Atelectasis is best described as?

• A. Inflammation of the pleura
• B. Accumulation of air in the pleural space
• C. Collapse of lung alveoli
• D. Excess mucus production

Answer: (C)

Atelectasis is the collapse or incomplete expansion of alveoli, so that parts of the lung have little or no air and cannot participate in gas exchange. This happens when air cannot reach the alveoli or when alveoli deflate after expansion—often due to airway obstruction (like mucus plugging), external pressure compressing the lung, or surfactant deficiency. The result is reduced lung volumes and a V/Q mismatch, with localized dullness on percussion and decreased breath sounds in the affected area. The other options describe different problems: pleural inflammation is pleuritis, air in the pleural space is pneumothorax, and excessive mucus production refers to secretions rather than alveolar collapse.