What are platelets?

In daily life, everyone will inevitably have some wounds. When there are some small wounds on the skin, bleeding will definitely occur. Under normal circumstances, bleeding will not continue to occur and will slowly stop. However, for some people, after a wound appears, the bleeding time will be very long. This may be due to the relatively small number of platelets in the blood. If you don’t know what platelets are, let’s learn about it in detail below.

What are platelets?

Platelets are small pieces of cytoplasm that detach from the cytoplasm of mature megakaryocytes in the bone marrow. Although megakaryocytes are the smallest in number among the hematopoietic cells in the bone marrow, accounting for only 0.05% of the total number of bone marrow nucleated cells, the platelets they produce are extremely important for the body's hemostatic function. When blood is lost due to vascular trauma, the functional activities of platelets in the physiological hemostasis process can be roughly divided into two stages: the first stage is mainly after the trauma occurs, platelets quickly adhere to the trauma site, aggregate into clumps, and form a relatively soft hemostatic plug; the second stage is mainly to promote blood coagulation and form a solid hemostatic plug.

It was not until 1882 that Italian physician J. B. It was Bizzolo who first proposed the name of platelets after discovering that they play an important role in hemostasis after vascular injury.

Lower vertebrates such as the Cyclostomes have spindle cells that play a role in coagulation, and fishes began to have specific thrombocytes. Thrombocytes are found in the blood of amphibians, reptiles and birds. Thrombocytes are spindle-shaped or oval cells with a nucleus and functions similar to platelets. Invertebrates do not have specialized thrombocytes, such as the amoebas of mollusks, which have both defensive and wound-healing functions. Crustaceans have only one type of blood cell, which also has the function of coagulation.

Platelets are disc-shaped, with diameters ranging from 1 to 4 microns to 7 to 8 microns, and there is great individual variation (5 to 12 cubic microns). Because platelets can move and deform, they appear in multiple forms when observed using general methods. The structure of platelets is complex. In short, it has three layers from the outside to the inside. The outer layer composed of the outer membrane, unit membrane and submembrane microfilament structure is the first layer; the second layer is the gel layer, in which microfilaments and microtubules parallel to the surrounding area can be seen under an electron microscope; the third layer is the micro-organ layer, which has structures such as mitochondria, dense bodies and residual nuclei.

Normal platelet count: (100 to 300)×10^9/L.