Essential thrombocythemia (NORD)

A 51-year-old female comes to the emergency department because of shortness of breath that began an hour ago. Three days ago, the patient returned from a business trip in Europe. Past medical history is notable for hypertension. The patient has been taking oral estrogen for management of menopausal symptoms. Her temperature is 37.8°C (100.0°F), blood pressure is 148/89, pulse is 130/min, and respiratory rate is 27/min. Oxygen saturation is 86% on room air. Physical examination reveals splenomegaly. Coagulation studies show a prothrombin time (PT) of 12 seconds and partial thromboplastin time (PTT) of 34 seconds. A peripheral blood smear shows the following:  



 Reproduced from: Wikimedia Commons  

Computed tomography subsequently confirms the presence of a pulmonary embolus. Which of the following best explains the pathophysiology of this patient presentation?