Hemostasis

Question 1

What are the four steps of primary hemostasis?

Answer 1

Injury, Adhesion, Activation, and Aggregation

Question 2

What occurs during the first step of primary hemostasis, injury?

Answer 2

von Willebrand Factor binds to exposed collagen upon endothelial damage.

Question 3

What occurs during the second step of primary hemostasis, adhesion?

Answer 3

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.

Question 4

What occurs during the third step of primary hemostasis, activation?

Answer 4

ADP binding to receptor induces GpIIb/IIIa expression at platelet surface.

Question 5

What occurs during the fourth step of primary hemostasis, aggregation?

Answer 5

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.

Question 6

What factors does Vitamin K help produce and how does warfarin counter its activity?

Answer 6

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.

Question 7

What is the activation process and activity of Protein C?

Answer 7

Protein C + Thrombin/Thrombomodulin complex = Activated Protein C (APC); APC + Protein S = cleavage and inactivation of Factors Va and VIIIa.

Question 8

What is the activation process and activity of Plasminogen?

Answer 8

Plasminogen + tPA = Plasmin; Plasmin = Fibrinolysis, cleavage of fibrin mesh, destruction of coagulation factors.

Question 9

What action does Ticlopidine and clopidogrel have on thrombogenesis?

Answer 9

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.

Question 10

What is the method of action of Abciximab?

Answer 10

Abciximab directly inhibits GpIIb/IIIa on the platelet surface.