Which cells in the alveoli are specialized for gas exchange and secrete surfactant?

• A. Pneumocytes
• B. Alveolar macrophages
• C. Goblet cells
• D. Ciliated cells

Answer: (A)

In the alveoli, the lining cells are called pneumocytes. Gas exchange is carried out mainly by the very thin Type I pneumocytes that form the walls of the alveoli, allowing oxygen and carbon dioxide to diffuse between air and blood. Surfactant, which lowers surface tension to prevent collapse, is produced by the other alveolar epithelial cells, the Type II pneumocytes. So, while no single cell does both jobs, the broad category of pneumocytes includes the cells responsible for both functions, making it the best answer for identifying alveolar epithelial cells. In contrast, alveolar macrophages handle debris cleanup, and goblet or ciliated cells belong to the conducting airways rather than the alveolar lining.