Blood continuously circulates in the system of blood vessels. It performs very important functions in the body: respiratory, transport, protective and regulatory, ensuring the constancy of the internal environment of our body.
Blood is one of the connective tissues, which consists of a liquid intercellular substance with a complex composition. It includes plasma and cells suspended in it, or the so-called blood cells: leukocytes, erythrocytes and platelets. It is known that in 1 mm3 of blood there are 5 to 8 thousand leukocytes, 4.5 to 5 million erythrocytes, and 200 to 400 thousand platelets.
The amount of blood in the body of a he althy person is approximately 4.5 to 5 liters. Plasma occupies 55-60% by volume, and 40-45% of the total volume remains for formed elements. Plasma is a translucent yellowish liquid, which contains water (90%), organic and mineral substances, vitamins, amino acids, hormones, metabolic products.
The structure of leukocytes
Leukocytes are blood cells that have a colorless cytoplasm. They canfound in plasma and lymph. In general, they are white blood cells, they have nuclei, but they do not have a permanent shape. This is the structural features of leukocytes. These cells are formed in the spleen, lymph nodes, red bone marrow. Features of the structure of leukocytes determine the duration of their life, it ranges from 2 to 4 days. They are then broken down in the spleen.
Leukocytes: structure and functions
If we consider the functional and morphological features of leukocytes, we can say that they are ordinary cells that contain a nucleus and protoplasm. Their main function is to protect the body from harmful factors. The structure of leukocytes allows them to destroy foreign organisms that have entered the body, they also take an active part in various pathological, often very painful processes and various reactions (for example, inflammation). But the structure of human leukocytes is diverse. Some of them have granular protoplasm (granulocytes), while others do not have granularity (agranulocytes). Let's consider these types of leukocytes in more detail.
Diversity of leukocytes
As mentioned above, leukocytes are different, and it is customary to divide them according to their appearance, structure and functions. This is the structural features of human leukocytes.
So, granulocytes include:
- basophils;
- neutrophils;
- eosinophils.
Agranulocytes are represented by the following types of cells:
- lymphocytes;
- monocytes.
Basophiles
This is the smallest type of cells in the blood, their maximum is 1% of the total number of leukocytes. The structure of leukocytes (more specifically, basophils) is simple. They are round in shape, have a segmented or stab nucleus. The cytoplasm contains granules of different shapes and sizes, which have a dark purple color, in appearance they resemble black caviar. These granules are called basophilic granules. They contain regulatory molecules, enzymes, proteins.
Basophils originate in the bone marrow, originate from a basophilic myeloblast cell. After full maturation, they enter the blood, the duration of their existence is no more than two days. After the cells go into the tissues of the body, but what happens to them then is still unknown.
In addition to participating in inflammatory reactions, basophils can reduce blood clotting and take an active part during the course of anaphylactic shock.
Neutrophils
Neutrophils in the blood is up to 70% of the total number of all leukocytes. Their cytoplasm contains purplish-brown granules with a fine granular appearance that can be stained with neutral dyes.
Neutrophils are white blood cells whose cell structure is unusual. They are round in shape, but the nucleus looks like a stick (“young” cell) or has 3-5 segments that are interconnected by thin strands (more “mature” cell).
All neutrophils are formed in the bone marrow from myeloblastneutrophilic. A mature cell lives only 2 weeks, then it is destroyed in the spleen or liver.
A neutrophil has up to 250 types of granules in its cytoplasm. All of them contain bactericidal substances, enzymes, regulatory molecules that help the neutrophil perform its functions. They protect the body by phagocytosis (the process by which a neutrophil approaches a bacterium or virus, captures it, moves it inward and destroys the pathogen with the help of granule enzymes). So, one neutrophil cell can neutralize up to 7 microbes. It is also involved in the inflammatory process.
Eosinophils
The structure of leukocytes is similar to each other. The eosinophil also has a round shape and a segmental or rod-shaped nucleus. In the cytoplasm of the cell there are large granules of the same shape and size, bright orange, resembling red caviar. They contain proteins, phospholipids and enzymes in their composition.
Eosinophil is formed in the bone marrow from eosinophilic myeloblast. It exists from 8 to 15 days, then it goes into tissues that have contact with the external environment.
Eosinophil is also capable of phagocytosis, but only in other places (intestine, genitourinary tract, mucous membranes of the respiratory tract). It is also related to the occurrence and development of allergic reactions.
Lymphocytes
Lymphocytes have a rounded shape and different sizes, as well as a large round nucleus. They appear in the bone marrow from the lymphoblast. The lymphocyte undergoes a special maturation process, as itimmunocompetent cell. It is able to provide a variety of immune responses, creates the body's immunity.
The lymphocytes that have finally matured in the thymus are T-lymphocytes, in the spleen or lymph nodes are B-lymphocytes. The first cells are smaller in size. There is a ratio of 80%:20% between different types of lymphocytes, respectively. All cells live for about 90 days.
The main function is protection through active participation in immune responses. T-lymphocytes are engaged in phagocytosis and immune reactions, which are called non-specific resistance (in relation to all pathogenic viruses, these cells act in the same way). But B-lymphocytes are able to produce antibodies (specific molecules) in the process of destroying bacteria. For each type of bacteria, they produce special substances that only these harmful agents can destroy. B-lymphocytes provide specific resistance, which is directed primarily against bacteria, not viruses.
Monocyte
There is no granularity in the monocyte cell. It is a fairly large triangular cell with a large nucleus that can be bean-shaped, round, rod-shaped, lobed and segmented.
Monocyte arises from a monoblast in the bone marrow. In the blood, its lifespan is 48 to 96 hours. After that, part of the monocytes is destroyed, and the other part goes into the tissues, where it “ripens”, macrophages appear. Monocytes are the largest blood cells with a round oroval-shaped, blue-colored cytoplasm with a large number of voids (vacuoles), which give it a foamy appearance.
Macrophages in body tissues can live for several months, where they become wandering or resident cells (remain in the same place).
Monocyte is able to produce various regulatory molecules and enzymes that can develop an inflammatory response or, conversely, slow it down. They also help speed up the wound healing process. Promote the growth of bone tissue and the restoration of nerve fibers. Macrophage in tissues performs a protective function. It inhibits the reproduction of viruses.
Erythrocytes
There are erythrocytes and leukocytes in the blood. Their structure and functions are different from each other. An erythrocyte is a cell that has the shape of a biconcave disc. It does not contain a nucleus, and most of the cytoplasm is occupied by a protein called hemoglobin. It consists of an iron atom and a protein part, has a complex structure. Hemoglobin carries oxygen in the body.
Erythrocytes appear in the bone marrow from erythroblast cells. Most erythrocytes are biconcave, but the rest may vary. For example, they can be spherical, oval, bitten, bowl-shaped, etc. It is known that the shape of these cells can be disturbed due to various diseases. Each red blood cell is in the blood for 90 to 120 days, and then dies. Hemolysis is the destruction of red blood cells, which occurs predominantly in the spleen, but also in the liver andvessels.
Platelets
The structure of leukocytes and platelets is also different. Platelets do not have a nucleus, they are small oval or round cells. If these cells are active, then outgrowths form on them, they resemble a star. Platelets appear in the bone marrow from a megakaryoblast. They "work" only from 8 to 11 days, then they die in the liver, spleen or lungs.
The function of platelets is very important. They are able to maintain the integrity of the vascular wall, restore it in case of damage. Platelets form a clot and thereby stop bleeding.
