What is blood short definition. Formed elements of blood

What are the functions of blood in the body of an animal?

What color is blood in animals and why?

Transport (nutritional), excretory, thermoregulatory, humoral, protective

The color of the blood of animals depends on the metals that are part of the blood cells (erythrocytes), or substances dissolved in the plasma. In all vertebrates, as well as in the earthworm, leeches, houseflies and some mollusks, iron oxide is found in a complex combination with blood hemoglobin. That is why their blood is red. The blood of many marine worms contains a similar substance, chlorocruorin, instead of hemoglobin. Ferrous iron was found in its composition, and therefore the color of the blood of these worms is green. And scorpions, spiders, crayfish, octopuses and cuttlefish have blue blood. Instead of hemoglobin, it contains hemocyanin, with copper as the metal. Copper also gives their blood a bluish color.

Page 82-83

1. What components does the internal environment consist of? How are they related?

The internal environment of the body consists of blood, tissue fluid and lymph. Blood moves through a system of closed vessels and does not directly contact tissue cells. Tissue fluid is formed from the liquid part of the blood. It got its name because it is located among the tissues of the body. Nutrients from the blood enter the tissue fluid and into the cells. The decay products move in the opposite direction. Lymph. Excess tissue fluid enters the veins and lymphatic vessels. In the lymphatic capillaries, it changes its composition and becomes lymph. Lymph moves slowly through the lymphatic vessels and eventually enters the blood again. Previously, lymph passes through special formations - lymph nodes, where it is filtered and disinfected, enriched with lymph cells.

2. What is the composition of blood and what is its significance for the body?

Blood is a red, opaque liquid composed of plasma and formed elements. There are red blood cells (erythrocytes), white blood cells (leukocytes) and platelets (platelets). In the human body, blood connects every organ, every cell of the body with each other. The blood carries the nutrients obtained from food to the digestive organs. It delivers oxygen from the lungs to the cells, and carbon dioxide, harmful, waste substances are carried to those organs that neutralize them or remove them from the body.

3. Name the blood cells and their functions.

Platelets are platelets. They are involved in blood clotting. Erythrocytes are red blood cells. The color of red blood cells, erythrocytes, depends on the hemoglobin they contain. Hemoglobin is able to easily combine with oxygen and easily give it away. Red blood cells carry oxygen from the lungs to all organs. Leukocytes are white blood cells. Leukocytes are extremely diverse and fight germs in many ways.

4. Who discovered the phenomenon of phagocytosis? How is it carried out?

The ability of certain leukocyte cells to capture microbes and destroy them was discovered by I.I. Mechnikov - the great Russian scientist, Nobel Prize winner. Leukocyte cells of this type I.I. Mechnikov called phagocytes, i.e., eaters, and the process of destroying microbes by phagocytes - phagocytosis

5. What are the functions of lymphocytes?

The lymphocyte has the appearance of a ball, on its surface there are numerous villi, similar to tentacles. With their help, the lymphocyte examines the surface of other cells, looking for foreign compounds - antigens. most often they are found on the surface of phagocytes that have destroyed foreign bodies. If only “own” molecules are found on the surface of cells, the lymphocyte moves on, and if strangers, the tentacles, like claws of cancer, close. Then the lymphocyte sends chemical signals through the blood to other lymphocytes, and they begin to produce chemical antidotes according to the found sample - antibodies consisting of gamma globulin protein. This protein is released into the blood and settles on various cells, such as red blood cells. Antibodies often go beyond the blood vessels and are located on the surface of skin cells, respiratory tract, and intestines. They are a kind of traps for foreign bodies, such as microbes and viruses. Antibodies either stick them together, or destroy them, or dissolve them, in short, disable them. At the same time, the constancy of the internal environment is restored.

6. How does blood coagulation occur?

When blood flows from the wound to the surface of the skin, the platelets stick together and break down, and the enzymes they contain are released into the blood plasma. In the presence of calcium and vitamin K salts, the plasma protein fibrinogen forms fibrin strands. Red blood cells and other blood cells get stuck in them, and a blood clot forms. It doesn't let blood flow out.

7. How are human erythrocytes different from frog erythrocytes?

1) Human erythrocytes do not have a nucleus, frog erythrocytes are nuclear.

2) Human erythrocytes are shaped like a biconcave disk, while frog erythrocytes are oval.

3) Human erythrocytes are 7-8 µm in diameter, frog erythrocytes are 15-20 µm long and about 10 µm wide and thick.

Blood- the internal environment of the body, providing homeostasis, reacts most early and sensitively to tissue damage. Blood is a mirror of homeostasis and a blood test is mandatory for any patient, the indicators of blood shifts are the most informative and play an important role in the diagnosis and prognosis of the course of diseases.

Blood distribution:

50% in the organs of the abdominal cavity and pelvis;

25% in the organs of the chest cavity;

25% on the periphery.

2/3 in venous vessels, 1/3 - in arterial.

Functions blood

1. Transport - the transfer of oxygen and nutrients to organs and tissues and metabolic products to the excretory organs.

2. Regulatory - ensuring humoral and hormonal regulation of the functions of various systems and tissues.

3. Homeostatic - maintaining body temperature, acid-base balance, water-salt metabolism, tissue homeostasis, tissue regeneration.

4. Secretory - the formation of biologically active substances by blood cells.

5. Protective - providing immune responses, blood and tissue barriers against infection.

blood properties.

1. Relative constancy of circulating blood volume.

The total amount of blood depends on body weight and in the body of an adult is normally 6–8%, i.e. approximately 1/130 of body weight, which, with a body weight of 60–70 kg, is 5–6 l. In a newborn - 155% of the mass.

In diseases, blood volume may increase - hypervolemia or decrease - hypovolemia. In this case, the ratio of formed elements and plasma can be preserved or changed.

Loss of 25-30% of blood is life-threatening. Lethal - 50%.

2. Blood viscosity.

The viscosity of blood is due to the presence of proteins and formed elements, especially erythrocytes, which, when moving, overcome the forces of external and internal friction. This indicator increases with thickening of the blood, i.e. loss of water and an increase in the number of red blood cells. Viscosity blood plasma is 1.7–2.2, and whole blood - about 5 conv. units in relation to water. The relative density (specific gravity) of whole blood ranges from 1.050-1.060.

3. suspension property.

Blood is a suspension in which the formed elements are in suspension.

Factors providing this property:

The number of formed elements, the more of them, the more pronounced the suspension properties of blood;

Blood viscosity - the greater the viscosity, the greater the suspension properties.

An indicator of suspension properties is the erythrocyte sedimentation rate (ESR). Average erythrocyte sedimentation rate (ESR) in men, 4–9 mm/hour; in women, 8–10 mm/hour.

4. electrolyte properties.

This property provides a certain value of the osmotic pressure of the blood due to the content of ions. Osmotic pressure is a fairly constant indicator, despite its small fluctuations due to the transition from plasma to tissues of large molecular substances (amino acids, fats, carbohydrates) and the entry of low molecular weight products of cellular metabolism from tissues into the blood.

5. Relative constancy of the acid-base composition of the blood (pH) (acid-base balance).

The constancy of the blood reaction is determined by the concentration of hydrogen ions. The constancy of the pH of the internal environment of the body is due to the combined action of buffer systems and a number of physiological mechanisms. The latter include the respiratory activity of the lungs and the excretory function of the kidneys.

The most important blood buffer systems are bicarbonate, phosphate, protein and most powerful hemoglobin. The buffer system is a conjugated acid-base pair consisting of an acceptor and a donor of hydrogen ions (protons).

Blood has a slightly alkaline reaction. It has been established that a certain range of blood pH fluctuations corresponds to the state of the norm - from 7.37 to 7.44 with an average value of 7.40, arterial blood pH is 7.4; and venous, due to the high content of carbon dioxide in it, - 7.35.

Alkalosis- an increase in the pH of the blood (and other tissues of the body) due to the accumulation of alkaline substances.

Acidosis- decrease in blood pH as a result of insufficient excretion and oxidation of organic acids (their accumulation in the body).

6. colloid properties.

They consist in the ability of proteins to retain water in the vascular bed - hydrophilic finely dispersed proteins have this property.

Composition of the blood.

1. Plasma (liquid intercellular substance) 55-60%;

2. Formed elements (cells in it) - 40-45%.

blood plasma is the liquid that remains after the removal of formed elements from it.

Blood plasma contains 90–92% water and 8–10% dry matter. It contains protein substances differing in their properties and functional significance: albumins (4.5%), globulins (2–3%) and fibrinogen (0.2–0.4%), as well as 0.9% salts, 0 ,1 % glucose. The total amount of proteins in human plasma is 7–8%. Blood plasma also contains enzymes, hormones, vitamins and other substances necessary for the body.

Figure - Blood cells:

1 - basophilic granulocyte; 2 - acidophilic granulocyte; 3 - segmented neutrophilic granulocyte; 4 - erythrocyte; 5 - monocyte; 6 - platelets; 7 - lymphocyte

A sharp decrease in the amount of glucose in the blood (up to 2.22 mmol / l) leads to an increase in the excitability of brain cells, the appearance of seizures. A further decrease in blood glucose leads to impaired breathing, circulation, loss of consciousness and even death.

Minerals in blood plasma are NaCl, KCI, CaCl NaHCO 2, NaH 2 PO 4 and other salts, as well as ions Na +, Ca 2+, K +, etc. The constancy of the ionic composition of the blood ensures the stability of the osmotic pressure and the preservation of the volume of fluid in the blood and cells of the body. Bleeding and loss of salts are dangerous for the body, for cells.

The formed elements (cells) of the blood include: erythrocytes, leukocytes, platelets.

Hematocrit- part of the volume of blood attributable to the proportion of formed elements.

For the normal functioning of the human body as a whole, it is necessary to have a connection between all its organs. The most important in this regard is the circulation of fluids in the body, primarily blood and lymph. Blood transfers hormones and biologically active substances involved in the regulation of the body. In the blood and lymph there are special cells that perform protective functions. Finally, these fluids play an important role in maintaining the physicochemical properties of the internal environment of the body, which ensures the existence of body cells in relatively constant conditions and reduces the influence of the external environment on them.

Blood consists of plasma and formed elements - blood cells. The latter include erythrocytes- red blood cells leukocytes- white blood cells and platelets- platelets (Fig. 1). The total amount of blood in an adult is 4-6 liters (about 7% of body weight). Men have slightly more blood - an average of 5.4 liters, women - 4.5 liters. Loss of 30% of blood is dangerous, 50% is fatal.

Plasma
Plasma is the liquid part of the blood, consisting of 90-93% water. Essentially, plasma is an intercellular substance of a liquid consistency. Plasma contains 6.5-8% proteins, another 2-3.5% are other organic and inorganic compounds. Plasma proteins, albumins and globulins, perform trophic, transport, protective functions, participate in blood coagulation and create a certain osmotic blood pressure. Plasma contains glucose (0.1%), amino acids, urea, uric acid, lipids. Inorganic substances make up less than 1% (ions Na, K, Mg, Ca, Cl, P, etc.).

Erythrocytes (from the Greek. erythros- red) - highly specialized cells designed to transport gaseous substances. Erythrocytes have the form of biconcave discs with a diameter of 7-10 microns, a thickness of 2-2.5 microns. This shape increases the surface for diffusion of gases, and also makes the erythrocyte easily deformable when moving through narrow tortuous capillaries. Erythrocytes do not have a nucleus. They contain protein hemoglobin, through which the transport of respiratory gases is carried out. The non-protein part of hemoglobin (heme) has an iron ion.

In the capillaries of the lungs, hemoglobin forms an unstable compound with oxygen - oxyhemoglobin (Fig. 2). Blood saturated with oxygen is called arterial blood and has a bright scarlet color. This blood is delivered through the vessels to every cell of the human body. Oxyhemoglobin gives oxygen to tissue cells and combines with carbon dioxide that has come from them. Oxygen-poor blood has a dark color and is called venous. Through the vascular system, venous blood from organs and tissues is delivered to the lungs, where it is again saturated with oxygen.

In adults, red blood cells are formed in the red bone marrow, which is located in the cancellous bone. 1 liter of blood contains 4.0-5.0×1012 erythrocytes. The total number of erythrocytes in an adult reaches 25×1012, and the surface area of ​​all erythrocytes is about 3800 m2. With a decrease in the number of red blood cells in the blood or a decrease in the amount of hemoglobin in red blood cells, the supply of oxygen to tissues is disrupted and anemia develops - anemia (see Fig. 2).

The duration of circulation of red blood cells in the blood is about 120 days, after which they are destroyed in the spleen and liver. The tissues of other organs are also capable of destroying red blood cells if necessary, as evidenced by the gradual disappearance of hemorrhages (bruises).

Leukocytes
Leukocytes (from the Greek. leukos- white) - cells with a nucleus of 10-15 microns in size, which can move independently. Leukocytes contain a large number of enzymes that can break down various substances. Unlike erythrocytes, which work while inside the blood vessels, leukocytes perform their functions directly in the tissues, where they enter through the intercellular gaps in the vessel wall. 1 liter of blood of an adult contains 4.0-9.0´109 leukocytes, the number may vary depending on the state of the organism.

There are several types of leukocytes. to the so-called granular leukocytes include neutrophilic, eosinophilic and basophilic leukocytes, non-granular- lymphocytes and monocytes. Leukocytes are formed in the red bone marrow, and non-granular leukocytes - also in the lymph nodes, spleen, tonsils, thymus (thymus gland). The life span of most leukocytes is from several hours to several months.

Neutrophilic leukocytes (neutrophils) make up 95% of granular leukocytes. They circulate in the blood for no more than 8-12 hours, and then migrate to the tissues. Neutrophils destroy bacteria and tissue breakdown products with their enzymes. The famous Russian scientist I.I. Mechnikov called the phenomenon of destruction of foreign bodies by leukocytes phagocytosis, and the leukocytes themselves - phagocytes. During phagocytosis, neutrophils die, and the enzymes they secrete destroy surrounding tissues, contributing to the formation of an abscess. Pus consists mainly of neutrophil residues and tissue breakdown products. The number of neutrophils in the blood increases sharply in acute inflammatory and infectious diseases.

Eosinophilic leukocytes (eosinophils)- This is about 5% of all leukocytes. Especially a lot of eosinophils in the intestinal mucosa and respiratory tract. These leukocytes are involved in the immune (defensive) reactions of the body. The number of eosinophils in the blood increases with helminthic invasions and allergic reactions.

Basophilic leukocytes make up about 1% of all leukocytes. Basophils produce biologically active substances heparin and histamine. Heparin of basophils prevents blood clotting in the focus of inflammation, and histamine dilates capillaries, which contributes to the processes of resorption and healing. Basophils also carry out phagocytosis and are involved in allergic reactions.

The number of lymphocytes reaches 25-40% of all leukocytes, but they prevail in the lymph. There are T-lymphocytes (formed in the thymus) and B-lymphocytes (formed in the red bone marrow). Lymphocytes perform important functions in immune responses.

Monocytes (1-8% of leukocytes) stay in the circulatory system for 2-3 days, after which they migrate to tissues, where they turn into macrophages and perform their main function - protecting the body from foreign substances (participate in immune reactions).

platelets
Platelets are small bodies of various shapes, 2-3 microns in size. Their number reaches 180.0-320.0´109 per 1 liter of blood. Platelets are involved in blood clotting and stopping bleeding. The life span of platelets is 5-8 days, after which they enter the spleen and lungs, where they are destroyed.

The most important defense mechanism that protects the body from blood loss. This is a stop of bleeding by the formation of a blood clot (thrombus), tightly clogging the hole in the damaged vessel. In a healthy person, bleeding when small vessels are injured stops within 1-3 minutes. When the wall of a blood vessel is damaged, platelets stick together and stick to the edges of the wound, biologically active substances are released from the platelets, which cause vasoconstriction.

With more significant damage, bleeding stops as a result of a complex multi-stage process of enzymatic chain reactions. Under the influence of external causes, blood coagulation factors are activated in damaged vessels: the plasma protein prothrombin, which is formed in the liver, turns into thrombin, which, in turn, causes the formation of insoluble fibrin from the soluble plasma protein fibrinogen. Fibrin threads form the main part of a thrombus, in which numerous blood cells get stuck (Fig. 3). The resulting thrombus clogs the injury site. Blood clotting occurs in 3-8 minutes, however, with some diseases, this time may increase or decrease.

Blood groups

Of practical interest is the knowledge of blood group. The division into groups is based on different types of combinations of erythrocyte antigens and plasma antibodies, which are a hereditary trait of blood and are formed at the initial stages of development of the organism.

It is customary to distinguish four main blood groups according to the AB0 system: 0 (I), A (II), B (III) and AB (IV), which is taken into account when it is transfused. In the middle of the 20th century, it was assumed that the blood of the 0 (I) Rh- group was compatible with any other groups. People with 0(I) blood group were considered universal donors, and their blood could be transfused to anyone in need, and they themselves - only blood of group I. People with IV blood group were considered universal recipients, they were injected with blood of any group, but their blood was given only to people with IV group.

Now in Russia, for health reasons and in the absence of blood components of the same group according to the AB0 system (with the exception of children), it is allowed to transfuse Rh-negative blood of the 0 (I) group to the recipient with any other blood group in an amount of up to 500 ml. In the absence of single-group plasma, the recipient may be transfused with group AB(IV) plasma.

If the blood groups of the donor and the recipient do not match, the erythrocytes of the transfused blood stick together and their subsequent destruction, which can lead to the death of the recipient.

In February 2012, US scientists, in collaboration with Japanese and French colleagues, discovered two new "additional" blood types that include two proteins on the surface of red blood cells - ABCB6 and ABCG2. They belong to transport proteins - they are involved in the transfer of metabolites, ions inside and out of the cell.

To date, more than 250 blood group antigens are known, combined into 28 additional systems in accordance with the patterns of their inheritance, most of which are much less common than AB0 and Rh factor.

Rh factor

When transfusing blood, the Rh factor (Rh factor) is also taken into account. Like blood groups, it was discovered by the Viennese scientist K. Landsteiner. This factor has 85% of people, their blood is Rh-positive (Rh +); others do not have this factor, their blood is Rh-negative (Rh-). The transfusion of the blood of a donor with Rh+ to a person with Rh- has severe consequences. The Rh factor is important for the health of the newborn and for re-pregnancy of an Rh-negative woman from an Rh-positive man.

Lymph

Lymph flows from the tissues through the lymphatic vessels, which are part of the cardiovascular system. Lymph is similar in composition to blood plasma, but contains fewer proteins. Lymph is formed from tissue fluid, which, in turn, arises due to the filtration of blood plasma from the blood capillaries.

Blood test

Blood tests are of great diagnostic value. The study of the blood picture is carried out according to many indicators, including the number of blood cells, the level of hemoglobin, the content of various substances in the plasma, etc. Each indicator, taken separately, is not specific in itself, but receives a certain value only in conjunction with other indicators and in connection with with the clinical picture of the disease. That is why every person repeatedly donates a drop of his blood for analysis during his life. Modern research methods allow, based on the study of this drop alone, to understand a lot in the state of human health.

The normal functioning of the cells of the body is possible only under the condition of the constancy of its internal environment. The true internal environment of the body is the intercellular (interstitial) fluid, which is in direct contact with the cells. However, the constancy of the intercellular fluid is largely determined by the composition of the blood and lymph, therefore, in a broad sense of the internal environment, its composition includes: intercellular fluid, blood and lymph, cerebrospinal, articular and pleural fluid. There is a constant exchange between the intercellular fluid and lymph, aimed at ensuring the continuous supply of necessary substances to the cells and the removal of their metabolic products from there.

The constancy of the chemical composition and physicochemical properties of the internal environment is called homeostasis.

homeostasis- this is the dynamic constancy of the internal environment, which is characterized by a set of relatively constant quantitative indicators, called physiological, or biological, constants. These constants provide optimal (best) conditions for the vital activity of body cells, and on the other hand, reflect its normal state.

The most important component of the internal environment of the body is blood. According to Lang, the concept of the blood system includes blood, the moral apparatus regulating its horn, as well as organs in which the formation and destruction of blood cells (bone marrow, lymph nodes, thymus gland, spleen and liver) take place.

Blood functions

Blood performs the following functions.

Transport function - is the transport of various substances (energy and information contained in them) and heat within the body by blood.

Respiratory function - blood carries respiratory gases - oxygen (0 2) and carbon dioxide (CO?) - both in physically dissolved and chemically bound form. Oxygen is delivered from the lungs to the cells of organs and tissues that consume it, and carbon dioxide, vice versa, from the cells to the lungs.

Nutritious function - the blood also carries blinking substances from the organs where they are absorbed or deposited to the place of their consumption.

Excretory (excretory) function - during the biological oxidation of nutrients, in addition to CO 2, other end products of metabolism (urea, uric acid) are formed in the cells, which are transported by the blood to the excretory organs: kidneys, lungs, sweat glands, intestines. Blood also transports hormones, other signaling molecules and biologically active substances.

Thermoregulating function - due to its high heat capacity, blood provides heat transfer and its redistribution in the body. About 70% of the heat generated in the internal organs is transferred by blood to the skin and lungs, which ensures the dissipation of heat by them into the environment.

Homeostatic function - blood is involved in water-salt metabolism in the body and ensures the maintenance of the constancy of its internal environment - homeostasis.

Protective the function is primarily to ensure immune responses, as well as the creation of blood and tissue barriers against foreign substances, microorganisms, defective cells of one's own body. The second manifestation of the protective function of blood is its participation in maintaining its liquid state of aggregation (fluidity), as well as stopping bleeding in case of damage to the walls of blood vessels and restoring their patency after repair of defects.

The blood system and its functions

The concept of blood as a system was created by our compatriot G.F. Lang in 1939. He included four parts in this system:

• peripheral blood circulating through the vessels;
• hematopoietic organs (red bone marrow, lymph nodes and spleen);
• blood-destroying organs;
• regulatory neurohumoral apparatus.

The blood system is one of the life support systems of the body and performs many functions:

• transport - circulating through the vessels, the blood performs a transport function, which determines a number of others;
• respiratory- binding and transfer of oxygen and carbon dioxide;
• trophic (nutritional) - blood provides all cells of the body with nutrients: glucose, amino acids, fats, minerals, water;
• excretory (excretory) - blood carries away from the tissues "slags" - the end products of metabolism: urea, uric acid and other substances removed from the body by excretory organs;
• thermoregulatory- blood cools energy-intensive organs and warms organs that lose heat. There are mechanisms in the body that ensure the rapid narrowing of the skin vessels with a decrease in ambient temperature and the expansion of blood vessels with an increase. This leads to a decrease or increase in heat loss, since the plasma consists of 90-92% of water and, as a result, has a high thermal conductivity and specific heat;
• homeostatic - blood maintains the stability of a number of homeostasis constants - osmotic pressure, etc .;
• security water-salt metabolism between blood and tissues - in the arterial part of the capillaries, liquid and salts enter the tissues, and in the venous part of the capillaries they return to the blood;
• protective - blood is the most important factor of immunity, i.e. protection of the body from living bodies and genetically alien substances. This is determined by the phagocytic activity of leukocytes (cellular immunity) and the presence of antibodies in the blood that neutralize microbes and their poisons (humoral immunity);
• humoral regulation - due to its transport function, blood provides chemical interaction between all parts of the body, i.e. humoral regulation. Blood carries hormones and other biologically active substances from the cells where they are formed to other cells;
• implementation of creative connections. Macromolecules carried by plasma and blood cells carry out intercellular information transfer, which provides regulation of intracellular processes of protein synthesis, preservation of the degree of cell differentiation, restoration and maintenance of tissue structure.

Blood, together with lymph and interstitial fluid, constitutes the internal environment of the body, in which the vital activity of all cells and tissues takes place.

Peculiarities:

1) is a liquid medium containing shaped elements;

2) is in constant motion;

3) constituent parts are mainly formed and destroyed outside of it.

Blood, together with hematopoietic and blood-destroying organs (bone marrow, spleen, liver and lymph nodes), makes up an integral blood system. The activity of this system is regulated by neurohumoral and reflex ways.

Thanks to the circulation in the vessels, blood performs the following important functions in the body:

14. Transport - the blood transports nutrients (glucose, amino acids, fats, etc.) to the cells, and the end products of metabolism (ammonia, urea, uric acid, etc.) - from them to the excretory organs.

15. Regulatory - carries out the transfer of hormones and other physiologically active substances that affect various organs and tissues; regulation of the constancy of body temperature - the transfer of heat from organs with its intensive formation to organs with less intense heat production and to places of cooling (skin).

16. Protective - due to the ability of leukocytes to phagocytosis and the presence of immune bodies in the blood, neutralizing microorganisms and their poisons, destroying foreign proteins.

17. Respiratory - delivery of oxygen from the lungs to the tissues, carbon dioxide - from the tissues to the lungs.

In an adult, the total amount of blood is 5-8% of body weight, which corresponds to 5-6 liters. The volume of blood is usually denoted in relation to body weight (ml / kg). On average, it is 61.5 ml/kg for men and 58.9 ml/kg for women.

Not all blood circulates in the blood vessels at rest. About 40-50% of it is in the blood depots (spleen, liver, blood vessels of the skin and lungs). Liver - up to 20%, spleen - up to 16%, subcutaneous vascular network - up to 10%

The composition of the blood. Blood consists of formed elements (55-58%) - erythrocytes, leukocytes and platelets - and a liquid part - plasma (42-45%).

red blood cells- specialized non-nuclear cells with a diameter of 7-8 microns. Formed in the red bone marrow, destroyed in the liver and spleen. There are 4–5 million erythrocytes in 1 mm3 of blood. The structure and composition of erythrocytes are determined by their function - gas transport. The shape of erythrocytes in the form of a biconcave disk increases contact with the environment, thereby contributing to the acceleration of gas exchange processes.

Hemoglobin has the ability to easily bind and split off oxygen. By attaching it, it becomes oxyhemoglobin. Giving oxygen in places with a low content, it turns into reduced (reduced) hemoglobin.

Skeletal and cardiac muscles contain muscle hemoglobin - myoglobin (an important role in supplying oxygen to working muscles).

Leukocytes, or white blood cells, according to morphological and functional features, are ordinary cells containing a nucleus and protoplasm of a specific structure. They are produced in the lymph nodes, spleen and bone marrow. In 1 mm 3 of human blood there are 5-6 thousand leukocytes.

Leukocytes are heterogeneous in their structure: in some of them, the protoplasm has a granular structure (granulocytes), in others there is no granularity (agronulocytes). Granulocytes make up 70-75% of all leukocytes and are divided depending on the ability to stain with neutral, acidic or basic dyes into neutrophils (60-70%), eosinophils (2-4%) and basophils (0.5-1%). Agranulocytes - lymphocytes (25-30%) and monocytes (4-8%).

Functions of leukocytes:

1) protective (phagocytosis, production of antibodies and destruction of toxins of protein origin);

2) participation in the breakdown of nutrients

platelets- plasma formations of oval or round shape with a diameter of 2-5 microns. In the blood of humans and mammals, they do not have a nucleus. Platelets are formed in the red bone marrow and in the spleen, and their number ranges from 200,000 to 600,000 per 1 mm3 of blood. They play an important role in the process of blood clotting.

The main function of leukocytes is immunogenesis (the ability to synthesize antibodies or immune bodies that neutralize microbes and their metabolic products). Leukocytes, having the ability to amoeboid movements, adsorb antibodies circulating in the blood and, penetrating through the walls of blood vessels, deliver them to the tissues to the foci of inflammation. Neutrophils, containing a large number of enzymes, have the ability to capture and digest pathogenic microbes (phagocytosis - from the Greek Phagos - devouring). The cells of the body are also digested, degenerating in the foci of inflammation.

Leukocytes are also involved in recovery processes after tissue inflammation.

Protecting the body from bleeding. This function is carried out due to the ability of blood to clot. The essence of blood coagulation is the transition of the fibrinogen protein dissolved in the plasma into an undissolved protein - fibrin, which forms threads glued to the edges of the wound. Blood clot. (thrombus) blocks further bleeding, protecting the body from blood loss.

The transformation of fibrogen into fibrin is carried out under the influence of the enzyme thrombin, which is formed from the prothrombin protein under the influence of thromboplastin, which appears in the blood when platelets are destroyed. The formation of thromboplastin and the conversion of prothrombin to thrombin proceed with the participation of calcium ions.

Blood groups. The doctrine of blood groups arose in connection with the problem of blood transfusion. In 1901, K. Landsteiner discovered agglutinogens A and B in human erythrocytes. Blood plasma contains agglutinins a and b (gamma globulins). According to the classification of K. Landsteiner and J. Jansky, depending on the presence or absence of agglutinogens and agglutinins in the blood of a particular person, 4 blood groups are distinguished. This system was called ABO. Blood groups in it are indicated by numbers and those agglutinogens that are contained in the erythrocytes of this group.

Group antigens are hereditary innate properties of blood that do not change throughout a person's life. There are no agglutinins in the blood plasma of newborns. They are formed during the first year of a child's life under the influence of substances supplied with food, as well as produced by the intestinal microflora, to those antigens that are not in his own erythrocytes.

Group I (O) - there are no agglutinogens in erythrocytes, plasma contains agglutinins a and b

Group II (A) - erythrocytes contain agglutinogen A, plasma - agglutinin b;

Group III (B) - agglutinogen B is in erythrocytes, agglutinin a is in plasma;

Group IV (AB) - agglutinogens A and B are found in erythrocytes, there are no agglutinins in plasma.

Among the inhabitants of Central Europe, blood type I occurs in 33.5%, group II - 37.5%, group III - 21%, group IV - 8%. 90% of Native Americans have I blood type. More than 20% of the population of Central Asia have III blood group.

Agglutination occurs when an agglutinogen with the same agglutinin occurs in the human blood: agglutinogen A with agglutinin a or agglutinogen B with agglutinin b. When incompatible blood is transfused, as a result of agglutination and their subsequent hemolysis, hemotransfusion shock develops, which can lead to death. Therefore, a rule was developed for the transfusion of small amounts of blood (200 ml), which took into account the presence of agglutinogens in the donor's erythrocytes and agglutinins in the recipient's plasma. Donor plasma was not taken into account because it was highly diluted with recipient plasma.

According to this rule, blood of group I can be transfused to people with all blood types (I, II, III, IV), therefore people with the first blood group are called universal donors. Blood of group II can be transfused to people with II and IY blood groups, blood of group III - with III and IV, Blood of group IV can only be transfused to people with the same blood type. At the same time, people with IV blood group can be transfused with any blood, so they are called universal recipients. If it is necessary to transfuse large amounts of blood, this rule cannot be used.