Flow-related platelet deposition on subendothelium.

The deposition of platelets on subendothelium is controlled both by flow factors that determine their transport to the surface through convective diffusion, and by the kinetics of their interactions with the surface. Red cells influence platelet transport by several mechanisms, and may also influence platelet reactivity. Platelets initially contact the surface through the binding of membrane GPIb to von Willebrand factor (vWf) that is present in the subendothelium or deposited there from plasma. Platelet spreading on the surface is promoted by the binding of the arg1744 gly1745 asp1746 (RGD) region of vWf (at high shear rates) to platelet GPIIb-IIIa. At high (arterial) shear rates, vWf binding to GPIIb-IIIa also promotes thrombus formation. At these shear rates, thrombin that is generated at the subendothelial surface is not involved in platelet adhesion or thrombus formation that occurs early in thrombogenesis, but is a major mediator of subsequent thrombus growth and/or stabilization.