What causes a pulmonary embolism?

A pulmonary embolism occurs when there is a blockage in one of the pulmonary arteries in the lungs, often caused by blood clots that travel to the lungs from the deep veins in the legs or other parts of the body. In this context, the term "embolus" specifically refers to a substance that travels through the bloodstream and lodges in a vessel, obstructing blood flow.

The blockage is often a result of a thrombus, which is a type of embolus that is primarily composed of fibrin, blood cells, and platelets that form a clot. This indicates that the presence of a clot is directly involved in the mechanism of a pulmonary embolism. Therefore, all the factors mentioned—blockage, embolus, and clot—contribute to the occurrence of a pulmonary embolism, each playing a significant role in the condition.

The understanding that pulmonary embolisms can result from various forms of blockage, including clots originating from other regions, establishes why selecting all of the above as the correct answer accurately reflects the multifaceted nature of this critical medical condition.