What role does blood play in the body? General properties and functions of blood

Blood is a vital component of the human body, accounting for 8% of body weight. Various functions are performed by blood, which are very significant, because the circulatory system connects all organs into a single whole, continuously circulating through the vessels. Therefore, you need to know the basic functions of blood, its structure and the organs of the hematopoietic system.

Blood is a type of connective tissue consisting of a liquid intercellular substance that has a complex composition. In structure, it consists of 60% plasma, and the remaining 40% of the intercellular substance consists of components such as erythrocytes, leukocytes, platelets and lymphocytes. There are about 5 million red blood cells, about 8 thousand white blood cells and 400 thousand platelets per 1 cubic millimeter.

Erythrocytes are represented by anucleate red blood cells that have the shape of biconcave discs and determine the color of blood. The structure of red cells is similar to a thin sponge, the pores of which contain hemoglobin. There are a huge number of these elements in the human body, since more than 2 million of them are formed in the bone marrow every second. Their main task is to move oxygen and carbon dioxide. The lifespan of the elements is 120-130 days. They are destroyed in the liver and spleen, resulting in the formation of bile pigment.

Leukocytes are white blood cells of different sizes. These elements are irregularly round in shape, as they have nuclei that are capable of moving independently. Their number is much smaller than red blood cells. What is the function of white bodies? Their main function is to resist viruses, bacteria, and infections that penetrate the body. Such bodies have enzymes that bind and break down breakdown products and foreign protein substances. Some types of white blood cells produce antibodies - protein particles that kill dangerous microorganisms that land on mucous membranes and other tissues. Life expectancy is 2-4 days, disintegrates in the spleen.

The next structural element is platelets, which are colorless, nuclear-free platelets of blood that move near the walls of blood vessels. The main function of blood platelets is to restore blood vessels during injury. These elements take an active part in coagulation.

Lymphocytes are mononuclear cells. They are divided into three groups: 0 cells, B cells, T cells. B cells are involved in the production of antibodies, and T lymphocytes are responsible for the transformation of group B cells. Group T cells are involved in the process of synthesis of macrophages and interferons. 0-cells do not have surface antigens; they destroy cells that have a cancerous structure and are infected with any virus.

Plasma is a viscous, thick liquid that flows throughout the body, creating the necessary chemical reaction, and is responsible for the functioning of the nervous system. Plasma contains antibodies that protect the body from various dangers. Its structure consists of water and solid microelements: salts, proteins, fats, hormones, vitamins, etc. The main properties of plasma are osmotic pressure and the movement of blood cells and nutrients. Plasma is in special contact with the kidneys, liver and other organs.

The importance of intercellular substance

The intercellular substance is an important internal environment, as it performs many physiological functions that are required for the full functioning of the body. The main functions of blood are as follows:

• transport;
• thermoregulatory;
• protective;
• homeostatic;
• humoral;
• excretory.

Blood is the main transporter of all microelements in the human body, therefore its transport function is the main one, since it is to ensure the continuous movement of micronutrients from the digestive organs: liver, intestines, stomach - to the cells. Otherwise, it is also called the trophic function of blood. The transport of oxygen from the lungs to the cells and carbon dioxide in the opposite direction is otherwise called the respiratory function of the blood.

Blood stabilizes cell temperature by moving thermal energy, so its thermoregulatory function is one of the most important. About 50% of the total energy of the human body is converted into heat, which is produced by the liver, intestines and muscle tissue. And it is thanks to thermoregulation that some organs do not overheat, while others do not freeze, since the blood moves heat to all cells and tissues. Any disturbances that occur in the connective tissue lead to the fact that the peripheral organs do not receive heat and begin to freeze. Most often this is observed with anemia and blood loss.

The protective function of blood is expressed due to the presence of leukocytes - immune cells - in the intercellular substance. It consists in preventing the occurrence of a critical increase in the level of toxic substances in cells. Viral microorganisms that get inside are destroyed by the protective system. When it is disrupted, the body becomes weak to resist infections, and, accordingly, the protective function of the blood cannot fully manifest itself.

Blood is responsible for maintaining the constancy of the internal environment of the body, primarily acid and water-salt balances, this is where its homeostatic function is manifested. Osmotic pressure and ionic composition of tissues are maintained. Excess amounts of some substances are removed from the cells, while other substances are introduced into the intercellular substance. Also, thanks to this function, blood is able to maintain its constant properties.

Humoral or regulatory function is associated with the activity of the endocrine gland. The thyroid, reproductive, and pancreas glands produce hormones, and the intercellular substance transports them to the right places. The regulatory function is important as it controls and normalizes blood pressure.

Excretory function is a separate type of transport function of blood, its essence is the removal of end products of metabolism (urea, uric acid), excess fluid, and mineral trace elements.

Homeostasis is an important function of the blood. When veins, arteries and bleeding occur at the site of injury, a blood clot forms, preventing severe blood loss.

Elements of the circulatory system

Blood is a system that consists of certain elements connected to each other. Its main elements:

• circulating blood, or peripheral;
• deposited blood;
• hematopoietic organs;
• organs of destruction.

The circulating fluid moves through the arteries and is pumped by the heart. is approximately 5-6 liters, but only 50% of this volume circulates at rest.

Deposited represents blood reserves in the liver and spleen. It is released by organs into the vascular system during physical or emotional stress, when the brain and muscles need increased amounts of oxygen and micronutrients. It is needed for unexpected bleeding. In the presence of pathology of the liver and spleen, reserves are significantly reduced, which poses a certain danger to humans.

The next element of the system, the hematopoietic organ, to which it belongs, is located in the pelvic bones and the ends of the tubular bones of the extremities. Lymphocytes and red blood cells are formed in this organ, and some immune cells are formed in the lymph nodes. Part of the system are the organs in which the blood breaks down. For example, red blood cells are utilized in the spleen, and lymphocytes in the lungs.

All of these parts of the system affect the health of the blood in the human body. Therefore, it is necessary to monitor its condition, the condition of the organs, because blood performs vital physiological functions for internal organs and tissues.

Blood - liquid connective tissue that, together with tissue fluid and lymph, forms the internal environment of the body. Blood performs many functions. The most important of them:

Transport (transport of nutrients, metabolic end products, gases, hormones);

Protective (cellular and humoral immunity, blood clotting);

Thermoregulatory;

Homeostatic.

All these functions are carried out thanks to the complex composition of blood. Blood consists of a liquid part - plasma and cells suspended in it - shaped elements: red blood cells, white blood cells and platelets.

Blood plasma contains 90-92% water and 8-10% dry matter. The dry residue consists of organic compounds and minerals. Blood plasma proteins perform a number of important functions. They are involved in maintaining blood pH at a constant level. Proteins give blood viscosity, which is important in maintaining blood pressure. They also participate in blood clotting, are immunity factors, serve as a reserve for the construction of tissue proteins and as carriers of a number of hormones, minerals and lipids.

The formed elements of blood have a number of features in connection with the functions they perform. So, red blood cells arose in the process of evolution as cells containing respiratory pigments that transport oxygen and carbon dioxide. They have the shape of a nuclear-free biconcave disk. This shape allows you to bring the internal contents as close as possible to the surface of the red blood cell. The same structure allows you to increase the total surface of red blood cells. All this contributes to the performance of the main function of red blood cells - transport.

A component of the red blood cell is hemoglobin, a protein that ensures the respiratory function of the blood. It easily attaches and releases oxygen without changing the valence of iron.

Leukocytes - white blood cells that perform a protective function. Leukocytes, unlike erythrocytes, are characterized by amoeboid movement, due to which they are able to move between cells of different tissues of the body and perform functions unique to them. They provide cellular immunity – the body’s protection from microorganisms and substances that carry genetically foreign information. Thus, the main task of the blood immune system is to maintain homeostasis in the body.

One of the body's forms of defense is phagocytosis– absorption of foreign particles by leukocytes and their intracellular digestion.

Another form of protection is humoral immunity carried out by lymphocytes. They form protective proteins - antibodies that destroy foreign proteins. Lymphocytes have immune memory, i.e. the ability to respond with an enhanced reaction to a repeated encounter with a foreign body. They perform this function due to the fact that, unlike other leukocytes, they live not just a few days, but 20 years or more.

Platelets - the smallest of the formed elements of blood. Their diameter is 0.003 mm, they are nuclear-free. Blood platelets are capable of agglutination (sticking together). Platelets take part in the blood clotting process due to the platelet factors contained in them and released when necessary. In this regard, they are able to quickly disintegrate and stick together into conglomerates, around which fibrin threads appear. Their lifespan is 5-8 days.

In maintaining a regular metabolic process, the blood performs numerous and varied functions. It participates in all natural as well as disturbed life processes.

For example, blockage of the bile ducts is not a blood disease, but due to an increase in the flow of bile into the blood and an increase in the content of bile pigment in the blood, the plasma becomes distinctly yellow, the blood “gets sick,” and its normal composition is disrupted. Even a purulent wound on the little finger can cause a disturbance in the general composition of the blood, an increase in the number of white cells and blood proteins.

It is necessary to distinguish the following most important functions of blood:

— transport (for nutrients, oxygen, metabolic products, medications, intermediate products, etc.);
— information (transfer of hormones and enzymes to the site of influence, transportation of activating and inhibitory substances);
- protective (with the help of leukocytes from pathogens, foreign proteins and other foreign bodies);
— maintaining a constant body temperature (by changing, if necessary, the blood supply to the skin and varying heat transfer);
- self-defense using a coagulation system (to prevent large blood loss and prolonged bleeding in case of injury);
— maintaining a constant internal environment and “internal order” in the body by regulating water and electrolyte management.

In addition, for a doctor, blood has an indirect auxiliary function: it allows one to determine the presence of diseases based on its composition. Therefore, it has additional diagnostic implications.

Oxygen transport
Transporting oxygen from inhaled air to all parts of the body, to all its cells, is one of the most important tasks of the blood. Although the main load in this regard is carried out by the red dye, hemoglobin, the tasks of transportation are solved by all other components of the blood. The constant composition of salts in the blood determines whether oxygen will be fully bound by hemoglobin, or whether the blood will not be fully charged with oxygen, which will complicate the flow of this important fuel to the cells.
When you inhale, air containing oxygen enters the smallest pulmonary alveoli, which are closely connected to the blood vessels. A certain amount of oxygen from the inhaled air is displaced into the blood plasma under gas pressure. This oxygen is immediately absorbed by the hemoglobin of the red blood cells, bound in the hemoglobin molecules by iron atoms, which allows the remaining oxygen, thanks to the higher partial pressure in the lungs, to enter the plasma. By binding oxygen, the blood dye changes its color, becoming light red. Oxygen-enriched hemoglobin has a higher acidity compared to depleted hemoglobin, which is of great importance for removing carbon dioxide bound by hemoglobin from tissues.
Oxygen-enriched red blood cells enter all human tissues and organs. In capillaries with a diameter that barely allows blood cells to pass through, red blood cells are in close contact with tissue that has a lower oxygen pressure due to oxygen consumption in the process of cellular metabolism. In accordance with physical (and more precisely, chemical) laws, oxygen moves from an area with a high degree of concentration to an area with low oxygen pressure, while chemical processes contribute to the release of oxygen bound by hemoglobin. In these tissues, the concentration of carbon dioxide, which is a metabolic product, is higher than in the inhaled air and in the blood, therefore, as if in exchange for oxygen, carbon dioxide and its salt ions accumulate in hemoglobin.
Red blood cells saturated with carbon dioxide are transported by the venous bloodstream to the lungs, where gas exchange occurs again, during which carbon dioxide is exhaled by the lungs and “charging” with new oxygen occurs - a very rationally organized transport system that eliminates empty flights.
Of course, other air gases (for example, nitrogen) are also dissolved in the blood in accordance with their partial pressure. However, they are not bound by hemoglobin, and their proportion in the dissolved state always remains small. If there is carbon monoxide in the air (as a component of the gaseous environment of urban air or smoke from the combustion process), the picture changes. Carbon monoxide dissolves well in the blood. It binds hemoglobin many times better than oxygen. To completely saturate hemoglobin, carbon monoxide requires significantly less than oxygen. This means that in case of gas poisoning (urban environment or carbon monoxide), the body is not sufficiently supplied with oxygen, because carbon monoxide takes up all the valences. There is a kind of internal suffocation of the body.
This explains the danger of carbon monoxide, that its relatively small concentration is sufficient to displace oxygen. Understanding these underlying processes allows us to understand the essence of measures to provide assistance in case of gas poisoning. For example, it makes no sense to perform artificial respiration in an environment filled with carbon monoxide or to drink milk for degassing purposes. The victim must be immediately taken out into fresh air, or taken to the hospital under an oxygen mask, since with higher oxygen pressure and the absence of carbon monoxide in the inhaled air, the hemoglobin is purified, allowing the regular function of the blood to transport oxygen to be carried out again.

Full saturation of the blood with oxygen may not occur if the gas exchange area in the lungs is too small, for example, with pneumonia or a sharp decrease in the number of red blood cells. Hemoglobin has a surprisingly high ability to form compounds. One gram of hemoglobin binds a maximum of 1.4 milliliters of oxygen. This means that 1 liter of blood containing 150 g of red blood dye combines with 210 ml of oxygen. Oxygen-enriched blood contains the same amount of O 2 as the inhaled air. As you know, the air contains 21% oxygen, i.e. also 210 ml per 1 liter of air. “Bad”, i.e. Air with a low oxygen content prevents the saturation of oxygen in the blood, and therefore the supply of oxygen to the body systems. You should also pay attention to the fact that air containing carbon monoxide is also inhaled during smoking. The smoker not only inhales nicotine and cancer-promoting substances, but also inhales low-grade air, which largely contains carbon monoxide. A certain percentage of a smoker's hemoglobin is constantly bound by carbon monoxide and does not participate in the transport of oxygen. For the body, this load is comparable to a smoker constantly living surrounded by a “thin” layer of air at an altitude of about 2000 meters.

Transport of other nutrients
Blood transports nutrients absorbed by the intestines from food during digestion. With the help of the bloodstream, this fuel, necessary for cellular metabolism, enters the liver and is mostly converted there. Sometimes it stays in the blood for a long time, which applies both to fats present in the blood in the form of tiny droplets, and to amino acids - the building material for proteins, as well as glucose - blood sugar. Typically, a certain blood sugar concentration does not change. With large expenditures of energy (for example, as a result of physical activity), new sugar is indirectly released from storage sites (muscles, liver) and enters the bloodstream. When blood sugar levels rise after a meal (in a healthy person), this increased amount is converted into storage forms (glycogens) and fats to be used when needed.

Any test for blood composition resembles a small inventory, checking the condition and transportation capabilities at the moment, and not the actual reserves available. Thus, a very thin person may show an increased fat content in the blood after eating, while at the same time, the blood of an overweight person during physical activity may show the presence of an extremely small amount of fat. In most cases, repeat samples are taken to confirm the results of a single analysis.

The above also applies to the transport of other substances found in the blood. For example, after taking medications, you may experience very high levels of the medication in your blood. However, after they accumulate in organs and tissues, the level of concentration in the blood decreases, although the medications remain in the body. A similar picture is observed with poisons. They can completely disappear from the blood, accumulating, however, in significant quantities in the organs. Because looking at a freight train, you can’t tell what the selection of goods is in the store.
We often hear that cholesterol (cholesterol) and other blood fats are metabolic waste products that, like garbage in a landfill, are deposited on the walls of the body's blood vessels, thereby causing atherosclerosis and arterial calcification. This opinion is not true. Typically, blood fats are a storehouse of energy-containing nutrients. When assessing blood tests, its transport function must be constantly taken into account. The above facts are clearly confirmed when conducting research using radioactive substances. In the course of such studies, it is possible to determine with accuracy how quickly a certain substance is dissolved and distributed in the blood, where and how it is deposited and disappears from it.

Transportation of metabolic end products
Sometimes there are still people who advocate, before the onset of spring, the so-called “blood cleansing” course of treatment to “remove” “toxins” from it. They are based on the idea that the body can be periodically freed from toxins, such as removing garbage, cleansing from “scale” or “heaps of ash”. Of course, this is a pseudoscientific approach. The toxins formed during the metabolic process are immediately and constantly eliminated from the body. If, as a result of disruption of the withdrawal process, their stagnation occurs, dangerous complications immediately arise in the body. An example is poisoning by harmful urine products (uremia), which occurs as a result of impaired excretory function of the kidneys. Many such wastes travel with the blood to the excretory organs. Dying red blood cells release hemoglobin, which, converted into bile pigments, enters the liver, bile ducts and intestines. Moreover, this bile juice - a product of the human body's economy - performs the function of digesting food. The blood constantly contains a certain part of this decaying hemoglobin (bilirubin), which is processed by the liver.

When liver function is impaired, its level in the blood increases, which can lead to yellowing of the sclera and skin. Consequently, evidence of the presence of excessive amounts of metabolic end products may be a disorder of organ function. Therefore, it is impossible to cleanse the blood once a year to remove toxins. All supporters of this method can be rebuffed on the basis of knowledge of the fundamental physiological processes of transport of substances in the blood. Anyone who understands that metabolic products are constantly formed in the body and are consistently eliminated from it is unlikely to fall under the influence of dubious advice regarding spring blood cleanses or other courses of miracle treatment that do not have a scientific basis.

Transfer of information
When listing the merits of the transport function, they sometimes forget the very significant “courier service”, also performed in blood. We are talking about a large amount of information on the self-regulation of life processes associated with the concentration of substances in the blood. So, due to the insignificant concentration of nutrients in the blood, the hunger center is probably stimulated; of course, this process is also influenced by many other mechanisms. The release of sugar from storage forms, as well as many other regulatory processes, depend on information entering the blood. The respiratory center also responds to the concentration of oxygen and carbon dioxide in the blood, regulating the depth and frequency of breathing. In addition to solving such information problems, blood must also transmit other information.
With the help of blood, hormones of the endocrine glands are delivered to the recipient, i.e. to the place of their influence. Thus, the blood represents, as it were, a second nervous system. A millionth of a gram of the hormone is enough to activate metabolism, speed up or slow down the functioning of the sex glands, cause hair growth, increase body size, and much more. All these hormones are carried throughout the body by the blood. Without blood circulation, the effective influence of hormones is impossible. Various endocrine glands communicate with each other through the bloodstream, which allows them to exert mutual influence on each other.
For example, the pituitary gland secretes a hormone that activates the activity of the adrenal cortex ( adrenocorticotropic hormone) and in turn causing the production of its hormones ( corticoids). Accumulating in the blood, they have a reverse effect on the pituitary gland. In this case, it stops secreting or secretes a small amount of hormones that affect the activity of the adrenal cortex. Such regulation and feedback is possible only with the help of blood. This is a very important information and regulatory activity.
This property of blood is also used by doctors in the treatment of various diseases. After all, when entering the bloodstream (for example, into a vein in the arm), medications can cause an effect in organs located in a completely different part of the body, even in the most distant one.

Protective function of blood
In a popular comparison, white blood cells are sometimes called the body's "police force." This comparison is completely true, given that the police not only neutralize and isolate troublemakers, but also solve the problems of preventing violations and regulating traffic.

The protective function of the blood in relation to such offenders as microbes, foreign substances, altered proteins, etc. is carried out, on the one hand, by the influence of specific protective substances dissolved in the blood ( antibodies), non-specific blood factors (for example, interferon) and leukocytes (neutrophil granulocytes). Surrounding with "devouring cells" ( phagocytes) penetrated bacteria or foreign cells (for example, foreign red blood cells) and by drawing them in, they thus assimilate them. In this case, white blood cells die. Subject to fatty degeneration, they form purulent cells in millions, together with other cells and discharge from the wound, so suppuration always means a conflict between leukocytes and foreign invaders. When leukocytes win, they destroy and remove pathogenic microbes. If white blood cells and other defense mechanisms do not prevail over the invading bacteria, sepsis, (“blood poisoning”) and the spread of pathogens throughout the body. Chemical substances ( leukotaxins) act on leukocytes as a bait or alarm signal. Appearing at the site of inflammation, these leukotaxins attract granulocytes from the surrounding capillaries, which, accumulating at the site of inflammation (abscess formation), begin their protective “battle” (abscess maturation). Destroyed offenders and dead blood cells are then excreted from the body with pus (“breakthrough” of the abscess).

By interfering in such a defensive struggle, squeezing out a still “immature” abscess, opening it with the tip of a needle or other auxiliary instrument, it is possible to disperse the pathogens of pus that have not yet been destroyed in the surrounding area of ​​the wound, which, entering through the lymphatic pathways into other areas of the tissue, will cause an expansion of the area of ​​​​inflammation. This explains the doctor’s constant warnings - not to undertake any manipulations with the abscess on your own!
Thermal effects improve blood circulation and metabolism. Local heating causes an increase in the number of leukocytes in the area of ​​the lesion and increases their “appetite”. When exposed to heat, the abscess matures faster, but significant tissue destruction can occur. It is not recommended to use only heat or only cold. Exposure to cold allows you to slow down the inflammatory process, limit or completely stop the formation of pus, however, depending on the circumstances, the spread and reproduction of infiltrated pathogens may continue. Along with the named white blood cells (granulocytes), it contains substances that do not purposefully prevent the proliferation of bacteria. They have not yet been fully studied.
Only recently opened interferon- a substance that prevents, for example, the proliferation of viruses. It is secreted by cells infected by viruses. It reaches other cells through the bloodstream or lymph, protecting them from damage by viruses. There are other protective substances in the blood, but each of them is not enough to prevent the proliferation of microbes. A special role in the protective function of blood is played by lymphocytes- The second largest group of white blood cells. They do not act as phagocytes, surrounding and neutralizing invading pathogens. In recent years, they have become the subject of particularly intensive research, because occupy a key position in the overall complex of immune defense.
Lymphocytes take part in various ways in the creation of certain specific antibodies that are targeted against individual protein substances.
The function of antibody production by lymphocytes has been known for decades. The subject of immunological research has recently become the question of how these cells recognize their “antigen”, how they distinguish between substances foreign and related to the body, how they “remember” certain foreign bodies, how they can produce a large number of specific protective substances. These studies were especially stimulated by the connection with the problem of organ transplantation, because antibody-producing lymphocytes play not only a “positive” role, destroying microbes and thereby preventing or eliminating infectious diseases. They also have a “negative” role, manifested in the destruction of foreign proteins, i.e. foreign donor organs. In addition, they may make mistakes and unexpectedly mistake substances in their body for foreign substances.

Heat exchange
“You are health itself!” - they readily say, flattering their rosy-cheeked and seemingly healthy interlocutor. A pale complexion, on the contrary, raises health concerns. For an experienced doctor, when making a diagnosis, the appearance of the skin has a certain meaning. Paleness can indeed mean lack of blood, poor circulation, kidney disease, etc.
But the blood supply to the skin also depends on many other factors - it not only provides blood supply to the skin, but also regulates the temperature in the body by reflecting heat over the entire surface of the body. If heat were not delivered by the bloodstream to the surface of the body, then constantly arising during the combustion process during the metabolism of all cells could cause “warming” inside the body by 1-10 ° C per hour. This factor plays a role in heat stroke, i.e. violation of thermoregulation and blood circulation in the heat. Under such conditions, an overheated body stops producing heat. If timely intervention is not taken to lower body temperature and restore blood circulation (pouring cold water, cold enemas), a serious threat to life may arise.
In this regard, it is necessary to recall the effects of alcohol. Along with many effects, alcohol, even in small doses, causes the blood vessels to lose their ability to respond to changes occurring in the body. The blood vessels of the skin remain dilated due to improved blood supply, which explains heat stroke when drinking alcohol in the heat, which many still consider a prophylactic against colds.

Importance of blood test for diagnosis
Doctors often resort to blood tests. Numerous blood samples even cause some patients to fear about its quantitative composition. Such concern is unfounded, because the amount of blood taken for research in each individual case is always very small to affect the process of hematopoiesis. This amount is quickly restored by the body.

Based on the degree of concentration of various substances in the blood, one can draw a conclusion about the presence and course of the disease in the body, but it must be taken into account that the indicators reflect their level in the blood at the moment the sample is taken. To clarify the diagnosis, dynamic studies are necessary. It is impossible to describe even briefly in all existing methods of blood testing. However, below we highlight some of the most important ones.

Erythrocyte sedimentation reaction (ESR)
Doctors resort to this research method quite often. It is a simple check for possible disturbances in the normal composition of the blood, especially the amount of its proteins. 2 ml of blood that loses coagulability as a result of exposure to the citrate solution is taken from a vein in the arm. This blood sample is placed in a graduated tube, where the suspended blood cells begin to gradually settle. Settlement rate indicators are recorded after one and two hours. As a rule, the cell suspension settles by several mm per hour. The proteins and electrical charge of the shaped components of blood keep the cells in suspension. When the quantity of proteins decreases or the composition of proteins changes due to the protein fractions of antibodies, the process of blood cell sedimentation occurs much faster. An identical effect occurs when there are too few red blood cells. These changes can occur in the blood with all kinds of inflammation, fever, kidney disease, tumors, liver disease and other organs.
A diagnosis cannot be made on the basis of accelerated cell sedimentation alone - this is just a nonspecific test. If its indicators differ greatly from the norm, one should look for the cause of the deviations, but even with normal indicators, the possibility of the presence of certain diseases cannot be excluded. If you do not interfere with the process of settling cells in a test tube until they all settle to the bottom, you can draw a conclusion about the ratio of blood cells and plasma. Typically, cells account for 45% of the total blood volume. If there are too few red blood cells (anemia), the cell boundary in the test tube will be lower than normal. Results can be obtained much faster by centrifuging small tubes of blood (hematocrit) or measuring the amount of hemoglobin in the blood (hemoglobin index).

Blood picture
A small drop of blood is placed on a glass slide, smeared and then treated with various dye solutions. Under a microscope, the number and appearance of various white blood cells, as well as abnormalities of red cells, are determined, the types of cells are counted and their percentage is determined.
In acute inflammatory processes, the number of neutrophilic granulocytes increases;
in chronic inflammation, the number of lymphocytes;
allergic diseases may be associated with an increase in eosinophil cells.
For diagnosis, indicators of atypical, immature blood cells are important; for example, a strong increase in the number of white blood cells may indicate leukemia, i.e. leukemia or leukemia. Of course, however, when making a diagnosis, the doctor is guided not only by the blood picture indicators.

Number of cells
Sometimes, to solve a number of questions, it is necessary to determine the total number of blood cells (of course, this does not involve counting billions of individual red blood cells), for which a small counting chamber of a known volume is filled with blood. The chamber has lines that allow you to count the number of cells in a certain volume. The measurement data is then converted to 1 mm 3 .

Blood groups
Sometimes in medieval engravings and drawings, brave warriors are depicted with a lamb on their back, which was supposed to serve as a donor in case of injury. It was an unnecessary burden, for the blood of any animal cannot replace human blood. The results of the first experiments in human-to-human blood transfer were also very different. Obvious successes alternated with fatal failures. At the turn of the twentieth century, it was possible to prove that human blood has different groups that cannot be mixed.

Initially, the Austrian Landsteiner described four human blood groups A, B, AB and 0.
People with blood type A have antibodies with Anti-B properties in their plasma. If a patient with blood type A is given donor blood of type B, the Anti-B properties of his blood will cause immediate clotting of the donor cells, and the Anti-A properties contained in the donor blood will destroy the recipient's blood cells.
Blood type 0 plasma contains both Anti-A and Anti-B properties.
Landsteiner's discovery meant a huge step forward in the development of medicine. In fact, it made it possible to begin blood transfusions. However, cases of unsuccessful outcome continued to occur. Only in 1940 was it possible to obtain evidence of the presence of other properties in blood groups, called the Rh system (Rh-positive or Rh-negative), which made it possible to more effectively resolve the issue of compatibility of donor blood and recipient blood.
Further, a number of naturally inherited blood groups were discovered, which was of great importance for forensic medicine. For blood transfusion, these groups are of secondary importance. It was possible to prove that not only red blood cells exhibit “their” compatibility properties, but white ones also have certain properties in relation to tissue compatibility (HL-A system). The study of these properties will create favorable preconditions for organ transplantation. For blood transfusions, they are taken into account only in special cases.

Therefore, for blood transfusion, determining the blood group is of primary importance. It is mandatory to produce it in the hospital, which, if necessary, allows you to quickly order the necessary canned blood. The provision of assistance, for example, in case of an accident, is facilitated by the presence of a blood type mark in the passport. To avoid possible errors, before each blood transfusion, despite the existing determination of the blood group, a compatibility test is taken again.

Thanks to the availability of serum tests, determining blood groups is quite simple. Small drops of blood are applied to plates containing known antisera. In the absence of compatibility, blood cell coagulation occurs. Type A blood (the most common) will clot when it reacts with the Anti-A and Anti-AB serum tests. An interesting fact is that carriers of certain blood groups may be more likely to be susceptible to certain diseases, for example, gastrointestinal ones.
This is partly explained by immunological processes.

The transport function of blood is that it carries gases, nutrients, metabolic products, hormones, mediators, electrolytes, enzymes, etc. These substances can remain unchanged in the blood or enter into various, mostly unstable compounds with plasma proteins (iron , copper, hormones, etc.), hemoglobin (oxygen) and in this form delivered to the tissues.

The respiratory function is that hemoglobin in red blood cells carries oxygen from the lungs to the tissues of the body, and carbon dioxide from the cells to the lungs. In addition, gases in small quantities are transported by the blood in a state of simple physical dissolution and as part of chemical compounds.

Nutritional function is the transfer of essential nutrients from the digestive organs to the tissues of the body. Depending on the needs of the body, nutrients are mobilized from the depot and transported to working organs.

The excretory function (excretory) is carried out due to the transport of “waste of life” - the final products of metabolism (urea, uric acid, etc.) and excess amounts of salts and water from tissues to the places of their excretion (kidneys, sweat glands, lungs, intestines).

The water balance of tissues depends on the concentration of salts and the amount of protein in the blood and tissues, as well as on the permeability of the vascular wall. For example, when the level of protein in the blood decreases (as a result of increased release of water from the vessels into the tissues), edema may develop, since protein has the ability to retain water in

vascular bed.

Body temperature regulation is carried out due to physiological mechanisms that promote rapid redistribution of blood in the vascular bed. When blood enters the capillaries of the skin, heat transfer increases, and its transfer into the vessels of internal* organs helps reduce heat loss.

Blood performs a protective function, being the most important factor of immunity. This is due to the presence in the blood of antibodies (specific proteins that neutralize bacteria and their metabolic products), enzymes, special blood proteins (properdin)* that have bactericidal properties, related to natural immunity factors, and formed elements. One of the most important properties of blood is its ability to clot, which in case of injury protects the body from blood loss.

The regulatory function lies in the fact that the products of the activity of the endocrine glands, digestive hormones, salts, hydrogen ions, etc. entering the blood through the central nervous system and individual organs (either directly or reflexively) change their activity.

The amount of blood in the body. The total amount of blood in the body of an adult is on average 6-8%, or "/is, of body weight, i.e. approximately 5-6 liters. In children, the amount of blood is relatively larger: in newborns it averages 15% of the weight body, and in children aged 1 year - 11%. Under physiological conditions, not all blood circulates in the blood vessels, some of it is in the so-called blood depots (liver, spleen, lungs, skin vessels). The total amount of blood in the body is stored at relatively constant level. If it is necessary to replenish the amount of circulating blood, for example, during blood loss, special physiological mechanisms promote the release of deposited blood into the general bloodstream. Loss of "/2-"/3 of the amount of blood can lead to death of the body. In these cases, an urgent blood transfusion is necessary or blood replacement fluids.

Viscosity and relative density (specific gravity) of blood. The viscosity of blood is due to the presence of proteins and red blood cells - erythrocytes. If the viscosity of water is taken to be 1, then the viscosity of plasma will be 1.7-2.2, and the viscosity of whole blood will be about 5.1.

The relative density of blood depends mainly on the number of red blood cells, the hemoglobin content in them and the protein composition of the blood plasma. The relative density of adult blood is 1.050-1.060, plasma -1.029-1.034. The highest relative density of blood is observed in newborns - 1.060-1.080. For men it is slightly higher (1.057) than for women (1.053). This difference is explained by the unequal content of red blood cells in the blood.

Blood composition. Peripheral blood consists of a liquid part - plasma and formed elements or blood cells (erythrocytes, leukocytes, platelets) suspended in it.

If you let the blood settle or centrifuge it, after mixing it with an anticoagulant, then two layers that differ sharply from each other are formed: the upper one is transparent, colorless or slightly yellowish - blood plasma; the lower one is red, consisting of red blood cells and platelets. Leukocytes, due to their lower relative density, are located on the surface of the lower layer in the form of a thin white film.

The volumetric ratios of plasma and formed elements are determined using hematocrit - a capillary with divisions, as well as using radioactive isotopes 32 P, 51 Cr, 59 Fe. In peripheral (circulating) and deposited blood these ratios are not the same. In peripheral blood, plasma makes up approximately 52-58% of blood volume, and formed elements 42-48%. In deposited blood, the opposite ratio is observed.

Blood is a liquid medium located inside our body. Its content in the human body is approximately 6-7%. It washes all internal organs and tissues and ensures balance. Due to heart contractions, it moves through the vessels and performs a number of important functions.

The composition includes two main components: plasma and various particles suspended in it. The particles are divided into platelets, erythrocytes and leukocytes. Thanks to them, blood performs a huge number of functions in the body.

List of blood functions

What function does blood perform in the human body? There are quite a lot of them and they are varied:

1. transport;
2. homeostatic;
3. regulatory;
4. trophic;
5. respiratory;
6. excretory;
7. protective;
8. thermoregulatory.

👉 Let's look at each function separately:

Transport. Blood is the main source of transport of nutrients to cells and waste products from them, and also carries the molecules that make up our body.

Homeostatic. Its essence is to maintain the functioning of all body systems at a certain constancy, maintaining water-salt and acid-base balance. This happens thanks to buffer systems that do not allow the fragile balance to be upset.

Regulatory. The liquid environment is constantly supplied with waste products of the endocrine glands, hormones, salts, and enzymes, which are transferred to certain organs and tissues. With this, the function of individual body systems is regulated.

Trophic. Transports nutrients - proteins, fats, carbohydrates, vitamins and minerals from the digestive organs to every cell of the body.

Respiratory. From the alveoli of the lungs, with the help of blood, oxygen is delivered to organs and tissues, and from them carbon dioxide is transferred in the opposite direction.

Excretory. The blood carries bacteria, toxins, salts, excess water, harmful microbes and viruses that have entered the body to the organs, which neutralize them and remove them from the body. These are the kidneys, intestines, sweat glands.

Protective. Blood is one of the main factors in the formation of immunity. It contains antibodies, special proteins and enzymes that fight foreign substances that enter the body.

Thermoregulatory. Since almost all the energy in the body is released as heat, thermoregulatory function is very important. The main part of the heat is produced by the liver and intestines. The blood carries this heat throughout the body, preventing organs, tissues, and limbs from freezing.

Blood structure

Structure of human blood (partially translated, but intuitively understandable)

• Leukocytes. White blood cells. Their function is to protect the body from harmful and foreign components. They have a nucleus and are mobile. Thanks to this, they move along with the blood throughout the body and perform their functions. Leukocytes provide cellular immunity. Using phagocytosis, they engulf cells that carry foreign information and digest them. Leukocytes die along with foreign components.
• Lymphocytes. A type of leukocyte. Their method of defense is humoral immunity. Lymphocytes, once encountering foreign cells, remember them and produce antibodies. They have immune memory, and when they encounter a foreign body again, they respond with an enhanced reaction. They live much longer than leukocytes, providing constant cellular immunity. Leukocytes and their types are produced by the bone marrow, thymus, and spleen.
• Platelets. The smallest cells. They are able to stick together. Due to this, their main function is to repair damaged blood vessels, that is, they are responsible for blood clotting. When a vessel is damaged, platelets stick together and close the hole, preventing bleeding. They produce serotonin, adrenaline, and other substances. Platelets are formed in the red bone marrow.
• Red blood cells. They color the blood red. These are nuclear-free cells, concave on both sides. Their function is to transport oxygen and carbon dioxide. They perform this function due to the presence of hemoglobin in their composition, which attaches and releases oxygen to cells and tissues. The formation of red blood cells occurs in the bone marrow throughout life.

📌 The elements listed above make up 40% of the total blood composition.

• Plasma- This is the liquid part of the bloodstream, accounting for 60% of the total. It contains electrolytes, proteins, amino acids, fats and carbohydrates, hormones, vitamins and cell waste products. 90% of plasma consists of water and only 10% is occupied by the above components.

Plasma functions

One of the main functions is to support osmotic pressure. Thanks to it, the fluid is evenly distributed inside the cell membranes. The osmotic pressure of the plasma is the same as the osmotic pressure in the blood cells, so a balance is achieved.

Another function is the transport of cells, metabolic products and nutrients to organs and tissues. Maintains homeostasis.

A larger percentage of plasma is occupied by proteins - albumins, globulins and fibrinogens. They, in turn, perform a number of functions:

1. maintain water balance;
2. carry out acid homeostasis;
3. thanks to them, the immune system functions stably;
4. maintain the state of aggregation;
5. participate in the coagulation process.

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