Adenosine diphosphate as a mediator of platelet aggregation in vivo: an editorial view.

Platelets in hemostasis When blood vessels are injured so that they bleed, circulating platelets adhere to the damaged vessel walls and aggregate, so diminishing or arresting the hemorrhage. This interaction between platelets and vessel walls therefore has an easily demonstrable physiologic function. There is much clinical and experimental evidence that a deficiency or defect in circulating platelets is associated with "spontaneous" hemorrhages from small vessels. This suggests that platelets are somehow essential for the functional integrity of these vessels, but if there is such a mechanism it has yet to be established.