Final answer:
A pulmonary embolus is an obstruction of the pulmonary arterial bed caused by a dislodged thrombus, also known as option b) Arterial, thrombus, which can result in serious health consequences.
Step-by-step explanation:
A pulmonary embolus is an obstruction of the pulmonary arterial bed by a dislodged thrombus or foreign substance. The correct answer to fill in the blanks would be option b) Arterial, thrombus. When a thrombus, which is an aggregation of platelets, erythrocytes, and white blood cells entrapped within fibrin, breaks free from the vessel wall and enters the circulation, it is known as an embolus. This embolus can travel through the bloodstream and become lodged in a pulmonary artery, blocking deoxygenated blood from reaching the lungs for oxygenation, leading to a pulmonary embolism. Such a blockage can result in serious consequences including lung damage or even sudden death due to the disruption of pulmonary circulation, which is a medical emergency.