Function: Platelets contribute to chemical blood clotting and to other aspects of hemostasis. Platelet factors are the chemicals released by platelets to initiate the first stage of (intrinsic pathway) chemical clotting. When a capillary ruptures, the exposed endothelium releases thrombin that attracts platelets; platelets adhere to one another and to the cut edges of the vessel, forming a platelet plug. Blood clotting may be beneficial (as in preventing blood loss from wounds) or may be harmful when it occurs within arteries or veins inside the body (as during coronary thrombosis). Blood clotting is a positive feedback cascade that may continue and occlude an unbroken vessel.