Place of formation of platelets. Structure and function of platelets

The smallest cells of blood are platelets. They look like non-nuclear disks. Their diameter is only up to 4 microns, and the thickness is up to 0.75 microns. In each liter of human blood, the platelet count is between 180 and 350 x 10 ⁹ .

The way of appearance of platelets

Blood plates appear during the fragmentation of the cytoplasm. They are separated from the huge cells of the bone marrow - megakaryocytes. They, in turn, appear as a result of endomitosis. After separation, 3-5 cycles occur, during which the chromosomes are doubled, but the cytoplasm is not separated. Experts call this process incomplete division.

It is important to understand that the place of formation of platelets is the red bone marrow. From it they exit and enter the bloodstream. But a third of them is immediately deposited in the spleen. This is due to a slower movement through the tortuous cords of the spleen. The remaining 2/3 circulate in the blood on average seven days. The maximum duration of their life can reach 12 days.

The process of nucleation of plates

To understand how the smallest blood cells appear, you need to know not only the place of formation of platelets. It is important to find out the process of their development. So, the ancestor is megakaryoblast. This is a large cell, whose size reaches 20 microns with the nucleus. It contains nucleotides. The megakaryoblast is transformed into promegakaryocyte. This structure is prone to core polymorphism, the cytoplasm is non-granular, basophilic.

The next stage of development is megakaryocyte. This is a huge cell in the bone marrow, whose diameter is from 60 to 120 microns. It contains a coarse core, which can take very bizarre forms. Its cytoplasm is large in size, it is granular with inclusions of pink-violet.

The penultimate stage is the appearance of thrombocytopenic megakaryocyte. After him, the platelets are immediately isolated. They are separated from the cytoplasm of the megakaryocyte. All this takes place in the bone marrow, this is the main place of platelet formation.

Selection of plates

Thrombocytopenic megakaryocytes in the bone marrow are located on the surface of the endothelium, called the sinus. Their cytoplasmic processes pass through it. Some of them penetrate the lumen of the sinus 1-2 μm and fix the megakaryocyte on the endothelium. They serve as anchors. Other processes are long cytoplasmic ribbons, the length of which reaches 120 microns. They pass through the lumen of the sinus. They are called prothrombocytes. Each megakaryocyte can have from 6 to 8.

In the lumen of the sinus, a local contraction of the cytoplasm begins. As a result, it bursts and appears around 1000 individual platelets. This place of formation of platelets is not the last. This is due to the fact that prothrombocytes also enter the bloodstream. They reach the microcirculatory bed of the lungs, full platelets are released there from them. This is why pulmonary veins have more of them than in the corresponding arteries. It is noteworthy that 7 to 17% of all thrombocytes passing through the blood stream can form in them.

Types of cells

Specialists distinguish several forms of the smallest blood cells. Isolate the young platelets. In comparison with mature forms, they are distinguished by a relatively large size, scanty graininess and bluish hyalomer. Their formation is affected by the increased work of the bone marrow, it is often associated with a significant loss of blood.

In appearance, the old platelets also differ. Photo under the microscope allows you to consider the presence of a narrow rim, a large number of vacuoles and granules. They differ in uneven outlines, a dense granulomer, which can occupy the entire platelet. Excessive number of them indicates the appearance of a malignant tumor.

Isolate forms of irritation. These are the ligaments from the megakaryocyte, which appear when the separation process is broken. Their presence indicates a blood disease. They often look like small or, on the contrary, giant blood platelets of a person's blood.

Normally, the blood should contain more than 90% of mature forms of platelets. They are disk-shaped with clear boundaries, centrally located granulomer, which consists of 5-20 azurophilic grains, lilac hyalomer.

Process of life activity

Appearing in the bone marrow, cells leave the main place of formation of platelets. By the way, their production is regulated by thrombocytopoietins. They, in turn, appear not only in the bone marrow, but also in the spleen, the liver. Specialists distinguish two groups of thrombocytopoietins. They can be of long or short duration. The first of them contribute to the full maturation and differentiation of megakaryocytes, while the latter enhance the cleavage of these small plates and accelerate their entry into the blood.

Thrombocytes are destroyed, photos of which can be seen at multiple magnifications, on average after a week of functioning. This process takes place mainly in the bone marrow, but these blood cells also disintegrate in the spleen and liver. Destruction takes place in specific cells of the system, called macrophages.

Structure of plates

Each mature platelet can be divided into three zones. The peripheral part is represented by a three-layer membrane. It contains receptors for collagen, serotonin, thrombin, epinephrine, ADP. On the outer part of the membrane there is a special amorphous layer consisting of factors responsible for coagulation of the blood plasma.

The middle is the sol-gel layer. It contains special channels with an outlet to the outer part of the membrane. Also, the layer contains microfilaments responsible for the disk-like shape of the plates. The properties of this part of the platelets depends on how the retraction of the blood clot will take place.

A zone of organelles is also isolated. It contains glycogen and alpha-granules, dense bodies, mitochondria.

Functions

After learning how the described small particles of blood appear, many are beginning to wonder what platelets do. They are designed to participate in hemostasis, help to repair damaged blood vessels. This is made possible by the fact that they can be attached to damaged walls and restore them. Also, these cells are necessary to prevent bleeding and release of the body's main body fluid from the bloodstream.

It is ensured that these functions are performed by the properties of platelets: adhesion and aggregation. So they are called their ability to attach to the subendothelium and stick together.