Platelets in pulmonary vascular physiology and pathology

Almost a trillion platelets pass through the pulmonary circulation every minute, yet little is known about how they support pulmonary physiology or contribute to the pathogenesis of lung diseases. When considering this conundrum, three questions jump out: Does platelet production in the lungs occur? Why does severe thrombocytopenia-which undercuts the principal physiological role of platelets to effect hemostasis-not lead to pulmonary hemorrhage? Why does atherothrombosis-which platelets initiate, maintain, and trigger is other critically important arterial beds-not develop in the pulmonary artery? The purpose of this review is to explore these and derivative questions by providing data within a conceptual framework that begins to organize a subject that is largely unassembled.