What is a blood clot? A blood clot is a solid mass of blood that clots in the heart or blood vessels called a thrombus. How does a blood clot form? There are mutually antagonistic coagulation and anticoagulation systems in the blood. In the physiological state, coagulation factors in the blood are constantly activated to produce thrombin, which forms microscopic fibrin that settles on the intima; at the same time, these microscopic fibrin are constantly dissolved by the activated fibrinolytic system, and the activated coagulation factors are constantly phagocytosed by the mononuclear phagocyte system. This dynamic balance between the coagulation and fibrinolytic systems ensures both the potential coagulability and the fluid state of the blood at all times. Sometimes the dynamic balance is disturbed by factors that promote the clotting process, triggering the clotting process and allowing the blood to coagulate in the cardiovascular cavity, forming a thrombus. What are the effects of blood clots on the body? The beneficial effect is that it can block the opening of blood vessels and reduce or stop bleeding; the thrombus in small vessels around inflammatory lesions also prevents the spread of pathogenic bacteria. The detrimental effect is the development of thrombotic disease. What is the final outcome of thrombosis? Smaller thrombi can be completely dissolved and absorbed by fibrinolytic enzymes. Larger thrombi are not completely dissolved and are mostly replaced by surrounding granulation tissue (mechanization), forming a revascularization. During the process of mechanization, a small amount of thrombus is dislodged into emboli, causing embolism; some thrombi form arterial and venous stones due to calcium salt deposition. What is thrombotic disease? Thrombosis is a group of diseases in which blood flow is significantly reduced or even completely interrupted, causing serious or even fatal damage to the body, and instead of being dissolved or mechanized soon after the formation of thrombus, it continues to grow or fall off slowly, blocking the lumen of blood vessels. What are the common thrombotic diseases? Arterial thrombotic diseases include atherosclerosis, cerebral thrombosis, coronary heart disease, myocardial infarction, thrombo-occlusive vasculitis, etc. Venous thrombotic diseases include pulmonary embolism, deep vein thrombosis, superficial vein thrombosis and thrombophlebitis. Microvascular thrombotic diseases include diffuse intravascular coagulation (DIC), adult respiratory distress syndrome, thrombotic thrombocytopenic purpura, central retinal artery obstruction, and sudden deafness. Intracardiac thrombotic disorders include rheumatic heart disease, atrial fibrillation, valve injury, and congestive heart failure.