Blood

Blood is a kind of connective tissue. Its intercellular substance is liquid - this is blood plasma. In the blood plasma there are ("floating") its cellular elements: erythrocytes, leukocytes, as well as platelets (blood plates). In a person with a body weight of 70 kg, an average of 5.0-5.5 liters of blood (this is 5-9% of the total body weight). Blood performs the following functions: the transfer of oxygen and nutrients to organs and tissues and the removal of metabolic products from them.

The blood consists of a plasma, which is the liquid that remains after the removal of the elemental cells from it. It contains 90-93% water, 7-8% of various protein substances (albumins, globulins, lipoproteins, fibrinogen), 0.9% salts, 0.1% glucose. In the blood plasma there are also enzymes, hormones, vitamins and other substances necessary for the body. Proteins of plasma participate in the process of blood coagulation, ensure the constancy of its reaction (pH 7.36), pressure in the blood vessels, makes the blood more viscous, prevent the accumulation of erythrocytes. The plasma contains immunoglobulins (antibodies) that participate in the protective reactions of the body.

The content of glucose in a healthy person is 80-120 mg% (4.44-6.66 mmol / l). A sharp decrease in the amount of glucose (up to 2.22 mmol / L) leads to a sharp increase in the excitability of brain cells. A further decrease in the glucose level in the blood leads to a violation of breathing, circulation, consciousness and can be fatal to humans.

Blood also contains minerals such as: NaCI, KCI, CaCl2, NaHCO2, NaH2PO and other salts, as well as ions Na +, Ca2 +, K +. The constancy of the ionic composition of blood ensures the stability of osmotic pressure and the preservation of the volume of fluid in the blood and cells of the body.

Blood also consists of uniform elements (cells): erythrocytes, leukocytes, platelets.

Erythrocytes (red blood cells) are nuclear-free cells that are not capable of division. In an adult male, blood in 1 μl contains 3.9-5.5 million (average 5.0 × 10'ol), in women - 3.7-4.9 million (average 4.5 × 1012 / L) and depends on the age , physical (muscular) or emotional load, hormones that enter the blood. With severe blood loss (and some diseases), the content of the bodies decreases, while the level of hemoglobin decreases. This condition is called anemia (anemia).

Each erythrocyte has the form of a biconcave disk with a diameter of 7-8 μm and a thickness of about 1 μm in the center, and up to 2-2.5 μm in the edge zone. The surface area of one body is approximately 125 μm2. The total surface of all red blood cells, if the blood in 5.5 liters, reaches 3500-3700 m2. Outside they are covered with a semipermeable membrane (shell) - a cytolemma through which water, gases and other elements selectively penetrate. In the cytoplasm there are no organelles: 34% of its volume is the pigment hemoglobin, whose function is the transfer of oxygen (O2) and carbon dioxide (CO2).

Hemoglobin consists of protein globin and a non-protein group - heme, containing iron. In one erythrocyte, up to 400 million molecules of hemoglobin. Hemoglobin carries oxygen from the lungs to organs and tissues, and carbon dioxide - from the organs and tissues to the lungs. Due to its high partial pressure, oxygen molecules attach to hemoglobin. Hemoglobin with the oxygen attached to it has a bright red color and is called oxyhemogyobin. At low oxygen pressure in tissues, oxygen is disconnected from hemoglobin and exits from the blood capillaries into the surrounding cells and tissues. After giving oxygen, the blood is saturated with carbon dioxide, whose pressure in the tissues is higher than that of the blood. Hemoglobin in conjunction with carbon dioxide is called carbogemoglobin. In the lungs, carbon dioxide leaves the blood, whose hemoglobin is again saturated with oxygen.

Hemoglobin readily compounds with carbon monoxide (CO), forming carboxyhemoglobin. The addition of carbon monoxide to hemoglobin occurs 300 times easier than the addition of oxygen. Therefore, the content in the air of even a small amount of carbon monoxide is enough to join the hemoglobin and block the entry of oxygen into the blood. As a result of lack of oxygen in the body, oxygen starvation occurs (carbon monoxide poisoning) and headache, vomiting, dizziness, loss of consciousness and even death occur.

White blood cells (white blood cells) have great mobility, but they have different morphological features. In an adult human blood in 1 liter contains from 3.8-109 to 9.0-109 leukocytes. In this number, according to outdated views, also include lymphocytes that share a common origin with leukocytes (from bone marrow stem cells), but related to the immune system. Lymphocytes account for 20-35% of the total number of "white" cells that have blood (not erythrocytes).

Leukocytes in tissues actively move towards various chemical factors, among which metabolism products play an important role. With the movement of leukocytes, the shape of the cell and nucleus changes.

All leukocytes due to the presence or absence of granules in their cytoplasm are divided into two groups: granular and non-granular leukocytes. A large group is granular white blood cells (granulocytes), which in their cytoplasm have a granularity in the form of small granules and a more or less segmented nucleus. Cells of the second group do not have granularity in the cytoplasm, their nuclei are not segmented. Such cells are called non-grained leukocytes (agranulocytes).

In granular white blood cells, coloration with both acidic and basic dyes reveals granularity. These are neutrophil (neutral) granulocytes (neutrophils). Other granulocytes have an affinity for acidic dyes. They are called eosinophilic granulocytes (eosinophils). Third granulocytes are stained with basic dyes. These are basophilic granulocytes (basophils). All granulocytes contain two types of granules: primary and secondary - specific.

Neutrophils are rounded, their diameter is 7-9 microns. Neutrophils account for 65-75% of the total number of "white" cells (including lymphocytes). The nucleus of neutrophils is segmented, consists of 2-3 lobules and more with thin bridges between them. Some neutrophils have a nucleus in the form of a curved rod (stab neutrophils). Bean-shaped nucleus in young (young) neutrophils. The number of such neutrophils is small - about 0.5%.

In the cytoplasm of neutrophils there is granularity, granule sizes from 0.1 to 0.8 μm. Some granules - primary (large azurophilic) - contain hydrolytic enzymes characteristic of lysosomes: acid protease and phosphatase, beta-hyaluronidases, etc. Other smaller neutrophil granules (secondary) have a diameter of 0.1-0.4 microns, contain alkaline phosphatase , phagocytins, aminopeptidases, cationic proteins. In the cytoplasm of neutrophils there are glycogen and lipids.

Neutrophilic granulocytes, being mobile cells, have rather high phagocytic activity. They capture bacteria and other particles that are destroyed (digested) under the action of hydrolytic enzymes. Neutrophilic granulocytes live up to 8 days. In the bloodstream, they are 8-12 hours, and then go into the connective tissue, where they perform their functions.

Eosinophils are also called acitophilic leukocytes because of the ability of their granules to stain with acidic dyes. The diameter of eosinophils is about 9-10 μm (up to 14 μm). Blood in 1L contains 1-5% of the total number of "white" cells. The nucleus of eosinophils usually consists of two or, more rarely, of three segments connected by a thin bridge. There are also rod-shaped and young forms of eosinophils. In the cytoplasm of eosinophils, two types of granules: small, 0.1-0.5 μm in size, containing hydrolytic enzymes, and large granules (specific) - 0.5-1.5 μm in size, which have peroxidase, acid phosphatase, histaminase, etc. Eosinophils have less mobility than neutrophils, but they also emerge from the blood in the tissues to the foci of inflammation. In the blood, eosinophils enter and remain up to 3-8 hours. The number of eosinophils depends on the level of secretion of glucocorticoid hormones. Eosinophils are able to inactivate histamine due to histamine, and also inhibit the release of histamine by mast cells.

Basophils entering the blood have a diameter of 9 μm. The number of these cells is 0.5-1%. The nucleus of basophils is lobular or spherical. In the cytoplasm there are granules of 0.5 to 1.2 μm in size, containing heparin, histamine, acid phosphatase, peroxidase, serotonin. Basophils are involved in the metabolism of heparin and histamine, affect the permeability of the blood capillaries, make the blood more viscous.

Non-grained white blood cells, or agranulocytes, include monocytes and leukocytes. Monocytes that enter the blood and account for 6-8% of the total number of leukocytes and blood in the lymphocytes. The diameter of monocytes is 9-12 microns (18-20 microns in smears that contain blood). The shape of the nucleus in monocytes varies from bean-shaped to lobate. The cytoplasm is weakly basophilic, it contains small lysosomes and pinocytosis vesicles. Monocytes derived from bone marrow stem cells belong to the so-called mononuclear phagocyte system (MPS). In the blood, monocytes enter and circulate from 36 to 104 hours, then go into tissues, where they turn into macrophages.

Platelets (blood plates) entering the blood are colorless rounded or fusiform plates 2-3 μm in diameter. Thrombocytes were formed by separation from megakaryocytes - giant bone marrow cells. Blood (1 L) contains from 200-109 to 300-109 platelets. In each platelet, the hyalomer and the granulomer in the form of granules of about 0.2 μm in size are isolated. In the hyalomeris there are fine filaments, and among the accumulation of granules of granulomera are the mitochondria and granules of glycogen. Thanks to the ability to disintegrate and stick together, platelets make the blood more viscous. The life span of platelets is 5-8 days.

Blood also has lymphoid cells (lymphocytes), which are the structural elements of the immune system. At the same time, in the scientific and educational literature these cells are still considered as ungrainous leukocytes, which is clearly wrong.

Blood has a large number of lymphocytes (1000-4000 in 1 mm3), predominate in lymph and are responsible for immunity. In the adult body, their number reaches 6-1012. Most of the lymphocytes constantly circulate and enter the blood and tissues, which contributes to the performance of their immune defenses. All lymphocytes have a spherical shape, but differ in size from each other. The diameter of most lymphocytes is about 8 μm (small lymphocytes). Approximately 10% of the cells have a diameter of about 12 μm (mean lymphocytes). In the organs of the immune system there are also large lymphocytes (lymphoblasts) with a diameter of about 18 μm. The latter do not normally enter circulating blood. These are young cells that are found in the organs of the immune system. The cytolemma of lymphocytes forms short microvilli. The rounded nucleus, filled mainly with condensed chromatin, occupies most of the cell. In the surrounding narrow ridge of the basophilic cytoplasm, a lot of free ribosomes, and 10% of the cells contain a small amount of azurophilic granules - lysosomes. Elements of the granular endoplasmic reticulum and mitochondria are few, the Golgi complex is weakly developed, the centrioles are small.

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