What cells does blood consist of? Cellular composition and main functions of blood

Definition of the concept of the blood system

Blood system(according to G.F. Lang, 1939) - the totality of blood itself, hematopoietic organs, blood destruction (red Bone marrow thymus, spleen, The lymph nodes) and neurohumoral mechanisms of regulation, due to which the constancy of the composition and function of the blood is preserved.

Currently, the blood system is functionally supplemented with organs for the synthesis of plasma proteins (liver), delivery to the bloodstream and excretion of water and electrolytes (intestines, nights). The most important features blood as a functional system are the following:

it can perform its functions only in a liquid state of aggregation and in constant motion (through the blood vessels and cavities of the heart);
all its constituent parts are formed outside the vascular bed;
it combines the work of many physiological systems of the body.

The composition and amount of blood in the body

Blood is a liquid connective tissue, which consists of a liquid part - and cells suspended in it - : (red blood cells), (white blood cells), (platelets). In an adult, blood cells make up about 40-48%, and plasma - 52-60%. This ratio is called hematocrit (from the Greek. haima- blood, kritos- index). The composition of the blood is shown in Fig. one.

Rice. 1. Composition of the blood

The total amount of blood (how much blood) in the body of an adult is normally 6-8% of body weight, i.e. about 5-6 liters.

Physico-chemical properties of blood and plasma

How much blood is in the human body?

The share of blood in an adult accounts for 6-8% of body weight, which corresponds to approximately 4.5-6.0 liters (with an average weight of 70 kg). In children and athletes, the blood volume is 1.5-2.0 times greater. In newborns, it is 15% of body weight, in children of the 1st year of life - 11%. In a person in conditions of physiological rest, not all blood actively circulates through cordially- vascular system. Part of it is in the blood depots - venules and veins of the liver, spleen, lungs, skin, in which the blood flow rate is significantly reduced. The total amount of blood in the body remains relatively constant. A rapid loss of 30-50% of the blood can lead the body to death. In these cases, an urgent transfusion of blood products or blood-substituting solutions is necessary.

Blood viscosity due to the presence in it of uniform elements, primarily erythrocytes, proteins and lipoproteins. If the viscosity of water is taken as 1, then the viscosity of whole blood of a healthy person will be about 4.5 (3.5-5.4), and plasma - about 2.2 (1.9-2.6). The relative density (specific gravity) of blood depends mainly on the number of erythrocytes and the content of proteins in the plasma. In a healthy adult, the relative density of whole blood is 1.050-1.060 kg/l, erythrocyte mass - 1.080-1.090 kg/l, blood plasma - 1.029-1.034 kg/l. In men, it is somewhat larger than in women. The highest relative density of whole blood (1.060-1.080 kg/l) is observed in newborns. These differences are explained by the difference in the number of red blood cells in the blood of people of different sex and age.

Hematocrit- part of the blood volume attributable to the proportion of formed elements (primarily erythrocytes). Normally, the hematocrit of the circulating blood of an adult is on average 40-45% (for men - 40-49%, for women - 36-42%). In newborns, it is about 10% higher, and in young children it is about the same amount lower than in an adult.

Blood plasma: composition and properties

The osmotic pressure of blood, lymph and tissue fluid determines the exchange of water between blood and tissues. A change in the osmotic pressure of the fluid surrounding the cells leads to a violation of their water metabolism. This can be seen in the example of erythrocytes, which in a hypertonic solution of NaCl (a lot of salt) lose water and shrivel. In a hypotonic solution of NaCl (little salt), erythrocytes, on the contrary, swell, increase in volume and may burst.

The osmotic pressure of blood depends on the salts dissolved in it. About 60% of this pressure is created by NaCl. The osmotic pressure of blood, lymph and tissue fluid is approximately the same (approximately 290-300 mosm / l, or 7.6 atm) and is constant. Even in cases where a significant amount of water or salt enters the blood, the osmotic pressure does not undergo significant changes. With excessive intake of water into the blood, water is quickly excreted by the kidneys and passes into the tissues, which restores the initial value of the osmotic pressure. If the concentration of salts in the blood rises, then water from the tissue fluid passes into the vascular bed, and the kidneys begin to excrete salt intensively. Digestion products of proteins, fats and carbohydrates, absorbed into the blood and lymph, as well as low molecular weight products of cellular metabolism, can change the osmotic pressure within a small range.

Maintaining a constant osmotic pressure plays a very important role in the life of cells.

Hydrogen ion concentration and blood pH regulation

Blood has a slightly alkaline environment: pH arterial blood equal to 7.4; The pH of venous blood due to the high content of carbon dioxide in it is 7.35. Inside the cells, the pH is somewhat lower (7.0-7.2), which is due to the formation of acidic products in them during metabolism. The extreme limits of pH changes compatible with life are values from 7.2 to 7.6. A shift in pH beyond these limits causes severe violations and can lead to death. At healthy people fluctuates between 7.35-7.40. A prolonged shift in pH in humans, even by 0.1-0.2, can be fatal.

So, at pH 6.95, loss of consciousness occurs, and if these shifts are not eliminated in the shortest possible time, then a fatal outcome is inevitable. If the pH becomes equal to 7.7, then severe convulsions (tetany) occur, which can also lead to death.

In the process of metabolism, tissues secrete “acidic” metabolic products into the tissue fluid, and, consequently, into the blood, which should lead to a shift in pH to the acid side. So, as a result of intense muscular activity, up to 90 g of lactic acid can enter the human blood within a few minutes. If this amount of lactic acid is added to a volume of distilled water equal to the volume of circulating blood, then the concentration of ions in it will increase by 40,000 times. The reaction of the blood under these conditions practically does not change, which is explained by the presence of buffer systems in the blood. In addition, the pH in the body is maintained due to the work of the kidneys and lungs, which remove carbon dioxide, excess salts, acids and alkalis from the blood.

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

Hemoglobin buffer system the most powerful. It accounts for 75% of the buffer capacity of the blood. This system consists of reduced hemoglobin (HHb) and its potassium salt(KNb). Its buffering properties are due to the fact that, with an excess of H + KHb, it gives up K + ions, and itself adds H + and becomes a very weakly dissociating acid. In tissues, the blood hemoglobin system performs the function of an alkali, preventing acidification of the blood due to the ingress of carbon dioxide and H + ions into it. In the lungs, hemoglobin behaves like an acid, preventing the blood from becoming alkaline after carbon dioxide is released from it.

Carbonate buffer system(H 2 CO 3 and NaHC0 3) in its power takes the second place after the hemoglobin system. It functions as follows: NaHCO 3 dissociates into Na + and HC0 3 - ions. When a stronger acid than carbonic acid enters the blood, an exchange reaction of Na + ions occurs with the formation of weakly dissociating and easily soluble H 2 CO 3. Thus, an increase in the concentration of H + ions in the blood is prevented. An increase in the content of carbonic acid in the blood leads to its breakdown (under the influence of a special enzyme found in erythrocytes - carbonic anhydrase) into water and carbon dioxide. The latter enters the lungs and is excreted in environment. As a result of these processes, the entry of acid into the blood leads to only a slight temporary increase in the content of neutral salt without a shift in pH. In the case of alkali entering the blood, it reacts with carbonic acid, forming bicarbonate (NaHC0 3) and water. The resulting deficiency of carbonic acid is immediately compensated by a decrease in the release of carbon dioxide by the lungs.

Phosphate buffer system formed by sodium dihydrophosphate (NaH 2 P0 4) and sodium hydrogen phosphate (Na 2 HP0 4). The first compound dissociates weakly and behaves like a weak acid. The second compound has alkaline properties. When a stronger acid is introduced into the blood, it reacts with Na,HP0 4 , forming a neutral salt and increasing the amount of slightly dissociating sodium dihydrogen phosphate. If a strong alkali is introduced into the blood, it interacts with sodium dihydrogen phosphate, forming weakly alkaline sodium hydrogen phosphate; The pH of the blood at the same time changes slightly. In both cases, excess sodium dihydrophosphate and sodium hydrogen phosphate are excreted in the urine.

Plasma proteins play the role of a buffer system due to their amphoteric properties. In an acidic environment, they behave like alkalis, binding acids. In an alkaline environment, proteins react as acids that bind alkalis.

Nervous regulation plays an important role in maintaining blood pH. In this case, the chemoreceptors of the vascular reflexogenic zones are predominantly irritated, the impulses from which enter the medulla and other parts of the central nervous system, which reflexively includes peripheral organs in the reaction - the kidneys, lungs, sweat glands, gastrointestinal tract, whose activity is aimed at restoring the initial pH values. So, when the pH shifts to the acid side, the kidneys intensively excrete the anion H 2 P0 4 - with urine. When the pH shifts to the alkaline side, the excretion of anions HP0 4 -2 and HC0 3 - by the kidneys increases. The human sweat glands are able to remove excess lactic acid, and the lungs - CO2.

With various pathological conditions a pH shift can be observed both in an acidic and in an alkaline environment. The first of these is called acidosis, second - alkalosis.

Blood- This is a type of connective tissue, which consists of a liquid plasma part and a dry residue (cellular elements).

In the human body, blood maintains the normal functioning of tissues and is the first to respond to changes in the biological environment as a result of injuries, infections, organic and functional disorders. You can determine how many liters of blood in a person by calculating 7% of body weight.

blood cells

Blood cells are represented by erythrocytes, platelets, leukocytes.

red blood cells- small cells in the form of a disk with concave edges, devoid of a nucleus. Their main function is considered to be the transfer of oxygen from the lungs to the organs due to hemoglobin, a protein that can attach oxygen molecules. In addition, red blood cells deliver carbon dioxide to the alveoli of the lungs, which is excreted from the body during respiration.

platelets- these are non-nuclear blood plates that take part in the formation of a clot. When the integrity of the blood vessels is violated, the cells stick together, interact with plasma coagulation factors, which leads to the formation of a clot at the site of damage.

Leukocytes are white blood cells that contain a nucleus. They are represented by granulocytic elements that contain numerous grains in the cytoplasm: basophils, eosinophils, neutrophils. Cells without granules are monocytes and lymphocytes. White blood cells take part in the processes of cellular and humoral immunity, protecting the body from foreign microorganisms and substances.

Blood functions

Circulating through the vascular system of the body, blood performs important biological functions.

In case of violation of the composition and functions of the blood, a change in its volume, pathological processes occur in the body, which can cause chronic diseases and even death.

ATTENTION! BEFORE USING ANY DRUG, MEDICINE OR METHOD OF TREATMENT, ALWAYS CONSULT WITH YOUR PHYSICIAN!

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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 particles in it in the form of a suspension. blood cells. 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 speed of movement. 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 - liquid component light yellow, 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 the 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 of blood coagulation, turning under the influence of coagulation factors into insoluble fibrin.

In addition, plasma contains hormones that are produced by endocrine glands, 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. The shape of the cells ensures the efficiency of 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. The main function of red blood cells is 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, return to the 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 of red blood cells in the blood 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:

Protective. The main role in protecting the body from infections and damage is played by leukocytes, namely neutrophils and monocytes. 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. Other types of white blood cells - lymphocytes - produce antibodies against harmful agents. In addition, leukocytes are involved in the removal of damaged and dead tissues from the body.
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.
Temperature regulation. A person needs blood to maintain a constant body temperature, 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 important functions. For normal life, it is necessary that all components are in the blood in the optimal ratio. Changes in the composition of the blood, detected during the analysis, make it possible to identify the pathology at an early stage.

The human body is extremely complex. Its elementary building particle is the cell. The combination of cells that are similar in structure and functions, forms a certain type of tissue. In total, four types of tissues are distinguished in the human body: epithelial, nervous, muscle and connective. It is to the latter type that blood belongs. Below in the article will be considered what it consists of.

General concepts

Blood is a fluid connective tissue that constantly circulates from the heart to all distant parts. human body and implements vital functions.

In all vertebrate organisms, it has a red color (of varying degrees of color intensity), acquired due to the presence of hemoglobin, a specific protein responsible for oxygen transport. The role of blood in the human body cannot be underestimated, since it is she who is responsible for the transfer of nutrients, trace elements and gases in it, which are necessary for the physiological course of cell metabolism processes.

Main components

In the structure of human blood, there are two main components - plasma and several types of formed elements located in it.

As a result of centrifugation, it can be seen that it is a transparent liquid component of a yellowish color. Its volume reaches 52 - 60% of the total blood volume. The composition of plasma in the blood is 90% water, where proteins, inorganic salts, nutrients, hormones, vitamins, enzymes and gases are dissolved. And what is human blood made of?

Blood cells are of the following types:

(red blood cells) - contains the most among all cells, their importance is in the transport of oxygen. The red color is due to the presence of hemoglobin in them.
(white blood cells) - part immune system human, carry out its protection from pathogenic factors.
(platelets) - guarantee the physiological course of blood clotting.

Platelets are colorless plates without a nucleus. In fact, these are fragments of the cytoplasm of megakaryocytes (giant cells in the bone marrow), which are surrounded by a cell membrane. The shape of platelets is diverse - oval, in the form of a sphere or sticks. The function of platelets is to ensure blood clotting, that is, to protect the body from.

Blood is a rapidly regenerating tissue. The renewal of blood cells takes place in the hematopoietic organs, the main of which is located in the pelvic and long tubular bones bone marrow.

What are the tasks of the blood
There are six functions of blood in the human body:

Nutrient - blood delivers from digestive organs to all cells of the body nutrients.

Excretory - the blood takes and carries away the products of decay and oxidation from cells and tissues to the organs of excretion.

Respiratory - transport of oxygen and carbon dioxide.

Protective - neutralization of pathogenic organisms and toxic products.

Regulatory - due to the transfer of hormones that regulate metabolic processes and the work of internal organs.

Maintenance of homeostasis (constancy of the internal environment of the body) - temperature, reaction of the environment, salt composition, etc.

The importance of blood in the body is enormous. The constancy of its composition and characteristics ensures the normal course of life processes. By changing its indicators, it is possible to identify the development of the pathological process in the early stages. We hope you learned what blood is, what it consists of and how it functions in the human body.

What is blood, everyone knows. We see her when we hurt skin, for example, if you 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, is 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 found in plasma active substances: 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, are 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. It's pretty a large number of. 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.