What condition is characterized by decreased surface area in the alveoli?

• A. Pneumonia
• B. Bronchitis
• C. Emphysema
• D. Cystic fibrosis

Answer: (C)

Gas exchange hinges on the surface area available in the alveoli for oxygen and carbon dioxide to diffuse. In emphysema, the walls between alveoli are destroyed, causing the alveoli to merge into larger air spaces and reducing the total alveolar surface area and the accompanying capillary bed. With less surface area, the diffusion capacity drops, so oxygen uptake and carbon dioxide removal become less efficient, even though the lungs may appear hyperinflated. This loss of surface area is the hallmark that points to emphysema. The other conditions involve airway inflammation or infection (pneumonia, bronchitis) or abnormal mucus production and obstruction (cystic fibrosis) rather than a primary reduction in alveolar surface area.