in blood vessels and capillaries. Responsible for the creation and distribution of all liquids. A decrease in its indicators is visualized by edema. The specificity of functioning is due to the high content of albumin (80%).

Osmotic pressure is affected by the salt content in the blood plasma

• Electrokinetic stability. It is determined by the electrokinetic potential of particles (proteins), which is expressed by their hydration and ability to repel each other and slide under solution conditions.
• Suspension stability is directly related to electrokinetic stability. Reflects the rate of connection of red blood cells, that is, blood clotting.
• The ability of plasma components, when moving, to provide resistance relative to the flow (viscosity). With viscosity, the pressure increases, with fluidity, it decreases.
• During physical work, osmotic pressure increases. A value of 1.155% sodium chloride causes a feeling of fatigue.
• Hormonal background.
• Metabolism. An excess of metabolic products and “pollution” of the body provokes an increase in blood pressure.

Osmosis rates are influenced by human habits, diet and beverage consumption.

Blood pressure is also affected by metabolism in the human body.

How does nutrition affect osmotic pressure?

A balanced, healthy diet is one of the ways to prevent jumps in indicators and their consequences. The following dietary habits negatively affect the osmotic and oncotic pressure of the blood:

Important! It is better not to get into a critical condition, but to regularly drink a glass of water and monitor the regime of its consumption and elimination from the body.

You will be told in detail about the features of measuring blood pressure in this video:

Blood, lymph, and tissue fluid make up the internal environment of the body. They have a relatively constant composition and physical and chemical properties, ensuring homeostasis of the body.

The blood system consists of peripheral blood, circulating vessels, hematopoietic organs nia(red bone marrow, lymph nodes, spleen), blood organs (liver, spleen), neurohumoral regulatory system.

The blood system performs the following functions:

1) transport;

2) respiratory (transfer of oxygen and carbon dioxide);

3) trophic (provides the body’s organs with nutrients)

4) excretory (removes metabolic products from the body);

5) thermoregulatory (maintains body temperature at a constant level)

6) protective (immunity, blood clotting)

7) humoral regulation (transport of hormones and biologically active substances);

8) maintaining a constant pH, osmotic pressure, etc.;

9) ensures water-salt exchange between blood and tissues;

10) implementation of creative connections (macromolecules, transported by plasma and formed elements, transfer information between cells).

Blood consists of plasma and cells (erythrocytes, leukocytes, platelets). The volume ratio of formed elements and plasma is called hematocrit. Formed elements make up 40-45% of blood volume, plasma - 55-60%. The amount of blood in the body of an adult is 4.5-6.0 liters (6-7% of body weight)

Blood plasma consists of 90-92% H20, organic and inorganic substances. Plasma proteins: albumen - 4,5%, globulins - 2.3% (albumin-globulin ratio is normally 1.2-2.0), fibrinogen - 0.2-0.4%. Proteins make up 7-8% of the blood plasma, and the rest are other organic compounds and mineral salts. Glucose - 4.44-6.66 mmol/l (according to Hagedorn - Jensen). Minerals plasma (0.9%) - cations Na + K +, Ca 2+ and anions Bot, HCO3_ and HPO42 +.

The value of blood plasma proteins:

1. Maintain oncotic pressure (C mm Hg).

2. There is a blood buffer system.

3. Provide blood viscosity (to maintain blood pressure).

4. Prevents the clotting of red blood cells.

5. Participate in blood clotting.

6. Participate in immunological reactions (globulins).

7. Transport hormones, lipids, carbohydrates, biologically active substances.

8. There is a reserve for the construction of tissue proteins.

Physicochemical properties of blood

If we take the viscosity of water as 1, then the viscosity of blood will be 5, the relative density will be 1.050-1.060.

Blood osmotic pressure

The osmotic pressure of the blood ensures the exchange of water between the blood and tissues. Osmotic pressure is the force that causes a solvent to move through a semipermeable membrane towards a higher concentration. For blood, this value is 7.6 atm. or 300 mOsmol. Resin is the osmotic pressure of a solution of one-molar concentration. Osmotic pressure is provided mainly by inorganic substances in the plasma. The portion of the osmotic pressure created by proteins is called "oncotic pressure." Provided primarily by albumin. The oncotic pressure of blood plasma is greater than that of intercellular fluid, since the latter has a significantly lower protein content. Due to the higher oncotic pressure in the blood plasma, water from the intercellular fluid returns to the blood. Up to 20 liters of fluid are released into the circulatory system per day. 2-4 liters of it in the form of lymph are returned by lymphatic vessels to the circulatory system. Together with the fluid from the blood, proteins circulating in the plasma enter the interstitium. Some of them are broken down by tissue cells, only some enter the lymph. Therefore, there are fewer proteins in lymph than in blood plasma. Lymph that flows from various organs contains different amounts of proteins from 20 g / l in lymph flowing from muscles; up to 62 g/l - from the liver (blood plasma contains 60-80 g/l of proteins). Lymph contains a large amount of lipids, lymphocytes, practically no red blood cells and no platelets.

As oncotic pressure decreases, edema develops. This is primarily due to the fact that water is not retained in the bloodstream.

Solutions that have the same osmotic pressure as blood are called isotonic. Such a solution is a 0.9% NaCl solution. It's called saline solution. Solutions that have greater osmotic pressure are called hypertonic, less - hypotonic. If blood cells are placed in a hypertonic solution, water flows out of them, they decrease in volume. This phenomenon is called plasmolysis. If When blood cells are placed in a hypotonic solution, excess water enters them. Cells (primarily red blood cells) increase in volume and are destroyed. This phenomenon is called hemolysis(osmotic). The ability of red blood cells to maintain membrane integrity in a hypotonic solution is called osmotic resistance of erythrocytes. To determine it red blood cells added to a series of test tubes with 0.2-0.8% NaCl solutions. With osmotic resistance, hemolysis of erythrocytes begins in a 0.45-0.52% NaCl solution (minimal osmotic resistance), 50% lysis occurs in a 0.40-0.42% NaCl solution, and complete lysis occurs in 0.28-0.35 % NaCl solution (maximum osmotic resistance).

Regulation of osmotic pressure occurs primarily through the mechanisms of thirst (see Motivations) and the secretion of vasopressin (ADH). When the effective osmotic pressure of the blood plasma increases, the osmoreceptors of the anterior hypothalamus are excited, the secretion of vasopressin increases, which stimulates the mechanisms of thirst. Fluid intake increases. Water is retained in the body, diluting the hypertonic blood plasma. The leading role in the regulation of blood osmotic pressure belongs to the kidneys (see Regulation of excretion).