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Old 05-19-2011
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Arrow Platelet Activation Steps

Here is a summary of all the different events that take place in platelet activation:

Platelet activation: occurs via the Gq signaling pathway
Stimulated by binding of vWF, ADP, and others to platelets
1) Synthesis of TXA2 from Arachidonic Acid by COX (Drugs: Aspirin, NSAIDs)
TXA2: Promotes platelet aggregation and stimulates vasoconstriction
2) Release of alpha-granule contents: vWF, Fibrinogen, PDGF, PF4
vWF: Platelet-Collagen adhesion via GP1b receptors (Defective in Bernard-Soulier)
Fibrinogen: Platelet-Platelet adhesion via GPIIb/IIIa receptors (Defective in Glanzmann's Thrombasthenia, Drug: Abciximab, eptifibadate, tirofiban - Last two have "fib" for fibrinogen receptor)
PDGF: Stimulates smooth muscle proliferation + Stimulates fibroblast deposition of collagen for tissue repair
Platelet Factor 4: Binds and inactivates Heparin - thought to be Antibody target in HIT
3) Release of delta-granule contents: ADP, Ca2+, Serotonin
ADP: Further platelet activation/degranulation, promotes platelet aggregation and binding to endothelium (Drugs: Clopidogrel, Ticlopidine block ADP receptors)
Ca2+: Needed for function of Vitamin K dependent Coagulation factors II, VII, IX, and X (Drug: Warfarin inhibits epoxide reductase needed for synthesis of these factors)
Serotonin: Causes vasoconstriction
See FA 2011 p 346-347 for reference
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