Relative density of blood. Composition and physicochemical properties of blood plasma. Physicochemical properties of blood

PHYSICAL AND CHEMICAL PROPERTIES OF BLOOD

The functions of blood are largely determined by its physicochemical properties, which include: color, relative density, viscosity, osmotic and oncotic pressure, colloidal stability, suspension stability, pH, temperature.

The color of blood. Determined by the presence of hemoglobin compounds in red blood cells. Arterial blood has a bright red color, which depends on the content of oxyhemoglobin in it. Venous blood is dark red with a bluish tint, which is explained by the presence in it of not only oxidized, but also reduced hemoglobin and carbohemoglobin. The more active the organ and the more oxygen the hemoglobin gives to tissues, the darker it looks

deoxygenated blood.

Relative density blood levels range from 1050 to 1060 g/l and depend on the number of red blood cells, the hemoglobin content in them, and the composition of the plasma. In men, due to the larger number of red blood cells, this figure is higher than in women. The relative density of plasma is 1025-1034 g/l,

erythrocytes -1090 g/l.

Blood viscosity- this is the ability to resist the flow of liquid when moving some particles relative to others due to internal friction. In this regard, blood viscosity is a complex effect of the relationship between water and colloidal macromolecules on the one hand, and plasma and formed elements on the other. Therefore, the viscosity of plasma is 1.7-2.2 times, and blood is 4-5 times higher than water. The more large molecular proteins (fibrinogen) and lipoproteins in the plasma, the greater its viscosity. Blood viscosity increases with increasing hematocrit number. An increase in viscosity is facilitated by a decrease in the suspension properties of blood when red blood cells begin to form aggregates. In this case, a positive feedback is noted - an increase in viscosity, in turn, enhances the aggregation of erythrocytes. Since blood is a heterogeneous medium and belongs to non-Newtonian fluids, which are characterized by structural viscosity, a decrease in flow pressure, for example, arterial, increases the viscosity of the blood, and with an increase in blood pressure, due to the destruction of its structure, the viscosity decreases.

Blood viscosity depends on the diameter of the capillaries. When it decreases to less than 150 microns, the viscosity of the blood begins to decrease, which facilitates its movement in the capillaries. The mechanism of this effect is associated with the formation of a wall layer of plasma, the viscosity of which is lower than that of whole blood, and the migration of erythrocytes into the axial flow. With a decrease in the diameter of the vessels, the thickness of the wall layer does not change. There are fewer red blood cells in the blood moving through narrow vessels in relation to the plasma layer, because Some of them are delayed when blood enters narrow vessels, and red blood cells in their flow move faster and the time they spend in a narrow vessel decreases.

The viscosity of venous blood is greater than that of arterial blood, which is due to the entry of carbon dioxide and water into red blood cells, due to which their size increases slightly. Blood viscosity increases when blood is desepted, because in the depot the content of red blood cells is higher. The viscosity of plasma and blood increases with abundant protein nutrition.

Blood viscosity affects peripheral vascular resistance, increasing it in direct proportion, and hence blood pressure.

Blood osmotic pressure- this is the force that causes a solvent (water for blood) to pass through a semi-permeable membrane from a less to a more concentrated solution. It is determined cryoscopically (by freezing temperature). In humans, blood freezes at temperatures below O by 0.56-0.58 ° C. At this temperature, a solution with an osmotic pressure of 7.6 atm freezes, which means this is an indicator of the osmotic pressure of the blood. The osmotic pressure of blood depends on the number of molecules of substances dissolved in it. At the same time, over 60% of its value is created by NaCl, and in total the share of inorganic substances accounts for up to 96%. The osmotic pressure of blood, lymph, tissue fluid, tissues is approximately the same and is one of the rigid homeostatic constants (possible fluctuations of 7.3-8 atm). Even in cases of excessive amounts of water or salt, the osmotic pressure does not change. When excess water enters the blood, it is quickly excreted by the kidneys and passes into tissues and cells, which restores the original value of osmotic pressure. If the concentration of salts in the blood increases, then water from the tissue fluid enters the vascular bed, and the kidneys begin to intensively remove salts.

Any solution that has an osmotic pressure equal to that of plasma is called isotonic. Accordingly, a solution with a higher osmotic pressure is called hypertonic, and a solution with a lower one is called hypotonic. Therefore, if the tissue fluid is hypertonic, then water will enter it from the blood and from the cells; on the contrary, with a hypotonic extracellular environment, water passes from it into the cells and blood.

A similar reaction can be observed on the part of red blood cells when the osmotic pressure of the plasma changes: when it is pshertonic, the red blood cells, giving up water, shrink, and when it is hylotonic, they swell and even burst. The latter is used in practice to determine the osmotic resistance of erythrocytes. Thus, isotonic to blood plasma are: 0.85-0.9% NaCl solution, 1.1% KS1 solution, 1.3% NaHCO3 solution, 5.5% glucose solution, etc. Red blood cells placed in these solutions do not change shape . In sharply hypotonic solutions and especially distilled water, red blood cells swell and burst. The destruction of red blood cells in hypotonic solutions is osmotic hemolysis. If you prepare a series of NaCl solutions with gradually decreasing concentrations and place a suspension of red blood cells in them, you can find the concentration of the hypotonic solution in which hemolysis begins and only single red blood cells are destroyed. This NaCl concentration characterizes the minimum osmotic resistance of erythrocytes, which in a healthy person is in the range of 0.42-0.48 (% NaCl solution). In more hypotonic solutions, an increasing number of red blood cells are hemolyzed, and the concentration of NaCl at which all red cells will be lysed is called maximum osmotic resistance. In a healthy person, it ranges from 0.34 to 0.30 (% NaCl solution). In some hemolytic anemias, the boundaries of minimum and maximum resistance shift towards increasing the concentration of the hypotonic solution.

Oncotic pressure- part of the osmotic pressure created by proteins in a colloidal solution, which is why it is also called colloid-osmotic. Due to the fact that blood plasma proteins do not pass well through the walls of capillaries into the tissue microenvironment, the oncotic pressure they create retains water in the blood. Oncotic pressure in the blood is higher than in the tissue fluid. In addition to poor permeability of barriers to proteins, their lower concentration in tissue fluid is associated with the leaching of proteins from the extracellular environment by lymph flow. The oncotic pressure of blood plasma is on average 25-30 mm Hg, and that of tissue fluid is 4-5 mm Hg. Since the protein in plasma contains the most albumin, and its molecule is smaller than other proteins, and the molar concentration is higher, the oncotic pressure of the plasma is created mainly by albumin. A decrease in their content in plasma leads to loss of water in the plasma and tissue edema, and an increase leads to water retention in the blood. In general, oncotic pressure affects the formation of tissue fluid, lymph, urine and water absorption in the intestine.

Colloidal stability of blood plasma is due to the nature of the hydration of proteins, the presence on their surface of a double electrical layer of ions, creating a surface phi potential. Part of this potential is the electro-kinetic (zeta) potential - this is the potential at the boundary between a colloidal particle capable of moving in an electric field and the surrounding liquid, i.e. sliding surface potential of a particle in a colloidal solution. The presence of zeta potential at the sliding boundaries of all dispersed particles forms like charges and electrostatic repulsive forces on them, which ensures stability

colloidal solution and prevents aggregation. The higher the absolute value of this potential, the greater the force of repulsion of protein particles from each other. Thus, zeta potential is a measure of the stability of a colloidal solution. Its value is significantly higher in albumins than in other proteins. Since there is much more albumin in plasma, the colloidal stability of blood plasma is predominantly determined by these proteins, which provide colloidal stability not only of other proteins, but also of carbohydrates and lipids.

Suspension resistance of blood associated with the colloidal stability of plasma proteins. Blood is a suspension, or suspension, because formed elements are suspended in it. The suspension of red blood cells in plasma is maintained by the hydrophilic nature of their surface, as well as by the fact that red blood cells (like other formed elements) carry a negative charge, due to which they repel each other. If the negative charge of the formed elements decreases, for example, in the presence of proteins (fibrinogen, gamma globulins, paraprotein) that are unstable in a colloidal solution and with a lower zeta potential, carrying a positive charge, then the electrical repulsion forces decrease and the red blood cells stick together, forming “coin” columns . In the presence of these proteins, suspension stability is reduced. In the presence of albumin, the suspension ability of blood increases. Suspension stability of erythrocytes is assessed by the erythrocyte sedimentation rate (ESR) in a stationary volume of blood. The essence of the method is to evaluate (in mm/hour) the settled plasma in a test tube with blood, to which sodium citrate is first added to prevent its clotting. The value of ESR depends on gender. In women - 2-15 mm/h, in men - 1-10 mm/h. This indicator also changes with age. Fibrinogen has the greatest effect on ESR: when its concentration increases to more than 4 g/l, it increases. ESR increases sharply during pregnancy due to a significant increase in plasma fibrinogen levels, with erythropenia, a decrease in blood viscosity and albumin content, as well as an increase in plasma globulins. Inflammatory, infectious and oncological diseases, as well as anemia, are accompanied by an increase in this indicator. A decrease in ESR is typical for erythremia, as well as for gastric ulcers, acute viral hepatitis, and cachexia.

Hydrogen ion concentration and regulation of blood pH. Normally, the pH of arterial blood is 7.37-7.43, on average 7.4 (40 nmol/l), venous - 7.35 (44 nmol/l), i.e. blood reaction is slightly alkaline. In cells and tissues, the pH reaches 7.2 and even 7.0, which depends on the intensity of the formation of “acidic” metabolic products. The extreme limits of blood pH fluctuations compatible with life are 7.0-7.8 (16-100 nmol/l).

During the process of metabolism, tissues release “acidic” metabolic products (lactic, carbonic acid) into the tissue fluid, and therefore into the blood, which should lead to a shift in pH to the acidic side. The blood reaction practically does not change, which is explained by the presence of blood buffer systems, as well as the work of the kidneys, lungs, and liver.

Physicochemical properties of blood

Hypervolemia polycythemic

Oligocythemic hypervolemia

Increasing blood volume due to plasma (decreasing hematocrit).

Develops when water is retained in the body due to kidney disease, with the introduction of blood substitutes. It can be simulated experimentally by intravenously injecting animals with isotonic sodium chloride solution.

An increase in blood volume due to an increase in the number of red blood cells (increase in hematocrit).

Observed during prolonged intense physical work.

It is also observed with a decrease in atmospheric pressure, as well as with various diseases associated with oxygen starvation (heart disease, emphysema) and is considered as a compensatory phenomenon.

However, with true erythremia (Vaquez disease) polycythaemic hypervolemia is a consequence of the proliferation of erythrocyte cells in the bone marrow.

May be observed in muscle work time[++736+ P.138-139]. Part of the plasma through the walls of the capillaries leaves the vascular bed into the intercellular space of working muscles [++736+ P.138-139] (muscle, tissue working edema [ND55]). As a result, the volume of circulating blood decreases [++736+ P.138-139]. Since the formed elements remain in the vascular bed, the hematocrit increases [++736+ P.138-139]. This phenomenon is called working hemoconcentration (for more details see [++736+ C.138-139]. 11 [++736+ C.138-139].2 [++736+ C.138-139].3) [++736+ C. 138-139].

Let's consider a specific case (task) [++736+ P.138-139].

How will the hematocrit change during physical work if the blood volume at rest is 5.5 l [++736+ P.138-139], the plasma volume is 2.9 l, which changes by 500 ml?

The blood volume at rest is 5.5 l [++736+ C.138-139]. Of this, 2.9 l is plasma and 2.6 l is blood cells, which corresponds to a hematocrit of 47% (2.6 / 5.5) [++736+ P.138-139]. If during work 500 ml of plasma leaves the vessels, the volume of circulating blood is reduced to 5 liters [++736+ P.138-139]. Since the volume of blood cells does not change, the hematocrit increases - up to 52% (2.6 / 5.0) [++736+ P.138-139].

More details Pokrovsky I volume P.280-284.

The physical and chemical properties of blood include:

Density (absolute and relative)

Viscosity (absolute and relative)

Osmotic pressure, including oncotic (colloid-osmotic) pressure

Temperature

Hydrogen ion concentration (pH)

Suspension resistance of blood, characterized by ESR

Blood color

Blood color determined by hemoglobin content, bright red color of arterial blood - oxyhemoglobin , dark red with a bluish tint of venous blood - reduced hemoglobin.

Density - volumetric mass

Relative blood density is 1.058 - 1.062 and depends mainly on the content of erythrocytes.

The relative density of blood plasma is mainly determined by the concentration of proteins and is 1.029-1.032.

Density of water (absolute) = 1000 kg m -3.

Blood viscosity

Read more Remizov ++636+ P.148

Viscosity is internal friction.

Water viscosity (at 20ºС) 0.001 Pa×s or 1 mPa×s.

The viscosity of human blood (at 37ºC) is normally 4-5 mPa×s; in pathology it ranges from 1.7 to 22.9 mPa×s.

Relative blood viscosity 4.5-5.0 times the viscosity of water. Plasma viscosity does not exceed 1.8-2.2.

The ratio of the viscosity of blood and the viscosity of water at the same temperature is called relative blood viscosity.

Changes in the viscosity of blood as a non-Newtonian fluid

Blood is a non-Newtonian fluid - abnormal viscosity, i.e. Blood viscosity is not a constant value.

Blood viscosity in vessels

The lower the speed of blood movement, the greater the viscosity of the blood. This is due to reversible aggregation of erythrocytes (formation of coin columns), adhesion of erythrocytes to the walls of blood vessels.

Fahraeus-Lindquist phenomenon

In vessels with a diameter of less than 500 microns, the viscosity decreases sharply and approaches the viscosity of plasma. This is due to the orientation of red blood cells along the axis of the vessel and the formation of a “cell-free marginal zone.”

Blood viscosity and hematocrit

Blood viscosity depends mainly on the content of red blood cells and to a lesser extent on plasma proteins.

An increase in Ht is accompanied by a more rapid increase in blood viscosity than with a linear dependence

The viscosity of venous blood is slightly greater than that of arterial blood [B56].

Blood viscosity increases when the blood depot containing a larger number of red blood cells is emptied.

Venous blood has a slightly higher viscosity than arterial blood. During heavy physical work, blood viscosity increases.

Some infectious diseases increase viscosity, while others, such as typhoid fever and tuberculosis, decrease it.

Blood viscosity affects erythrocyte sedimentation rate (ESR).

Methods for determining blood viscosity

The set of methods for measuring viscosity is called viscometry, and devices used for such purposes - viscometers.

The most common viscometry methods:

falling ball

capillary

rotary.

Capillary method is based on the Poiseuille formula and consists in measuring the time of flow of a liquid of a known mass through a capillary under the influence of gravity at a certain pressure difference.

The falling ball method is used in viscometers based on Stokes' law.

The osmotic pressure of the blood depends on the concentration in the blood plasma of the molecules of substances dissolved in it (electrolytes and non-electrolytes) and is the sum of the osmotic pressures of the ingredients contained in it. In this case, over 60% of the osmotic pressure is created by sodium chloride, and in total, inorganic electrolytes account for up to 96% of the total osmotic pressure. Osmotic pressure is one of the rigid homeostatic constants and in a healthy person averages 7.6 atm with a possible range of fluctuations of 7.3-8.0 atm.

Isotonic solution. If the internal fluid or artificially prepared solution has the same osmotic pressure as normal blood plasma, such a liquid medium or solution is called isotonic.
Hypertonic solution. A fluid with a higher osmotic pressure is called hypertonic.
Hypotonic solution. Fluid with lower osmotic pressure is called hypotonic.

Osmotic pressure ensures the transition of the solvent through a semi-permeable membrane from a less concentrated solution to a more concentrated solution, therefore it plays an important role in the distribution of water between the internal environment and the cells of the body. So, if the tissue fluid is hypertonic, then water will enter it from two sides - from the blood and from the cells; on the contrary, when the extracellular environment is hypotonic, water passes into the cells and blood.

A similar reaction can be observed on the part of red blood cells when the osmotic pressure of the plasma changes: when the plasma is hypertonic, the red blood cells, giving up water, shrink, and when the plasma is hypotonic, they swell and even burst. The latter is used in practice to determine osmotic resistance of red blood cells. Thus, a 0.89% NaCl solution is isotonic to blood plasma. Red blood cells placed in this solution do not change shape. In sharply hypotonic solutions and, especially, water, red blood cells swell and burst. The destruction of red blood cells is called hemolysis, and in hypotonic solutions - osmotic hemolysis . If you prepare a series of NaCl solutions with a gradually decreasing concentration of table salt, i.e. hypotonic solutions, and stir a suspension of red blood cells into them, then you can find the concentration of the hypotonic solution at which hemolysis begins and individual red blood cells are destroyed or hemolyzed. This NaCl concentration characterizes minimal osmotic resistance erythrocytes (minimal hemolysis), which in a healthy person is in the range of 0.5-0.4 (% NaCl solution). In more hypotonic solutions, an increasing number of erythrocytes are hemolyzed and the concentration of NaCl at which all erythrocytes will be lysed is called maximum osmotic resistance(maximum hemolysis). In a healthy person, it ranges from 0.34 to 0.30 (% NaCl solution).
The mechanisms of regulation of osmotic homeostasis are outlined in Chapter 12.

Oncotic pressure

Oncotic pressure is the osmotic pressure created by proteins in a colloidal solution, which is why it is also called colloid-osmotic. Due to the fact that blood plasma proteins do not pass well through the walls of capillaries into the tissue microenvironment, the oncotic pressure they create ensures the retention of water in the blood. If the osmotic pressure caused by salts and small organic molecules, due to the permeability of histohematic barriers, is the same in plasma and tissue fluid, then the oncotic pressure in the blood is significantly higher. In addition to poor permeability of barriers to proteins, their lower concentration in tissue fluid is associated with the leaching of proteins from the extracellular environment by lymph flow. Thus, between the blood and tissue fluid there is a gradient of protein concentration and, accordingly, a gradient of oncotic pressure. So, if the oncotic pressure of blood plasma averages 25-30 mm Hg, and in tissue fluid - 4-5 mm Hg, then the pressure gradient is 20-25 mm Hg. Since the blood plasma contains the most proteins among proteins, and the albumin molecule is smaller than other proteins and its molal concentration is therefore almost 6 times higher, the oncotic pressure of the plasma is created mainly by albumins. A decrease in their content in the blood plasma leads to loss of water in the plasma and tissue edema, and an increase leads to water retention in the blood.

Colloidal stability

The colloidal stability of blood plasma is due to the nature of the hydration of protein molecules and the presence on their surface of a double electrical layer of ions, creating a surface or phi potential. Part of the phi potential is electrokinetic(zeta) potential. Zeta potential is the potential at the boundary between a colloidal particle capable of moving in an electric field and the surrounding liquid, i.e. sliding surface potential of a particle in a colloidal solution. The presence of zeta potential at the sliding boundaries of all dispersed particles forms like charges and electrostatic repulsive forces on them, which ensures the stability of the colloidal solution and prevents aggregation. The higher the absolute value of this potential, the greater the force of repulsion of protein particles from each other. Thus, zeta potential is a measure of the stability of a colloidal solution. The magnitude of this potential is significantly higher for plasma albumins than for other proteins. Since there are significantly more albumins in plasma, the colloidal stability of blood plasma is predominantly determined by these proteins, which ensure the colloidal stability of not only other proteins, but also carbohydrates and lipids.

Suspension properties

The suspension properties of blood are associated with the colloidal stability of plasma proteins, i.e. maintaining cellular elements in suspension. The magnitude of the suspension properties of blood can be assessed by erythrocyte sedimentation rate(ESR) in a stationary volume of blood.

Thus, the higher the content of albumin compared to other, less stable colloidal particles, the greater the suspension capacity of the blood, since albumin is adsorbed on the surface of erythrocytes. On the contrary, with an increase in the blood level of globulins, fibrinogen, and other large-molecular proteins that are unstable in a colloidal solution, the erythrocyte sedimentation rate increases, i.e. the suspension properties of blood decrease. Normal ESR in men is 4-10 mm/h, and in women - 5-12 mm/h.

Blood viscosity

Viscosity is the ability to resist the flow of a liquid when some particles move relative to others due to internal friction. In this regard, blood viscosity is a complex effect of the relationship between water and colloidal macromolecules on the one hand, and plasma and formed elements on the other. Therefore, the viscosity of plasma and the viscosity of whole blood are significantly different: the viscosity of plasma is 1.8-2.5 times higher than that of water, and the viscosity of blood is 4-5 times higher than the viscosity of water. The more large-molecular proteins, especially fibrinogen and lipoproteins, in the blood plasma, the higher the viscosity of the plasma. With an increase in the number of red blood cells, especially their ratio with plasma, i.e. hematocrit, blood viscosity increases sharply. An increase in viscosity is also facilitated by a decrease in the suspension properties of blood, when red blood cells begin to form aggregates. In this case, a positive feedback is noted - an increase in viscosity, in turn, increases the aggregation of erythrocytes - which can lead to a vicious circle. Since blood is a heterogeneous medium and belongs to non-Newtonian fluids, which are characterized by structural viscosity, a decrease in flow pressure, for example, blood pressure, increases the viscosity of the blood, and with an increase in pressure due to the destruction of the structure of the system, the viscosity decreases.

Another feature of blood as a system, which, along with Newtonian and structural viscosity, is, Fahraeus-Lindquist effect. In a homogeneous Newtonian fluid, according to Poiseuille's law, as the diameter of the tube decreases, the viscosity increases. Blood, which is a heterogeneous non-Newtonian fluid, behaves differently. As the capillary radius decreases to less than 150 microns, blood viscosity begins to decrease. The Fahraeus-Lindquist effect facilitates the movement of blood in the capillaries of the bloodstream. The mechanism of this effect is associated with the formation of a wall plasma layer, the viscosity of which is lower than that of whole blood, and the migration of erythrocytes into the axial flow. With a decrease in the diameter of the vessels, the thickness of the wall layer does not change. There are fewer red blood cells in the blood moving through narrow vessels in relation to the plasma layer, because Some of them are delayed when blood enters narrow vessels, and red blood cells in their flow move faster and the time they spend in a narrow vessel decreases.

Blood viscosity directly proportionally affects the value of the total peripheral vascular resistance to blood flow, i.e. affects the functional state of the cardiovascular system.

Specific gravity of blood

The specific gravity of blood in a healthy middle-aged person ranges from 1.052 to 1.064 and depends on the number of red blood cells, the hemoglobin content in them, and the composition of the plasma.
In men, the specific gravity is higher than in women due to the different content of red blood cells. The specific gravity of erythrocytes (1.094-1.107) is significantly higher than that of plasma (1.024-1.030), therefore, in all cases of increased hematocrit, for example, with thickening of the blood due to loss of fluid during sweating under conditions of heavy physical work and high ambient temperatures, it is noted increase in blood specific gravity.

4. Determination of osmotic resistance of erythrocytes:

The osmotic resistance of erythrocytes characterizes their resistance to destructive factors: chemical, temperature, mechanical. In laboratory experiments, special attention is paid to their resistance to hypotonic NaCl solutions, namely, what concentration causes hemolysis. Normally functioning cells resist osmosis and will remain strong. This ability characterizes osmotic stability, or resistance of erythrocytes.
If they become weak, they are flagged by the immune system and then removed from the body.
Research method: The main laboratory method for determining the resistance of red blood cells to destruction is the reaction of a hypotonic saline solution and blood mixed in equal volumes. The analysis reveals the stability of the cell membrane. An alternative method for determining BSE is photocolorimetric, in which measurements are made with a special apparatus - a photocolorimeter. Saline solution is a mixture of distilled water and sodium chloride. In a solution with a concentration of 0.85%, red blood cells are not destroyed; it is called isotonic. A higher concentration will result in a hypertonic solution, and a lower concentration will result in a hypotonic solution.
In them, red blood cells die, shrinking in a hypertonic solution, and swelling in a hypotonic solution.
How is the procedure performed? The determination of BER is carried out by adding an equal amount of blood (usually 0.22 ml) to a hypotonic NaCl solution of various concentrations (0.7-0.22%). After an hour of exposure, the mixture is centrifuged. Depending on the color, the beginning of decay and complete hemolysis are determined. At the beginning of the process, the solution has a slightly pink color, and bright red indicates the complete breakdown of red blood cells. The result is expressed in two characteristics of resistance, having a percentage expression - minimum and maximum.
In the presence of secondary hemolytic anemia due to deficiency of glucose-6-phosphate dihydrogenase, the analysis may show a normal BER, which must be taken into account before conducting the study
Normal indicators The resistance norm for an adult, regardless of gender, is as follows (%): Maximum - 0.34-0.32. Minimum – 0.48-0.46.
In children under 2 years of age, osmotic stability is slightly higher than the normal value, and the RES rate in older people is usually lower than the standard minimum value.

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The functions of blood are largely determined by its physicochemical properties, among which the most important are

Osmotic pressure, Oncotic pressure, Colloidal stability, Suspension stability, Specific gravity and viscosity.

Osmotic pressure

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Isotonic solution. If the internal fluid or artificially prepared solution has the same osmotic pressure as normal blood plasma, such a liquid medium or solution is called isotonic.
Hypertonic solution. A fluid with a higher osmotic pressure is called hypertonic.
Hypotonic solution. Fluid with lower osmotic pressure is called hypotonic.

A similar reaction can be observed on the part of red blood cells when the osmotic pressure of the plasma changes: when the plasma is hypertonic, the red blood cells, giving up water, shrink, and when the plasma is hypotonic, they swell and even burst. The latter is used in practice to determine osmotic resistancered blood cells. Thus, a 0.89% NaCl solution is isotonic to blood plasma. Red blood cells placed in this solution do not change shape. In sharply hypotonic solutions and, especially, water, red blood cells swell and burst. The destruction of red blood cells is called hemolysis, and in hypotonic solutions - osmotic hemolysis . If you prepare a series of NaCl solutions with a gradually decreasing concentration of table salt, i.e. hypotonic solutions, and stir a suspension of red blood cells into them, then you can find the concentration of the hypotonic solution at which hemolysis begins and individual red blood cells are destroyed or hemolyzed. This NaCl concentration characterizes minimal osmotic resistance erythrocytes (minimal hemolysis), which in a healthy person is in the range of 0.5-0.4 (% NaCl solution). In more hypotonic solutions, an increasing number of erythrocytes are hemolyzed and the concentration of NaCl at which all erythrocytes will be lysed is called maximum osmotic resistance(maximum hemolysis). In a healthy person, it ranges from 0.34 to 0.30 (% NaCl solution).
The mechanisms of regulation of osmotic homeostasis are outlined in Chapter 12.

Oncotic pressure

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Colloidal stability

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The colloidal stability of blood plasma is due to the nature of the hydration of protein molecules and the presence on their surface of a double electrical layer of ions, creating a surface or phi potential. Part of the phi potential is electrokineticcue(zeta) potential. Zeta potential is the potential at the boundary between a colloidal particle capable of moving in an electric field and the surrounding liquid, i.e. sliding surface potential of a particle in a colloidal solution. The presence of zeta potential at the sliding boundaries of all dispersed particles forms like charges and electrostatic repulsive forces on them, which ensures the stability of the colloidal solution and prevents aggregation. The higher the absolute value of this potential, the greater the force of repulsion of protein particles from each other. Thus, zeta potential is a measure of the stability of a colloidal solution. The magnitude of this potential is significantly higher for plasma albumins than for other proteins. Since there are significantly more albumins in plasma, the colloidal stability of blood plasma is predominantly determined by these proteins, which ensure the colloidal stability of not only other proteins, but also carbohydrates and lipids.

Suspension properties

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Blood viscosity

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Blood viscosity directly proportionally affects the value of the total peripheral vascular resistance to blood flow, i.e. affects the functional state of the cardiovascular system.

Specific gravity of blood

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Blood color determined by the presence of hemoglobin. Arterial blood is characterized by a bright red color, which depends on the content of oxygenated hemoglobin (oxyhemoglobin) in it. Venous blood has a dark red color with a bluish tint, which is explained by the presence in it not only of oxyhemoglobin, but also of reduced hemoglobin, which accounts for approximately 1/3 of its total content. The more active the organ, and the more hemoglobin has given oxygen to the tissues, the darker the venous blood looks.

Relative blood density depends on the content of red blood cells and their saturation with hemoglobin. It ranges from 1.052 to 1.062. In women, the relative density of blood is slightly lower than in men. The relative density of blood plasma is mainly determined by the concentration of proteins and is 1.029 - 1.032.

Blood viscosity is determined in relation to the viscosity of water and corresponds to 4.5 – 5.0. Consequently, human blood is 4.5 – 5 times more viscous than water. Blood viscosity depends mainly on the content of red blood cells and, to a much lesser extent, on plasma proteins. At the same time, the viscosity of venous blood is slightly higher than that of arterial blood, which is associated with the entry of carbon dioxide into erythrocytes, due to which their size slightly increases. Blood viscosity increases when the blood depot containing a larger number of red blood cells is emptied.

Plasma viscosity does not exceed 1.8–2.2. The protein fibrinogen most affects plasma viscosity. Thus, the viscosity of plasma compared to the viscosity of serum, in which fibrinogen is absent, is approximately 20% higher. With an abundant protein diet, the viscosity of the plasma, and, consequently, the blood, can increase. An increase in blood viscosity is an unfavorable prognostic sign for people with atherosclerosis and predisposed to diseases such as coronary heart disease (angina, myocardial infarction), obliterating endarteritis, strokes (cerebral hemorrhage or blood clots in the vessels of the brain).

Blood osmotic pressure. Osmotic pressure is the force that forces a solvent (for blood this is water) to pass through a semi-permeable membrane from a less concentrated to a more concentrated solution. The osmotic pressure of the blood is calculated using the cryoscopic method by determining the depression (freezing point), which for blood is 0.54°-0.58°. The depression of a molar solution (a solution in which 1 gram molecule of a substance is dissolved in a liter of water) corresponds to 1.86°. The total molecular concentration in plasma and red blood cells is approximately 0.3 gram molecules per liter. Substituting the values into the Clapeyron equation (P = cRT, where P is the osmotic pressure, c is the molecular concentration, R is the gas constant equal to 0.082 liter-atmosphere, and T is the absolute temperature), it is easy to calculate that the osmotic pressure for blood at a temperature of 37 °C is 7.6 atmospheres (0.3x0.082x310=7.6). In a healthy person, osmotic pressure ranges from 7.3 to 7.6 atmospheres.

The osmotic pressure of blood depends mainly on low molecular weight compounds dissolved in it, mainly salts. About 95% of the total osmotic pressure comes from inorganic electrolytes, of which 60% comes from NaCl. The osmotic pressure in the blood, lymph, tissue fluid, and tissues is approximately the same and is characterized by enviable constancy. Even if a significant amount of water or salt enters the blood, even in these cases the osmotic pressure does not undergo significant changes. When excess water enters the blood, it is quickly excreted by the kidneys and also passes into tissues and cells, which restores the original value of osmotic pressure. If an increased concentration of salt enters the blood, then water from the tissue fluid enters the vascular bed, and the kidneys begin to intensively remove salts. Osmotic pressure can be influenced within small limits by the products of digestion of proteins, fats and carbohydrates, absorbed into the blood and lymph, as well as low-molecular-weight products of cellular metabolism.

Maintaining a constant osmotic pressure plays an extremely important role in the life of cells. Their existence under conditions of sharp fluctuations in osmotic pressure would become impossible due to tissue dehydration (with an increase in osmotic pressure) or as a result of swelling from excess water (with a decrease in osmotic pressure).

Oncotic pressure is part of the osmotic pressure and depends on the content of large molecular compounds (proteins) in the solution. Although the concentration of proteins in plasma is quite high, the total number of molecules due to their large molecular weight is relatively small, due to which the oncotic pressure does not exceed 25-30 mmHg. pillar Oncotic pressure is largely dependent on albumin (they account for up to 80% of oncotic pressure), which is due to their relatively low molecular weight and large number of molecules in plasma.

Oncotic pressure plays an important role in the regulation of water metabolism. The greater its value, the more water is retained in the vascular bed and the less it passes into the tissue, and vice versa. Oncotic pressure not only affects the formation of tissue fluid and lymph, but also regulates the processes of urine formation, as well as the absorption of water in the intestines.

If the protein concentration in the plasma decreases, which is observed during protein starvation, as well as with severe kidney damage, then edema occurs, as water is no longer retained in the vascular bed and passes into the tissues.

Blood temperature largely depends on the metabolic rate of the organ from which it flows. The more intense the metabolism in an organ, the higher the temperature of the blood flowing from it. Consequently, in the same organ the temperature of venous blood is always higher than that of arterial blood. This rule, however, does not apply to superficial veins of the skin that are in contact with atmospheric air and are directly involved in heat exchange. In warm-blooded (homeothermic) animals and humans, the resting blood temperature in various vessels ranges from 37° to 40°. Thus, blood flowing from the liver through the veins can have a temperature of 39.7°. Blood temperature rises sharply during intense muscular work.

When blood moves, not only does some temperature equalization occur in various vessels, but also conditions are created for the release or retention of heat in the body. In hot weather, more blood flows through the skin vessels, which promotes heat loss. In cold weather, skin vessels narrow, blood is forced into the vessels of the abdominal cavity, which leads to heat conservation.

Hydrogen ion concentration and blood pH regulation. It is known that the blood reaction is determined by the concentration of hydrogen ions. An H+ ion is a hydrogen atom that carries a positive charge. The degree of acidity of any medium depends on the number of H+ ions present in the solution. On the other hand, the degree of alkalinity of a solution is determined by the concentration of hydroxyl (OH -) ions, which carry a negative charge. Pure distilled water under normal conditions is considered neutral because it contains the same amount of H + - and OH - ions.

Ten million liters of pure water at a temperature of 22°C contains 1.0 grams of hydrogen ions, or 1/10 7, which corresponds to 10 - 7.

Currently, the acidity of solutions is usually expressed as the negative logarithm of the absolute number of hydrogen ions contained in a unit volume of liquid, for which the generally accepted designation pH is used. Therefore, the pH of neutral distilled water is 7. If the pH is less than 7, then H+ ions will prevail in the solution over OH - ions, and then the medium will be acidic, but if the pH is greater than 7, then the medium will be alkaline, because it will be dominated by OH - ions over H+ ions.

Normally, the pH of the blood averages 7.36.±0.03 i.e. the reaction is weakly basic. The pH of the blood is remarkably constant. His fluctuations are extremely insignificant. Thus, under resting conditions, the pH of arterial blood corresponds to 7.4, and that of venous blood to 7.34. In cells and tissues, the pH reaches 7.2 and even 7.0, which depends on the formation of acidic metabolic products in them during the metabolic process. Under various physiological conditions, the pH of the blood can change both in the acidic (up to 7.3) and alkaline (up to 7.5) directions. More significant pH deviations are accompanied by severe consequences for the body. So, at a blood pH of 6.95, loss of consciousness occurs, and if these changes are not eliminated as soon as possible, then death is inevitable. If the concentration of H+ decreases and the pH becomes equal to 7.7, then severe convulsions (tetany) occur, which can also lead to death.

During the metabolic process, tissues release acidic metabolic products into the tissue fluid, and, consequently, into the blood, which should lead to a shift in pH to the acidic side. As a result of intense muscular activity, up to 90 g of lactic acid can enter the human blood within a few minutes. If this amount of lactic acid were added to the same amount of distilled water, the concentration of hydrogen ions in it would increase 40,000 times. The blood reaction under these conditions practically does not change, which is explained by the presence of blood buffer systems. In addition, the body maintains a constant pH due to the work of the kidneys and lungs, which remove CO2 and excess acids and alkalis from the blood.

The constancy of blood pH is maintained by buffer systems: hemoglobin, carbonate, phosphate and plasma proteins.

The most powerful is hemoglobin buffer system. It accounts for 75% of the buffer capacity of the blood. This system includes reduced hemoglobin (HHb) and the potassium salt of reduced hemoglobin (KHb). The buffering properties of the system are due to the fact that KHb, being a salt of a weak acid, donates the K+ ion and attaches the H+ ion, forming a weakly dissociated acid: H+ + KHb = K+ + HHb.

The pH of the blood flowing to the tissues, thanks to reduced hemoglobin, which can bind CO2 and H+ ions, remains constant. Under these conditions, HHb acts as an alkali. In the lungs, hemoglobin behaves like an acid (oxyhemoglobin, HHbO2, is a stronger acid than carbon dioxide), which prevents the blood from becoming alkalized.

Carbonate buffer system(H2CO3/NaHCO3) ranks second in its power. Its functions are carried out as follows: NaHCO3 dissociates into Na+ and HCO3 -. If an acid stronger than carbonic acid enters the blood, then an exchange of Na+ ions occurs with the formation of weakly dissociated and easily soluble carbonic acid, which prevents an increase in the concentration of H+ in the blood. An increase in the content of carbonic acid leads to its breakdown (this occurs under the influence of the enzyme carbonic anhydrase found in red blood cells) into water and carbon dioxide. The latter enters the lungs and is released out. If alkali penetrates into the blood, it reacts with carbonic acid, forming sodium bicarbonate (NaHCO3) and water, which again prevents the pH from shifting to the alkaline side.

Phosphate buffer system formed by sodium dihydrogen phosphate (NaH2PO4) and sodium hydrogen phosphate (Na2HPO4). The first of them behaves like a weak acid, the second - like a salt of a weak acid. If a stronger acid enters the blood, it reacts with Na2HPO4, forming a neutral salt and increasing the amount of poorly dissociated NaH 2 PO4 -:

Na 2 HPO4 + H 2 CO 3 = NaHCO 3 + NaH2PO4.

Excessive amounts of sodium dihydrogen phosphate will be removed in the urine, so the ratio of NaH2PO4 to Na2HPO4 will not change.

If a strong base is introduced into the blood, it will react with sodium dihydrogen phosphate, forming weakly basic sodium hydrogen phosphate. In this case, the pH of the blood will change extremely slightly. In this situation, excess sodium hydrogen phosphate will be excreted in the urine.

Blood plasma proteins play the role of a buffer, because they have amphoteric properties, due to which they behave like bases in an acidic environment, and like acids in a basic environment.

Buffer systems are also present in tissues, where they maintain pH at a relatively constant level. The main tissue buffers are cellular proteins and phosphates. During metabolism, more acidic products are formed than basic ones. That is why the danger of a pH shift to the acidic side is greater. Due to this, in the process of evolution, the buffer systems of blood and tissues have acquired greater resistance to the action of acids than bases. Thus, to shift the pH of plasma to the alkaline side, it is necessary to add 40-70 times more NaOH to it than to distilled water. To shift the pH to the acidic side, it is necessary to add 300-350 times more HCl to the plasma than to water. Basic salts of weak acids contained in the blood form the so-called alkaline blood reserve. Its value is determined by the amount of carbon dioxide that can be bound by 100 ml of blood at a CO2 voltage of 40 mmHg. Art.

The constant ratio between acid and alkaline equivalents allows us to talk about acid-base balance blood.

Nervous regulation plays an important role in maintaining a constant pH. In this case, the chemoreceptors of the vascular reflexogenic zones are predominantly irritated, impulses from which enter the medulla oblongata and other parts of the central nervous system, which reflexively includes peripheral organs in the reaction - kidneys, lungs, sweat glands, gastrointestinal tract, the activity of which is aimed at restoring the original pH value. It has been established that when the pH shifts to the acidic side, the kidneys intensively excrete the H 2 PO 4 - anion in the urine. When blood pH shifts to the alkaline side, the kidneys secrete HPO 2 - and HCO 3 - anions. Human sweat glands are able to remove excess lactic acid, and the lungs – CO 2.

Under various pathological conditions, a pH shift can be observed both in the acidic and alkaline directions. The first of them is called acidosis, second - alkalosis. More dramatic changes in pH occur in the presence of a pathological focus directly in the tissues.

Suspension stability of blood (erythrocyte sedimentation rate - ESR). From a physicochemical point of view, blood is a suspension, or suspension, because the formed elements of blood are suspended in plasma. A suspension, or suspension, is a liquid containing evenly distributed particles of another substance. The suspension of red blood cells in plasma is maintained by the hydrophilic nature of their surface, as well as by the fact that they (like other formed elements) carry a negative charge, due to which they repel each other. If the negative charge of formed elements decreases, which may be due to the adsorption of positively charged proteins or cations, then favorable conditions are created for the gluing of red blood cells to each other. Particularly sharp adhesion of erythrocytes is observed with an increase in the plasma concentration of fibrinogen, haptoglobin, ceruloplasmin, a- and b-lipoproteins, as well as immunoglobulins, the concentration of which can increase during pregnancy, inflammatory, infectious and oncological diseases. In this case, the named proteins, adsorbed on erythrocytes, form bridges between them, due to which the so-called coin columns (aggregates) appear. The net force of aggregation is the difference between the force in the formed bridges, the force of electrostatic repulsion of negatively charged red blood cells, and the shear force that causes the disintegration of aggregates. It is possible that the adhesion of protein molecules on the surface of erythrocytes occurs due to weak hydrogen bonds and disperse van der Waals forces.

The resistance of “monent columns” to friction is less than the total resistance of their constituent elements, since when aggregates form, the ratio of surface to volume decreases, due to which they settle faster.

“Coin columns” forming in the bloodstream can get stuck in the capillaries and thereby interfere with the normal blood supply to cells, tissues and organs.

If blood is placed in a test tube, having previously added substances that prevent clotting, then after some time it will be possible to see that it is divided into two layers: the upper one consists of plasma, and the lower one consists of formed elements, mainly red blood cells. Based on these properties, Ferreus proposed studying the suspension stability of erythrocytes by determining the rate of their sedimentation in the blood, the coagulability of which is eliminated by the preliminary addition of sodium citrate. This reaction is now called " erythrocyte sedimentation rate (ESR).

The ESR is determined using a Panchenkov capillary, on which millimeter divisions are applied. The capillary is placed on a stand for 1 hour and then the size of the plasma layer above the surface of the deposited red blood cells is determined.

Normal ESR is due to a normal plasma proteinogram. The ESR value depends on age and gender. In men it is 6-12 mm/hour, in adult women – 8-15 mm/hour, in old people of both sexes up to 15-20 mm/hour. The greatest contribution to the increase in ESR is made by the protein fibrinogen; when its concentration increases to more than 3 g/liter, the ESR increases. A decrease in ESR is often observed with an increase in albumin levels. As the hematocrit number increases (polycythemia), the ESR decreases. When the hematocrit number decreases (anemia), the ESR always increases.

ESR increases sharply during pregnancy, when the fibrinogen content in plasma increases significantly. An increase in ESR is observed in the presence of inflammatory, infectious and oncological diseases, with burns, frostbite, as well as with a sharp decrease in the number of red blood cells in the blood. A decrease in ESR below 3 mm/hour is an unfavorable sign, because it indicates an increase in blood viscosity.

The value of ESR depends to a greater extent on the properties of plasma rather than erythrocytes. So, if you place the red blood cells of a man with a normal ESR into the plasma of a pregnant woman, they will begin to sediment at the same rate as in women during pregnancy.