A condition in which alveoli collapse, leading to reduced gas exchange.

• A. Emphysema
• B. Pneumothorax
• C. Pulmonary Edema
• D. Atelectasis

Answer: (D)

Atelectasis is the collapse of alveoli, which reduces the surface area available for gas exchange. When lung air sacs lose their air and shut off, they don’t participate in oxygen uptake or CO2 removal, leading to lower blood oxygen levels. This condition can arise from airway obstruction (like mucus plugs), external compression (such as fluid in the chest or a mass), or surfactant deficiency that causes the alveoli to stick shut. It differs from emphysema, where alveolar walls are damaged and air trapping occurs; from a pneumothorax, where air in the pleural space collapses part of the lung rather than the alveoli themselves; and from pulmonary edema, where fluid in the lungs impairs gas exchange without alveolar collapse. Treating the underlying cause and encouraging deep breathing or incentive spirometry helps re-expand the affected alveoli and restore gas exchange.