Flashcards in Hemostasis Deck (10)
What are the four steps of primary hemostasis?
Injury, Adhesion, Activation, and Aggregation
What occurs during the first step of primary hemostasis, injury?
von Willebrand Factor binds to exposed collagen upon endothelial damage.
What occurs during the second step of primary hemostasis, adhesion?
Platelets bind vWF via GpIb receptor at the site of injury only. Platelets release ADP and Ca2+ which are necessary for coagulation cascade. ADP helps platelets adhere to endothelium.
What occurs during the third step of primary hemostasis, activation?
ADP binding to receptor induces GpIIb/IIIa expression at platelet surface.
What occurs during the fourth step of primary hemostasis, aggregation?
Fibrinogen binds GpIIb/IIIa receptors and cross-links platelets. Balance of pro- and anti-coagulation factors begins: Platelets produce TXA2, procoag factor decreases blood flow and increases platelet aggregation; Endothelial cells release PGI2 and NO, anti-coag factors that increase blood flow and decrease platelet aggregation.
What factors does Vitamin K help produce and how does warfarin counter its activity?
II, VII, IX, X, Protein C, Protein S. Only reduced Vitamin K can carry out its function. Warfarin inhibits epoxide reductase enzyme from reducing Vitamin K, producing a Vit K shortage.
What is the activation process and activity of Protein C?
Protein C + Thrombin/Thrombomodulin complex = Activated Protein C (APC); APC + Protein S = cleavage and inactivation of Factors Va and VIIIa.
What is the activation process and activity of Plasminogen?
Plasminogen + tPA = Plasmin; Plasmin = Fibrinolysis, cleavage of fibrin mesh, destruction of coagulation factors.
What action does Ticlopidine and clopidogrel have on thrombogenesis?
Ticlopidine and clopidogrel irreversibly block the ADP receptor on platelet surface membranes, inhibiting the expression of GpIIb/IIIa, and thus inhibiting cross linking of platelets.