What is the role of Type II pneumocytes in the alveolar epithelium?

• A. Secrete surfactant to reduce surface tension
• B. Transport oxygen across the alveolar wall
• C. Form alveolar capillary barrier
• D. They are responsible for alveolar macrophages

Answer: (C)

Type II pneumocytes are the cuboidal cells in the alveolar lining that produce surfactant, a lipoprotein mixture that lowers surface tension at the air–liquid interface and prevents alveolar collapse during exhalation. They also act as progenitors for repair, capable of dividing and differentiating into Type I pneumocytes to restore the thin gas-exchange surface after injury. This is why their primary role centers on surfactant secretion and epithelial regeneration rather than forming the gas-exchange barrier or performing macrophage functions. The actual thin barrier for gas exchange is formed mainly by Type I pneumocytes, while alveolar macrophages handle debris clearance in the airspaces. Oxygen transport across the alveolar wall occurs by diffusion through the Type I pneumocytes and the capillary endothelium, not through Type II cells.