The most important function of blood platelets is involved in primary hemostasis comprising forming the stud part in the hemostatic and secondary hemostasis , or clotting factor activation and production of thrombin. Platelets are also involved in many physiological and pathological processes , including in wound healing , defense against bacterial infections , metastasis of tumor cells and the formation and development of inflammation and atherosclerosis . Resting platelets do not adhere to unstimulated endothelial cells and do not react with the wall of the blood vessel.