The fibrinolytic system is the most important anticoagulation system in the body. During lysis, thrombin hydrolyzes fibrin, releasing soluble fibrin monomers, which, under the action of factor xIIIa, form stable cross-linked fibrin. In late stages of disseminated intravascular coagulation, the fibrinolytic system is activated due to intravascular coagulation, resulting in secondary fibrinolysis and more pronounced bleeding symptoms. What are the causes of secondary enhanced fibrinolysis? 1, vaso-activators Vaso-activators are synthesized in the endothelial cells of small vessels and released into the blood. If a blood clot appears in the blood vessel, it can cause the vascular endothelial cells to release a large amount of this activator and be adsorbed on top of the blood fibrin clot. Tissue activators exist in many kinds of tissue cells, with the highest levels in the uterus, thyroid and lymph nodes, followed by the lungs and ovaries. 3, urinary activators Urine contains fibrinogen activator, called urokinase. It is released by the epithelial cells of the kidney and urinary tract. Tumor cells such as adenocarcinoma (especially prostate cancer and pancreatic cancer) and acute promyelocytic leukemia (APL) can release fibrinogen activator, of which u-PA is common. This spontaneous fibrinolytic activity of tumor cells can promote primary fibrinolysis to produce large amounts of fibrinolytic enzymes, and fibrinolytic enzyme α2AP complexes can be measured in the depleted α2AP cycle. Tissues such as prostate, pancreas, uterus, ovary, placenta, lung, and thyroid are rich in t-PA, and fibrinolysis is induced by the release of t-PA into the blood when tumor trauma occurs or surgery is performed in these organs. Genitourinary tract trauma and surgery can cause fibrinolysis due to the release of u-PA into the blood. Some venomous snakes have direct fibrinolytic activation or protein hydrolase activity, which alters fibrinolytic system activity by degrading fibrinogen and reducing α2AP levels. Severe hemorrhagic manifestations can occur rapidly when bitten by them.