Introduction to platelets

Platelet is one of the visible components of mammalian blood and is a biologically active small cytoplasm that is shed from the cytoplasmic cleavage of megakaryocytes from bone marrow. Small size, irregular shape, a plasma membrane, no nuclei, generally round, smaller than red blood cells and white blood cells. Platelets are seen in the long term as non-functional cell debris in the blood. Platelets have specific morphological and biochemical composition. The number of platelets in adult blood is (1~3)×10^11/L, and there is a constant number of normal blood in the hemostasis, wound healing, inflammatory response, thrombosis and organ transplant rejection and other physiological and pathological processes have an important role. But too much platelets will form thrombosis, not easy to blood flow. Platelets are present only in mammalian blood. There is no cell structure,no chromosome.

Concept of platelets

Until 1882 Italian physician J. B. Bizzawa found that they play an important role in the process of hemostasis after vascular injury, first proposed platelet name.

Low vertebrate round mouth with spindle cells from the clotting effect, the fish began to have specific thrombosis cells. Amphibious, crawling and bird animals have blood thrombosis cells, thrombosis cells are nuclei of the shuttle formation of oval cells, similar to the function and platelets. Invertebrates do not have specific thrombotic cells, such as mollusks, deformed cells that both have a defense and a wound healing effect. Crustaceans have only one blood cell, both coagulation.

Platelets are discoid, ranging from 1~4 microns to 7~8 microns, and individual differences are large. Platelets due to movement and deformation, so the general method of observation when the performance of multi-form. Platelet structure is complex, in short, from outside to inside the three-tier structure, that is, from the outer membrane, membrane and membrane microfilament structure of the periphery of the first layer; the second layer for the gel layer, Surrounded by parallel microfilaments and microtubules structure; the third layer for the micro-organ layer, with mitochondria, dense body, residual nuclear and other structures.

The significance of platelet count

The concept of platelet count is the number of platelets in the blood volume of the unit, and the normal value of the platelet count is 100~300×10^9/L. Thrombocytopenia is caused by prolonged bleeding, severe injury or bleeding in the state of shock. When the platelet count<50×10^9/L, mild injury can cause skin and mucous membranes, bleeding after surgery; when the platelet count<20×10^9/L, often spontaneous bleeding. It is generally believed that when the platelet count<20×10^9 the="" need="" for="" prophylactic="" input="" platelets.="" if="" platelet="" count="">50×10^9/L, and platelet function is normal, the surgical process will not appear obvious bleeding.

1. Platelet enlargement: when the platelet count>400×10^9/L is the platelet increase, primary platelet enlargement common in myeloproliferative diseases such as chronic myeloid leukemia, polycythemia vera, primary thrombocytosis, etc. ; Thrombocytosis common in acute and chronic inflammation, iron deficiency anemia and cancer patients, such an increase is generally not more than 500×10^9/L, after treatment to improve the situation, the number of platelets will soon drop to normal levels. Splenectomy platelet will be significantly increased, often higher than 600×10^9/L, then slowly down to the normal range.

2. Thrombocytopenia: when the platelet count<100×10^9/L is thrombocytopenia, common in plateletogenesis disorders, such as aplastic anemia, acute leukemia, acute radiation sickness; platelet damage increased, such as primary thrombocytopenic purpura , Hypersplenism, such as diffuse intravascular coagulation, familial thrombocytopenia, such as giant platelet syndrome.

Platelet function

The main function of platelets is blood clotting and hemostasis, repairing damaged blood vessels. Platelet surface sugar coating can adsorb plasma protein and coagulation factor Ⅲ, platelet particles containing coagulation-related substances. When the blood vessels damaged or ruptured, the platelets by the stimulus, from the static phase into the functional phase, the rapid deformation, surface viscosity increases, condensed into groups; the same time in the role of the third factor, the plasma prothrombin Into thrombin, which also catalyzes fibrinogen into filamentous fibrin, together with the blood cells to form a blood clot to stop bleeding. The release of platelet granules is further promoted by hemostasis and coagulation. Platelets also protect the vascular endothelium, involved in endothelial repair, to prevent the role of atherosclerosis. Blood platelets in the blood less than 100,000/μ1 (100×10^9/L) for thrombocytopenia, less than 50,000/μL (50×10^9/L) bleeding risk.

Platelet aggregation function determination

Agglutination is another important physiological feature of platelets, which refers to the adhesion between platelets and platelets, showing the interaction of platelet interaction into the characteristics of the platelet is involved in hemostasis and thrombosis process is one of the important factors. The determination of platelet aggregation is of great clinical significance in the diagnosis of prethrombotic state and thrombotic disease. In the PRP or whole blood by adding inducer continuous stirring can induce platelet aggregation, aggregation reaction has two phases: I phase: vascular wall injury site platelet adhesion, through the damaged tissue or red blood cells caused by the release of ADP. Is characterized by aggregation of rapid, reversible accumulation of platelets and self-separation (called depolymerization); Ⅱphase: aggregation is released by the platelet itself induced by ADP, characterized by the aggregation process is slow, irreversible. Platelet aggregation detection principle is to add in the PRP inducer, the platelet aggregation, and the corresponding changes in blood turbidity, according to the tracing curve to calculate the degree and speed of platelet aggregation, mainly filter pressure method, turbidimetric method, shear induction Platelet aggregation assay, radioactive particle detection method, whole blood electrical impedance method, platelet count method and trace reaction plate method.