Pulmonary embolus is defined as which of the following?

• A. A collapsed lung due to air in the pleural space
• B. Obstruction of the hepatic artery by a thrombus
• C. A blockage of the aorta
• D. Obstruction of the pulmonary artery or one of its branches by a thrombus from the venous system or right side of the heart

Answer: (D)

Pulmonary embolism happens when a clot that formed in the venous system (usually a deep vein thrombosis) or in the right side of the heart breaks loose and travels to the lungs, lodging in a pulmonary artery or one of its branches. This obstructs blood flow to portions of the lung and disrupts gas exchange, which is why the definition focuses on an artery blockage caused by a thrombus from the venous system or right heart.

That description matches the option describing obstruction of the pulmonary artery or its branches by a thrombus from the venous system or right side of the heart. The other scenarios refer to conditions not constituting a pulmonary embolism: a collapsed lung from air in the pleural space (pneumothorax), hepatic artery thrombosis, or an aortic blockage.