What tissue is blood formed from? Blood as a type of connective tissue

Many people do not even realize that blood is a connective tissue. Most believe that this liquid is a mixture of many elements and nothing more. However, this is not the case. Blood is red in color and constantly in motion. This liquid performs important and quite complex functions in our body. Blood circulates throughout the circulatory system constantly. Thanks to this, it transports all the gaseous components and dissolved substances necessary for metabolic processes. But why is blood classified as tissue? She's liquid.

Blood composition

To understand what tissue blood belongs to and why, one should consider not only its main functions, but also its structure. What is it? Blood is a tissue made up of cells and plasma. Moreover, each of the elements performs certain functions and has its own properties.

Plasma is an almost transparent liquid that has a slightly yellowish tint. This component makes up the majority of the total blood volume in the human body. Plasma contains three main types of formed elements:

1. Platelets are blood platelets that have an oval or spherical shape.
2. Leukocytes are white cells.
3. Red blood cells are red cells that give the blood its characteristic hue due to its high hemoglobin content.

Not everyone knows how much of this liquid is contained in our body. About 4-5 liters of blood constantly circulates through the human circulatory system. At the same time, 55% of the total volume is occupied by plasma, and the remaining percentages are formed elements, of which the majority are erythrocytes - 90%.

Blood color

So, what tissue blood belongs to is more or less clear. But not everyone knows that this liquid can have different shades. For example, blood that flows through the arteries first enters the heart from the lungs and then carries oxygen throughout the body. It has a bright scarlet color. After the O2 element is distributed throughout the tissues, the blood flows back to the heart through the veins. Here this liquid becomes darker.

Properties of blood

What type of tissue is blood and what properties does it have? First of all, it should be said that this is not just a liquid. This is a substance whose viscosity depends on the percentage of red blood cells and proteins in it. Such properties affect the speed of movement, as well as blood pressure. It is the movement of the components of the composition and the density of the substance that determines the fluidity of the fabric. Individual blood cells move in completely different ways. They are able to move not only individually, but also in small groups, for example, this applies to red blood cells. These shaped elements are able to move in the center of the vessels in the form of “stacks”, which externally resemble folded coins. Of course, red blood cells can move alone. As for white cells, they usually stay along the walls of blood vessels and only one at a time.

What is plasma?

To understand what tissue blood belongs to, you should take a closer look at its components. What is plasma? This blood component is a light yellow liquid. It is almost transparent. Its shade is due to the presence of colored particles and bile pigment in its composition. Plasma is approximately 90% water. The rest of the volume is occupied by minerals and organic substances dissolved in the liquid. It is worth noting that its composition is not constant. The percentage of the same components may vary. These indicators depend on what kind of food a person ate, how much salt was in it and how much water. The composition of substances in plasma is as follows:

1. 1% - minerals, including potassium, magnesium, iron, calcium, sodium cations, iodine, sulfur, phosphorus, chlorine anions.
2. Organic substances, including about 2% uric, lactic and other acids, amino acids and fats, 7% proteins and about 0.1% glucose.

Plasma composition

Proteins that make up plasma take an active part in the exchange of water, as well as in its distribution between the blood and tissue fluid. Of course, these are not all the functions of these components. Proteins make the blood more viscous. In addition, some components are antibodies that neutralize foreign agents in the body. A special role is given to fibrinogen, a soluble protein. This substance is involved in the processes Under the influence of certain light factors, it turns into fibrin, which does not dissolve.

Blood is a type of tissue that performs special functions in the human body. Its composition is unique. Plasma also contains hormones produced by the endocrine glands. This blood component also contains substances that are necessary for the normal functioning of our body. As a rule, these are bioactive elements.

It is worth noting that plasma that does not contain fibrinogen is usually called

Red blood cells

To understand what tissue blood belongs to and why, we need to take a closer look not only at its composition, but also at what functions certain components perform. And there are not so many of them. Most of the blood contains red blood cells. These components account for 44 to 48% of the total volume. Red blood cells are disc-shaped cells that are biconcave in the center. Their diameter is approximately 7.5 microns. This form of red blood cells increases the efficiency of all physiological processes. Due to their concavity, cells have a larger area. This factor is very important for better exchange of gases. It is worth noting that mature red blood cells do not have nuclei. The main function of these blood cells is to transfer such an important substance as oxygen from the lungs to other tissues. This fact suggests that blood is a tissue that performs transport functions.

Basic properties of red blood cells

The name red blood cells means “red” in Greek. Cells owe their color to the protein hemoglobin. This substance has a very complex structure and is able to bind with oxygen. Several main parts have been identified in the composition of hemoglobin: protein - globulin, and non-protein, which contains iron. The latter substance allows oxygen to be added to cells.

Red blood cells are usually produced in the bone marrow. Full ripening occurs after five days. - no more than 120 days. These cells are destroyed in the liver and spleen. In this case, hemoglobin breaks down into globulin and non-protein components. The release of iron ions is also observed. They are returned to the bone marrow and used in the re-creation of blood cells. After the release of iron, the non-protein component of hemoglobin is converted into bilirubin, a bile pigment that enters the digestive tract along with bile. A decrease in the level of red blood cells in a person’s blood, as a rule, leads to the development of anemia, or anemia.

Leukocytes

Blood belongs to the tissues of the internal environment. In addition to plasma and red blood cells, it also contains leukocytes. These cells are completely colorless. They protect the body from exposure to harmful agents. In this case, white bodies are divided into non-granular - agranulocytes, and granular - granulocytes. The latter include eosinophils, basophils, and neutrophils. They differ in their reactions to certain dyes. Granular cells include lymphocytes and monocytes. They have granules in the cytoplasm, as well as a nucleus, which consists of segments.

Granulocytes protect the body from microorganisms. These components are able to accumulate in areas of infection and leave the vessels. The main function of monocytes is the absorption of harmful agents, and lymphocytes are the production of interferon and antibodies, as well as the destruction of cancer cells.

Platelets

It also includes platelets. These are small, colorless and nuclear-free plates, which, in fact, are fragments of cells found in the bone marrow - megakaryocytes. Platelets can be rod-shaped, spherical or oval in shape. Their lifespan is no more than 10 days. The main function of platelets is to participate in processes associated with blood clotting. These are capable of secreting substances that take part in certain reactions that are triggered when the walls of blood vessels are damaged. In this case, fibrinogen gradually turns into filaments of insoluble fibrin. Blood cells become entangled in them, resulting in a blood clot.

Basic functions of blood

Blood and lymph belong to the tissue that not only carries oxygen and other useful components to the organs, but also performs several other main functions. No one doubts that these liquids are important for humans. But not everyone knows what blood is needed for.

This fabric performs several important functions:

1. Blood refers to the tissue that protects the human body from various injuries and infections. In this case, the main role is played by leukocytes: monocytes and neutrophils. They rush to the affected areas and accumulate in this particular place. Their main function is phagocytosis, in other words, the absorption of microorganisms. In this case, monocytes are classified as macrophages, and neutrophils are classified as microphages. As for other types of white blood cells, such as lymphocytes, they produce antibodies that fight harmful agents. In addition, these blood cells are involved in removing dead and damaged tissue from the body.
2. Also, do not forget that blood is a tissue that performs transport functions. These properties are very important for the body. After all, blood supply affects almost all processes, such as breathing and digestion. Cells of liquid tissue carry oxygen throughout the body and remove carbon dioxide, end products and organic substances, transport bioactive elements and hormones.

Special function of blood

Blood is a tissue that regulates temperature. This fluid is necessary for a person to function properly in all organs. It is the blood that allows you to maintain a constant temperature. However, normally this indicator fluctuates within a fairly narrow range - approximately 37 °C.

A collection of cells and intercellular substance similar in origin, structure and functions is called cloth. In the human body they secrete 4 main groups of fabrics: epithelial, connective, muscular, nervous.

Epithelial tissue(epithelium) forms a layer of cells that make up the integument of the body and the mucous membranes of all internal organs and cavities of the body and some glands. The exchange of substances between the body and the environment occurs through epithelial tissue. In epithelial tissue, cells are very close to each other, there is little intercellular substance.

This creates an obstacle to the penetration of microbes and harmful substances and reliable protection of the tissues underlying the epithelium. Due to the fact that the epithelium is constantly exposed to various external influences, its cells die in large quantities and are replaced by new ones. Cell replacement occurs due to the ability of epithelial cells and rapid.

There are several types of epithelium - skin, intestinal, respiratory.

Derivatives of the skin epithelium include nails and hair. The intestinal epithelium is monosyllabic. It also forms glands. These are, for example, the pancreas, liver, salivary, sweat glands, etc. Enzymes secreted by the glands break down nutrients. The breakdown products of nutrients are absorbed by the intestinal epithelium and enter the blood vessels. The respiratory tract is lined with ciliated epithelium. Its cells have outward-facing motile cilia. With their help, particulate matter trapped in the air is removed from the body.

Connective tissue. A feature of connective tissue is the strong development of intercellular substance.

The main functions of connective tissue are nutritional and supporting. Connective tissue includes blood, lymph, cartilage, bone, and adipose tissue. Blood and lymph consist of a liquid intercellular substance and blood cells floating in it. These tissues provide communication between organisms, carrying various gases and substances. Fibrous and connective tissue consists of cells connected to each other by an intercellular substance in the form of fibers. The fibers can lie tightly or loosely. Fibrous connective tissue is found in all organs. Adipose tissue also looks like loose tissue. It is rich in cells that are filled with fat.

IN cartilage tissue the cells are large, the intercellular substance is elastic, dense, contains elastic and other fibers. There is a lot of cartilage tissue in the joints, between the vertebral bodies.

Bone consists of bone plates, inside of which lie cells. The cells are connected to each other by numerous thin processes. Bone tissue is hard.

Muscle. This tissue is formed by muscles. Their cytoplasm contains thin filaments capable of contraction. Smooth and striated muscle tissue is distinguished.

The fabric is called cross-striped because its fibers have a transverse striation, which is an alternation of light and dark areas. Smooth muscle tissue is part of the walls of internal organs (stomach, intestines, bladder, blood vessels). Striated muscle tissue is divided into skeletal and cardiac. Skeletal muscle tissue consists of elongated fibers reaching a length of 10–12 cm. Cardiac muscle tissue, like skeletal muscle tissue, has transverse striations. However, unlike skeletal muscle, there are special areas where the muscle fibers close tightly together. Thanks to this structure, the contraction of one fiber is quickly transmitted to neighboring ones. This ensures simultaneous contraction of large areas of the heart muscle. Muscle contraction is of great importance. The contraction of skeletal muscles ensures the movement of the body in space and the movement of some parts in relation to others. Due to smooth muscles, internal organs contract and the diameter of blood vessels changes.

Nervous tissue. The structural unit of nervous tissue is a nerve cell - a neuron.

A neuron consists of a body and processes. The neuron body can be of various shapes - oval, stellate, polygonal. A neuron has one nucleus, usually located in the center of the cell. Most neurons have short, thick, strongly branching processes near the body and long (up to 1.5 m), thin, and branching processes only at the very end. Long processes of nerve cells form nerve fibers. The main properties of a neuron are the ability to be excited and the ability to conduct this excitation along nerve fibers. In nervous tissue these properties are especially well expressed, although they are also characteristic of muscles and glands. Excitation is transmitted along the neuron and can be transmitted to other neurons or muscles connected to it, causing it to contract. The importance of the nervous tissue that forms the nervous system is enormous. Nervous tissue not only forms part of the body as part of it, but also ensures the unification of the functions of all other parts of the body.

Blood is a type of connective tissue consisting of a liquid intercellular substance of complex composition and cells suspended in it - blood cells: erythrocytes (red blood cells), leukocytes (white blood cells) and platelets (blood platelets) (Fig.). 1 mm 3 of blood contains 4.5-5 million red blood cells, 5-8 thousand leukocytes, 200-400 thousand platelets.

When blood cells precipitate in the presence of anticoagulants, a supernatant called plasma is produced. Plasma is an opalescent liquid containing all the extracellular components of blood [show] .

Most of the plasma contains sodium and chloride ions, therefore, in case of large blood losses, an isotonic solution containing 0.85% sodium chloride is injected into the veins to maintain heart function.

The red color of blood is given by red blood cells containing red respiratory pigment - hemoglobin, which absorbs oxygen in the lungs and releases it to the tissues. Blood saturated with oxygen is called arterial, and blood depleted of oxygen is called venous.

Normal blood volume averages 5200 ml in men and 3900 ml in women, or 7-8% of body weight. Plasma makes up 55% of blood volume and formed elements make up 44% of total blood volume, while other cells account for only about 1%.

If blood is allowed to clot and then the clot is separated, blood serum is obtained. Serum is the same plasma, devoid of fibrinogen, which is part of the blood clot.

According to its physicochemical properties, blood is a viscous liquid. The viscosity and density of blood depend on the relative content of blood cells and plasma proteins. Normally, the relative density of whole blood is 1.050-1.064, plasma - 1.024-1.030, cells - 1.080-1.097. The viscosity of blood is 4-5 times higher than the viscosity of water. Viscosity is important in maintaining blood pressure at a constant level.

Blood, carrying out the transport of chemical substances in the body, combines biochemical processes occurring in different cells and intercellular spaces into a single system. Such a close relationship between blood and all tissues of the body makes it possible to maintain a relatively constant chemical composition of the blood due to powerful regulatory mechanisms (CNS, hormonal system, etc.) that ensure a clear relationship in the work of such important organs and tissues as the liver, kidneys, lungs and heart. -vascular system. All random fluctuations in the composition of the blood in a healthy body quickly level out.

In many pathological processes, more or less sharp changes are observed in the chemical composition of the blood, which signal disturbances in the state of human health, make it possible to monitor the development of the pathological process and judge the effectiveness of therapeutic measures.

Erythrocytes, or red blood cells, are small (7-8 microns in diameter) anucleate cells, shaped like a biconcave disk. The absence of a nucleus allows the red blood cell to accommodate a large amount of hemoglobin, and its shape helps to increase its surface area. There are 4-5 million red blood cells in 1 mm 3 of blood. The number of red blood cells in the blood is not constant. It increases with increasing altitude, large losses of water, etc.

Throughout a person's life, red blood cells are formed from nucleated cells in the red bone marrow of the spongy bone. During the process of maturation, they lose their nucleus and enter the blood. The lifespan of human red blood cells is about 120 days, then they are destroyed in the liver and spleen and bile pigment is formed from hemoglobin.

The function of red blood cells is to transport oxygen and partially carbon dioxide. Red blood cells perform this function due to the presence of hemoglobin in them.

Hemoglobin is a red iron-containing pigment consisting of an iron porphyrin group (heme) and globin protein. 100 ml of human blood contains an average of 14 g of hemoglobin. In the pulmonary capillaries, hemoglobin, combining with oxygen, forms a fragile compound - oxidized hemoglobin (oxyhemoglobin) due to divalent heme iron. In the capillaries of tissues, hemoglobin gives up its oxygen and turns into reduced hemoglobin of a darker color, so venous blood flowing from tissues is dark red, and arterial blood, rich in oxygen, is scarlet.

Hemoglobin carries carbon dioxide from tissue capillaries to the lungs [show] .

Carbon dioxide formed in tissues enters red blood cells and, interacting with hemoglobin, is converted into carbonic acid salts - bicarbonates. This transformation occurs in several stages. Oxyhemoglobin in arterial blood erythrocytes is in the form of potassium salt - KHbO 2. In tissue capillaries, oxyhemoglobin gives up its oxygen and loses its acid properties; At the same time, carbon dioxide diffuses into the erythrocyte from the tissues through the blood plasma and, with the help of the enzyme present there - carbonic anhydrase - combines with water, forming carbonic acid - H 2 CO 3. The latter, as an acid stronger than reduced hemoglobin, reacts with its potassium salt, exchanging cations with it:

KHbO 2 → KHb + O 2; CO 2 + H 2 O → H + · NSO - 3;
KHb + H + · НСО — 3 → Н · Нb + K + · НСО — 3 ;

The potassium bicarbonate formed as a result of the reaction dissociates and its anion, due to its high concentration in the erythrocyte and the permeability of the erythrocyte membrane to it, diffuses from the cell into the plasma. The resulting lack of anions in the erythrocyte is compensated by chlorine ions, which diffuse from the plasma into the erythrocytes. In this case, a dissociated sodium salt of bicarbonate is formed in the plasma, and the same dissociated potassium chloride salt is formed in the erythrocyte:

Note that the erythrocyte membrane is impermeable to K and Na cations and that the diffusion of HCO - 3 from the erythrocyte occurs only until its concentration in the erythrocyte and plasma is equalized.

In the capillaries of the lungs, these processes go in the opposite direction:

H Hb + O 2 → H Hb0 2;
H HbO 2 + K HCO 3 → H HCO 3 + K HbO 2.

The resulting carbonic acid is broken down by the same enzyme to H 2 O and CO 2, but as the HCO 3 content in the erythrocyte decreases, these anions from the plasma diffuse into it, and the corresponding amount of Cl anions leaves the erythrocyte into the plasma. Consequently, oxygen in the blood is bound to hemoglobin, and carbon dioxide exists in the form of bicarbonate salts.

100 ml of arterial blood contains 20 ml of oxygen and 40-50 ml of carbon dioxide, venous blood contains 12 ml of oxygen and 45-55 ml of carbon dioxide. Only a very small portion of these gases are directly dissolved in the blood plasma. The bulk of blood gases, as can be seen from the above, are in a chemically bound form. With a reduced number of red blood cells in the blood or hemoglobin in red blood cells, a person develops anemia: the blood is poorly saturated with oxygen, so organs and tissues receive insufficient amounts of it (hypoxia).

Leukocytes, or white blood cells, - colorless blood cells with a diameter of 8-30 microns, of variable shape, having a nucleus; The normal number of leukocytes in the blood is 6-8 thousand per 1 mm3. Leukocytes are formed in the red bone marrow, liver, spleen, lymph nodes; their lifespan can vary from several hours (neutrophils) to 100-200 or more days (lymphocytes). They are also destroyed in the spleen.

Based on their structure, leukocytes are divided into several [the link is available to registered users who have 15 messages on the forum], each of which performs specific functions. The percentage of these groups of leukocytes in the blood is called the leukocyte formula.

The main function of leukocytes is to protect the body from bacteria, foreign proteins, and foreign bodies. [show] .

According to modern views, the body’s defense, i.e. its immunity to various factors that carry genetically foreign information is ensured by immunity, represented by a variety of cells: leukocytes, lymphocytes, macrophages, etc., thanks to which foreign cells or complex organic substances that enter the body, different from the cells and substances of the body, are destroyed and eliminated .

Immunity maintains the genetic constancy of the organism in ontogenesis. When cells divide as a result of mutations in the body, cells with an altered genome are often formed. To ensure that these mutant cells during further division do not lead to disturbances in the development of organs and tissues, they are destroyed by the body’s immune systems. In addition, immunity is manifested in the body's immunity to transplanted organs and tissues from other organisms.

The first scientific explanation of the nature of immunity was given by I. I. Mechnikov, who came to the conclusion that immunity is provided due to the phagocytic properties of leukocytes. Later it was found that, in addition to phagocytosis (cellular immunity), the ability of leukocytes to produce protective substances - antibodies, which are soluble protein substances - immunoglobulins (humoral immunity), produced in response to the appearance of foreign proteins in the body, is of great importance for immunity. In blood plasma, antibodies glue foreign proteins together or break them down. Antibodies that neutralize microbial poisons (toxins) are called antitoxins.

All antibodies are specific: they are active only against certain microbes or their toxins. If a person’s body has specific antibodies, it becomes immune to certain infectious diseases.

There are innate and acquired immunity. The first provides immunity to a particular infectious disease from the moment of birth and is inherited from parents, and immune bodies can penetrate through the placenta from the vessels of the mother’s body into the vessels of the embryo or newborns receive them with mother’s milk.

Acquired immunity appears after suffering an infectious disease, when antibodies are formed in the blood plasma in response to foreign proteins of a given microorganism. In this case, natural, acquired immunity occurs.

Immunity can be developed artificially by introducing weakened or killed pathogens of a disease into the human body (for example, smallpox vaccination). This immunity does not occur immediately. For its manifestation, time is required for the body to produce antibodies against the introduced weakened microorganism. Such immunity usually lasts for years and is called active.

The world's first vaccination against smallpox was carried out by the English doctor E. Jenner.

Immunity acquired by introducing immune serum from the blood of animals or humans into the body is called passive (for example, anti-measles serum). It appears immediately after the administration of the serum, persists for 4-6 weeks, and then the antibodies are gradually destroyed, immunity weakens, and repeated administration of the immune serum is necessary to maintain it.

The ability of leukocytes to move independently with the help of pseudopods allows them, making amoeboid movements, to penetrate through the walls of capillaries into the intercellular spaces. They are sensitive to the chemical composition of substances secreted by microbes or decayed cells of the body, and move towards these substances or decayed cells. Having come into contact with them, leukocytes envelop them with their pseudopods and pull them into the cell, where they are broken down with the participation of enzymes (intracellular digestion). In the process of interaction with foreign bodies, many leukocytes die. In this case, decay products accumulate around the foreign body and pus is formed.

This phenomenon was discovered by I.I. Mechnikov. I. I. Mechnikov called leukocytes that capture various microorganisms and digest them phagocytes, and the phenomenon of absorption and digestion itself was called phagocytosis. Phagocytosis is a protective reaction of the body.

The phagocytic ability of leukocytes is extremely important because it protects the body from infection. But in certain cases, this property of white blood cells can be harmful, for example during organ transplantation. Leukocytes react to transplanted organs in the same way as to pathogenic microorganisms - they phagocytose and destroy them. To avoid an undesirable reaction of leukocytes, phagocytosis is inhibited with special substances.

Platelets, or blood platelets, - colorless cells 2-4 microns in size, the number of which is 200-400 thousand in 1 mm 3 of blood. They are formed in the bone marrow. Platelets are very fragile and are easily destroyed when blood vessels are damaged or when blood comes into contact with air. At the same time, a special substance thromboplastin is released from them, which promotes blood clotting.

Blood plasma proteins

Of the 9-10% of the dry residue of blood plasma, proteins account for 6.5-8.5%. Using the method of salting out with neutral salts, blood plasma proteins can be divided into three groups: albumins, globulins, fibrinogen. The normal content of albumin in blood plasma is 40-50 g/l, globulin - 20-30 g/l, fibrinogen - 2-4 g/l. Blood plasma devoid of fibrinogen is called serum.

The synthesis of blood plasma proteins occurs primarily in the cells of the liver and reticuloendothelial system. The physiological role of blood plasma proteins is multifaceted.

1. Proteins maintain colloid osmotic (oncotic) pressure and thereby maintain a constant blood volume. The protein content in plasma is significantly higher than in tissue fluid. Proteins, being colloids, bind water and retain it, preventing it from leaving the bloodstream. Despite the fact that oncotic pressure makes up only a small part (about 0.5%) of the total osmotic pressure, it determines the predominance of the osmotic pressure of the blood over the osmotic pressure of the tissue fluid. It is known that in the arterial part of the capillaries, as a result of hydrostatic pressure, protein-free blood fluid penetrates into the tissue space. This occurs up to a certain point - the “turning point”, when the falling hydrostatic pressure becomes equal to the colloid-osmotic pressure. After the “turning” moment, a reverse flow of fluid from the tissue occurs in the venous part of the capillaries, since now the hydrostatic pressure is less than the colloid osmotic pressure. Under other conditions, as a result of hydrostatic pressure in the circulatory system, water would seep into the tissues, which would cause swelling of various organs and subcutaneous tissue.
2. Plasma proteins take an active part in blood clotting. A number of plasma proteins, including fibrinogen, are the main components of the blood coagulation system.
3. Plasma proteins to a certain extent determine the viscosity of the blood, which, as already noted, is 4-5 times higher than the viscosity of water and plays an important role in maintaining hemodynamic relations in the circulatory system.
4. Plasma proteins take part in maintaining a constant blood pH, as they constitute one of the most important buffer systems in the blood.
5. The transport function of blood plasma proteins is also important: combining with a number of substances (cholesterol, bilirubin, etc.), as well as with drugs (penicillin, salicylates, etc.), they transport them into the tissue.
6. Blood plasma proteins play an important role in immune processes (especially immunoglobulins).
7. As a result of the formation of non-dialyzable compounds with plasma proteins, the level of cations in the blood is maintained. For example, 40-50% of serum calcium is bound to proteins, and a significant portion of iron, magnesium, copper and other elements are also bound to whey proteins.
8. Finally, blood plasma proteins can serve as a reserve of amino acids.

Modern physicochemical research methods have made it possible to discover and describe about 100 different protein components of blood plasma. At the same time, the electrophoretic separation of blood plasma (serum) proteins has acquired particular importance. [show] .

In the blood serum of a healthy person, electrophoresis on paper can detect five fractions: albumin, α 1, α 2, β- and γ-globulins (Fig. 125). By electrophoresis in agar gel, up to 7-8 fractions are detected in blood serum, and by electrophoresis in starch or polyacrylamide gel - up to 16-17 fractions.

It should be remembered that the terminology of protein fractions obtained by various types of electrophoresis has not yet been completely established. When changing electrophoresis conditions, as well as during electrophoresis in different media (for example, in starch or polyacrylamide gel), the migration rate and, consequently, the order of protein zones can change.

An even larger number of protein fractions (about 30) can be obtained using the immunoelectrophoresis method. Immunoelectrophoresis is a unique combination of electrophoretic and immunological methods for analyzing proteins. In other words, the term “immunoelectrophoresis” means carrying out electrophoresis and precipitation reactions in the same medium, i.e. directly on the gel block. With this method, using a serological precipitation reaction, a significant increase in the analytical sensitivity of the electrophoretic method is achieved. In Fig. 126 shows a typical immunoelectropherogram of human serum proteins.

Characteristics of the main protein fractions

• Albumin [show] .

  Albumin accounts for more than half (55-60%) of human blood plasma proteins. The molecular weight of albumin is about 70,000. Serum albumin is renewed relatively quickly (the half-life of human albumin is 7 days).

  Due to their high hydrophilicity, especially due to the relatively small size of the molecules and significant concentration in serum, albumins play an important role in maintaining colloid osmotic pressure of the blood. It is known that serum albumin concentrations below 30 g/l cause significant changes in blood oncotic pressure, which leads to edema. Albumins perform an important function in transporting many biologically active substances (in particular, hormones). They are able to bind to cholesterol and bile pigments. A significant portion of serum calcium is also bound to albumin.

  When electrophoresis in starch gel, the albumin fraction in some people is sometimes divided into two (albumin A and albumin B), i.e., such people have two independent genetic loci that control albumin synthesis. The additional fraction (albumin B) differs from regular serum albumin in that the molecules of this protein contain two or more dicarboxylic amino acid residues that replace tyrosine or cystine residues in the polypeptide chain of regular albumin. There are other rare variants of albumin (Reading albumin, Gent albumin, Maki albumin). Inheritance of albumin polymorphism occurs in an autosomal codominant manner and is observed over several generations.

  In addition to hereditary albumin polymorphism, transient bisalbuminemia occurs, which in some cases can be mistaken for congenital. The appearance of a fast component of albumin in patients receiving large doses of penicillin has been described. After discontinuation of penicillin, this fast component of albumin soon disappeared from the blood. There is an assumption that the increase in the electrophoretic mobility of the albumin-antibiotic fraction is associated with an increase in the negative charge of the complex due to the COOH groups of penicillin.

• Globulins [show] .

  When salted out with neutral salts, serum globulins can be divided into two fractions - euglobulins and pseudoglobulins. It is believed that the euglobulin fraction mainly consists of γ-globulins, and the pseudoglobulin fraction includes α-, β- and γ-globulins.

  α-, β- and γ-globulins are heterogeneous fractions that, during electrophoresis, especially in starch or polyacrylamide gels, can be separated into a number of subfractions. It is known that α- and β-globulin fractions contain lipoproteins and glycoproteins. Among the components of α- and β-globulins there are also metal-bound proteins. Most of the antibodies contained in serum are in the γ-globulin fraction. A decrease in the protein content of this fraction sharply reduces the body's defenses.

In clinical practice, there are conditions characterized by changes in both the total amount of blood plasma proteins and the percentage of individual protein fractions.

As noted, α- and β-globulin fractions of serum proteins contain lipoproteins and glycoproteins. The carbohydrate part of blood glycoproteins mainly includes the following monosaccharides and their derivatives: galactose, mannose, fucose, rhamnose, glucosamine, galactosamine, neuraminic acid and its derivatives (sialic acids). The ratio of these carbohydrate components in individual serum glycoproteins is different.

Most often, aspartic acid (its carboxyl) and glucosamine take part in the connection between the protein and carbohydrate parts of the glycoprotein molecule. Somewhat less common is the connection between the hydroxyl of threonine or serine and hexosamines or hexoses.

Neuramic acid and its derivatives (sialic acids) are the most labile and active components of glycoproteins. They occupy the final position in the carbohydrate chain of the glycoprotein molecule and largely determine the properties of this glycoprotein.

Glycoproteins are present in almost all protein fractions of blood serum. When electrophoresis on paper, glycoproteins are detected in greater quantities in the α 1 - and α 2 -fractions of globulins. Glycoproteins associated with α-globulin fractions contain little fucose; at the same time, glycoproteins detected in the β- and especially γ-globulin fractions contain significant amounts of fucose.

An increased content of glycoproteins in plasma or serum is observed in tuberculosis, pleurisy, pneumonia, acute rheumatism, glomerulonephritis, nephrotic syndrome, diabetes, myocardial infarction, gout, as well as in acute and chronic leukemia, myeloma, lymphosarcoma and some other diseases. In patients with rheumatism, an increase in the content of glycoproteins in the serum corresponds to the severity of the disease. This is explained, according to a number of researchers, by depolymerization of the main substance of connective tissue during rheumatism, which leads to the entry of glycoproteins into the blood.

Plasma lipoproteins- these are complex complex compounds with a characteristic structure: inside the lipoprotein particle there is a fat drop (core) containing non-polar lipids (triglycerides, esterified cholesterol). The fat droplet is surrounded by a membrane that contains phospholipids, protein and free cholesterol. The main function of plasma lipoproteins is the transport of lipids in the body.

Several classes of lipoproteins have been found in human blood plasma.

• α-lipoproteins, or high-density lipoproteins (HDL). During electrophoresis on paper, they migrate together with α-globulins. HDL is rich in protein and phospholipids, and is constantly found in the blood plasma of healthy people at a concentration of 1.25-4.25 g/l in men and 2.5-6.5 g/l in women.
• β-lipoproteins, or low-density lipoproteins (LDL). They correspond in electrophoretic mobility to β-globulins. They are the most cholesterol-rich class of lipoproteins. The level of LDL in the blood plasma of healthy people is 3.0-4.5 g/l.
• pre-β-lipoproteins, or very low density lipoproteins (VLDL). Located on the lipoproteinogram between α- and β-lipoproteins (electrophoresis on paper), they serve as the main transport form of endogenous triglycerides.
• Chylomicrons (CM). They do not move during electrophoresis either to the cathode or to the anode and remain at the start (the place where the test plasma or serum sample is applied). They are formed in the intestinal wall during the absorption of exogenous triglycerides and cholesterol. First, chemical substances enter the thoracic lymphatic duct, and from it into the bloodstream. ChMs are the main transport form of exogenous triglycerides. The blood plasma of healthy people who have not eaten for 12-14 hours does not contain CM.

It is believed that the main place of formation of plasma pre-β-lipoproteins and α-lipoproteins is the liver, and β-lipoproteins are formed from pre-β-lipoproteins in the blood plasma under the action of lipoprotein lipase.

It should be noted that electrophoresis of lipoproteins can be carried out both on paper and in agar, starch and polyacrylamide gels, cellulose acetate. When choosing an electrophoresis method, the main criterion is to clearly obtain four types of lipoproteins. Electrophoresis of lipoproteins in polyacrylamide gel is currently the most promising. In this case, the fraction of pre-β-lipoproteins is detected between CM and β-lipoproteins.

In a number of diseases, the lipoprotein spectrum of blood serum may change.

According to the existing classification of hyperlipoproteinemia, the following five types of deviation of the lipoprotein spectrum from the norm have been established [show] .

• Type I - hyperchylomicronemia. The main changes in the lipoproteinogram are as follows: high content of CM, normal or slightly increased content of pre-β-lipoproteins. A sharp increase in serum triglyceride levels. Clinically, this condition manifests itself as xanthomatosis.
• Type II - hyper-β-lipoproteinemia. This type is divided into two subtypes:
  • IIa, characterized by a high level of p-lipoproteins (LDL) in the blood,
  • IIb, characterized by a high content of two classes of lipoproteins simultaneously - β-lipoproteins (LDL) and pre-β-lipoproteins (VLDL).

  In type II, there is a high, and in some cases very high, cholesterol content in the blood plasma. The content of triglycerides in the blood can be either normal (type IIa) or elevated (type IIb). Type II is clinically manifested by atherosclerotic disorders, and coronary heart disease often develops.

• Type III - “floating” hyperlipoproteinemia or dys-β-lipoproteinemia. Lipoproteins with an unusually high cholesterol content and high electrophoretic mobility (“pathological” or “floating” β-lipoproteins) appear in the blood serum. They accumulate in the blood due to a violation of the conversion of pre-β-lipoproteins into β-lipoproteins. This type of hyperlipoproteinemia is often combined with various manifestations of atherosclerosis, including coronary heart disease and damage to the blood vessels of the legs.
• Type IV - hyperpre-β-lipoproteinemia. Increased levels of pre-β-lipoproteins, normal levels of β-lipoproteins, absence of CM. Increased triglyceride levels with normal or slightly elevated cholesterol levels. Clinically, this type is combined with diabetes, obesity, and coronary heart disease.
• Type V - hyperpre-β-lipoproteinemia and chylomicronemia. There is an increase in the level of pre-β-lipoproteins and the presence of CM. Clinically manifested by xanthomatosis, sometimes combined with latent diabetes. Coronary heart disease is not observed with this type of hyperlipoproteinemia.

Some of the most studied and clinically interesting plasma proteins

• Haptoglobin [show] .

  Haptoglobin is part of the α 2 -globulin fraction. This protein has the ability to bind to hemoglobin. The resulting haptoglobin-hemoglobin complex can be absorbed by the reticuloendothelial system, thereby preventing the loss of iron, which is part of hemoglobin, both during physiological and pathological release from erythrocytes.

  Electrophoresis revealed three groups of haptoglobins, which were designated as Hp 1-1, Hp 2-1 and Hp 2-2. It has been established that there is a connection between the inheritance of haptoglobin types and Rh antibodies.

• Trypsin inhibitors [show] .

  It is known that during electrophoresis of blood plasma proteins, proteins capable of inhibiting trypsin and other proteolytic enzymes move in the zone of α 1 and α 2 globulins. Normally, the content of these proteins is 2.0-2.5 g/l, but during inflammatory processes in the body, during pregnancy and a number of other conditions, the content of proteins - inhibitors of proteolytic enzymes increases.

• Transferrin [show] .

  Transferrin belongs to β-globulins and has the ability to combine with iron. Its complex with iron is orange. In the iron transferrin complex, iron is in the trivalent form. The concentration of transferrin in the blood serum is about 2.9 g/l. Normally, only 1/3 of transferrin is saturated with iron. Consequently, there is a certain reserve of transferrin capable of binding iron. Transferrin can be of different types in different people. 19 types of transferrin have been identified, differing in the charge of the protein molecule, its amino acid composition and the number of sialic acid molecules associated with the protein. The detection of different types of transferrins is associated with heredity.

• Ceruloplasmin [show] .

  This protein has a bluish color due to the presence of 0.32% copper in its composition. Ceruloplasmin is an oxidase of ascorbic acid, adrenaline, dioxyphenylalanine and some other compounds. In hepatolenticular degeneration (Wilson-Konovalov disease), the content of ceruloplasmin in the blood serum is significantly reduced, which is an important diagnostic test.

  Using enzyme electrophoresis, the presence of four isoenzymes of ceruloplasmin was established. Normally, two isoenzymes are found in the blood serum of adults, which differ markedly in their mobility when electrophoresed in acetate buffer at pH 5.5. Two fractions were also found in the serum of newborn children, but these fractions have a higher electrophoretic mobility than adult ceruloplasmin isoenzymes. It should be noted that in terms of its electrophoretic mobility, the isoenzyme spectrum of ceruloplasmin in blood serum in Wilson-Konovalov disease is similar to the isoenzyme spectrum of newborn children.

• C-reactive protein [show] .

  This protein received its name as a result of its ability to undergo a precipitation reaction with the C-polysaccharide of pneumococci. C-reactive protein is absent in the blood serum of a healthy body, but is found in many pathological conditions accompanied by inflammation and tissue necrosis.

  C-reactive protein appears during the acute period of the disease, so it is sometimes called the “acute phase” protein. With the transition to the chronic phase of the disease, C-reactive protein disappears from the blood and appears again when the process worsens. During electrophoresis, the protein moves together with α 2 globulins.

• Cryoglobulin [show] .

  Cryoglobulin is also absent in the blood serum of healthy people and appears in it under pathological conditions. A distinctive property of this protein is the ability to precipitate or gel when the temperature drops below 37°C. During electrophoresis, cryoglobulin most often moves together with γ-globulins. Cryoglobulin can be detected in blood serum in cases of myeloma, nephrosis, liver cirrhosis, rheumatism, lymphosarcoma, leukemia and other diseases.

• Interferon [show] .

  Interferon- a specific protein synthesized in the cells of the body as a result of exposure to viruses. In turn, this protein has the ability to inhibit the reproduction of the virus in cells, but does not destroy existing viral particles. The interferon formed in the cells easily enters the bloodstream and from there re-enters the tissues and cells. Interferon is species specific, although not absolute. For example, monkey interferon inhibits the reproduction of the virus in human cell culture. The protective effect of interferon largely depends on the ratio between the rates of spread of the virus and interferon in the blood and tissues.

• Immunoglobulins [show] .

  Until recently, four main classes of immunoglobulins included in the γ-globulin fraction were known: IgG, IgM, IgA and IgD. In recent years, a fifth class of immunoglobulins, IgE, has been discovered. Immunoglobulins practically have a single structure plan; they consist of two heavy polypeptide chains H (mol. wt 50,000-75,000) and two light chains L (mol. wt ~ 23,000), connected by three disulfide bridges. In this case, human immunoglobulins can contain two types of L chains (K or λ). In addition, each class of immunoglobulins has its own type of heavy chain H: IgG - γ-chain, IgA - α-chain, IgM - μ-chain, IgD - σ-chain and IgE - ε-chain, which differ in amino acid composition. IgA and IgM are oligomers, i.e. the four-chain structure in them is repeated several times.

  
  

  Each type of immunoglobulin can specifically interact with a specific antigen. The term "immunoglobulins" refers not only to normal classes of antibodies, but also to a larger number of so-called pathological proteins, for example myeloma proteins, the increased synthesis of which occurs in multiple myeloma. As already noted, in the blood of this disease, myeloma proteins accumulate in relatively high concentrations, and Bence-Jones protein is found in the urine. It turned out that Bence-Jones protein consists of L-chains, which are apparently synthesized in the patient's body in excess quantities compared to H-chains and are therefore excreted in the urine. The C-terminal half of the polypeptide chain of Bence-Jones protein molecules (actually L-chains) in all patients with multiple myeloma has the same sequence, and the N-terminal half (107 amino acid residues) of the L-chains has a different primary structure. A study of the N-chains of myeloma blood plasma proteins also revealed an important pattern: the N-terminal fragments of these chains in different patients have different primary structures, while the rest of the chain remains unchanged. It was concluded that the variable regions of the L- and H-chains of immunoglobulins are the site of specific binding of antigens.

  In many pathological processes, the content of immunoglobulins in blood serum changes significantly. Thus, with chronic aggressive hepatitis there is an increase in IgG, with alcoholic cirrhosis - IgA and with primary biliary cirrhosis - IgM. It has been shown that the concentration of IgE in blood serum increases in bronchial asthma, nonspecific eczema, ascariasis and some other diseases. It is important to note that children who have IgA deficiency are more likely to develop infectious diseases. It can be assumed that this is a consequence of insufficient synthesis of a certain part of the antibodies.

  Complement system

  The complement system of human blood serum includes 11 proteins with a molecular weight from 79,000 to 400,000. The cascade mechanism of their activation is triggered during the reaction (interaction) of an antigen with an antibody:

  

  As a result of the action of complement, the destruction of cells through their lysis, as well as the activation of leukocytes and their absorption of foreign cells as a result of phagocytosis are observed.

  According to the sequence of functioning, proteins of the human serum complement system can be divided into three groups:

  1. “recognition group”, which includes three proteins and binds the antibody on the surface of the target cell (this process is accompanied by the release of two peptides);
  2. both peptides on another part of the surface of the target cell interact with three proteins of the “activating group” of the complement system, and two peptides are also formed;
  3. newly isolated peptides contribute to the formation of a group of “membrane attack” proteins, consisting of 5 proteins of the complement system, cooperatively interacting with each other on the third area of ​​the surface of the target cell. The binding of membrane attack proteins to the cell surface destroys it by forming end-to-end channels in the membrane.

  Blood plasma (serum) enzymes

  Enzymes that are normally found in plasma or serum can, however somewhat arbitrarily, be divided into three groups:

  • Secretory - synthesized in the liver, they are normally released into the blood plasma, where they play a certain physiological role. Typical representatives of this group are enzymes involved in the process of blood clotting (see p. 639). Serum cholinesterase belongs to this group.
  • Indicator (cellular) enzymes perform certain intracellular functions in tissues. Some of them are concentrated mainly in the cytoplasm of the cell (lactate dehydrogenase, aldolase), others - in mitochondria (glutamate dehydrogenase), others - in lysosomes (β-glucuronidase, acid phosphatase), etc. Most of the indicator enzymes in blood serum are determined only in trace amounts. When certain tissues are damaged, the activity of many indicator enzymes increases sharply in the blood serum.
  • Excretory enzymes are synthesized mainly in the liver (leucine aminopeptidase, alkaline phosphatase, etc.). Under physiological conditions, these enzymes are mainly excreted in bile. The mechanisms regulating the entry of these enzymes into bile capillaries have not yet been fully elucidated. In many pathological processes, the release of these enzymes with bile is disrupted and the activity of excretory enzymes in the blood plasma increases.

  Of particular clinical interest is the study of the activity of indicator enzymes in blood serum, since the appearance of a number of tissue enzymes in unusual quantities in plasma or serum can indicate the functional state and disease of various organs (for example, liver, cardiac and skeletal muscles).

  Thus, from the point of view of diagnostic value, studies of enzyme activity in blood serum during acute myocardial infarction can be compared with the electrocardiographic diagnostic method introduced several decades ago. Determination of enzyme activity during myocardial infarction is advisable in cases where the course of the disease and electrocardiographic data are atypical. In acute myocardial infarction, it is especially important to study the activity of creatine kinase, aspartate aminotransferase, lactate dehydrogenase and hydroxybutyrate dehydrogenase.

  In case of liver diseases, in particular with viral hepatitis (Botkin's disease), the activity of alanine and aspartate aminotransferases, sorbitol dehydrogenase, glutamate dehydrogenase and some other enzymes in the blood serum changes significantly, and the activity of histidase and urocaninase appears. Most of the enzymes contained in the liver are also present in other organs and tissues. However, there are enzymes that are more or less specific to liver tissue. Organ-specific enzymes for the liver are: histidase, urocaninase, ketose-1-phosphate aldolase, sorbitol dehydrogenase; ornithine carbamoyltransferase and, to a slightly lesser extent, glutamate dehydrogenase. Changes in the activity of these enzymes in the blood serum indicate damage to the liver tissue.

  In the last decade, the study of isoenzyme activity in blood serum, in particular lactate dehydrogenase isoenzymes, has become a particularly important laboratory test.

  It is known that in the heart muscle the isoenzymes LDH 1 and LDH 2 are most active, and in the liver tissue - LDH 4 and LDH 5. It has been established that in patients with acute myocardial infarction, the activity of isoenzymes LDH 1 and partly LDH 2 sharply increases in the blood serum. The isoenzyme spectrum of lactate dehydrogenase in blood serum during myocardial infarction resembles the isoenzyme spectrum of the heart muscle. On the contrary, with parenchymal hepatitis in the blood serum the activity of the isoenzymes LDH 5 and LDH 4 increases significantly and the activity of LDH 1 and LDH 2 decreases.

  The study of the activity of creatine kinase isoenzymes in blood serum is also of diagnostic importance. There are at least three creatine kinase isoenzymes: BB, MM and MB. The BB isoenzyme is mainly present in brain tissue, and the MM form is present in skeletal muscles. The heart contains predominantly the MM form, as well as the MV form.

  Creatine kinase isoenzymes are especially important to study in acute myocardial infarction, since the MB form is found in significant quantities almost only in the heart muscle. Therefore, an increase in the activity of the MB form in the blood serum indicates damage to the heart muscle. Apparently, the increase in enzyme activity in the blood serum in many pathological processes is explained by at least two reasons: 1) the release of enzymes into the bloodstream from damaged areas of organs or tissues against the background of their ongoing biosynthesis in damaged tissues and 2) a simultaneous sharp increase in catalytic activity tissue enzymes that pass into the blood.

  It is possible that a sharp increase in enzyme activity when the mechanisms of intracellular regulation of metabolism break down is associated with the cessation of the action of the corresponding enzyme inhibitors, a change under the influence of various factors in the secondary, tertiary and quaternary structures of enzyme macromolecules, which determine their catalytic activity.

  Non-protein nitrogenous components of blood

  The content of non-protein nitrogen in whole blood and plasma is almost the same and is 15-25 mmol/l in the blood. Non-protein nitrogen in the blood includes urea nitrogen (50% of the total amount of non-protein nitrogen), amino acids (25%), ergothioneine - a compound found in red blood cells (8%), uric acid (4%), creatine (5%), creatinine ( 2.5%), ammonia and indican (0.5%) and other non-protein substances containing nitrogen (polypeptides, nucleotides, nucleosides, glutathione, bilirubin, choline, histamine, etc.). Thus, the composition of non-protein nitrogen in the blood consists mainly of nitrogen from the end products of metabolism of simple and complex proteins.

  Non-protein nitrogen in the blood is also called residual nitrogen, that is, remaining in the filtrate after precipitation of proteins. In a healthy person, fluctuations in the content of non-protein, or residual, blood nitrogen are insignificant and mainly depend on the amount of protein ingested from food. In a number of pathological conditions, the level of non-protein nitrogen in the blood increases. This condition is called azotemia. Azotemia, depending on the reasons that caused it, is divided into retention and production. Retention azotemia occurs as a result of insufficient excretion of nitrogen-containing products in the urine during their normal entry into the bloodstream. It, in turn, can be renal or extrarenal.

  With renal retention azotemia, the concentration of residual nitrogen in the blood increases due to a weakening of the cleansing (excretory) function of the kidneys. A sharp increase in the content of residual nitrogen during retention renal azotemia occurs mainly due to urea. In these cases, urea nitrogen accounts for 90% of the non-protein nitrogen in the blood instead of 50% normally. Extrarenal retention azotemia may result from severe circulatory failure, decreased blood pressure, and decreased renal blood flow. Often, extrarenal retention azotemia is the result of an obstruction to the outflow of urine after its formation in the kidney.

  Table 46. Content of free amino acids in human blood plasma
  Amino acids	Content, µmol/l
  Alanin	360-630
  Arginine	92-172
  Asparagine	50-150
  Aspartic acid	150-400
  Valin	188-274
  Glutamic acid	54-175
  Glutamine	514-568
  Glycine	100-400
  Histidine	110-135
  Isoleucine	122-153
  Leucine	130-252
  Lysine	144-363
  Methionine	20-34
  Ornithine	30-100
  Proline	50-200
  Serin	110
  Threonine	160-176
  Tryptophan	49
  Tyrosine	78-83
  Phenylalanine	85-115
  Citrulline	10-50
  Cystine	84-125

  Productive azotemia observed when there is an excessive intake of nitrogen-containing products into the blood, as a result of increased breakdown of tissue proteins. Mixed azotemia is often observed.

  As already noted, in terms of quantity, the main end product of protein metabolism in the body is urea. It is generally accepted that urea is 18 times less toxic than other nitrogenous substances. In acute renal failure, the concentration of urea in the blood reaches 50-83 mmol/l (normal 3.3-6.6 mmol/l). An increase in the urea content in the blood to 16.6-20.0 mmol/l (calculated on urea nitrogen [The value of the urea nitrogen content is approximately 2 times, or more precisely 2.14 times less than the number expressing the concentration of urea.]) is a sign renal dysfunction of moderate severity, up to 33.3 mmol/l - severe and over 50 mmol/l - very severe impairment with an unfavorable prognosis. Sometimes a special coefficient is determined or, more precisely, the ratio of blood urea nitrogen to residual blood nitrogen, expressed as a percentage: (Urea Nitrogen / Residual Nitrogen) X 100

  Normally the ratio is below 48%. With renal failure, this figure increases and can reach 90%, and if the urea-forming function of the liver is impaired, the coefficient decreases (below 45%).

  Uric acid is also an important protein-free nitrogenous substance in the blood. Let us recall that in humans, uric acid is the end product of the metabolism of purine bases. Normally, the concentration of uric acid in whole blood is 0.18-0.24 mmol/l (in serum - about 0.29 mmol/l). An increase in uric acid in the blood (hyperuricemia) is the main symptom of gout. With gout, the level of uric acid in the blood serum increases to 0.47-0.89 mmol/l and even to 1.1 mmol/l; The residual nitrogen also includes nitrogen from amino acids and polypeptides.

  The blood always contains a certain amount of free amino acids. Some of them are of exogenous origin, that is, they enter the blood from the gastrointestinal tract, while the other part of the amino acids is formed as a result of the breakdown of tissue proteins. Almost a fifth of the amino acids contained in plasma are glutamic acid and glutamine (Table 46). Naturally, the blood contains aspartic acid, asparagine, cysteine, and many other amino acids that are part of natural proteins. The content of free amino acids in serum and blood plasma is almost the same, but differs from their level in erythrocytes. Normally, the ratio of the amino acid nitrogen concentration in erythrocytes to the amino acid nitrogen content in plasma ranges from 1.52 to 1.82. This ratio (coefficient) is characterized by great constancy, and only in some diseases is its deviation from the norm observed.

  Total determination of the level of polypeptides in the blood is performed relatively rarely. However, it should be remembered that many of the blood polypeptides are biologically active compounds and their determination is of great clinical interest. Such compounds, in particular, include kinins.

  Kinins and blood kinin system

  Kinins are sometimes called kinin hormones, or local hormones. They are not produced in specific endocrine glands, but are released from inactive precursors that are constantly present in the interstitial fluid of a number of tissues and in the blood plasma. Kinins are characterized by a wide range of biological effects. This action is mainly aimed at the smooth muscles of blood vessels and the capillary membrane; hypotensive effect is one of the main manifestations of the biological activity of kinins.

  

  The most important plasma kinins are bradykinin, kallidin and methionyl-lysyl-bradykinin. In fact, they form a kinin system, which ensures the regulation of local and general blood flow and the permeability of the vascular wall.

  The structure of these kinins has been fully established. Bradykinin is a polypeptide of 9 amino acids, kallidin (lysyl-bradykinin) is a polypeptide of 10 amino acids.

  In blood plasma, the content of kinins is usually very low (for example, bradykinin 1-18 nmol/l). The substrate from which kinins are released is called kininogen. There are several kininogens in the blood plasma (at least three). Kininogens are proteins associated in the blood plasma with the α 2 -globulin fraction. The site of kininogen synthesis is the liver.

  The formation (cleavage) of kinins from kininogens occurs with the participation of specific enzymes - kininogenases, which are called kallikreins (see diagram). Kallikreins are trypsin-type proteinases; they break peptide bonds in the formation of which the NOOS groups of arginine or lysine are involved; Proteolysis of proteins in a broad sense is not characteristic of these enzymes.

  There are blood plasma kallikreins and tissue kallikreins. One of the kallikrein inhibitors is a polyvalent inhibitor isolated from the lungs and salivary gland of a bovine, known as trasylol. It is also a trypsin inhibitor and is used therapeutically for acute pancreatitis.

  Part of bradykinin can be formed from kallidin as a result of cleavage of lysine with the participation of aminopeptidases.

  In blood plasma and tissues, kallikreins are found mainly in the form of their precursors - kallikreinogens. It has been proven that the direct activator of kallikreinogen in blood plasma is the Hageman factor (see p. 641).

  Kinins have a short-term effect in the body; they are quickly inactivated. This is explained by the high activity of kininases - enzymes that inactivate kinins. Kininases are found in blood plasma and almost all tissues. It is the high activity of kininases in blood plasma and tissues that determines the local nature of the action of kinins.

  As already noted, the physiological role of the kinin system is reduced mainly to the regulation of hemodynamics. Bradykinin is the most powerful vasodilator. Kinins act directly on vascular smooth muscle, causing it to relax. They also actively influence capillary permeability. Bradykinin in this regard is 10-15 times more active than histamine.

  There is evidence that bradykinin, by increasing vascular permeability, promotes the development of atherosclerosis. A close connection between the kinin system and the pathogenesis of inflammation has been established. It is possible that the kinin system plays an important role in the pathogenesis of rheumatism, and the therapeutic effect of salicylates is explained by inhibition of bradykinin formation. Vascular abnormalities characteristic of shock are also likely associated with shifts in the kinin system. The participation of kinins in the pathogenesis of acute pancreatitis is also known.

  An interesting feature of kinins is their bronchoconstrictor effect. It has been shown that the activity of kininases in the blood of asthma sufferers is sharply reduced, which creates favorable conditions for the manifestation of the action of bradykinin. There is no doubt that research into the role of the kinin system in bronchial asthma is very promising.

  Nitrogen-free organic blood components

  The group of nitrogen-free organic substances in the blood includes carbohydrates, fats, lipoids, organic acids and some other substances. All these compounds are either products of intermediate metabolism of carbohydrates and fats, or play the role of nutrients. Basic data characterizing the content of various nitrogen-free organic substances in the blood are presented in table. 43. In the clinic, great importance is attached to the quantitative determination of these components in the blood.

  Electrolyte composition of blood plasma

  It is known that the total water content in the human body is 60-65% of body weight, i.e. approximately 40-45 l (if body weight is 70 kg); 2/3 of the total amount of water is intracellular fluid, 1/3 is extracellular fluid. Part of the extracellular water is in the vascular bed (5% of body weight), while the majority is outside the vascular bed - this is interstitial, or tissue, fluid (15% of body weight). In addition, a distinction is made between “free water”, which forms the basis of intra- and extracellular fluids, and water associated with colloids (“bound water”).

  The distribution of electrolytes in body fluids is very specific in its quantitative and qualitative composition.

  Of the plasma cations, sodium occupies a leading place and makes up 93% of their total quantity. Among the anions, chlorine should be distinguished first, followed by bicarbonate. The sum of anions and cations is almost the same, i.e. the entire system is electrically neutral.

  Tab. 47. Ratios of concentrations of hydrogen and hydroxyl ions and pH values ​​(according to Mitchell, 1975)
  H+	pH value	OH-
  10 0 or 1.0	0,0	10 -14 or 0.00000000000001
  10 -1 or 0.1	1,0	10 -13 or 0.0000000000001
  10 -2 or 0.01	2,0	10 -12 or 0.000000000001
  10 -3 or 0.001	3,0	10 -11 or 0.00000000001
  10 -4 or 0.0001	4,0	10 -10 or 0.0000000001
  10 -5 or 0.00001	5,0	10 -9 or 0.000000001
  10 -6 or 0.000001	6,0	10 -8 or 0.00000001
  10 -7 or 0.0000001	7,0	10 -7 or 0.0000001
  10 -8 or 0.00000001	8,0	10 -6 or 0.000001
  10 -9 or 0.000000001	9,0	10 -5 or 0.00001
  10 -10 or 0.0000000001	10,0	10 -4 or 0.0001
  10 -11 or 0.00000000001	11,0	10 -3 or 0.001
  10 -12 or 0.000000000001	12,0	10 -2 or 0.01
  10 -13 or 0.0000000000001	13,0	10 -1 or 0.1
  10 -14 or 0.00000000000001	14,0	10 0 or 1.0

  • Sodium [show] .

    Sodium is the main osmotically active ion in the extracellular space. In blood plasma, the concentration of Na + is approximately 8 times higher (132-150 mmol/l) than in erythrocytes (17-20 mmol/l).

    With hypernatremia, as a rule, a syndrome associated with overhydration of the body develops. The accumulation of sodium in the blood plasma is observed in a special kidney disease, the so-called parenchymal nephritis, in patients with congenital heart failure, in primary and secondary hyperaldosteronism.

    Hyponatremia is accompanied by dehydration of the body. Correction of sodium metabolism is carried out by introducing sodium chloride solutions with the calculation of its deficiency in the extracellular space and cell.

  • Potassium [show] .

    Plasma K+ concentration ranges from 3.8 to 5.4 mmol/L; in erythrocytes it is approximately 20 times more (up to 115 mmol/l). The level of potassium in cells is much higher than in the extracellular space, therefore, in diseases accompanied by increased cellular breakdown or hemolysis, the potassium content in the blood serum increases.

    Hyperkalemia is observed in acute renal failure and hypofunction of the adrenal cortex. Lack of aldosterone leads to increased urinary excretion of sodium and water and retention of potassium in the body.

    On the contrary, with increased production of aldosterone by the adrenal cortex, hypokalemia occurs. At the same time, the excretion of potassium in the urine increases, which is combined with sodium retention in the tissues. Developing hypokalemia causes severe disturbances in the functioning of the heart, as evidenced by ECG data. A decrease in serum potassium is sometimes observed when large doses of adrenal hormones are administered for therapeutic purposes.

  • Calcium [show] .

    Traces of calcium are found in erythrocytes, while in plasma its content is 2.25-2.80 mmol/l.

    There are several fractions of calcium: ionized calcium, non-ionized calcium, but capable of dialysis, and non-dialyzable (non-diffusing) protein-bound calcium.

    Calcium takes an active part in the processes of neuromuscular excitability as an antagonist of K +, muscle contraction, blood clotting, forms the structural basis of the bone skeleton, affects the permeability of cell membranes, etc.

    A distinct increase in the level of calcium in the blood plasma is observed with the development of tumors in the bones, hyperplasia or adenoma of the parathyroid glands. In these cases, calcium comes into the plasma from the bones, which become brittle.

    The determination of calcium in hypocalcemia is of great diagnostic importance. The state of hypocalcemia is observed in hypoparathyroidism. Loss of function of the parathyroid glands leads to a sharp decrease in the content of ionized calcium in the blood, which may be accompanied by convulsive attacks (tetany). A decrease in plasma calcium concentration is also noted in rickets, sprue, obstructive jaundice, nephrosis and glomerulonephritis.

  • Magnesium [show] .

    This is mainly an intracellular divalent ion contained in the body in an amount of 15 mmol per 1 kg of body weight; the concentration of magnesium in plasma is 0.8-1.5 mmol/l, in erythrocytes 2.4-2.8 mmol/l. There is 10 times more magnesium in muscle tissue than in blood plasma. The level of magnesium in plasma, even with significant losses, can remain stable for a long time, replenished from the muscle depot.

  • Phosphorus [show] .

    In the clinic, when testing blood, the following fractions of phosphorus are distinguished: total phosphate, acid-soluble phosphate, lipoid phosphate and inorganic phosphate. For clinical purposes, the determination of inorganic phosphate in blood plasma (serum) is often used.

    Hypophosphatemia (decreased plasma phosphorus levels) is especially characteristic of rickets. It is very important that a decrease in the level of inorganic phosphate in the blood plasma is observed in the early stages of the development of rickets, when clinical symptoms are not sufficiently pronounced. Hypophosphatemia is also observed with insulin administration, hyperparathyroidism, osteomalacia, sprue and some other diseases.

  • Iron [show] .

    In whole blood, iron is contained mainly in erythrocytes (- 18.5 mmol/l), in plasma its concentration averages 0.02 mmol/l. Every day, during the breakdown of hemoglobin in erythrocytes in the spleen and liver, about 25 mg of iron is released and the same amount is consumed during the synthesis of hemoglobin in the cells of hematopoietic tissues. The bone marrow (the main erythropoietic tissue of humans) contains a labile supply of iron that exceeds 5 times the daily requirement for iron. The supply of iron in the liver and spleen is significantly greater (about 1000 mg, i.e. a 40-day supply). An increase in iron content in blood plasma is observed with weakened hemoglobin synthesis or increased breakdown of red blood cells.

    With anemia of various origins, the need for iron and its absorption in the intestine increase sharply. It is known that in the intestine, iron is absorbed in the duodenum in the form of ferrous iron (Fe 2+). In the cells of the intestinal mucosa, iron combines with the protein apoferritin to form ferritin. It is assumed that the amount of iron entering the blood from the intestines depends on the content of apoferritin in the intestinal walls. Further transport of iron from the intestine to the hematopoietic organs occurs in the form of a complex with the blood plasma protein transferrin. Iron in this complex is in trivalent form. In the bone marrow, liver and spleen, iron is deposited in the form of ferritin - a kind of reserve of easily mobilized iron. In addition, excess iron can be deposited in tissues in the form of metabolically inert hemosiderin, well known to morphologists.

    Lack of iron in the body can cause disruption of the last stage of heme synthesis - the conversion of protoporphyrin IX into heme. As a result of this, anemia develops, accompanied by an increase in the content of porphyrins, in particular protoporphyrin IX, in erythrocytes.

    Mineral substances found in tissues, including in the blood, in very small quantities (10 -6 -10 -12%) are called microelements. These include iodine, copper, zinc, cobalt, selenium, etc. It is believed that most trace elements in the blood are in a protein-bound state. Thus, plasma copper is part of ceruloplasmin, erythrocyte zinc belongs entirely to carbonic anhydrase, 65-76% of blood iodine is in organically bound form - in the form of thyroxine. Thyroxine is found in the blood mainly in protein-bound form. It complexes predominantly with the globulin that specifically binds it, which is located during electrophoresis of serum proteins between two fractions of α-globulin. Therefore, thyroxine-binding protein is called interalphaglobulin. Cobalt found in the blood is also found in protein-bound form and only partially as a structural component of vitamin B12. A significant portion of selenium in the blood is part of the active site of the enzyme glutathione peroxidase and is also associated with other proteins.

  Acid-base state

  The acid-base state is the ratio of the concentrations of hydrogen and hydroxyl ions in biological media.

  Considering the difficulty of using in practical calculations values ​​of the order of 0.0000001, which approximately reflect the concentration of hydrogen ions, Zörenson (1909) proposed the use of negative decimal logarithms of the concentration of hydrogen ions. This indicator is named pH after the first letters of the Latin words puissance (potenz, power) hygrogen - “hydrogen power”. The ratios of the concentrations of acidic and basic ions corresponding to different pH values ​​are given in table. 47.

  It has been established that only a certain range of fluctuations in blood pH corresponds to the normal state - from 7.37 to 7.44 with an average value of 7.40. (In other biological fluids and in cells, the pH may differ from the pH of blood. For example, in red blood cells the pH is 7.19 ± 0.02, differing from the pH of blood by 0.2.)

  No matter how small the limits of physiological pH fluctuations seem to us, nevertheless, if they are expressed in millimoles per 1 liter (mmol/l), it turns out that these fluctuations are relatively significant - from 36 to 44 ppm millimoles per 1 liter, i.e. e. constitute approximately 12% of the average concentration. More significant changes in blood pH towards increasing or decreasing the concentration of hydrogen ions are associated with pathological conditions.

  Regulatory systems that directly ensure the constancy of blood pH are the buffer systems of the blood and tissues, the activity of the lungs and the excretory function of the kidneys.

  Blood buffer systems

  Buffer properties, i.e. the ability to counteract changes in pH when acids or bases are added to the system, are possessed by mixtures consisting of a weak acid and its salt with a strong base or a weak base with a salt of a strong acid.

  The most important blood buffer systems are:

  • [show] .

    Bicarbonate buffer system- a powerful and, perhaps, the most controllable system of extracellular fluid and blood. The bicarbonate buffer accounts for about 10% of the total buffer capacity of the blood. The bicarbonate system consists of carbon dioxide (H 2 CO 3) and bicarbonates (NaHCO 3 - in extracellular fluids and KHCO 3 - inside cells). The concentration of hydrogen ions in a solution can be expressed through the dissociation constant of carbonic acid and the logarithm of the concentration of undissociated H 2 CO 3 molecules and HCO 3 - ions. This formula is known as the Henderson-Hesselbach equation:

    

    Since the true concentration of H 2 CO 3 is insignificant and is directly dependent on the concentration of dissolved CO 2, it is more convenient to use a version of the Henderson-Hesselbach equation containing the “apparent” dissociation constant of H 2 CO 3 (K 1), which takes into account the total concentration of CO 2 in solution. (The molar concentration of H 2 CO 3 compared to the concentration of CO 2 in the blood plasma is very low. At PCO 2 = 53.3 hPa (40 mm Hg), there are approximately 500 molecules of CO 2 per 1 molecule of H 2 CO 3.)

    Then, instead of the concentration of H 2 CO 3, the concentration of CO 2 can be substituted:

    

    

    In other words, at pH 7.4, the ratio between carbon dioxide physically dissolved in the blood plasma and the amount of carbon dioxide bound in the form of sodium bicarbonate is 1:20.

    The mechanism of the buffering action of this system is that when large quantities of acidic products are released into the blood, hydrogen ions combine with bicarbonate anions, which leads to the formation of weakly dissociating carbonic acid.

    In addition, excess carbon dioxide immediately decomposes into water and carbon dioxide, which is removed through the lungs as a result of their hyperventilation. Thus, despite a slight decrease in the concentration of bicarbonate in the blood, the normal ratio between the concentration of H 2 CO 3 and bicarbonate (1:20) is maintained. This ensures that the blood pH is kept within normal limits.

    If the number of basic ions in the blood increases, they combine with weak carbonic acid to form bicarbonate anions and water. To maintain the normal ratio of the main components of the buffer system, in this case, physiological mechanisms for regulating the acid-base state are activated: a certain amount of CO 2 is retained in the blood plasma as a result of hypoventilation of the lungs, and the kidneys begin to secrete basic salts in larger quantities than usual (for example, Na 2 HP0 4). All this helps maintain a normal ratio between the concentration of free carbon dioxide and bicarbonate in the blood.

  • Phosphate buffer system [show] .

    Phosphate buffer system constitutes only 1% of the buffer capacity of the blood. However, in tissues this system is one of the main ones. The role of acid in this system is played by monobasic phosphate (NaH 2 PO 4):

    NaH 2 PO 4 -> Na + + H 2 PO 4 - (H 2 PO 4 - -> H + + HPO 4 2-),

    
    and the role of the salt is dibasic phosphate (Na 2 HP0 4):

    Na 2 HP0 4 -> 2Na + + HPO 4 2- (HPO 4 2- + H + -> H 2 PO 4 -).

    For a phosphate buffer system, the following equation holds:

    

    At pH 7.4, the ratio of the molar concentrations of monobasic and dibasic phosphates is 1:4.

    The buffering effect of the phosphate system is based on the possibility of binding hydrogen ions with HPO 4 2- ions to form H 2 PO 4 - (H + + HPO 4 2- -> H 2 PO 4 -), as well as on the interaction of OH - ions with H 2 ions PO 4 - (OH - + H 4 PO 4 - -> HPO 4 2- + H 2 O).

    The phosphate buffer in the blood is in close connection with the bicarbonate buffer system.

  • Protein buffer system [show] .

    Protein buffer system- a fairly powerful buffer system of blood plasma. Since blood plasma proteins contain a sufficient amount of acidic and basic radicals, the buffering properties are associated mainly with the content of actively ionized amino acid residues—monoaminodicarboxylic and diaminomonocarboxylic acids—in the polypeptide chains. When the pH shifts to the alkaline side (remember the isoelectric point of the protein), the dissociation of basic groups is inhibited and the protein behaves like an acid (HPr). By binding with a base, this acid produces a salt (NaPr). For a given buffer system, the following equation can be written:

    

    As pH increases, the amount of proteins in the form of salt increases, and as pH decreases, the amount of plasma proteins in the form of acid increases.

  • [show] .

    Hemoglobin buffer system- the most powerful blood system. It is 9 times more powerful than bicarbonate: it accounts for 75% of the total buffer capacity of the blood. The participation of hemoglobin in the regulation of blood pH is associated with its role in the transport of oxygen and carbon dioxide. The dissociation constant of the acid groups of hemoglobin changes depending on its oxygen saturation. When hemoglobin is saturated with oxygen, it becomes a stronger acid (HHbO 2) and increases the release of hydrogen ions into the solution. If hemoglobin gives up oxygen, it becomes a very weak organic acid (HHb). The dependence of blood pH on the concentrations of HHb and KHb (or, respectively, HHbO 2 and KHb0 2) can be expressed by the following comparisons:

    The hemoglobin and oxyhemoglobin systems are interconvertible systems and exist as a single whole; the buffer properties of hemoglobin are primarily due to the possibility of interaction of acid-reactive compounds with the potassium salt of hemoglobin to form an equivalent amount of the corresponding potassium salt of the acid and free hemoglobin:

    KHb + H 2 CO 3 -> KHCO 3 + HHb.

    It is in this way that the conversion of the potassium salt of hemoglobin of erythrocytes into free HHb with the formation of an equivalent amount of bicarbonate ensures that the pH of the blood remains within physiologically acceptable values, despite the entry into the venous blood of a huge amount of carbon dioxide and other acid-reactive metabolic products.

    Once in the capillaries of the lungs, hemoglobin (HHb) is converted into oxyhemoglobin (HHbO 2), which leads to some acidification of the blood, displacement of some H 2 CO 3 from bicarbonates and a decrease in the alkaline reserve of the blood.

    The alkaline reserve of the blood - the ability of the blood to bind CO 2 - is studied in the same way as total CO 2, but under conditions of balancing the blood plasma at PCO 2 = 53.3 hPa (40 mm Hg); determine the total amount of CO 2 and the amount of physically dissolved CO 2 in the test plasma. By subtracting the second from the first digit, we get a value called reserve blood alkalinity. It is expressed in volume percent CO 2 (volume of CO 2 in milliliters per 100 ml of plasma). Normally, a person's reserve alkalinity is 50-65 vol.% CO 2.

  So, the listed blood buffer systems play an important role in the regulation of acid-base status. As noted, in this process, in addition to the blood buffer systems, the respiratory system and the urinary system also take an active part.

  Acid-base disorders

  In a condition where the body's compensatory mechanisms are unable to prevent changes in the concentration of hydrogen ions, a disorder of the acid-base state occurs. In this case, two opposite conditions are observed - acidosis and alkalosis.

  Acidosis is characterized by a concentration of hydrogen ions above normal limits. In this case, naturally, the pH decreases. A decrease in pH value below 6.8 causes death.

  In cases where the concentration of hydrogen ions decreases (accordingly, the pH increases), a state of alkalosis occurs. The limit of compatibility with life is pH 8.0. In clinics, pH values ​​such as 6.8 and 8.0 are practically not found.

  Depending on the mechanism, the development of acid-base disorders, respiratory (gas) and non-respiratory (metabolic) acidosis or alkalosis are distinguished.

  • acidosis [show] .

    Respiratory (gas) acidosis may occur as a result of a decrease in minute breathing volume (for example, with bronchitis, bronchial asthma, emphysema, mechanical asphyxia, etc.). All these diseases lead to hypoventilation of the lungs and hypercapnia, i.e., an increase in arterial blood PCO 2. Naturally, the development of acidosis is prevented by blood buffer systems, in particular the bicarbonate buffer. The bicarbonate content increases, i.e. the alkaline reserve of the blood increases. At the same time, the excretion in urine of free and bound ammonium salts of acids increases.

    Non-respiratory (metabolic) acidosis caused by the accumulation of organic acids in tissues and blood. This type of acidosis is associated with metabolic disorders. Non-respiratory acidosis is possible with diabetes (accumulation of ketone bodies), fasting, fever and other diseases. Excessive accumulation of hydrogen ions in these cases is initially compensated by reducing the alkaline reserve of the blood. The CO 2 content in the alveolar air is also reduced, and pulmonary ventilation is accelerated. The acidity of urine and the concentration of ammonia in the urine are increased.

  • alkalosis [show] .

    Respiratory (gas) alkalosis occurs with a sharp increase in the respiratory function of the lungs (hyperventilation). For example, when inhaling pure oxygen, compensatory shortness of breath that accompanies a number of diseases, when being in a rarefied atmosphere and other conditions, respiratory alkalosis can be observed.

    Due to a decrease in the content of carbonic acid in the blood, a shift occurs in the bicarbonate buffer system: part of the bicarbonates is converted into carbonic acid, i.e., the reserve alkalinity of the blood decreases. It should also be noted that PCO 2 in the alveolar air is reduced, pulmonary ventilation is accelerated, urine has low acidity and the ammonia content in urine is reduced.

    Non-respiratory (metabolic) alkalosis develops with the loss of a large number of acid equivalents (for example, uncontrollable vomiting, etc.) and the absorption of alkaline equivalents of intestinal juice, which have not been neutralized by acidic gastric juice, as well as with the accumulation of alkaline equivalents in tissues (for example, with tetany) and in the case of unreasonable correction metabolic acidosis. At the same time, the alkaline reserve of the blood and PCO 2 in the avelveolar air increase. Pulmonary ventilation is slowed down, the acidity of urine and the ammonia content in it are reduced (Table 48).

    Table 48. The simplest indicators for assessing acid-base status
    Shifts (changes) in acid-base state	Urine, pH	Plasma, HCO 2 -, mmol/l	Plasma, HCO 2 -, mmol/l
    Norm	6-7	25	0,625
    Respiratory acidosis	reduced	increased	increased
    Respiratory alkalosis	increased	reduced	reduced
    Metabolic acidosis	reduced	reduced	reduced
    Metabolic alkalosis	increased	increased	increased

  In practice, isolated forms of respiratory or non-respiratory disorders are extremely rare. Determining a set of indicators of acid-base status helps to clarify the nature of the disorders and the degree of compensation. Over the past decades, sensitive electrodes for direct measurement of pH and PCO 2 of blood have become widespread to study indicators of acid-base status. In clinical settings, it is convenient to use devices such as "Astrup" or domestic devices - AZIV, AKOR. Using these instruments and corresponding nomograms, the following basic indicators of acid-base status can be determined:

  1. actual blood pH is the negative logarithm of the concentration of hydrogen ions in the blood under physiological conditions;
  2. actual PCO 2 of whole blood - partial pressure of carbon dioxide (H 2 CO 3 + CO 2) in the blood under physiological conditions;
  3. actual bicarbonate (AB) - the concentration of bicarbonate in blood plasma under physiological conditions;
  4. standard blood plasma bicarbonate (SB) - the concentration of bicarbonate in blood plasma, balanced by alveolar air and at full saturation with oxygen;
  5. buffer bases of whole blood or plasma (BB) - an indicator of the power of the entire buffer system of blood or plasma;
  6. normal whole blood buffer bases (NBB) - whole blood buffer bases at physiological pH and PCO 2 values ​​of alveolar air;
  7. base excess (BE) is an indicator of excess or lack of buffer capacity (BB - NBB).

  Blood functions Blood ensures the vital functions of the body and performs the following important functions: respiratory - supplies cells with oxygen from the respiratory organs and removes carbon dioxide (carbon dioxide) from them; nutritious - carries nutrients throughout the body that, during digestion, enter the blood vessels from the intestines; excretory - removes from organs decay products formed in cells as a result of their vital activity; regulatory - transports hormones that regulate metabolism and the functioning of various organs, carries out humoral communication between organs; protective - microorganisms that enter the blood are absorbed and neutralized by leukocytes, and the toxic waste products of microorganisms are neutralized with the participation of special blood proteins - antibodies. All these functions are often combined under a common name - the transport function of blood. In addition, blood maintains the constancy of the internal environment of the body - temperature, salt composition, environmental reaction, etc. Nutrients from the intestines, oxygen from the lungs, and metabolic products from tissues enter the blood. However, blood plasma remains relatively constant in composition and physicochemical properties. The constancy of the internal environment of the body - homeostasis is maintained by the continuous work of the digestive, respiratory, and excretory organs. The activity of these organs is regulated by the nervous system, which responds to changes in the external environment and ensures the equalization of shifts or disturbances in the body. In the kidneys, the blood is freed from excess mineral salts, water and metabolic products, in the lungs - from carbon dioxide. If the concentration of any substance in the blood changes, then neurohormonal mechanisms, regulating the activity of a number of systems, reduce or increase its release from the body.

  Some blood plasma proteins play an important role in blood coagulation and anticoagulation systems.

  Blood clotting- a protective reaction of the body that protects it from blood loss. People whose blood is unable to clot suffer from a serious disease - hemophilia.

  The mechanism of blood clotting is very complex. Its essence is the formation of a blood clot - a thrombus that clogs the wound area and stops bleeding. A blood clot is formed from the soluble protein fibrinogen, which during the blood clotting process turns into the insoluble protein fibrin. The conversion of soluble fibrinogen into insoluble fibrin occurs under the influence of thrombin, an active enzyme protein, as well as a number of substances, including those released during the destruction of platelets.

  The blood clotting mechanism is triggered by a cut, puncture, or injury, leading to damage to the platelet membrane. The process takes place in several stages.

  When platelets are destroyed, the enzyme protein thromboplastin is formed, which, when combined with calcium ions present in the blood plasma, converts the inactive plasma protein enzyme prothrombin into active thrombin.

  In addition to calcium, other factors also take part in the blood clotting process, such as vitamin K, without which the formation of prothrombin is disrupted.

  Thrombin is also an enzyme. It completes the formation of fibrin. The soluble protein fibrinogen turns into insoluble fibrin and precipitates in the form of long threads. From the network of these threads and blood cells that linger in the network, an insoluble clot is formed - a thrombus.

  These processes occur only in the presence of calcium salts. Therefore, if calcium is removed from the blood by binding it chemically (for example, with sodium citrate), then such blood loses its ability to clot. This method is used to prevent blood clotting during preservation and transfusion.

  Internal environment of the body

  Blood capillaries do not approach every cell, so the exchange of substances between cells and blood, communication between the organs of digestion, respiration, excretion, etc. carried out through the internal environment of the body, which consists of blood, tissue fluid and lymph.

  Internal environment	Compound	Location	Source and place of formation	Functions
  Blood	Plasma (50-60% of blood volume): water 90-92%, proteins 7%, fats 0.8%, glucose 0.12%, urea 0.05%, mineral salts 0.9%	Blood vessels: arteries, veins, capillaries	Due to the absorption of proteins, fats and carbohydrates, as well as mineral salts of food and water	The relationship of all organs of the body as a whole with the external environment; nutritional (delivery of nutrients), excretory (removal of dissimilation products, CO 2 from the body); protective (immunity, coagulation); regulatory (humoral)
  	Formed elements (40-50% of blood volume): red blood cells, leukocytes, platelets	Blood plasma	Red bone marrow, spleen, lymph nodes, lymphoid tissue	Transport (respiratory) - red blood cells transport O 2 and partially CO 2; protective - leukocytes (phagocytes) neutralize pathogens; platelets provide blood clotting
  Tissue fluid	Water, nutrient organic and inorganic substances dissolved in it, O 2, CO 2, dissimilation products released from cells	The spaces between the cells of all tissues. Volume 20 l (for an adult)	Due to blood plasma and end products of dissimilation	It is an intermediate medium between blood and body cells. Transfers O2, nutrients, mineral salts, and hormones from the blood to the cells of organs. Returns water and dissimilation products to the bloodstream through lymph. Transfers CO2 released from cells into the bloodstream
  Lymph	Water, decay products of organic substances dissolved in it	Lymphatic system, consisting of lymphatic capillaries ending in sacs and vessels merging into two ducts that empty into the vena cava of the circulatory system in the neck	Due to tissue fluid absorbed through sacs at the ends of lymphatic capillaries	Return of tissue fluid to the bloodstream. Filtration and disinfection of tissue fluid, which is carried out in the lymph nodes where lymphocytes are produced

  The liquid part of the blood - plasma - passes through the walls of the thinnest blood vessels - capillaries - and forms intercellular, or tissue, fluid. This fluid washes all the cells of the body, gives them nutrients and takes away metabolic products. In the human body there is up to 20 liters of tissue fluid; it forms the internal environment of the body. Most of this fluid returns to the blood capillaries, and a smaller part, penetrating into the lymphatic capillaries closed at one end, forms lymph.

  The color of the lymph is yellowish-straw. It is 95% water and contains proteins, mineral salts, fats, glucose, and lymphocytes (a type of white blood cell). The composition of lymph resembles that of plasma, but there are fewer proteins, and it has its own characteristics in different parts of the body. For example, in the intestinal area there are a lot of fat droplets, which gives it a whitish color. Lymph travels through the lymphatic vessels to the thoracic duct and through it enters the blood.

  Nutrients and oxygen from the capillaries, according to the laws of diffusion, first enter the tissue fluid, and from it are absorbed by the cells. This is how the connection between capillaries and cells occurs. Carbon dioxide, water and other metabolic products formed in cells are also released from the cells first into the tissue fluid due to the difference in concentrations, and then enter the capillaries. Arterial blood becomes venous and delivers waste products to the kidneys, lungs, and skin, through which they are removed from the body.

Connective tissue makes up up to 50% of the mass of the human body. This is the connecting link between all tissues of the body. There are 3 types of connective tissue:
- connective tissue itself;
- cartilaginous connective tissue;
- bone connective tissue
Connective tissue can perform both independent functions and be included as layers in other tissues.

FUNCTIONS OF CONNECTIVE TISSUE

1. Structural
2. Ensuring constant tissue permeability
3. Ensuring water-salt balance
4. Participation in the body's immune defense

COMPOSITION AND STRUCTURE OF CONNECTIVE TISSUE

In connective tissue there are: INTERCELLULAR (BASIC) SUBSTANCE, CELLULAR ELEMENTS, FIBROUS STRUCTURES (collagen fibers). Feature: there is much more intercellular substance than cellular elements.

INTERCELLULAR (BASIC) SUBSTANCE

Blood is a type of connective tissue consisting of a liquid intercellular substance of complex composition - plasma and cells suspended in it - blood cells: erythrocytes (red blood cells), leukocytes (white blood cells) and platelets (blood platelets). 1 mm 3 of blood contains 4.5–5 million erythrocytes, 5–8 thousand leukocytes, 200–400 thousand platelets.

In the human body, the amount of blood is on average 4.5–5 liters or 1/13 of his body weight. Blood plasma by volume is 55–60%, and formed elements 40–45%. Blood plasma is a yellowish translucent liquid. It consists of water (90–92%), mineral and organic substances (8–10%), 7% proteins. 0.7% fat, 0.1% glucose, the rest of the dense remainder of plasma - hormones, vitamins, amino acids, metabolic products.

Red blood cells(red blood cells) are highly specialized cells. They have a biconcave shape. Human red blood cells do not have nuclei. A healthy person contains erythrocytes in the amount of 4.5 * 10 6 -5 * 10 6 in 1 mm 3 of blood. They are anucleate cells, shaped like a biconcave disc. The cytoplasm of red blood cells contains a coloring protein substance - hemoglobin, which causes the red color of blood. The most important function of red blood cells is that they are a carrier of oxygen. As blood flows through the lungs, the hemoglobin in red blood cells absorbs oxygen; The oxygenated (arterial) blood is then distributed throughout the body. In organs, oxygen is separated from hemoglobin and supplied to tissues. Hemoglobin is also involved in the transfer of carbon dioxide from tissues to the lungs, where it passes from the blood into the air. Most of the carbon dioxide is transported as part of the blood plasma.

The number of red blood cells changes due to external factors: muscle work, emotions, fluid loss (the concentration of red blood cells increases).

Increase in the number of red blood cells - erythrocytosis.

Reduction in the number of red blood cells - erythropenia.

Red blood cells are produced in the red bone marrow (about 10 7 every second). This replenishment of blood with red blood cells is necessary, since their life expectancy does not exceed 120 days. The destruction of old red blood cells occurs in the cells of the mononuclear phagocytic system (spleen, liver, etc.).

Hemoglobin- a coloring protein pigment that performs a respiratory function and is part of red blood cells. Hemoglobin consists of protein globulin and iron. For its synthesis, vitamin B 12 is necessary (which is found in beef with blood, cherry plum).

Normally, the blood contains about 140 g/l of hemoglobin: in men 130-155 g/l, in women 120-138 g/l.

Myoglobin(analogue of hemoglobin) - oxygen-binding protein of skeletal muscles and heart muscles - supplies muscles with oxygen.

43.Features of the structure and function of nervous tissue. Nervous tissue is one of the tissues of the body that performs the functions of sensing stimuli and conducting nerve impulses. Nervous tissue consists of neurons(nerve cells) and neuroglia(intercellular substance). Nerve cells have different shapes. A nerve cell is equipped with tree-like processes - dendrites, which transmit stimuli from receptors to the cell body, and a long process - an axon, which ends on the effector cell. Sometimes the axon is not covered by a myelin sheath.

Each neuron consists of a body, processes; dendrites and axon. According to the number of processes, unipolar (single-process), bipolar (double-process) and multipolar (multi-process) neurons are distinguished. Some processes conduct nerve impulses to the cell (dendrites), others - from the cell (axons). Based on their functional characteristics, afferent (sensitive), associative (intercalary) and efferent (motor) neurons are distinguished. The body of a neuron is its trophic center, violation of the integrity of which leads the cell to death. The body consists of a nucleus and cytoplasm (neuroplasm). In addition to the usual organelles, the neuroplasm contains special organelles - neurofibrils and Nissl's substance (tigroid). Neurofibrils are thin filaments located in different directions and form a dense network; they consist of very thin (70-200 A) protofibrils. Neurofibrils serve as the supporting framework of the neuron. The tigroid consists of clumps of basophilic substance located around the nucleus and extending into the bases of the dendrites. The tigroid takes part in the processes of synthesis of substances necessary to maintain the structural integrity of the neuron and its specific functioning. The synthesized substances are continuously transported from the body of the neuron to its processes. The extensions of a neuron are called nerve fibers. Each fiber consists of an axial cylinder (axon), inside which there is axoplasm, neurofibrils, mitochondria and synaptic vesicles. Depending on the structure of the membranes enveloping the axons, pulpy (myelin) and non-pulp fibers are distinguished. The non-pulpal fiber consists of 7-12 thin axons that pass within a cord formed by a chain of neuroglial cells. Each axon is separated from the cytoplasm of the glial cell by its own membrane. The pulp fiber consists of one thicker axon, which, in addition to the glial sheath, is wrapped in a myelin sheath. Due to the presence of the pulpy membrane and its segmented structure, the speed of nerve impulse transmission significantly increases. Peripheral branchings of fibers form nerve endings. Depending on their function, these endings are divided into receptor (sensitive) and effecisolatory (motor). Receptors can be encapsulated or non-encapsulated. The former are separated from other tissues by connective tissue capsules (Vater-Pacini, Meissner, Krause flasks, etc.), the latter are in direct contact with the innervated tissues. Effector endings are formed by branches of the axons of motor cells. On striated muscle fibers, motor fibers form nerve endings - the so-called motor plaques. The endings of the axons of one neuron on the body and processes of another are called interneuronal synapses. Functions: supporting, trophic. Demarcation, maintenance homeostasis around neurons protective, secretory.

Glia of the central nervous system: macroglia and microglia.

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 gases and substances dissolved in it necessary for metabolic processes.

Blood structure

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

• erythrocytes are red cells that give the blood a red color due to the hemoglobin they contain;
• leukocytes – white cells;
• platelets are blood 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.

About 4 to 5 liters of blood circulate in the circulatory system of an adult. Approximately 55% of the volume is occupied by plasma, the rest is formed elements, with the majority being erythrocytes - more than 90%.

Blood is a viscous substance. Viscosity depends on the amount of proteins and red blood cells contained 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 differently. They can move in groups or alone. Red blood cells can move either individually or in whole “stacks,” just as stacked coins tend to 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 caused by a small amount of bile pigment and other colored particles. It consists of approximately 90% water and approximately 10% 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 tissue fluid and blood, and give the blood viscosity. Some of the proteins are antibodies and neutralize foreign agents. An important role is played by the soluble protein fibrinogen. It takes part in the process, turning under the influence of coagulation factors into insoluble fibrin.

In addition, plasma contains hormones that are produced by the endocrine glands, and other bioactive elements necessary for the functioning of the body's 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 disks, biconcave in the center, with a diameter of about 7.5 microns. The shape of cells ensures the efficiency of physiological processes. Due to concavity, the surface area of ​​the sides of the red blood cell increases, which is important for the exchange of gases. Mature cells do not contain nuclei. The main function of red blood cells is to deliver 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 called hemoglobin, which is capable of binding to oxygen. Hemoglobin contains a protein part, called globin, and a non-protein part (heme), which contains iron. It is thanks to iron that hemoglobin can attach oxygen molecules.

Red blood cells are produced in the bone marrow. Their full ripening period is approximately five days. The lifespan of red cells is about 120 days. The destruction of red blood cells occurs in the spleen and liver. Hemoglobin breaks 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 into 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 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 first include neutrophils, basophils, eosinophils, which are distinguished by their reaction to different dyes. The second group includes 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 round shape.

Granulocytes are formed in the bone marrow. After ripening, when granularity and segmentation are formed, they enter the blood, where they move along the walls, making amoeboid movements. They protect the body primarily from bacteria and are able to leave blood vessels and accumulate in areas of infection.

Monocytes are large cells that are formed 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, 0-lymphocytes), each of which performs its own function. These cells produce antibodies, interferons, macrophage activation factors, and kill cancer cells.

Platelets

Small, nuclear-free, colorless plates that are fragments of megakaryocyte cells found in the bone marrow. They can have an oval, spherical, rod-shaped shape. Life expectancy is about ten days. The main function is participation in the process of blood clotting. Platelets release substances that take part in a chain of reactions that are triggered when a blood vessel is damaged. As a result, the fibrinogen protein is converted into insoluble fibrin strands, in which blood elements become entangled and a blood clot is formed.

Blood functions

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

1. 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 classified as microphages, and monocytes are classified as macrophages. Others - lymphocytes - produce antibodies against harmful agents. In addition, leukocytes are involved in removing damaged and dead tissue from the body.
2. Transport. Blood supply influences almost all processes occurring in the body, including the most important ones - breathing and digestion. With the help of blood, oxygen is transported 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, and the transport of hormones and other bioactive substances.
3. 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 that 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 an optimal ratio. Changes in the composition of the blood detected during the analysis make it possible to identify pathology at an early stage.