The value, function and structure of leukocytes and platelets
From school, many people remember that blood is a fluid, mobile plasma in which thousands of cells are suspended - red blood cells called red blood cells, unstained white blood cells, fragments of cytoplasm, or platelets. The structure of erythrocytes, leukocytes and platelets has significant differences, which determines their role in mammals, and in particular humans. The blood is red in color because there are significantly more red blood cells in it than all the other cells taken together. Red blood cells themselves redden their hemoglobin, an iron-containing protein. Their main role is to transport oxygen and carbon dioxide. Platelets, of which much smaller than erythrocytes, provide thrombosis of damaged vessels. Plasma leukocytes are also quite a bit, but their role is difficult to overestimate. According to morphological features, they are divided into several groups.The structure and significance of leukocytes in each group is somewhat different, but together they protect the body from the introduction and pathological activity of malicious agents. The study of the activities of these little white blood cells was introduced by I. Mechnikov and P. Erlich, for which both scientists were awarded the Nobel Prize.
In fresh blood, lymphocytes are not stained, for which they received a second name - white blood cells. Only about 0.15% of the total volume of erythrocytes in their plasma, but this number is not constant. It changes especially sharply in the direction of an increase when an irritant agent enters the body - viruses, bacteria, other harmful living organisms and non-living particles. And during the day, the number of leukocytes changes not only in sick people, but also in healthy people, for example, after eating, after high loads, towards evening, and so on. When asked about the structure and significance of leukocytes in the body, there is no definite answer, because the term “leukocyte” refers to a whole group of cells that are similar in morphological features. Representatives of each have differences and similarities.All leukocytes are endowed with the ability to move in the direction of the stimulus, which is called chemotaxis. They are formed in the lymph nodes and in the bone marrow.This process is called leukopoiesis. If for some reason too many white blood cells appear in the blood, this condition is called leukocytosis. If the lymphocytes in the blood are less than normal, this condition is called leukopenia.
To say exactly what the structure and value of leukocytes in humans, you must first tell what types of white blood cells are known at the moment.
In general, they are divided into two types:
Granular leukocytes have a different name - granulocytes. The structure of leukocytes of this group has common distinctive features: a large nucleus and granular cytoplasm. Granulocytes, in turn, are divided into groups:
Non-granular leukocytes are differently called agranulocytes. Their core is simple, non-segmented, and the cytoplasm is without specific grit.
Agranulocytes are divided into groups:
Consider them in more detail.
These blood cells received this name for their ability to be stained with both the acid dye eosin and the main dyes, for example, methylene blue.In the total volume of all leukocytes from 48 to 78%. They live up to 8 days. The structure of leukocytes of this group, depending on their age (stage of development) varies. Neutrophils are formed from neutrophilic promyelocytes, successively turning into myelocytes, metamyelocytes, stab neutrophils and, finally, into segmented neutrophils.At the final stage, each neutrophil has a large nucleus of 3, a maximum of 5 segments, connected by thin bridges. The size of a mature cell is up to 12 microns. The structure of the cytoplasm of the neutrophil is heterogeneous. Inside it is filled with organelles and a small number of mitochondria. The surface part of the cytoplasm contains glycogen granules, microtubules and filaments, which allow the neutrophil to move in the right direction. Granules are represented by two types:
- specific (contain bactericidal substances muromidazu, phosphatase, lactoferrin);
- azurophilic (contain lysosomal enzymes and myeloperoxidase).
The role of neutrophils
Features of the structure of leukocytes - neutrophils allow them to perform the following functions in the body of all mammals:
Neutrophils are essentially microphages, that is, they can capture and destroy various pathogenic microorganisms and particles that have entered the blood. All types of white blood cells are able to leak through the endothelium of capillaries and move in amoeba-like manner to the stimulus. Having reached it, neutrophils surround the "enemy" with cytoplasm. In the future, several scenarios are possible:
- enzymatic (removal of iron from enzymes of microbes, which causes their death);
- non-enzymatic (cationic proteins increase the permeability of the membranes of enemies, as a result, their contents are poured out).
Neutrophils adsorb amino acids and some enzymes on their surface and transfer them to the right place for the body.
This name is given to cells because they, when stained according to Romanovsky, are capable of absorbing well the basic dyes and not reacting to the acid dye eosin. The structure of the leukocytes of the basophilic group has its own characteristics.So, these cells are relatively large, reach a diameter of 9-12 microns, are produced in the bone marrow and live up to 2 days. In the blood of about 1% of the total mass of white blood cells.Their nucleus is shaped like a bob, not clearly divided into 3 lobes, and the cytoplasm contains all forms of organelles - ribosomes, mitochondria, actin filaments, the Golgi apparatus, glycogen, endoplasmic reticulum. Basophils can seep through capillary walls and live outside the circulatory system. With their structure, they resemble mast cells and are their close "relatives". The difference lies in the fact that basophils emerge from the bone marrow already fully formed, and mast cells enter the blood immature.
The role of basophils
The structure of leukocytes - basophils determines their functions in the body:
- Protective(they block poisons, preventing them from spreading throughout the body, and are capable of phagocytosis).
- Transport(Immunoglobulin E and other protein compounds are located on their surface.
- Synthetic(produce histamine, heparin).
Basophils are capable of degranulation (with a lot of histamine, leukotrienes, heparin, serotonin, prostaglandins entering the blood). In humans, it causes an allergic response to various stimuli.
Degranulation provokes an instantaneous increase in blood flow and better vascular permeability,which contributes to the speedy achievement of an irritant agent with other leukocytes and its subsequent destruction. Many scientists are inclined to believe that the mobilization of other white blood cells to fight the “enemy” that has fallen into the blood is the main function of basophils.
This type of white blood cells is so named because when they are stained according to Romanovsky, they react to eosin (an acidic dye). The structure and function of leukocytes of the eosinophilic group has significant differences from the previous two.The number of these cells in the blood should not exceed 5% by weight of all white blood cells. In eosinophils, the nucleus of two segments connected by a bridge is clearly visible. In the cytoplasm there are organelles and granules of two types - specific and azurophilic. At the same time, the specific ones almost completely fill the cytoplasm. In their center, they have a crystalloid, including a protein rich in arginine, hydrolytic lysosomal enzymes, histaminase, peroxidase, cationic eosinophilic protein, phospholipase D, collagenase, ketapsin. In the blood, these cells live up to two weeks.
The role of eosinophils
The leukocyte structure of the eosinophilic group allows them to perform phagocytosis,however, more of these cells have a cytotoxic effect. They are able to kill the larvae of parasites that have entered the blood. Upon reaching the microbe, eosinophils stick to it, envelop and degranulate (throw the contents of their granules into the environment). In this case, the protein that kills the parasite is released. Plasmolemma of eosinophils has Fc - receptors specific for immunoglobulin Ig E. Leukocytes - eosinophils can bind histamine and some other allergy mediators, but under certain conditions they, on the contrary, release these substances, that is, they can perform antiallergic and proallergic action.
Approximately 30-40% of the volume of all leukocytes accounts for lymphocytes. What is the structure and value of leukocytes of this group? They are spherical bodies with a very large nucleus and a thin rim of the cytoplasm, in which there is a minimum of organelles, but there are cytoplasmic processes.
The main role of lymphocytes is to provide humoral and cellular immunity. They also regulate the activity of other cells.
There are several types of lymphocytes:
- Nk (natural killers).They contain heparin granules, killing all foreign cells, including cancer cells.
- T-killers or T-leukocytes.On their surface there are T-helper cells (CD4 +), secreting cytokines, and cytotoxic lymphocytes (CD8 +).
- B-cells.Under the action of an antigen, they are able to activate and become plasma cells, producing appropriate antibodies against a specific antigen.
These are large spherical cells with a diameter of up to 20 microns. Inside they have a polymorphic non-segmented nucleus with a chromatin network and cytoplasm with many lysosomes. They live no more than 2 days. The structure of leukocytes of this group determines their main role - they are macrophages capable of capturing 100 or more microorganisms. At the same time, monocytes in size increase significantly. These blood cells do especially great work in chronic diseases, while, for example, neutrophils are more active in acute infections. In addition to phagocytosis, monocytes are able to produce antibodies and synthesize interferon, lysozyme.
What is the structure of leukocytes in the body, we have disassembled.Now consider what are platelets. They, like leukocytes, are formed in the bone marrow. Their "ancestors" are megacaryocytes oxyphilic, whose dimensions for cells are simply gigantic - 70 microns. One such large cell is capable of producing more than 10 thousand platelets, the size of which does not exceed 4 microns. In essence, they are fragments of the cytoplasm of megakaryocytes encased in a membrane. Platelets do not have a nucleus, and their forms are somewhat different, depending on age. So, there are young, mature and old platelets. In addition, there are forms of irritation of these particles and a small percentage of degenerative forms. The main role of platelets is the formation of blood clots (blood clots) in places where a ruptured blood vessel.
Red blood cells
The structure of leukocytes and platelets allows them to protect the body against harmful agents and against blood loss. The role of red blood cells is completely different. They serve to carry oxygen from organs and tissues from the lungs, and to return carbon dioxide to the lungs. Their structure is quite simple. Red blood cells resemble round disks with a surface bent on both sides. This slightly increases the contact area and thus facilitates gas exchange.Inside the red blood cells are filled with cytoplasm, 98% of which is hemoglobin. The size of these blood cells is 10 microns, but they are so elastic that they can leak through the pores of the vessels, whose dimensions are only about 3 microns. Erythrocytes are produced in the bone marrow, live for about 3 months, after which they are absorbed by leukocytes - macrophages.