Hemostasis: Blood coagulation and fibrinolysis - Part 1 Flashcards
Objectives: Hemostasis •Outline the four phases of hemostasis. •Discuss vascular spasm and the role of endothelin. •Describe the platelet plug formation. •Explain the role of integrins GPIb and GPIa. •Describe the role of platelet-activating factors (ADP, serotonin, TXA2and thrombin). •Describe the role of integrinGPIIb/IIIain platelet aggregation. •Describe the coagulation cascade, including the extrinsic, intrinsic and common pathways. •Indicate the role of calcium in hemostasis •Disc
What are the four phases of hemostasis?
1) Vascular spasm/ vasoconstriction
2) Platelet plug formation/ primary hemostasis
3) Blood coagulation/ secondary hemostasis
4) Dissolution of the fibrin clot/ tertiary hemostasis
What occurs, in general, in primary hemostasis phase?
Platelet plug formation
What occurs, in general, in secondary hemostasis?
Blood coagulation
What occurs, in general, in tertiary hemostasis?
Dissolution of the fibrin clot
What is the role of endothelin in the vascular spasm phase of hemostasis?
Stimulates nervous reflexes upon trauma which lead to smooth muscle contraction
What occurs, specifically, during the vascular spasm phase of hemostasis?
-Vessel wall trauma results in smooth muscle contraction
What two factors are released from the injured vessel wall which leads to local myogenic spasm in the blood vessel during the Vascular spasm phase of hemostasis?
-Endothelin
-Serotonin
What are the stages of platelet plug formation during primary hemostasis?
- Platelet adhesion to the damaged surface and activation
-Platelet aggregation
Under normal cicumstances, what prevents platelet adherence and activation?
Negative charges on both the platelets and endothelial cells
During platelet adhesion, which glycoprotein on the platelet surface binds to collagen? What change does this promote?
- GpIa
- Development of pseudopods to promote platelet-platelet interactions
Once GpIa binds to collagen in the beginning of Platelet adhesion, what happens next?
Von Willebrand fator (located on the subendothelial collagen) binds to platelet receptor, Glycoprotein Ib (GpIb) resulting in changes in the platelet membrane
The binding of GpIa to collagen and GpIb to Von Willebrand factor exposes what?
GPIIb/IIIa (located on platelet membrane) for binding of fibrinogen.
What is the role of Von Willebrand factor in platelet adhesion?
-vWf acts as a bridge between specific glycoproteins (GPIb) on the surface of platelets and collagen fibres - facilitates platelet adhesion to the vessel wall and platelet aggregation.
-Complexes with factor VIII; carries it, stabilizes it and prevents its degrdation
Von Willebrand deficiency is associated with what?
A defect in the formation of the platelet plug (primary hemostasis)
Once initial platelet adhesion occurs, the activation of platelets leads to a shape change which results in what?
-Release of granule contents (ADP, CA2+), that activates other platelets, promoting aggregation.
- Increased levels of calcium stimulate the synthesis and release of thromboxane A2.
