Coagulation Enzymes Review and Review of Hemostasis: Putting It All Together
Hemostasis is a well-coordinated interplay of cells and biochemical substrates which can quickly respond to vascular injury and form a local thrombus to stop hemorrhage. In addition, this prothrombotic response is balanced by endogenous antithrombotic elements to prevent excessive thrombus generation and to clear a clot once bleeding is controlled and tissue healing progresses. This first part of this chapter reviews the major biochemical mediators involved in thrombus formation (coagulation factors) and prevention and dissolution of thrombi (antithrombotic factors).
The second part of this chapter focuses on how the three components of hemostasis—local tissues and platelets (described in the previous chapter) and coagulation factors—interact in a well-orchestrated and tightly regulated explosion of reactions leading to thrombus formation and cessation of bleeding. Two models of hemostasis are reviewed. The first is the model by which the physiology of hemostasis has traditionally been taught and studied. This model is referred to as the cascade or biochemical model. This ubiquitously reported model elucidates the multiple reactions and sequencing of these reactions leading to formation of a thrombus. The second model is referred to as the cell-based model of hemostasis and is widely reported to more accurately describe in greater detail where reactions are occurring in vivo and how they relate to clinical hemostasis and better explain pathologies of hemostasis.
KeywordsCoagulation Coagulation factor Antithrombotic factor Antithrombin Fibrin Fibrinogen Thrombin Tissue factor Antihemophilic factor Christmas factor Vitamin K Fibrinolysis Tissue factor pathway inhibitor Thrombomodulin Protein C Plasminogen Plasmin Biochemical model Cell-based model Extrinsic pathway Initiator pathway Tissue factor pathway Intrinsic pathway Propagator pathway Common pathway
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