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Hemostasis and Thrombosis - part 2

Mặc dù không phải trong con đường mới, bệnh nhân bị thiếu hụt các yếu tố XI làm chảy máu triển lãm, đặc biệt là sau khi phẫu thuật. Thrombin có thể kích hoạt yếu tố XI, sau đó nguồn cấp dữ liệu để kích hoạt các yếu tố IX. Điều này sau đó dẫn đến nhiều thế hệ thrombin. | Basics of Coagulation 9 Fig. 1.12. Natural anticoagulants. The Role of Factor XI The new pathway leaves out the role of several proteins found in the older pathways. The contact system factors XII etc. appears to play a role in inflammation but patients with deficiency of these proteins do not have hemostatic defects. The role of factor XI is more confusing. Although not in the new pathway patients with deficiencies of factor XI do exhibit bleeding especially after surgery. Thrombin can activate factor XI which then feeds back to activate factor IX. This then leads to more thrombin generation. More thrombin formation leads to activation of TAFI. This theory is consistent with the finding that patients lacking factor XI often have bleeding in sites of fibrinolytic activity such as the mouth after oral surgery. Fibrinolysis The fibrinolytic system is responsible for breaking down blood clots once they have formed. Obviously this is an important process to prevent thrombi from getting too large to aid wound healing and to prevent thrombosis in an undesirable place. Recent research has also implicated roles for proteins from the fibrinolytic system in diverse processes such as cancer metastasis and memory. Fibrinolytic Proteins The key proteins in the fibrinolytic system are Fig. 1.13 Plasmin This is a serine protease produced by the liver which cleaves bonds in fibrin Fig. 1.13. The fibrinolytic pathway. 10 Hemostasis and Thrombosis Fig. 1.14. Physiologic fibrinolysis. Free tPA can bins to fibrin and efficiently activate plasminogen to plasmin. Any free tPA or plasma is inactivated by circulating inhibitors. and fibrinogen. Normally it circulates as an inactive precursor plasminogen but it can be converted to plasmin by Tissue plasminogen activator tPA This is produced by endothelial cells. tPA is the physiologic activator of plasminogen. Urokinase UK This is secreted in the urine hence its name and in many other cells. It is also a potent activator of plasminogen. .