At

Heparan

Lysis of fibrin

Plasmin

Plasminogen activators (t-PA u-PA)

Figure 11.7. Mechanisms (a-d) whereby endothelial cells prevent inopportune platelet plug formation and coagulation. Endothelial cells synthesize NO, PGI2 (prostacyclin), thrombomodulin, heparin and plasminogen activators, all of which prevent thrombosis and thereby help preserve vascular patency. AT III: antithrombin III (modified from Colman RW et al. Chapter 1, In: Colman RW et al. (eds), Hemostasis and Thrombosis: Basic Principles and Clinical Practice, 3rd edn. Philadelphia: JB Lippincott Company, 1994).

tissue

Figure 11.8. A diagrammatic representation of the role of platelets in coagulation. After a breach in the endothelial cell lining, platelets in the presence of vWF, adhere to the exposed matrix. Activated platelets provide a template for activation of the coagulation cascades and thus formation of fibrin (modified from Jandl, 1996).

tissue

Figure 11.8. A diagrammatic representation of the role of platelets in coagulation. After a breach in the endothelial cell lining, platelets in the presence of vWF, adhere to the exposed matrix. Activated platelets provide a template for activation of the coagulation cascades and thus formation of fibrin (modified from Jandl, 1996).

intrinsic (initiated by circulating factors) pathway, although it is now recognized that these two pathways are not the full story.

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