Platelets, or platelets, are thickened, non-nucleated plates with a diameter of 3-4 microns. The number of platelets in the blood is not constant. At different times in 1 mm³ there may be 200 to 400 thousand of them. The formation of platelets occurs constantly, they are formed in the red bone marrow. The platelets live for several days and then are destroyed in the spleen.
The main function of platelets is to help stop bleeding. They have the property of changing their shape (flattening, shrinking, etc.), ensuring the formation of a blood clot (thrombus).
Clotting of blood is a defense reaction of the body. It stops bleeding when a blood vessel is damaged.
Losing large amounts of blood can be fatal. For women, there is a danger to life with the loss of 2.5 liters of blood, while for men this figure is less – 1.5–2.0 liters of blood.
Blood clotting is a complex process, during which special biologically active substances are released from destroyed platelets, damaged muscle and vascular tissues – blood clotting factors (there are more than 10 of them).
When a vessel is damaged (for example, with a cut), platelets in this place are destroyed and prothrombin is released, which converts the soluble blood plasma protein fibrinogen into the insoluble protein fibrin. Long filaments of fibrin are intertwined into a network, where blood cells are retained, and a blood clot forms, covering the wound and stopping bleeding. Thrombus formation occurs within 3–8 minutes. Over time, the vessel wall is restored, and the blood clot dissolves.
When blood coagulates outside the body, after the separation of a blood clot from it, blood serum is formed. Serum almost corresponds to plasma in terms of blood composition, but it lacks fibrinogen.
Blood clotting disorders
The absence of clotting factors in the blood or a violation of their formation in the body leads to serious diseases. One of them is hemophilia. In a patient with hemophilia, blood does not clot, and the person may die from bleeding with the slightest damage to the vessels. Only men suffer from hemophilia (since in the human body a gene located on the male sex chromosome is responsible for its development). But the susceptibility to this disease in the family is transmitted through the female line.
the son of the last Russian emperor Nicholas II, Tsarevich Alexei, suffered from hemophilia, which he inherited from his mother, Empress Alexandra Feodorovna (the grand-niece of Queen Victoria of England, who was a carrier of the hemophilia gene).
Calcium salts also play an important role in the process of blood clotting. If they are removed, then the blood loses its ability to clot.