Dissolved in the liquid part of the blood minerals- salt. In mammals their concentration is about 0.9%. They are in a dissociated state in the form of cations and anions. The osmotic pressure of the blood mainly depends on the content of these substances.

Osmotic pressure is the force that causes the movement of a solvent through a semipermeable 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 dissolved substances hardly pass through. Therefore, changes in osmotic pressure in the blood and tissues can lead to cell swelling or loss of water. Even minor changes in the salt composition of the 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 part of 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 enter the blood. The skin is of great importance in this regard, connective tissue which absorbs excess water from the blood or releases it into the blood when the osmotic pressure of the latter increases.

The value of osmotic pressure is usually determined by indirect methods. The most convenient and common cryoscopic method is when depression or a decrease in the freezing point of the blood is found. It is known that the freezing temperature of a solution is lower, the higher the concentration of particles dissolved in it, that is, the higher its osmotic pressure. The freezing point of mammalian blood 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 plasma proteins is called oncotic pressure. It is significant less pressure, created by salts dissolved in the plasma, since proteins have a huge molecular weight, and, despite their greater content in the blood plasma by mass than salts, the number of their gram-molecules turns out to be relatively small, and they are also 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.

Oncotic pressure prevents excessive transfer of water from the blood into tissues and promotes its reabsorption from tissue spaces, therefore, when the amount of proteins in the blood plasma decreases, tissue edema develops.

Human health and well-being depend on the balance of water and salts, as well as normal blood supply to organs. Balanced, normalized exchange of water from one structure of the body to another (osmosis) is the basis healthy image life, as well as a means of preventing a number of serious illnesses(obesity, vegetative-vascular dystonia, systolic hypertension, heart disease) and weapons 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 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 state of the body, the content of salts and minerals in the blood is osmotic pressure

Blood osmotic pressure is an important vital indicator that reflects its concentration 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 – component(0.5%) osmosis, whose value (necessary for normal functioning 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 grow sharply when 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 normal pressure(7.5 – 8 atm) this value ranges from -0.56 °C to – 0.58 °C.

To measure blood pressure in this case, use special device– 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 matters of treatment serious inflammation, infections, suppurations. Increasing 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.

One more important role– 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 nutrients.

What affects osmosis rates

Indicators of osmotic pressure 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. Main component– ionized sodium chloride (60%). However, from chemical composition osmotic pressure is not affected. 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, playing main 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 operation is determined high content 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.
• At 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?

Balanced proper nutrition– 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 allow a critical condition, but to regularly drink a glass of water and monitor the regime of its consumption and elimination from the body.

About measurement features blood pressure They will tell you in detail in this video:

If two solutions, one of which is more concentrated, that is, contains more solute than the second, are separated by a semi-permeable membrane that allows a solvent, such as water, to pass through, but does not allow a solute to pass through, then the water passes into a more concentrated solution. The force that causes solvent to move across a semipermeable membrane is called osmotic pressure.

The osmotic pressure of a solution can be measured using an osmometer. The latter consists of two vessels separated by a semi-permeable membrane. A more concentrated solution of a substance is poured into one of these vessels, and a less concentrated solution or pure solvent is poured into the other. The first of these vessels is closed with a stopper through which a vertical manometric tube passes. The solvent passes into a vessel with a more concentrated solution, and the liquid rises in the manometric tube. The pressure of the water column expresses the magnitude of the osmotic pressure.

The osmotic pressure of blood, lymph and tissue fluid has great value in the regulation of water exchange between blood and tissues. A change in the osmotic pressure of the fluid surrounding the cells leads to disturbances in water metabolism in them. This can be seen in the example of red blood cells, which, when immersed in NaCl solution, which has a higher osmotic pressure than blood plasma, lose water, sharply decrease in volume and shrink. Red blood cells placed in a NaCl solution with lower osmotic pressure, on the contrary, swell, increase in volume and can ultimately be destroyed.

The value of blood osmotic pressure can be determined cryoscopically, i.e., by measuring the freezing temperature. As is known, the freezing temperature of a solution is lower, the higher its osmotic pressure, i.e., the greater the total concentration of molecules, ions and colloidal particles in the solution.

Lowering the freezing point below 0° (Δ t°), in other words, unimolar aqueous solution nonelectrolyte is 1.85°, and the osmotic pressure of such a solution is 22.4 atm. Knowing the freezing point of the solution under study, it is possible to calculate the value of its osmotic pressure.

In humans, blood depression is 0.56-0.58°, and therefore the osmotic pressure is 7.6-8.1 atm. About 60% of this pressure comes from NaCl. The osmotic pressure of red blood cells and other body cells is the same as that of the fluid surrounding them.

The osmotic pressure of the blood of mammals and humans remains at a relatively constant level, as can be seen from the following experiment. 7 liters of 5% sodium sulfate solution was injected into the horse's vein, which, according to calculations, should have doubled the osmotic pressure of the blood plasma. However, within 10 minutes the plasma osmotic pressure returned almost to normal, and after 2 hours it became completely normal. This was due to the excretion of a significant amount of salts in urine, liquid feces and saliva. The secretions contained not only introduced sulfates, but also chlorides and carbonates; sulfates could be detected in the blood even after the osmotic pressure became normal. This shows that normal osmotic pressure is first restored in the body and only later the constancy of the ionic composition of the blood is restored. The constancy of the osmotic pressure of the blood is relative, since small fluctuations always occur in the body due to the transition of large-molecular substances (amino acids, fats, carbohydrates) from the blood into the tissues and the entry of low-molecular-weight products of cellular metabolism from the tissues into the blood.

Excretory organs, mainly the kidneys and sweat glands, are regulators of osmotic pressure. Thanks to their activity, metabolic products that are constantly formed in the body usually do not have a significant effect on the value of osmotic pressure. Unlike the osmotic pressure of blood, the osmotic pressure of urine and sweat fluctuates over a fairly wide range. Sweat depression is 0.18-0.60°, and urine depression is 0.2-2.2°. Particularly significant shifts in blood osmotic pressure are caused by intense muscular work.

What is osmotic pressure

Osmosis is the one-way spontaneous diffusion of solvent molecules through a semi-permeable membrane from the least concentrated solution to a more concentrated solution. A semi-permeable membrane is one that is permeable to solvent cells and impermeable to dissolved particles. By definition, osmotic pressure is the application of which to a given solution can stop the diffusion of particles, that is, osmosis.

Osmosis is widespread in nature. It is common to everyone biological organisms. Osmotic pressure occurs when solutions are separated by a semipermeable membrane. For example, let’s take the fluids found in cells and intercellular space. Normally, extracellular and intracellular osmotic pressure are the same. But if the interstitial fluid loses water, its pressure increases. Under the influence of increased osmotic pressure, water from the cells begins to diffuse into the intercellular space. Diffusion will stop only when the pressure levels are equalized.

What does osmotic pressure depend on?

The pressure during osmosis depends on how many dissolved particles are contained in a unit volume. These can be molecules, ions or others. The osmotic pressure of a solution can be said to be related to the concentration of all osmotically active particles per unit volume. From chemical properties it does not depend on the solvent and the substances dissolved in it.

Scientists have found that osmotic pressure obeys the same laws as gas pressure. It can be measured using instruments called osmometers. They are a special kind of pressure gauges. These devices use semi-permeable animal membranes and artificial origin. show its direct dependence on

The law of osmotic pressure, discovered by Van Hoff, states that its value is numerically equal to the pressure that the substance of a given solution would exert if it were at the same temperature with the condition that its volume would be equal to the volume of the solution.

The law is described by the equation: p=i C R T

C is the concentration of the solution, expressed in moles;

R is the value of the universal gas constant;

T is thermodynamic temperature.

The importance of osmotic pressure for living organisms

Osmosis is inherent in living nature, since all cells of plants and animal organisms have membranes that are permeable to water and impermeable to other substances. In living tissues, at the border of the cell and the intercellular fluid, osmotic pressure is constantly operating. It ensures the rise of nutrients and water from the ground to the leaves of plants and the turgor of plants, the vital activity of cells.

Solutions with the same osmotic pressure are called isotonic. Those with higher pressure are called hypertonic, and those with lower pressure are called hypotonic.

The osmotic pressure in human blood is 7.7 atm. People are able to sense its slightest vibrations. For example, thirst after eating salty food is associated with its increase. Local swelling during inflammation also occurs due to an increase in osmotic pressure at the site of inflammation.

Knowledge of the laws of osmotic pressure in medicine is necessary when carrying out therapeutic measures. So, doctors know that for intravenous injections You can only use a 0.9% NaCl solution that is isotonic to blood plasma. It does not cause tissue irritation. On the contrary, hypertonic 3-5% NaCl is used for better cleansing purulent wounds from microorganisms and pus.

Knowledge of the laws of osmosis is necessary not only in medicine and biology. Many species cannot do without it human activity, including industry and energy.

Blood volume – total quantity 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 dissolved in it active substances, mainly by inorganic electrolytes, and to a much lesser extent by 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 saline solution, having 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 proteins plasma. 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 exits from the vessels into the interstitial space, which leads to tissue edema.

Acid-base status of blood (ABS). Active reaction blood is determined by the ratio of hydrogen and hydroxyl ions. To determine the active blood reaction, use pH value pH is the concentration of hydrogen ions, which is expressed negative decimal logarithm molar concentration of hydrogen ions. Normal pH is 7.36 (weakly basic reaction); arterial blood– 7.4; venous – 7.35. At different 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.