The loop is initiated when injured tissue releases signal chemicals that activate platelets in the blood.

These tissue fragments are very clot-promoting, containing collagen and tissue factor; they activate platelets and activate the system of coagulation.

It does not require a binding cofactor such as antithrombin and does not activate platelets.

Thrombin also promotes further thrombin generation, and activates platelets, stimulating aggregation and granule release.

Another strategy being explored is to inactivate a substance that itself activates platelets, the particles that contribute to blood clotting.

Ultrastructure expression of p-selectin on surface activated platelets.

Cocaine activates platelets and increases the formation of circulating platelet containing microaggregates in humans.

It is found on mature B cells, activated macrophages, eosinophils, follicular dendritic cells, and platelets.

The PF4-heparin complex can activate platelets and may cause venous and arterial thrombosis.

HIT is caused by the formation of abnormal antibodies that activate platelets.