The structure and functions of blood. Erythropoiesis - what is it? Formed elements in blood plasma

Blood is a red liquid connective tissue that is constantly in motion and performs many complex and important functions for the body. It constantly circulates in the circulatory system and carries the gases and substances dissolved in it necessary for metabolic processes.

The structure of the blood

What is blood? This is a tissue that consists of plasma and special blood cells that are in it in the form of a suspension. Plasma is a clear yellowish liquid that makes up more than half of the total volume of blood. . It contains three main types of shaped elements:

  • erythrocytes - red cells that give the blood a red color due to the hemoglobin in them;
  • leukocytes - white cells;
  • platelets are platelets.

Arterial blood, which comes from the lungs to the heart and then spreads to all organs, is enriched with oxygen and has a bright scarlet color. After the blood gives oxygen to the tissues, it returns through the veins to the heart. Deprived of oxygen, it becomes darker.

AT circulatory system an adult human circulates about 4 to 5 liters of blood. Approximately 55% of the volume is occupied by plasma, the rest is accounted for by formed elements, while the majority are erythrocytes - more than 90%.

Blood is a viscous substance. Viscosity depends on the amount of proteins and red blood cells in it. This quality affects blood pressure and movement speed. The density of blood and the nature of the movement of formed elements determine its fluidity. Blood cells move in different ways. They can move in groups or singly. RBCs can move either individually or in whole "stacks", like stacked coins, as a rule, create a flow in the center of the vessel. White cells move singly and usually stay near the walls.

Plasma is a liquid component of a light yellow color, which is due to a small amount of bile pigment and other colored particles. Approximately 90% it consists of water and approximately 10% of organic matter and minerals dissolved in it. Its composition is not constant and varies depending on food taken, the amount of water and salts. The composition of substances dissolved in plasma is as follows:

  • organic - about 0.1% glucose, about 7% proteins and about 2% fats, amino acids, lactic and uric acid and others;
  • minerals make up 1% (anions of chlorine, phosphorus, sulfur, iodine and cations of sodium, calcium, iron, magnesium, potassium.

Plasma proteins take part in the exchange of water, distribute it between the tissue fluid and blood, give blood viscosity. Some of the proteins are antibodies and neutralize foreign agents. An important role is given to the soluble protein fibrinogen. He takes part in the process, turning under the influence of coagulation factors into insoluble fibrin.

In addition, there are hormones in plasma that are produced by glands. internal secretion, and other bioactive elements necessary for the functioning of body systems.

Plasma devoid of fibrinogen is called blood serum. You can read more about blood plasma here.

red blood cells

The most numerous blood cells, making up about 44-48% of its volume. They have the form of discs, biconcave in the center, with a diameter of about 7.5 microns. Cell Shape Provides Efficiency physiological processes. Due to the concavity, the surface area of ​​the sides of the erythrocyte increases, which is important for gas exchange. Mature cells do not contain nuclei. Main function erythrocytes - the delivery of oxygen from the lungs to the tissues of the body.

Their name is translated from Greek as "red". Red blood cells owe their color to a very complex protein, hemoglobin, which is able to bind with oxygen. Hemoglobin consists of a protein part called globin and a non-protein part (heme) containing iron. It is thanks to iron that hemoglobin can attach oxygen molecules.

Red blood cells are produced in the bone marrow. The term of their full maturation is approximately five days. The lifespan of red cells is about 120 days. RBC destruction occurs in the spleen and liver. Hemoglobin is broken down into globin and heme. What happens to globin is unknown, but iron ions are released from heme and return to Bone marrow and go to the production of new red blood cells. Heme without iron is converted into the bile pigment bilirubin, which enters the digestive tract with bile.

A decrease in the level leads to a condition such as anemia, or anemia.

Leukocytes

Colorless peripheral blood cells that protect the body from external infections and pathologically altered own cells. White bodies are divided into granular (granulocytes) and non-granular (agranulocytes). The former include neutrophils, basophils, eosinophils, which are distinguished by their reaction to different dyes. To the second - monocytes and lymphocytes. Granular leukocytes have granules in the cytoplasm and a nucleus consisting of segments. Agranulocytes are devoid of granularity, their nucleus usually has a regular rounded shape.

Granulocytes are produced in the bone marrow. After maturation, when granularity and segmentation are formed, they enter the blood, where they move along the walls, making amoeboid movements. They protect the body mainly from bacteria, are able to leave the vessels and accumulate in the foci of infections.

Monocytes are large cells that form in the bone marrow, lymph nodes, and spleen. Their main function is phagocytosis. Lymphocytes are small cells that are divided into three types (B-, T, O-lymphocytes), each of which performs its own function. These cells produce antibodies, interferons, macrophage activating factors, and kill cancer cells.

platelets

Small non-nuclear colorless plates, which are fragments of megakaryocyte cells located in the bone marrow. They can be oval, spherical, rod-shaped. Life expectancy is about ten days. The main function is participation in the process of blood coagulation. Platelets secrete substances that take part in a chain of reactions that are triggered when a blood vessel is damaged. As a result, the fibrinogen protein turns into insoluble fibrin strands, in which blood elements become entangled and a blood clot forms.

Blood functions

It is unlikely that anyone doubts that blood is necessary for the body, but why it is needed, perhaps not everyone can answer. This liquid tissue performs several functions, including:

  1. Protective. main role leukocytes, namely neutrophils and monocytes, play in protecting the body from infections and damage. They rush and accumulate at the site of damage. Their main purpose is phagocytosis, that is, the absorption of microorganisms. Neutrophils are microphages and monocytes are macrophages. Others - lymphocytes - produce antibodies against harmful agents. In addition, leukocytes are involved in the removal of damaged and dead tissues from the body.
  2. Transport. Blood supply affects almost all processes in the body, including the most important - respiration and digestion. With the help of blood, oxygen is transferred from the lungs to the tissues and carbon dioxide from the tissues to the lungs, organic substances from the intestines to the cells, end products, which are then excreted by the kidneys, transportation of hormones and other bioactive substances.
  3. Temperature regulation. Man needs blood to maintain constant temperature body, the norm of which is in a very narrow range - about 37 ° C.

Conclusion

Blood is one of the tissues of the body, which has a certain composition and performs a number of functions. essential functions. For normal life, it is necessary that all components are in the blood in optimal ratio. Changes in the composition of the blood, detected during the analysis, make it possible to identify the pathology at an early stage.

1. Blood is a liquid tissue that circulates through the vessels, carrying out transport various substances within the body and providing nutrition and metabolism of all cells of the body. The red color of blood is due to hemoglobin contained in erythrocytes.

In multicellular organisms, most cells do not have direct contact with the external environment; their vital activity is ensured by the presence internal environment(blood, lymph, tissue fluid). From it they receive the substances necessary for life and secrete metabolic products into it. The internal environment of the body is characterized by a relative dynamic constancy of composition and physico-chemical properties, which is called homeostasis. morphological substrate that regulates metabolic processes between blood and tissues and maintaining homeostasis, are histo-hematic barriers, consisting of capillary endothelium, basement membrane, connective tissue, cell lipoprotein membranes.

The concept of "blood system" includes: blood, hematopoietic organs (red bone marrow, lymph nodes, etc.), organs of blood destruction and regulatory mechanisms (regulating neurohumoral apparatus). The blood system is one of the most important life support systems of the body and performs many functions. Cardiac arrest and cessation of blood flow immediately leads the body to death.

Physiological functions of blood:

4) thermoregulatory - regulation of body temperature by cooling energy-intensive organs and warming organs that lose heat;

5) homeostatic - maintaining the stability of a number of homeostasis constants: pH, osmotic pressure, isoionic, etc.;

Leukocytes perform many functions:

1) protective - the fight against foreign agents; they phagocytize (absorb) foreign bodies and destroy them;

2) antitoxic - the production of antitoxins that neutralize the waste products of microbes;

3) the production of antibodies that provide immunity, i.e. immunity to infectious diseases;

4) participate in the development of all stages of inflammation, stimulate recovery (regenerative) processes in the body and accelerate wound healing;

5) enzymatic - they contain various enzymes necessary for the implementation of phagocytosis;

6) participate in the processes of blood coagulation and fibrinolysis by producing heparin, gnetamine, plasminogen activator, etc.;

7) are the central link immune system organism, carrying out the function of immune surveillance ("censorship"), protection from everything alien and maintaining genetic homeostasis (T-lymphocytes);

8) provide transplant rejection reaction, destruction of own mutant cells;

9) form active (endogenous) pyrogens and form a feverish reaction;

10) carry macromolecules with the information necessary to control the genetic apparatus of other body cells; through such intercellular interactions (creator connections), the integrity of the organism is restored and maintained.

4 . Platelet or platelet, - a shaped element involved in blood coagulation, necessary to maintain integrity vascular wall. It is a round or oval non-nuclear formation with a diameter of 2-5 microns. Platelets are formed in the red bone marrow from giant cells - megakaryocytes. In 1 μl (mm 3) of human blood, 180-320 thousand platelets are normally contained. An increase in the number of platelets in the peripheral blood is called thrombocytosis, a decrease is called thrombocytopenia. The life span of platelets is 2-10 days.

The main physiological properties of platelets are:

1) amoeboid mobility due to the formation of prolegs;

2) phagocytosis, i.e. absorption foreign bodies and microbes;

3) sticking to a foreign surface and gluing together, while they form 2-10 processes, due to which attachment occurs;

4) easy destructibility;

5) release and absorption of various biologically active substances such as serotonin, adrenaline, norepinephrine, etc.;

All these properties of platelets determine their participation in stopping bleeding.

Platelet Functions:

1) actively participate in the process of blood coagulation and dissolution blood clot(fibrinolysis);

2) participate in stopping bleeding (hemostasis) due to the biologically active compounds present in them;

3) perform protective function due to gluing (agglutination) of microbes and phagocytosis;

4) produce some enzymes (amylolytic, proteolytic, etc.) necessary for the normal functioning of platelets and for the process of stopping bleeding;

5) influence the state of histohematic barriers between blood and tissue fluid by changing the permeability of capillary walls;

6) carry out the transport of creative substances that are important for maintaining the structure of the vascular wall; Without interaction with platelets, the vascular endothelium undergoes dystrophy and begins to let red blood cells through itself.

Rate (reaction) of erythrocyte sedimentation(abbreviated as ESR) - an indicator that reflects changes in the physicochemical properties of blood and the measured value of the plasma column released from erythrocytes when they settle from a citrate mixture (5% sodium citrate solution) for 1 hour in a special pipette of the device T.P. Panchenkov.

Normally, ESR is equal to:

In men - 1-10 mm / hour;

In women - 2-15 mm / hour;

Newborns - from 2 to 4 mm / h;

Children of the first year of life - from 3 to 10 mm / h;

Children aged 1-5 years - from 5 to 11 mm / h;

Children 6-14 years old - from 4 to 12 mm / h;

Over 14 years old - for girls - from 2 to 15 mm / h, and for boys - from 1 to 10 mm / h.

in pregnant women before childbirth - 40-50 mm / hour.

An increase in ESR more than the indicated values ​​is, as a rule, a sign of pathology. The ESR value does not depend on the properties of erythrocytes, but on the properties of plasma, primarily on the content of large molecular proteins in it - globulins and especially fibrinogen. The concentration of these proteins increases in all inflammatory processes. During pregnancy, the content of fibrinogen before childbirth is almost 2 times higher than normal, so the ESR reaches 40-50 mm/hour.

Leukocytes have their own settling regime independent of erythrocytes. However, the leukocyte sedimentation rate in the clinic is not taken into account.

Hemostasis (Greek haime - blood, stasis - immobile state) is the stoppage of the movement of blood through a blood vessel, i.e. stop bleeding.

There are 2 mechanisms to stop bleeding:

1) vascular-platelet (microcirculatory) hemostasis;

2) coagulation hemostasis (blood clotting).

The first mechanism is capable of independently stopping bleeding from the most frequently injured small vessels with rather low blood pressure in a few minutes.

It consists of two processes:

1) vascular spasm, leading to a temporary stop or decrease in bleeding;

2) formation, compaction and reduction of platelet plug, leading to a complete stop of bleeding.

The second mechanism for stopping bleeding - blood coagulation (hemocoagulation) ensures the cessation of blood loss in case of damage to large vessels, mainly of the muscular type.

It is carried out in three phases:

I phase - the formation of prothrombinase;

Phase II - the formation of thrombin;

Phase III - the transformation of fibrinogen into fibrin.

In the mechanism of blood coagulation, in addition to the walls of blood vessels and uniform elements, 15 plasma factors: fibrinogen, prothrombin, tissue thromboplastin, calcium, proaccelerin, convertin, antihemophilic globulins A and B, fibrin stabilizing factor, prekallikrein (Fletcher factor), high molecular weight kininogen (Fitzgerald factor), etc.

Most of these factors are formed in the liver with the participation of vitamin K and are proenzymes related to the globulin fraction of plasma proteins. AT active form- enzymes they pass in the process of coagulation. Moreover, each reaction is catalyzed by an enzyme formed as a result of the previous reaction.

The trigger for blood clotting is the release of thromboplastin by damaged tissue and decaying platelets. Calcium ions are necessary for the implementation of all phases of the coagulation process.

A blood clot is formed by a network of insoluble fibrin fibers and entangled erythrocytes, leukocytes and platelets. The strength of the formed blood clot is provided by factor XIII, a fibrin-stabilizing factor (fibrinase enzyme synthesized in the liver). Blood plasma devoid of fibrinogen and some other substances involved in coagulation is called serum. And the blood from which fibrin is removed is called defibrinated.

The time of complete coagulation of capillary blood is normally 3-5 minutes, venous blood- 5-10 min.

In addition to the coagulation system, there are two more systems in the body at the same time: anticoagulant and fibrinolytic.

The anticoagulant system interferes with the processes of intravascular blood coagulation or slows down hemocoagulation. The main anticoagulant of this system is heparin, secreted from lung and liver tissues and produced by basophilic leukocytes and tissue basophils ( mast cells connective tissue). The number of basophilic leukocytes is very small, but all tissue basophils of the body have a mass of 1.5 kg. Heparin inhibits all phases of the blood coagulation process, inhibits the activity of many plasma factors and the dynamic transformation of platelets. Allocated salivary glands medicinal leeches gi-rudin has a depressing effect on the third stage of the blood coagulation process, i.e. prevents the formation of fibrin.

The fibrinolytic system is able to dissolve the formed fibrin and blood clots and is the antipode of the coagulation system. The main function of fibrinolysis is the splitting of fibrin and the restoration of the lumen of a vessel clogged with a clot. Cleavage of fibrin is carried out by the proteolytic enzyme plasmin (fibrinolysin), which is present in plasma as the proenzyme plasminogen. For its transformation into plasmin, there are activators contained in the blood and tissues, and inhibitors (Latin inhibere - restrain, stop) that inhibit the transformation of plasminogen into plasmin.

Violation of the functional relationships between the coagulation, anticoagulation and fibrinolytic systems can lead to serious illnesses: increased bleeding, intravascular thrombosis and even embolism.

Blood groups- a set of features that characterize antigenic structure erythrocytes and the specificity of anti-erythrocyte antibodies, which are taken into account when selecting blood for transfusions (lat. transfusio - transfusion).

In 1901, the Austrian K. Landsteiner and in 1903 the Czech J. Jansky discovered that when the blood of different people is mixed, erythrocytes often stick together - the phenomenon of agglutination (Latin agglutinatio - gluing) with their subsequent destruction (hemolysis ). It was found that erythrocytes contain agglutinogens A and B, glued substances of a glycolipid structure, and antigens. In plasma, agglutinins α and β, modified proteins of the globulin fraction, antibodies that stick together erythrocytes were found.

Agglutinogens A and B in erythrocytes, as well as agglutinins α and β in plasma, may be present alone or together, or absent in different people. Agglutinogen A and agglutinin α, as well as B and β are called of the same name. Bonding of erythrocytes occurs if the erythrocytes of the donor (of the person giving blood) meet with the same agglutinins of the recipient (of the person receiving blood), i.e. A + α, B + β or AB + αβ. From this it is clear that in the blood of each person there are opposite agglutinogen and agglutinin.

According to the classification of J. Jansky and K. Landsteiner, people have 4 combinations of agglutinogens and agglutinins, which are designated as follows: I (0) - αβ., II (A) - A β, W (V) - B α and IV(AB). From these designations it follows that in people of group 1, agglutinogens A and B are absent in erythrocytes, and both α and β agglutinins are present in plasma. In people of group II, erythrocytes have agglutinogen A, and plasma - agglutinin β. To III groups This includes people who have agglutinogen B in their erythrocytes and agglutinin α in their plasma. In people of group IV, erythrocytes contain both agglutinogens A and B, and there are no agglutinins in plasma. Based on this, it is not difficult to imagine which groups can be transfused with the blood of a certain group (Scheme 24).

As can be seen from the diagram, people of group I can only receive blood from this group. The blood of group I can be transfused to people of all groups. Therefore, people with blood group I are called universal donors. People with group IV can be transfused with blood of all groups, so these people are called universal recipients. Group IV blood can be transfused to people with group IV blood. The blood of people of II and III groups can be transfused to people with the same name, as well as with IV blood group.

However, at present in clinical practice only one-group blood is transfused, and in small quantities (no more than 500 ml), or the missing blood components are transfused (component therapy). This is due to the fact that:

firstly, during large massive transfusions, the donor agglutinins do not dilute, and they stick together the recipient's erythrocytes;

secondly, with a careful study of people with blood of group I, immune agglutinins anti-A and anti-B were found (in 10-20% of people); transfusion of such blood to people with other blood types causes severe complications. Therefore, people with blood group I, containing anti-A and anti-B agglutinins, are now called dangerous universal donors;

thirdly, many variants of each agglutinogen were revealed in the ABO system. Thus, agglutinogen A exists in more than 10 variants. The difference between them is that A1 is the strongest, while A2-A7 and other variants have weak agglutination properties. Therefore, the blood of such individuals may be erroneously assigned to group I, which can lead to blood transfusion complications when transfusing it to patients with groups I and III. Agglutinogen B also exists in several variants, the activity of which decreases in the order of their numbering.

In 1930, K. Landsteiner, speaking at the Nobel Prize ceremony for the discovery of blood groups, suggested that new agglutinogens would be discovered in the future, and the number of blood groups would grow until it reached the number of people living on earth . This assumption of the scientist turned out to be correct. To date, more than 500 different agglutinogens have been found in human erythrocytes. Only from these agglutinogens, more than 400 million combinations, or group signs of blood, can be made.

If we take into account all the other agglutinogens found in the blood, then the number of combinations will reach 700 billion, i.e. significantly more than people on the globe. This determines the amazing antigenic uniqueness, and in this sense, each person has his own blood type. These agglutinogen systems differ from the ABO system in that they do not contain natural agglutinins in plasma, similar to α- and β-agglutinins. But at certain conditions immune antibodies - agglutinins - can be produced to these agglutinogens. Therefore, it is not recommended to repeatedly transfuse a patient with blood from the same donor.

To determine blood groups, you need to have standard sera containing known agglutinins, or anti-A and anti-B coliclones containing diagnostic monoclonal antibodies. If you mix a drop of blood of a person whose group needs to be determined with the serum of groups I, II, III or with anti-A and anti-B coliclones, then by the onset of agglutination, you can determine his group.

Despite the simplicity of the method, in 7-10% of cases, the blood group is determined incorrectly, and incompatible blood is administered to patients.

To avoid such a complication, before a blood transfusion, it is necessary to carry out:

1) determination of the blood group of the donor and recipient;

2) Rh-affiliation of the blood of the donor and recipient;

3) test for individual compatibility;

4) a biological test for compatibility during transfusion: first, 10-15 ml of donor blood is poured in and then the patient's condition is monitored for 3-5 minutes.

Transfused blood always acts in many ways. In clinical practice, there are:

1) replacement action - replacement of lost blood;

2) immunostimulating effect - in order to stimulate the protective forces;

3) hemostatic (hemostatic) action - in order to stop bleeding, especially internal;

4) neutralizing (detoxifying) action - in order to reduce intoxication;

5) nutritional action - the introduction of proteins, fats, carbohydrates in an easily digestible form.

in addition to the main agglutinogens A and B, there may be other additional ones in erythrocytes, in particular the so-called Rh agglutinogen (Rhesus factor). It was first found in 1940 by K. Landsteiner and I. Wiener in the blood of a rhesus monkey. 85% of people have the same Rh agglutinogen in their blood. Such blood is called Rh-positive. Blood that lacks Rh agglutinogen is called Rh negative (in 15% of people). The Rh system has more than 40 varieties of agglutinogens - O, C, E, of which O is the most active.

A feature of the Rh factor is that people do not have anti-Rh agglutinins. However, if a person with Rh-negative blood is re-transfused with Rh-positive blood, then under the influence of the injected Rh agglutinogen, specific anti-Rh agglutinins and hemolysins are produced in the blood. In this case, transfusion of Rh-positive blood to this person can cause agglutination and hemolysis of red blood cells - there will be a hemotransfusion shock.

Rh factor is inherited and has special meaning for the course of pregnancy. For example, if the mother does not have an Rh factor, and the father does (the probability of such a marriage is 50%), then the fetus can inherit the Rh factor from the father and turn out to be Rh-positive. The blood of the fetus enters the mother's body, causing the formation of anti-Rh agglutinins in her blood. If these antibodies pass through the placenta back into the fetal blood, agglutination will occur. With a high concentration of anti-Rh agglutinins, fetal death and miscarriage can occur. In mild forms of Rh incompatibility, the fetus is born alive, but with hemolytic jaundice.

Rhesus conflict occurs only when high concentration anti-rhesus gglutinins. Most often, the first child is born normal, since the titer of these antibodies in the mother's blood increases relatively slowly (over several months). But at repeated pregnancy For an Rh-negative woman with an Rh-positive fetus, the threat of an Rh conflict increases due to the formation of new portions of anti-Rh agglutinins. Rh incompatibility during pregnancy is not very common: about one in 700 births.

To prevent Rh conflict, pregnant Rh-negative women are prescribed anti-Rh-gamma globulin, which neutralizes the Rh-positive antigens of the fetus.

Blood- a fluid that circulates in the circulatory system and carries gases and other dissolved substances necessary for metabolism or formed as a result of metabolic processes.

Blood is made up of plasma clear liquid pale yellow) and suspended in it cellular elements. There are three main types of blood cells: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (platelets). The red color of blood is determined by the presence of the red pigment hemoglobin in erythrocytes. In the arteries, through which the blood that has entered the heart from the lungs is transferred to the tissues of the body, hemoglobin is saturated with oxygen and is colored bright red; in the veins, through which blood flows from the tissues to the heart, hemoglobin is practically devoid of oxygen and darker in color.

Blood is a rather viscous liquid, and its viscosity is determined by the content of red blood cells and dissolved proteins. Blood viscosity largely determines the rate at which blood flows through the arteries (semi-elastic structures) and blood pressure. The fluidity of blood is also determined by its density and the nature of the movement of various types of cells. Leukocytes, for example, move singly, in close proximity to the walls of blood vessels; erythrocytes can move both individually and in groups, like stacked coins, creating an axial, i.e. concentrated in the center of the vessel, flow. The blood volume of an adult male is approximately 75 ml per kilogram of body weight; in an adult woman, this figure is approximately 66 ml. Accordingly, the total blood volume in an adult male is on average about 5 liters; more than half of the volume is plasma, and the rest is mainly erythrocytes.

Blood functions

The functions of the blood are much more complex than just the transport of nutrients and waste products of metabolism. The blood also carries hormones that control many vital functions. important processes; blood regulates body temperature and protects the body from damage and infection in any part of it.

Transport function of blood. Almost all processes related to digestion and respiration, two functions of the body, without which life is impossible, are closely related to blood and blood supply. The connection with respiration is expressed in the fact that the blood provides gas exchange in the lungs and transport of the corresponding gases: oxygen - from the lungs to the tissues, carbon dioxide (carbon dioxide) - from the tissues to the lungs. The transport of nutrients begins from the capillaries of the small intestine; here, the blood captures them from the digestive tract and transfers them to all organs and tissues, starting with the liver, where nutrients (glucose, amino acids, fatty acids) are modified, and the liver cells regulate their level in the blood depending on the needs of the body (tissue metabolism) . The transition of transported substances from the blood into tissues is carried out in tissue capillaries; at the same time, end products enter the blood from the tissues, which are then excreted through the kidneys with urine (for example, urea and uric acid). The blood also carries secretion products endocrine glands- hormones - and thus provides communication between various organs and coordination of their activities.

Body temperature regulation. Blood plays a key role in maintaining a constant body temperature in homeothermic or warm-blooded organisms. Temperature human body in the normal state, it fluctuates in a very narrow range of about 37 ° C. The release and absorption of heat by various parts of the body must be balanced, which is achieved by heat transfer through the blood. The center of temperature regulation is located in the hypothalamus diencephalon. This center, being highly sensitive to small changes in the temperature of the blood passing through it, regulates those physiological processes in which heat is released or absorbed. One mechanism is to regulate heat loss through the skin by changing the diameter of the skin blood vessels in the skin and, accordingly, the volume of blood flowing near the surface of the body, where heat is more easily lost. In case of infection certain products the vital activity of microorganisms or the products of tissue decay caused by them interact with leukocytes, causing the formation of chemicals that stimulate the temperature regulation center in the brain. As a result, there is a rise in body temperature, felt as heat.

Protecting the body from damage and infection. Two types of leukocytes play a special role in the implementation of this blood function: polymorphonuclear neutrophils and monocytes. They rush to the site of damage and accumulate near it, and most of these cells migrate from the bloodstream through the walls of nearby blood vessels. They are attracted to the place of damage chemical substances released damaged tissues. These cells are able to engulf bacteria and destroy them with their enzymes.

Thus, they prevent the spread of infection in the body.

Leukocytes are also involved in the removal of dead or damaged tissue. The process of absorption by a cell of a bacterium or a fragment of dead tissue is called phagocytosis, and the neutrophils and monocytes that carry it out are called phagocytes. An actively phagocytic monocyte is called a macrophage, and a neutrophil is called a microphage. In the fight against infection, an important role belongs to plasma proteins, namely immunoglobulins, which include many specific antibodies. Antibodies are formed by other types of leukocytes - lymphocytes and plasma cells, which are activated when specific antigens of a bacterial or viral origin(or present on cells foreign to the organism). It may take several weeks for lymphocytes to develop antibodies against an antigen that the body encounters for the first time, but the resulting immunity lasts for a long time. Although the level of antibodies in the blood begins to fall slowly after a few months, upon repeated contact with the antigen, it rises again rapidly. This phenomenon is called immunological memory. P

When interacting with an antibody, microorganisms either stick together or become more vulnerable to absorption by phagocytes. In addition, antibodies prevent the virus from entering the cells of the host body.

blood pH. pH is a measure of the concentration of hydrogen (H) ions, numerically equal to the negative logarithm (denoted Latin letter"p") of this value. The acidity and alkalinity of solutions are expressed in units of the pH scale, which ranges from 1 (strong acid) to 14 (strong alkali). Normally, the pH of arterial blood is 7.4, i.e. close to neutral. Venous blood is somewhat acidified due to the carbon dioxide dissolved in it: carbon dioxide (CO2), which is formed during metabolic processes, when dissolved in the blood, it reacts with water (H2O), forming carbonic acid (H2CO3).

Maintaining blood pH at a constant level, i.e., in other words, acid-base balance, is extremely important. So, if the pH drops noticeably, the activity of enzymes in the tissues decreases, which is dangerous for the body. A change in blood pH that goes beyond the range of 6.8-7.7 is incompatible with life. The maintenance of this indicator at a constant level is facilitated, in particular, by the kidneys, since they, as needed, remove acids or urea from the body (which gives alkaline reaction). On the other hand, pH is maintained by the presence in the plasma of certain proteins and electrolytes that have a buffering effect (ie, the ability to neutralize some excess acid or alkali).

Physico-chemical properties of blood. The density of whole blood depends mainly on the content of erythrocytes, proteins and lipids in it. The color of the blood changes from scarlet to dark red, depending on the ratio of oxygenated (scarlet) and non-oxygenated forms of hemoglobin, as well as the presence of hemoglobin derivatives - methemoglobin, carboxyhemoglobin, etc. The color of plasma depends on the presence of red and yellow pigments in it - mainly carotenoids and bilirubin, a large amount of which, in pathology, gives the plasma a yellow color. Blood is a colloid-polymer solution in which water is a solvent, salts and low-molecular organic plasma islands are dissolved substances, and proteins and their complexes are a colloidal component. On the surface of blood cells there is a double layer of electrical charges, consisting of negative charges firmly bound to the membrane and a diffuse layer of positive charges balancing them. Due to the double electric layer, an electrokinetic potential arises, which plays important role stabilization of cells, preventing their aggregation. With an increase in the ionic strength of the plasma due to the ingress of multiply charged positive ions into it, the diffuse layer shrinks and the barrier that prevents cell aggregation decreases. One of the manifestations of blood microheterogeneity is the phenomenon of erythrocyte sedimentation. It lies in the fact that in the blood outside the bloodstream (if its clotting is prevented), the cells settle (sediment), leaving a layer of plasma on top.

Erythrocyte sedimentation rate (ESR) increases with various diseases, mainly inflammatory nature, due to changes in the protein composition of the plasma. The sedimentation of erythrocytes is preceded by their aggregation with the formation of certain structures such as coin columns. ESR depends on how they are formed. The concentration of plasma hydrogen ions is expressed in terms of pH, i.e. negative logarithm of the activity of hydrogen ions. The average blood pH is 7.4. Maintenance of a constancy of this size big fiziol. value, since it determines the speed of so many chem. and fiz.-chem. processes in the body.

Normally, the pH of arterial K. 7.35-7.47 of venous blood is 0.02 lower, the content of erythrocytes usually has a 0.1-0.2 more acidic reaction than plasma. One of the most important properties of blood - fluidity - is the subject of study of biorheology. In the bloodstream, blood normally behaves like a non-Newtonian fluid, changing its viscosity depending on the flow conditions. As a result, blood viscosity large vessels and capillaries differs significantly, and the data on viscosity given in the literature are conditional. The patterns of blood flow (blood rheology) are not well understood. The non-Newtonian behavior of blood is explained by the high volumetric concentration of blood cells, their asymmetry, the presence of proteins in the plasma, and other factors. Measured on capillary viscometers (with a capillary diameter of a few tenths of a millimeter), the viscosity of blood is 4-5 times higher than the viscosity of water.

With pathology and injuries, blood fluidity changes significantly due to the action of certain factors of the blood coagulation system. Basically, the work of this system consists in the enzymatic synthesis of a linear polymer - fabrin, which forms a network structure and gives blood the properties of a jelly. This “jelly” has a viscosity that is hundreds and thousands higher than the viscosity of blood in a liquid state, exhibits strength properties and high adhesive ability, which allows the clot to stay on the wound and protect it from mechanical damage. The formation of clots on the walls of blood vessels in case of imbalance in the coagulation system is one of the causes of thrombosis. The formation of a fibrin clot is prevented by the anticoagulant system of blood; the destruction of the formed clots occurs under the action of the fibrinolytic system. The resulting fibrin clot initially has a loose structure, then becomes denser, and the clot is retracted.

Blood components

Plasma. After the separation of cellular elements suspended in the blood remains water solution complex composition called plasma. As a rule, plasma is a clear or slightly opalescent liquid, yellowish color which is determined by the presence in it of a small amount of bile pigment and other colored organic substances. However, after the consumption of fatty foods, many droplets of fat (chylomicrons) enter the bloodstream, as a result of which the plasma becomes cloudy and oily. Plasma is involved in many life processes of the body. It carries blood cells, nutrients and metabolic products and serves as a link between all extravascular (i.e. outside the blood vessels) fluids; the latter include, in particular, the intercellular fluid, and through it communication with the cells and their contents is carried out.

Thus, the plasma contacts with the kidneys, liver and other organs and thereby maintains the constancy of the internal environment of the body, i.e. homeostasis. The main plasma components and their concentrations are given in the table. Among the substances dissolved in the plasma are low molecular weight organic compounds (urea, uric acid, amino acids, etc.); large and very complex protein molecules; partially ionized inorganic salts. The most important cations (positively charged ions) are sodium (Na+), potassium (K+), calcium (Ca2+) and magnesium (Mg2+) cations; the most important anions (negatively charged ions) are chloride anions (Cl-), bicarbonate (HCO3-) and phosphate (HPO42- or H2PO4-). The main protein components of plasma are albumin, globulins and fibrinogen.

Plasma proteins. Of all proteins, albumin, synthesized in the liver, is present in the highest concentration in plasma. It is necessary to maintain osmotic balance, which ensures the normal distribution of fluid between the blood vessels and the extravascular space. With starvation or insufficient intake of proteins from food, the content of albumin in plasma falls, which can lead to increased accumulation of water in the tissues (edema). This condition associated with protein deficiency is called starvation edema. There are several types or classes of globulins in plasma, the most important of which are denoted by the Greek letters a (alpha), b (beta) and g (gamma), and the corresponding proteins are a1, a2, b, g1 and g2. After separation of globulins (by electrophoresis), antibodies are found only in fractions g1, g2 and b. Although antibodies are often referred to as gamma globulins, the fact that some of them are also present in the b-fraction led to the introduction of the term "immunoglobulin". The a- and b-fractions contain many different proteins that ensure the transport of iron, vitamin B12, steroids and other hormones in the blood. This group of proteins also includes coagulation factors, which, along with fibrinogen, are involved in the process of blood coagulation. The main function of fibrinogen is to form blood clots (thrombi). In the process of blood clotting, whether in vivo (in a living organism) or in vitro (outside the body), fibrinogen is converted to fibrin, which forms the basis of a blood clot; fibrinogen-free plasma, usually a clear, pale yellow liquid, is called blood serum.

red blood cells. Red blood cells, or erythrocytes, are round discs with a diameter of 7.2-7.9 microns and medium thickness 2 µm (µm = micron = 1/106 m). 1 mm3 of blood contains 5-6 million erythrocytes. They make up 44-48% of the total blood volume. Erythrocytes have the shape of a biconcave disc, i.e. the flat sides of the disc are sort of compressed, making it look like a donut without a hole. Mature erythrocytes do not have nuclei. They contain mainly hemoglobin, the concentration of which in the intracellular aqueous medium is about 34%. [In terms of dry weight, the hemoglobin content in erythrocytes is 95%; per 100 ml of blood, the hemoglobin content is normally 12-16 g (12-16 g%), and in men it is slightly higher than in women.] In addition to hemoglobin, erythrocytes contain dissolved inorganic ions (mainly K +) and various enzymes. The two concave sides provide the erythrocyte with an optimal surface area through which the exchange of gases, carbon dioxide and oxygen, can take place.

Thus, the shape of cells largely determines the efficiency of physiological processes. In humans, the surface area through which gas exchange takes place averages 3820 m2, which is 2000 times the surface of the body. In the fetus, primitive red blood cells are first formed in the liver, spleen, and thymus. From the fifth month prenatal development in the bone marrow, erythropoiesis gradually begins - the formation of full-fledged red blood cells. In exceptional circumstances (for example, when normal bone marrow is replaced by cancerous tissue), the adult body can again switch to the formation of red blood cells in the liver and spleen. However, in normal conditions erythropoiesis in an adult occurs only in flat bones (ribs, sternum, pelvic bones, skull and spine).

Erythrocytes develop from precursor cells, the source of which is the so-called. stem cells. In the early stages of erythrocyte formation (in cells still in the bone marrow), the cell nucleus is clearly identified. As the cell matures, hemoglobin accumulates, which is formed during enzymatic reactions. Before entering the bloodstream, the cell loses its nucleus - due to extrusion (squeezing out) or destruction by cellular enzymes. With significant blood loss, erythrocytes are formed faster than normal, and in this case, immature forms, containing the nucleus; apparently this is due to the fact that the cells leave the bone marrow too quickly.

The period of maturation of erythrocytes in the bone marrow - from the moment the youngest cell, recognizable as a precursor of an erythrocyte, to its full maturation - is 4-5 days. The life span of a mature erythrocyte in peripheral blood is an average of 120 days. However, with some anomalies of these cells themselves, a number of diseases, or under the influence of certain medicines the life span of erythrocytes may be shortened. Most of red blood cells are destroyed in the liver and spleen; in this case, hemoglobin is released and decomposed into its constituent heme and globin. Further fate globin was not traced; as for heme, iron ions are released (and returned to the bone marrow) from it. Losing iron, heme turns into bilirubin, a red-brown bile pigment. After minor modifications occurring in the liver, bilirubin in the bile is excreted through the gallbladder into the digestive tract. According to the content of the end product of its transformations in the feces, it is possible to calculate the rate of destruction of erythrocytes. On average, in an adult body, 200 billion red blood cells are destroyed and re-formed daily, which is approximately 0.8% of their total number (25 trillion).

Hemoglobin. The main function of the erythrocyte is to transport oxygen from the lungs to the tissues of the body. A key role in this process is played by hemoglobin, an organic red pigment consisting of heme (a compound of porphyrin with iron) and globin protein. Hemoglobin has a high affinity for oxygen, due to which the blood is able to carry much more oxygen than a normal aqueous solution.

The degree of oxygen binding to hemoglobin depends primarily on the concentration of oxygen dissolved in the plasma. In the lungs, where there is a lot of oxygen, it diffuses from the pulmonary alveoli through the walls of blood vessels and the aqueous plasma environment and enters the red blood cells; where it binds to hemoglobin to form oxyhemoglobin. In tissues where the oxygen concentration is low, oxygen molecules are separated from hemoglobin and penetrate into tissues by diffusion. Insufficiency of erythrocytes or hemoglobin leads to a decrease in oxygen transport and thereby to a violation biological processes in tissues. In humans, fetal hemoglobin (type F, from fetus - fetus) and adult hemoglobin (type A, from adult - adult) are distinguished. Many genetic variants of hemoglobin are known, the formation of which leads to abnormalities of red blood cells or their function. Among them, hemoglobin S is the most well-known, causing sickle cell anemia.

Leukocytes. White cells of peripheral blood, or leukocytes, are divided into two classes depending on the presence or absence of special granules in their cytoplasm. Cells that do not contain granules (agranulocytes) are lymphocytes and monocytes; their nuclei are predominantly regular round in shape. Cells with specific granules (granulocytes) are characterized, as a rule, by the presence of irregularly shaped nuclei with many lobes and are therefore called polymorphonuclear leukocytes. They are divided into three varieties: neutrophils, basophils and eosinophils. They differ from each other in the pattern of staining of granules with different dyes. In a healthy person, 1 mm3 of blood contains from 4,000 to 10,000 leukocytes (about 6,000 on average), which is 0.5-1% of the blood volume. Ratio certain types cells in the composition of leukocytes can vary significantly in different people and even in the same person at different times.

Polymorphonuclear leukocytes(neutrophils, eosinophils and basophils) are formed in the bone marrow from progenitor cells that originate from stem cells, probably the same ones that give rise to erythrocyte precursors. As the nucleus matures, granules appear in the cells, typical for each type of cell. In the bloodstream, these cells move along the walls of the capillaries primarily due to amoeboid movements. Neutrophils are able to leave inner space vessel and accumulate at the site of infection. The life span of granulocytes appears to be about 10 days, after which they are destroyed in the spleen. The diameter of neutrophils is 12-14 microns. Most dyes stain their core in purple; the nucleus of peripheral blood neutrophils can have from one to five lobes. The cytoplasm stains pinkish; under a microscope, many intense pink granules can be distinguished in it. In women, approximately 1% of neutrophils carry sex chromatin (formed by one of the two X chromosomes), a drumstick-shaped body attached to one of the nuclear lobes. These so-called. Barr bodies allow sex determination in the study of blood samples. Eosinophils are similar in size to neutrophils. Their nucleus rarely has more than three lobes, and the cytoplasm contains many large granules that are clearly stained bright red with eosin dye. Unlike eosinophils in basophils, cytoplasmic granules are stained blue with basic dyes.

Monocytes. The diameter of these non-granular leukocytes is 15-20 microns. The nucleus is oval or bean-shaped, and only in a small part of the cells is it divided into large lobes that overlap each other. The cytoplasm is bluish-gray when stained, contains a small number of inclusions, stained with azure dye in a blue-violet color. Monocytes are produced both in the bone marrow and in the spleen and lymph nodes. Their main function is phagocytosis.

Lymphocytes. These are small mononuclear cells. Most peripheral blood lymphocytes are less than 10 µm in diameter, but lymphocytes with a larger diameter (16 µm) are occasionally found. Cell nuclei are dense and round, the cytoplasm is bluish in color, with very rare granules. Despite the fact that lymphocytes look morphologically homogeneous, they clearly differ in their functions and properties. cell membrane. They are divided into three broad categories: B cells, T cells, and O cells (null cells, or neither B nor T). B-lymphocytes mature in the human bone marrow, after which they migrate to the lymphoid organs. They serve as precursors to cells that form antibodies, the so-called. plasma. In order for B cells to transform into plasma cells, the presence of T cells is required. T-cell maturation begins in the bone marrow, where prothymocytes are formed, which then migrate to the thymus (thymus gland), an organ located in the chest behind the sternum. There they differentiate into T-lymphocytes - a highly heterogeneous population of immune system cells that perform various functions. Thus, they synthesize macrophage activating factors, B-cell growth factors and interferons. Among T cells, there are inductor (helper) cells that stimulate the production of antibodies by B cells. There are also suppressor cells that suppress the functions of B-cells and synthesize the growth factor of T-cells - interleukin-2 (one of the lymphokines). O cells differ from B and T cells in that they do not have surface antigens. Some of them serve as "natural killers", ie. kill cancer cells and cells infected with the virus. However, in general, the role of 0-cells is unclear.

platelets are colorless, nuclear-free bodies of spherical, oval or rod-shaped shape with a diameter of 2-4 microns. Normally, the content of platelets in peripheral blood is 200,000-400,000 per 1 mm3. Their life expectancy is 8-10 days. With standard dyes (azure-eosin), they are stained in a uniform pale pink color. Using electron microscopy, it was shown that platelets are similar to ordinary cells in the structure of the cytoplasm; however, in fact, they are not cells, but fragments of the cytoplasm of very large cells (megakaryocytes) present in the bone marrow. Megakaryocytes are descended from the same stem cells that give rise to erythrocytes and leukocytes. As will be shown in next section Platelets play a key role in blood clotting. Bone marrow damage from drugs, ionizing radiation, or cancer can lead to a significant decrease in the content of platelets in the blood, which causes spontaneous hematomas and bleeding.

blood clotting Blood clotting, or coagulation, is the process of converting liquid blood into an elastic clot (thrombus). Blood clotting at the site of injury is a vital reaction to stop bleeding. However, the same process also underlies vascular thrombosis - an extremely unfavorable phenomenon in which there is a complete or partial blockage of their lumen, which prevents blood flow.

Hemostasis (stop bleeding). When a thin or even medium blood vessel is damaged, for example, when tissue is cut or squeezed, internal or external bleeding (hemorrhage) occurs. As a rule, bleeding stops due to the formation of a blood clot at the site of injury. A few seconds after injury, the lumen of the vessel contracts in response to the action of released chemicals and nerve impulses. When the endothelial lining of the blood vessels is damaged, the collagen underlying the endothelium is exposed, on which platelets circulating in the blood quickly adhere. They release chemicals that cause vasoconstriction (vasoconstrictors). Platelets also secrete other substances that are involved in a complex chain of reactions leading to the conversion of fibrinogen (a soluble blood protein) into insoluble fibrin. Fibrin forms a blood clot, the threads of which capture blood cells. One of the most important properties of fibrin is its ability to polymerize to form long fibers that contract and push the blood serum out of the clot.

Thrombosis- abnormal blood clotting in the arteries or veins. As a result of arterial thrombosis, the blood supply to the tissues worsens, which causes their damage. This occurs with myocardial infarction caused by thrombosis of the coronary artery, or with a stroke caused by thrombosis of cerebral vessels. Venous thrombosis prevents the normal outflow of blood from the tissues. When does clot blockage occur? large vein, near the site of blockage, edema occurs, which sometimes spreads, for example, to the entire limb. It happens that part of the venous thrombus breaks off and enters the bloodstream in the form of a moving clot (embolus), which over time can end up in the heart or lungs and lead to a life-threatening circulatory disorder.

Several factors predisposing to intravascular thrombosis have been identified; These include:

  1. slowing of venous blood flow due to low physical activity;
  2. vascular changes caused by increased blood pressure;
  3. local compaction inner surface blood vessels due to inflammatory processes or - in the case of arteries - due to the so-called. atheromatosis (deposits of lipids on the walls of arteries);
  4. increased blood viscosity due to polycythemia ( high content in the blood of erythrocytes);
  5. an increase in the number of platelets in the blood.

Studies have shown that the last of these factors plays a special role in the development of thrombosis. The fact is that a number of substances contained in platelets stimulate the formation of a blood clot, and therefore any effects causing damage platelets can speed up this process. When damaged, the surface of platelets becomes more sticky, which leads to their connection with each other (aggregation) and the release of their contents. The endothelial lining of blood vessels contains the so-called. prostacyclin, which inhibits the release of a thrombogenic substance, thromboxane A2, from platelets. Other plasma components also play an important role, preventing thrombosis in the vessels by suppressing a number of enzymes of the blood coagulation system. Attempts to prevent thrombosis have so far yielded only partial results. Preventive measures include regular exercise, lowering high blood pressure, and treatment with anticoagulants; It is recommended to start walking as soon as possible after surgery. It should be noted that even a small dose of aspirin daily (300 mg) reduces platelet aggregation and significantly reduces the likelihood of thrombosis.

Blood transfusion Since the late 1930s, the transfusion of blood or its individual fractions has become widespread in medicine, especially in the military. The main purpose of blood transfusion (hemotransfusion) is to replace the patient's red blood cells and restore blood volume after massive blood loss. The latter can occur either spontaneously (for example, with a duodenal ulcer), or as a result of trauma, during surgery, or during childbirth. Blood transfusion is also used to restore the level of red blood cells in some anemias, when the body loses the ability to produce new blood cells at the rate required for normal functioning. The general opinion of reputable physicians is that blood transfusion should be performed only in case of strict necessity, since it is associated with the risk of complications and the transmission of an infectious disease to the patient - hepatitis, malaria or AIDS.

Blood typing. Before transfusion, the compatibility of the blood of the donor and the recipient is determined, for which blood typing is performed. Currently typing is being done qualified specialists. A small amount of erythrocytes is added to an antiserum containing a large amount of antibodies to certain erythrocyte antigens. Antiserum is obtained from the blood of donors specially immunized with the appropriate blood antigens. Agglutination of erythrocytes is observed with the naked eye or under a microscope. The table shows how anti-A and anti-B antibodies can be used to determine the blood groups of the AB0 system. As an additional in vitro test, you can mix the donor's erythrocytes with the recipient's serum, and vice versa, the donor's serum with the recipient's erythrocytes - and see if there is any agglutination. This test is called cross-typing. If, when mixing the erythrocytes of the donor and the recipient's serum, it agglutinates at least a small amount of cells, blood is considered incompatible.

Blood transfusion and storage. The original methods of direct blood transfusion from a donor to a recipient are a thing of the past. Today donated blood taken from a vein under sterile conditions in specially prepared containers, where an anticoagulant and glucose have been previously added (the latter is used as a nutrient medium for erythrocytes during storage). Of the anticoagulants, sodium citrate is most often used, which binds calcium ions in the blood, which are necessary for blood clotting. Liquid blood is stored at 4°C for up to three weeks; during this time, 70% of the original number of viable erythrocytes remains. Since this level of live red blood cells is considered the minimum acceptable, blood that has been stored for more than three weeks is not used for transfusion. Due to the growing need for blood transfusion, methods have emerged to preserve the viability of red blood cells for a longer time. In the presence of glycerol and other substances, erythrocytes can be stored for an arbitrarily long time at a temperature from -20 to -197 ° C. For storage at -197 ° C, metal containers with liquid nitrogen are used, into which containers with blood are immersed. Frozen blood is successfully used for transfusion. Freezing allows not only to create stocks of ordinary blood, but also to collect and store rare blood groups in special blood banks (repositories).

Previously, blood was stored in glass containers, but now it is mostly plastic containers that are used for this purpose. One of the main advantages of a plastic bag is that several bags can be attached to a single container of anticoagulant, and then all three cell types and plasma can be separated from the blood using differential centrifugation in a “closed” system. This very important innovation fundamentally changed the approach to blood transfusion.

Today they are already talking about component therapy, when transfusion means the replacement of only those blood elements that the recipient needs. Most anemic people need only whole red blood cells; patients with leukemia require mainly platelets; Patients with hemophilia need only certain components of plasma. All of these fractions can be isolated from the same donated blood, leaving only albumin and gamma globulin (both have their uses). Whole blood is used only to compensate for very large blood loss, and is now used for transfusion in less than 25% of cases.

blood banks. In all developed countries, a network of blood transfusion stations has been created that provide civilian medicine. necessary quantity blood for transfusion. At the stations, as a rule, they only collect donated blood, and store it in blood banks (storages). The latter provide blood at the request of hospitals and clinics desired group. In addition, they usually have a special service that collects both plasma and individual fractions (for example, gamma globulin) from expired whole blood. Many banks also have qualified specialists who carry out complete blood typing and study possible reactions incompatibility.

Blood formation is called hematopoiesis. Hematopoiesis in humans is carried out by hematopoietic organs, primarily by the myeloid tissue of the red bone marrow. Some of the lymphocytes develop in the lymph nodes, spleen, thymus(thymus), which, together with the red bone marrow, form a system of hematopoietic organs.

The precursors of all blood cells are pluripotent hematopoietic stem cells of the bone marrow, which can differentiate in two ways: into precursors of myeloid cells (myelopoiesis) and precursors of lymphoid cells (lymphopoiesis).

Myelopoiesis
With myelopoiesis (myelopoesis; myelo- + Greek poiesis production, formation), all blood cells are formed in the bone marrow, except for lymphocytes. Myelopoiesis occurs in myeloid tissue located in the epiphyses of tubular and cavities of many spongy bones. The tissue in which myelopoiesis occurs is called myeloid tissue.

The precursors of leukoid cells, passing through several stages of differentiation, form leukocytes of various types (lymphopoiesis), in the case of myelopoiesis, differentiation leads to the formation of erythrocytes, granulocytes, monocytes and platelets. A feature of human myelopoiesis is a change in the karyotype of cells in the process of differentiation, for example, the precursors of platelets are polyploid megakaryocytes, and erythroblasts lose their nuclei when transformed into erythrocytes.

Lymphopoiesis
Lymphopoiesis occurs in the lymph nodes, spleen, thymus, and bone marrow.

Blood is created in the bone marrow.

Blood in the human body is a transport system, it carries nutrients and oxygen from one organ to another, ensures the removal of "waste" and toxins, and is involved in protection against infections. Therefore, all changes in the human condition - slight inflammation, malnutrition, fatigue, various diseases- immediately reflected in the composition of the blood. A blood test can be used to judge the functioning of the liver, immune system, spleen and many other organs. Before starting a course of treatment, the doctor always sends the patient to a blood test to find out the cause of the disease.

Bone marrow - the most important body hematopoietic system, carrying out hematopoiesis, or hematopoiesis - the process of creating new blood cells to replace those that die and die. It is also one of the organs of immunopoiesis. For the human immune system, the bone marrow, together with peripheral lymphoid organs, is a functional analogue of the so-called bursa of Fabricius found in birds.

The bone marrow is the only tissue of an adult organism that normally contains a large number of immature, undifferentiated and poorly differentiated cells, the so-called stem cells, similar in structure to embryonic cells. All other immature cells, such as immature skin cells, still have a greater degree of differentiation and maturity than bone marrow cells, and already have a given specialization.

The red, or hematopoietic, bone marrow in humans is located mainly inside the pelvic bones and, to a lesser extent, inside the epiphyses of long bones and, to an even lesser extent, inside the vertebral bodies. Normally, it is protected by an immunological tolerance barrier to prevent the destruction of immature and maturing cells by the body's own lymphocytes. In violation of the immunological tolerance of lymphocytes to bone marrow cells, autoimmune cytopenias develop, in particular autoimmune thrombocytopenia, autoimmune leukopenia, and even aplastic anemia. [source not specified 171 days]

The red bone marrow is made up of fibrous tissue stroma and hematopoietic tissue proper. In the hematopoietic tissue of the bone marrow, several sprouts of hematopoiesis are isolated (also called lines, English cell lines), the number of which increases with maturation. There are five mature lineages in the red bone marrow: erythrocyte, granulocytic, lymphocytic, monocytic, and macrophage. Each of these roskov gives, respectively, the following cells and post-cellular elements: erythrocytes; eosinophils, neutrophils and basophils; lymphocytes; monocytes; platelets.

The development of germs of hematopoiesis is a complex process of cell differentiation. The ancestors of all sprouts are called pluripotent cells for their ability to differentiate into cells of all sprouts of hematopoiesis under the action of cytokines. Also, these cells are called colony-forming elements (CFE) for their local location in the bone marrow. The number of pluripotent stem cells, that is, cells that are the very first precursors in a series of hematopoietic cells, is limited in the bone marrow, and they cannot multiply, maintaining pluripotency, and thereby restore their numbers. For at the very first division, a pluripotent cell chooses the path of development, and its daughter cells become either multipotent cells, in which the choice is more limited (only into erythrocyte or leukocyte sprouts), or megakaryoblasts and then megakaryocytes - cells from which platelets are detached.

What is blood, everyone knows. We see it when we injure the skin, for example, if we cut or prick. We know it's thick and red. But what is blood made of? Not everyone knows this. Meanwhile, its composition is complex and heterogeneous. It's not just red liquid. It is not the plasma that gives it its color, but the shaped particles that are in it. Let's see what our blood is.

What is blood made of?

The entire volume of blood in the human body can be divided into two parts. Of course, this division is conditional. The first part is peripheral, that is, the one that flows in the arteries, veins and capillaries, the second is the blood located in the hematopoietic organs and tissues. Naturally, it constantly circulates through the body, and therefore this division is formal. Human blood consists of two components - plasma and shaped particles that are in it. These are erythrocytes, leukocytes and platelets. They differ from each other not only in structure, but also in their function in the body. Some particles more, some less. In addition to uniform components, various antibodies and other particles are found in human blood. Normally, blood is sterile. But with pathological processes of an infectious nature, bacteria and viruses can be found in it. So, what does blood consist of, and what are the ratios of these components? This question has long been studied, and science has accurate data. In an adult, the volume of the plasma itself is from 50 to 60%, and of the formed components - from 40 to 50% of all blood. Is it important to know? Of course, knowing the percentage of erythrocytes or one can assess the state of human health. The ratio of formed particles to the total volume of blood is called hematocrit. Most often, it does not focus on all components, but only on red blood cells. This indicator is determined using a graduated glass tube into which blood is placed and centrifuged. In this case, heavy components sink to the bottom, while the plasma, on the contrary, rises up. It's like the blood is shedding. After that, laboratory assistants can only calculate what part is occupied by one or another component. In medicine, such analyzes are widely used. Currently they are made on automatic

blood plasma

Plasma is the liquid component of the blood, which contains suspended cells, proteins and other compounds. Through it they are delivered to organs and tissues. What it consists of About 85% is water. The remaining 15% are organic and inorganic substances. There are also gases in the blood plasma. This, of course, carbon dioxide and oxygen. It accounts for 3-4%. These are anions (PO 4 3-, HCO 3-, SO 4 2-) and cations (Mg 2+, K +, Na +). Organic substances (approximately 10%) are divided into nitrogen-free (cholesterol, glucose, lactate, phospholipids) and nitrogen-containing substances (amino acids, proteins, urea). Also, biologically active substances are found in the blood plasma: enzymes, hormones and vitamins. They account for about 1%. From the point of view of histology, plasma is nothing more than an intercellular fluid.

red blood cells

So, what is human blood made of? In addition to plasma, it also contains shaped particles. Red blood cells, or erythrocytes, is perhaps the most numerous group of these components. Erythrocytes in a mature state do not have a nucleus. In shape, they resemble biconcave discs. The period of their life is 120 days, after which they are destroyed. It occurs in the spleen and liver. Red blood cells contain an important protein - hemoglobin. It plays a key role in the process of gas exchange. In these particles, oxygen is transported and it is the protein hemoglobin that makes the blood red.

platelets

What does human blood consist of, besides plasma and red blood cells? It contains platelets. They have great importance. These small diameters of only 2-4 micrometers play a crucial role in thrombosis and homeostasis. Platelets are disc-shaped. They circulate freely in the bloodstream. But their distinguishing feature is the ability to sensitively respond to vascular damage. This is their main function. When the wall of a blood vessel is injured, they, connecting with each other, “close up” the damage, forming a very dense clot that prevents blood from flowing out. Platelets are formed after the fragmentation of their larger megakaryocyte precursors. They are in the bone marrow. In total, up to 10 thousand platelets are formed from one megakaryocyte. This is quite a large number. The lifespan of platelets is 9 days. Of course, they can last even less, as they die during the clogging of the damage in the blood vessel. Old platelets are broken down in the spleen by phagocytosis and in the liver by Kupffer cells.

Leukocytes

White blood cells, or leukocytes, are agents of the body's immune system. This is the only particle of those that is part of the blood, which can leave the bloodstream and penetrate into the tissues. This ability actively contributes to the performance of its main function - protection from alien agents. Leukocytes destroy pathogenic proteins and other compounds. They participate in immune responses, while producing T-cells that can recognize viruses, foreign proteins and other substances. Also, lymphocytes secrete B-cells that produce antibodies, and macrophages that devour large pathogenic cells. It is very important when diagnosing diseases to know the composition of the blood. It is the increased number of leukocytes in it that indicates the developing inflammation.

Hematopoietic organs

So, having analyzed the composition, it remains to find out where its main particles are formed. They have a short lifespan, so you need to constantly update them. The physiological regeneration of blood components is based on the processes of destruction of old cells and, accordingly, the formation of new ones. It occurs in the organs of hematopoiesis. The most important of them in humans is the bone marrow. It is located in the long tubular and pelvic bones. The blood is filtered in the spleen and liver. In these organs, its immunological control is also carried out.

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