(1) Receptor complexes tether platelets to sites of vascular injury: glycoprotein Ib/V/IX and platelet surface collagen receptors glycoprotein VI and Ia
(2) Mediators of adhesion phase, and amplification and sustenance of platelet response: adenosine diphosphate (ADP), thrombin, epinephrine, and TXA2
(3) Final activation pathway by involvement of agonists: activation of platelet integrin glycoprotein IIb/IIIa receptor for adhesion and aggregation