Primary Hemostasis Flashcards
What is primary hemostasis?
formation of a weak platelet plug.
What is secondary hemostasis?
Stabilization of the platelet plug, mediated by the coagulation cascade.
What are the four steps of primary hemostasis?
- Transient vasoconstriction (endothelin)
- Platelet adhesion to damaged wall
- Platelet degranulation
- Platelet aggregation
What does vWF bind to?
exposed subendothelial collagen
How does the platelet bind vWF?
GP 1b receptor
Where is vWF stored?
endothelium- Weibel-Palade bodies
alpha granules of platelets
Describe platelet degranulation?
ADP release from dense granules promotes exposure of GP IIb. TXA2 (COX) promotes aggregation (next step)
What molecule crosslinks GPIIb receptors
fibrinogen
What is the most common cause of thrombocytopenia?
ITP. Immune thrombocytopenic purpura
In ITP IgG targets what receptor?
GP IIb
What are the lab findings in ITP?
decreased platelet count
Normal PT/PTT (secondary hemostasis unaffected)
increased megokaryocytes
What are two microangiopathic hemolytic anemias?
TTP. Thrombotic thrombocytopenic purpura
HUS. Hemolytic uremic syndrome
What is the pathogenesis of TTP?
Decreased ADAMTS13 leaves uncleaved multimers of vWF leading to abnormal platelet adhesion. Usually due to an autoantibody. Most commonly seen in adult females.
What causes HUS?
E coli O157:H7, usually in children
What are the lab findings of microangiopathic hemolytic anemias?
Thrombocytopenia Increased bleeding time Normal PT/PTT Anemia with schistocytes increased megokaryocytes
