Osmotic pressure of blood. Osmotic pressure in the human body The value of the osmotic pressure of blood plasma is equal to

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 the 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. Relative density of blood plasma - 1.025 - 1.034, determined by the concentration of proteins. Blood viscosity - 5 conventional units, plasma - 1.7 - 2.2 conventional units, if the viscosity of water is taken as 1. Due to the presence of erythrocytes in the blood and in lesser degree of plasma proteins.

The 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 blood pressure is calculated by the cryoscopic method by determining the freezing point of blood (depression), which for it is 0.56 - 0.58 C. The osmotic blood pressure averages 7.6 atm. It is due to osmotically active substances dissolved in it, mainly inorganic electrolytes, 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 be carried out only with a relative stability of osmotic pressure. If erythrocytes are placed in a saline solution having an osmotic pressure equal to that of blood, they do not change their volume. Such a solution is called isotonic, or physiological. It can be 0.85% sodium chloride solution. In a solution whose osmotic pressure is higher than the osmotic pressure of blood, erythrocytes shrivel as water escapes from them into the solution. In a solution with an osmotic pressure lower 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.

Oncotic blood 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 due to albumin. Due to their small size and high hydrophilicity, they have a pronounced ability to attract water to themselves, due to which it is retained in the vascular bed. When the oncotic blood pressure decreases, water escapes from the vessels into the interstitial space, which leads to tissue edema.

Acid-base state of the blood (ACS). The active reaction of the blood is due to the ratio of hydrogen and hydroxide ions. To determine the active reaction of the blood, the pH indicator is used - the concentration of hydrogen ions, which is expressed as a 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 reaction of the blood is a rigid constant that ensures enzymatic activity. The extreme limits of blood pH compatible with life are 7.0 - 7.8. The shift of the reaction to the acid side is called acidosis, which is caused by an increase in hydrogen ions in the blood. The shift in the reaction of the blood to the alkaline side is called alkalosis. This is due to an increase in the concentration of OH hydroxide ions 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.

Osmotic homeostasis

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

The value of osmotic pressure, as is known, depends on the concentration of the solution and on 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, evenly distributed over a surface of 1 m 2. 1 atm = 760 mmHg Art. 10 5 Pa = 100 kPa (kilopascal) = 0.1 MPa (megapascal). For a more accurate conversion: 1 atm = 101325 Pa, 1 mm Hg. st. = 133.322 Pa.

Blood plasma, which is a complex solution containing various non-electrolyte molecules (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 contained in it. In table. 21 shows the concentrations of the main plasma components and the generated name osmotic pressure.

As can be seen from Table. 21, the osmotic pressure of the plasma is determined mainly by Na + , C1 - , HCO - 3 and K + ions, since their molar concentration is relatively high, while the molecular weight is negligible. The osmotic pressure due to high molecular weight colloidal substances is called oncotic pressure. Despite the significant content of protein in plasma, its share in the creation of 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 mosmmol, and globulins and fibrinogen, whose molecular weight is even higher, create an oncotic pressure of 0.2 mosmmol.

The constancy of the electrolyte composition and osmotic properties of the extracellular and intracellular sectors is closely related to 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 k) - on 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 excretion 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 links: the entry 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 performs a damping role between the external and internal environment, 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. Water is another main component providing osmotic homeostasis. 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 system of water-salt homeostasis. Thirst is an evolutionarily worked out reaction that ensures adequate (under conditions of normal life activity of the organism) intake of water into the body. The feeling of thirst usually occurs due to either dehydration or increased intake of salts or insufficient excretion of salts. Currently, there is no single view on the mechanism of the emergence 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 saliva secretion. The correctness of this theory of "dry mouth" is confirmed by experiments with ligation of the salivary ducts, with the removal of the salivary glands, with anesthesia of the oral cavity and pharynx.

Proponents of general theories of thirst believe that this feeling arises due to 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 hypothalamus and other areas of the body (Ginetsinsky A. G., 1964; Verneu E. V., 1947). It is believed that osmoreceptors, when excited, form a feeling of thirst and cause appropriate behavioral responses aimed at searching for and absorbing water (Anokhin P.K., 1962). Thirst quenching is provided 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 impact on the extero- and interoreceptors of the digestive tract, and the final restoration of water comfort is provided by the humoral way (Zhuravlev I . N., 1954).

Recently, data have been obtained on the role of the renin-giotensin system in the formation of thirst. In the hypothalamic region, receptors were found, the irritation of which with angiotensin II leads to thirst (Fitzimos J., 1971). Angiotensin, apparently, increases the sensitivity of the osmoreceptors of the hypothalamic region to the action of sodium (Andersson B., 1973). The formation of the sensation of thirst occurs not only at the level of the hypothalamic region, but also in the limbic system of the forebrain, which is connected with the hypothalamic 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 mainly due to the state of the extracellular sector, and salt appetite - 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.

At present, a large role of behavioral responses in maintaining osmotic homeostasis is known. So, in experiments on dogs exposed to overheating, it was found that animals instinctively choose for drinking from the proposed saline solutions the one whose salts are not enough in the body. During periods of overheating, dogs preferred potassium chloride solution over sodium chloride. After the cessation of overheating, the appetite for potassium decreased, and 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 against the background of overheating. In the event that 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. So, in experiments with strophanthin, which inhibits the potassium-sodium pump and consequently leads to an increase in the sodium content in the cell and a decrease in its extracellular concentration (changes of the opposite nature were noted with respect to potassium), sodium appetite sharply decreased and potassium appetite increased. These experiments testify to the dependence of salt appetite not so much on the general 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 excretion 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 are data confirming the existence of structures in the hypothalamic region, the destruction of which changes salt appetites. For example, the destruction of the ventromedial nuclei of the hypothalamic region leads to a decrease in sodium appetite, and the destruction of the lateral regions causes a loss of preference for sodium chloride solutions over water. If the central zones are damaged, the appetite for sodium chloride sharply increases. Thus, there is reason to speak about the presence of central mechanisms for the regulation of sodium appetite.

It is known that shifts in the normal sodium balance cause corresponding precisely coordinated changes in the intake and excretion of sodium chloride. For example, bloodletting, infusion of liquids into the blood, dehydration, etc. naturally change natriuresis, which increases with an increase in the volume of circulating blood and decreases with a decrease in its volume. This effect has two explanations. 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 passes into the vascular bed during hypovolemia. Hence, one could assume a double localization of the receptive fields that "monitor" the level of sodium in the blood. In favor of tissue localization, experiments with intravenous administration of protein testify (Goodyer A. V. N. et al., 1949), in which a decrease in the volume of interstitial fluid, due to its transition 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 the fluid located there. This leads to a weakening of the stimuli that ensure the activation of sodium retention mechanisms in the body. An increase in intravascular volume by the introduction of 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 are reasons to assume that natriuresis is regulated not only by signals from tissue receptors. Their intravascular localization is equally likely. In particular, it has been established that stretching of the right atrium causes a natriuretic effect (Kappagoda ST et al., 1978). It has also been shown that stretching of 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 blood substances in the left atrium (Mitrakova OK, 1971). Similar receptor zones were found in the place of the thyroid-carotid branching; occlusion of the common carotid arteries caused a decrease in sodium excretion in the urine. This effect disappeared on the background of preliminary denervation of the vascular walls. Similar receptors are found in the vascular bed of the pancreas (Inchina V.I. et al., 1964).

All reflexes that affect natriuresis equally and unequivocally affect diuresis. The localization of both receptors is practically the same. Most of the currently known volumoreceptive formations are located in the same place where the baroreceptor zones are found. According to most researchers, volomoreceptors by their nature do not differ from baroreceptors, and the different effect of excitation of both is explained by the arrival of impulses in different centers. This indicates a very close relationship between the mechanisms of regulation of water-salt homeostasis and blood circulation (see diagram and Fig. 40). This connection, which was first discovered at the level of the afferent link, is currently extended to effector formations. In particular, after the works of F. Gross (1958), who suggested the aldosterone-stimulating function of renin, and on the basis of the hypothesis of juxtaglomerular control of circulating blood volume, there were grounds to consider the kidneys not only as an effector link in the system of water-salt homeostasis, but also as a source of information about changes in volume blood.

The volume receptor apparatus can, obviously, regulate not only the volume of the liquid, but also indirectly - the osmotic pressure of the internal environment. At the same time, it is logical to assume that there should be a special osmoregulatory mechanism. The existence of receptors sensitive to changes in osmotic pressure was shown in the laboratory of K. M. Bykov (Borschevskaya E. A., 1945). However, fundamental studies of the problem of osmoregulation belong 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 ​​the nervous tissue in the region of the supraoptic nucleus. Several tens of a special kind of hollow neurons were found here, which are 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 the hormone of the posterior 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 works of A. G. Ginetsinsky and co-workers, who showed that Verney's osmoreceptors are 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 unequivocal 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 a change in the osmotic pressure of the blood, and not by the chemical nature of the osmotically active substances. This gave the authors grounds to consider the obtained effects as osmoregulatory reflexes due to stimulation of osmoreceptors.

As a result of modern research, the existence of sodium chemoreceptors in the liver, spleen, skeletal muscles, region of the III ventricle of the brain, lungs has been established (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, apparently, is represented by receptors of a different nature: osmoreceptors of a general type, specific sodium chemoreceptors, extra- and intravascular volumoreceptors. It is believed that under normal conditions, these receptors act unidirectionally, and only under pathological conditions is it possible for their functions to be discoordinated.

The main role in maintaining osmotic homeostasis belongs to three systemic mechanisms: adenohypophyseal, 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 hypothalamic region, in which neurosecretion is synthesized, which is then converted into vasopressin and oxytocin. The function of this nucleus is influenced by afferent pulsation from the receptor zones of the vessels and the 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 an increase in 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 of regulation of aldosterone secretion is located in the midbrain, in the region of the Sylvian aqueduct. This center consists of two zones, of which one - the anterior one, located closer to the posterior hypotuberous 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 the link between the central nervous system and the glomerular zone of the adrenal cortex.

There are also data on the effect on the secretion of aldosterone hormone of the anterior pituitary - 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 C. C. et al., 1961). Apparently, there are several options for switching on the renin-aldosterone mechanism: by directly changing blood pressure in the vas afferens region; through a reflex effect from volumoreceptors through sympathetic nerves on the tone of 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. On the basement membranes of the proximal and distal tubules, adrenergic nerve endings were found, the 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 assumed that the formation of osmotically concentrated urine is carried out as a result of the extraction of salt-free water from the iso-osmotic plasma of the tubular fluid. According to H. W. Smith (1951, 1956), the process of dilution and concentration of 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 alignment of the composition of the tubular fluid and blood occurs. At the suggestion of N. W. Smith, water reabsorption in the proximal tubules and a 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 water is actively reabsorbed against the osmotic gradient. Later it was proved that active reabsorption of sodium against the concentration gradient is also possible in the proximal tubule (Windhager E. E. et al., 1961; Hugh J. C. 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 iso-osmotic to the blood plasma. At the same time, the wall of the proximal tubule has a low water permeability compared to the glomerular membrane. In the proximal tubule, a direct relationship was found between the glomerular filtration rate and reabsorption.

From the quantitative point of view, sodium reabsorption in the distal part of the neuron turned out to be 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.

The regulation of sodium reabsorption in the cells of the renal tubules is carried out in at least two ways. Vasopressin increases the permeability of cell membranes by stimulating adenylcyclase, under the influence of which cAMP is formed from ATP, which activates 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 sodium permeability of the apical membrane of renal tubular cells, the other activates the sodium pump (Janacek K. et al., 1971; Wiederhol M. et al., 1974).

The transport of sodium under the influence of aldosterone is closely related to the activity of the enzymes of the tricarboxylic acid cycle, 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, the regulation of sodium excretion can be carried out without changing the production of aldosterone. 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). Established intrarenal non-aldosterone mechanisms of regulation of natriuresis (Zeyssac R. R., 1967).

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

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Viscometer Hess.

In the clinic, rotational viscometers are more often used.

In them, the liquid is in the gap between two coaxial bodies, such as cylinders. One of the cylinders (rotor) rotates, while the other is stationary. Viscosity is measured by the angular velocity of the rotor, which creates a certain moment of force on a stationary cylinder, or by the moment of force acting on a stationary cylinder, at a given angular velocity of rotation of the rotor.

In rotational viscometers, it is possible to change the velocity gradient by setting different angular velocities of rotation of the rotor. This makes it possible to measure viscosity at different velocity gradients. , which varies for non-Newtonian fluids such as blood.

Blood temperature

It largely depends on the intensity of the metabolism of the organ from which the blood flows, and varies between 37-40 ° C. When blood moves, not only does the temperature in various vessels equalize to some extent, but conditions are also created for the release or preservation of heat in the body.

Osmotic called blood pressure , which causes the transition of the solvent (water) through a semi-permeable membrane from a less to a more concentrated solution.

In other words, the movement of the solvent is directed from lower to higher osmotic pressure. Compare with hydrostatic pressure: the movement of a fluid is directed from higher to lower pressure.

Note! You can't say "... pressure... is called force...» ++601[B67] ++.

The osmotic pressure of the blood is approximately 7.6 atm. or 5776 mm Hg. (7.6´760).

The osmotic pressure of blood depends mainly on the low molecular weight compounds dissolved in it, mainly salts. About 60% of this pressure is created by NaCl. Osmotic pressure in the blood, lymph, tissue fluid, tissues is approximately the same and is constant. Even in cases where a significant amount of water or salt enters the blood, the osmotic pressure does not undergo significant changes.

Oncotic pressure- part of the osmotic pressure due to proteins. 80% of oncotic pressure is created albumins .

Oncotic pressure does not exceed 30 mm Hg. Art., i.e. is 1/200 of the osmotic pressure.

Several indicators of osmotic pressure are used:

Pressure units atm. Or mmHg

Plasma osmotic activity[B68] is the concentration of kinetically (osmotically) active particles per unit volume. The most commonly used unit is milliosmol per liter - mosmol/L.

1 osmol = 6.23 ´ 1023 particles

Normal osmotic activity of plasma = 285-310 mosmol/l.

Mosmol = mmol

In practice, the concepts of osmolarity are often used - mmol / l and osmolality mmol / kg (liter and kg of solvent)

The greater the oncotic pressure, the more water is retained in the vascular bed and the less it passes into the tissues and vice versa. Oncotic pressure affects the formation of tissue fluid, lymph, urine and water absorption in the intestine. Therefore, blood-substituting solutions should contain colloidal substances capable of retaining water [++601++].

With a decrease in the concentration of protein in the plasma, edema develops, since water ceases to be retained in the vascular bed and passes into the tissues.

Oncotic pressure plays a more important role in the regulation of water metabolism than osmotic pressure. Why? After all, it is 200 times less than osmotic. The fact is that the gradient concentration of electrolytes (which determine the osmotic pressure) on both sides of the biological barriers

In clinical and scientific practice such concepts as isotonic, hypotonic and hypertonic solutions are widely used. Isotonic solutions have a total ion concentration not exceeding 285-310 mmol/l. This may be 0.85% sodium chloride solution (often referred to as "physiological" solution, although this does not fully reflect the situation), 1.1% potassium chloride solution, 1.3% sodium bicarbonate solution, 5.5% glucose solution and etc. Hypotonic solutions have a lower concentration of ions - less than 285 mmol / l, and hypertonic solutions, on the contrary, have a higher concentration above 310 mmol / l.

Erythrocytes, as you know, in an isotonic solution do not change their volume, in a hypertonic solution they decrease it, and in a hypotonic solution they increase in proportion to the degree of hypotension, up to the rupture of the erythrocyte (hemolysis). The phenomenon of osmotic hemolysis of erythrocytes is used in clinical and scientific practice to determine the qualitative characteristics of erythrocytes (a method for determining the osmotic resistance of erythrocytes).

Osmotic pressure of blood. Functional system for maintaining the constancy of osmotic pressure.

This is the force that causes the solvent to move through a semi-permeable membrane from a less concentrated solution to a more concentrated one. Tissue cells and the cells of the blood itself are surrounded by semi-permeable membranes through which water easily passes and solutes hardly pass. For this reason, changes in osmotic pressure in the blood and tissues can cause cells to swell or lose water. Even slight changes in the salt composition of blood plasma are detrimental to many tissues, and above all to the cells of the blood itself. The osmotic pressure of the blood is kept at a relatively constant level due to the functioning of regulatory mechanisms. In the walls of blood vessels, in tissues, in the diencephalon - the hypothalamus, there are special receptors that respond to changes in osmotic pressure - osmoreceptors.

Irritation of osmoreceptors causes a reflex change in the activity of the excretory organs, and they remove excess water or salts that have entered the blood. Of great importance in this regard is the skin, the connective tissue of which absorbs excess water from the blood or gives it to the blood with an increase in the osmotic pressure of the latter.

The value of osmotic pressure is usually determined by indirect methods. The most convenient and common cryoscopic method is when depression is found, or a decrease in the freezing point of blood. It is known that the freezing point of a solution is the lower, the greater the concentration of particles dissolved in it, that is, the greater its osmotic pressure. The freezing point of the blood of mammals is 0.56-0.58 °C lower than the freezing point of water, which corresponds to an osmotic pressure of 7.6 atm, or 768.2 kPa.

Plasma proteins also create a certain osmotic pressure. It is 1/220 of the total osmotic pressure of blood plasma and ranges from 3.325 to 3.99 kPa, or 0.03-0.04 atm, or 25-30 mm Hg. Art. The osmotic pressure of blood plasma proteins is called oncotic pressure. It is much less than the pressure created by salts dissolved in plasma, since proteins have a huge molecular weight, and, despite their greater content in blood plasma by weight than salts, the number of their gram molecules is relatively small, and besides, they are much less mobile than ions. And for the value of osmotic pressure, it is not the mass of dissolved particles that matters, but their number and mobility.

Osmotic pressure of blood. Functional system for maintaining the constancy of osmotic pressure. - concept and types. Classification and features of the category "Osmotic blood pressure. Functional system for maintaining the constancy of osmotic pressure." 2017, 2018.

Human health and well-being depend on the balance of water and salts, as well as the normal blood supply to organs. A balanced normalized exchange of water from one body structure to another (osmosis) is the basis of a healthy lifestyle, as well as a means of preventing a number of serious diseases (obesity, vegetovascular 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 they do not delve into the origins of the process, dependencies within the system, and the definition of structure and relationships. As a result, people remain illiterate in this matter.

The concept of osmotic and oncotic pressure

Osmosis is the process of fluid transfer from a solution with a lower concentration (hypotonic) to an adjacent solution with a higher concentration (hypertonic). Such a transition is possible only under appropriate conditions: when liquids are “neighbored” and when a transmissive (semi-permeable) partition is separated. At the same time, they exert a certain pressure on each other, which in medicine is commonly 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.

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

It is scientifically determined that this force corresponds to the pressure in saline. So doctors call sodium chloride solution with a concentration of 0.9%, one of the main functions of which is plasma replacement and hydration, which allows you to fight dehydration, exhaustion in case of large blood loss, and it also protects red blood cells from destruction when drugs are administered. That is, with respect to blood, it is isotonic (equal).

Oncotic blood pressure is an integral part (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, the oncotic pressure is much less than the osmotic one, 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.

The analysis of the plasma structure, reflected in the table, helps to present 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 given by the hypothalamus, which responds to irritation of osmoreceptors (nerve endings in blood vessel cells).

The level of this pressure directly depends on the work of the hypothalamus.

For proper functioning and viability of the body, blood pressure must correspond to cellular, tissue and lymphatic pressure. With the correct and well-coordinated work of the body systems, its value remains constant.

It can grow sharply during physical exertion, 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 situation.

Cryoscopic method

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

In this case, a special device is used to measure blood pressure - an osmometer.

Measurement with an osmometer

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

For the life of an organism, 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 the case of its excess, erythrocytes increase, their membrane bursts (osmotic hemolysis), with a deficiency, the opposite process occurs - drying out. This process underlies the work of each level (cellular, molecular). All body cells are semi-permeable membranes. Fluctuations caused by incorrect circulation of water lead to swelling or dehydration of cells and, as a result, organs.

Oncotic pressure of blood plasma is indispensable in the treatment of serious inflammation, infection, suppuration. Growing in the very place where the bacteria are located (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 the influence on the functioning and life span of each cell. The proteins responsible for oncotic pressure are important for blood clotting and viscosity, maintaining the Ph-environment, and protecting red blood cells from sticking together. They also provide the synthesis and transport of nutrients.

What affects osmosis performance

Osmotic pressure indicators can change for various reasons:

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

The osmotic pressure is influenced 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 the ability to repel each other and slide in solution conditions.
• Suspension stability, directly related to electrokinetic. Reflects the speed of connection of erythrocytes, that is, blood clotting.
• The ability of plasma components, when moving, to resist the flow (viscosity). With ductility, the pressure rises, 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, "pollution" of the body provokes an increase in pressure.

Osmosis rates are influenced by human habits, food and drink consumption.

The metabolism in the human body also affects the pressure.

How nutrition affects osmotic pressure

Balanced proper nutrition is one of the ways to prevent jumps in indicators and their consequences. The following dietary habits negatively affect the osmotic and oncotic blood pressure:

Important! It is better not to allow a critical condition, but regularly drink a glass of water and monitor the mode of its consumption and excretion from the body.

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