Physiology - Clinical Flashcards
What happens during primary and secondary hemostasis?
Primary: formation of weak platelet plug
Secondary: stabilization of platelet plug - coagulation cascade
Immediate reaction to injury (aka first step of primary hemostasis)? Mediators?
Transient vasoconstriction mediated by:
- reflex neural stimulation
- endothelin (released by endothelial cells)
Role of Von Willebrand (vWF) factor?
After transient vasoconstriction (step 1):
- vWF binds to subendothelial collagen –> platelet ADHESION (bridge between collagen and platelets)
Platelet receptor that binds vWF
GpIb
What is vWF derived from?
1) Weibel-Palade bodies of endothelial cells
2) alpha-granules of platelets
Big picture steps of primary hemostasis
1) Transient vasoconstriction of injured vessel
2) Binding of vWF to subendothelial collagen
3) PLATELET ADHESION to vWF triggers conformational change and release of ADP, Ca2+, TXA2
4a) PLATELET ACTIVATION: ADP binding activates other platelets by inducing expression of GpIIb/IIIa.
4b) PLATELET AGGREGATION: Fibrinogen binds GpIIb/IIIa to link platelets together to form platelet plug
Primary hemostasis: role of ADP? what releases it?
Increases GpIIb/IIIa expression on platelets
Released by platelet dense granules
Primary hemostasis: role of TXA2? what produces it?
Platelet cyclooxygenase (COX) Promotes platelet aggregation
Thrombin: function
Convert fibrinogen to fibrin, which can be cross-linked –> stabilizes platelet-fibrin thrombus
Extrinsic pathway factors
3 (tissue factor), 7
Intrinsic pathway factors
12, 11, 9, 8
Common pathway factors
10, 5, 2 (prothrombin), 1 (fibrinogen), 13 (cross-links)
**
2a = thrombin
1a = fibrin
Prostacyclin: effects
Vasodilation
Inhibitor of platelet aggregation
Protein C: function
Inactivates factors Va (5a) and VIIIa (8a)
“Proteins C and S are Clot Stoppers”
Protein S: function
Co-factor to Protein C
“Proteins C and S are Clot Stoppers”
