Atelectasis is best described as which of the following?

• A. Collapse of alveoli
• B. Expanding alveoli due to air
• C. Fluid in pleural space
• D. Enlarged lungs

Answer: (A)

Atelectasis is the collapse of alveoli, meaning parts of the lung lose air and deflate, leading to reduced lung volume in the affected area and impaired gas exchange. This collapse happens when air is absorbed from blocked or under-ventilated alveoli, or when external forces compress the lung tissue, such as from mucus plugs, tumors, fluid in the pleural space, or shallow breathing after surgery. The key idea is that the alveoli are not inflated anymore, rather than simply being enlarged or filled with fluid.

So why the others don’t fit: expanding alveoli would indicate overinflation, not collapse. Fluid in the pleural space describes a pleural effusion, which can contribute to atelectasis by compression but is not the description of atelectasis itself. Enlarged lungs suggest hyperinflation or pathology causing expansion, not the loss of aerated lung units that defines atelectasis.