Which statement accurately defines an embolism?

• A. A clot that forms at a site and remains there
• B. A thrombus that breaks loose to become an embolism and occlude downstream blood flow
• C. Air bubbles trapped in the bloodstream
• D. An infection of the blood vessel

Answer: (B)

An embolism is a traveling obstruction in the bloodstream. The key idea is that material from one site travels through the vessels and lodges elsewhere to block blood flow downstream. The best description captures this movement and blockage: a clot that forms and then breaks loose, travels through the circulation, and occludes a vessel downstream. This aligns with how emboli form and cause problems in distant sites.

A clot that forms at a single spot and remains there isn’t traveling, so it’s a thrombus at its origin rather than an embolus. Air bubbles are one possible material that can become an embolus, so they describe a specific type rather than the general process. An infection of the blood vessel isn’t an embolism.