Integrin signaling in hemostasis. Platelet adhesion to the damaged vessel wall is initiated by platelet rolling, an integrin-independent event mediated by binding of GP Ib-V-X to vWF (left panel). Subsequent stationary adhesion and primary platelet aggregation require inside-out signaling through and ligand binding to α_IIbβ₃ (center panel). Full platelet spreading, aggregation, and effective hemostatic plug formation also require outside-in signaling through α_IIbβ₃ (right panel).