Surfactant is found in which lung structure?

• A. Alveoli
• B. Bronchi
• C. Trachea
• D. Pleura

Answer: (A)

Surfactant reduces surface tension at the air–liquid interface inside the alveoli, helping keep the tiny air sacs open and making breathing easier. It’s produced by type II pneumocytes in the walls of the alveoli and released into the alveolar lining, so its functional site is the alveoli. The bronchi and trachea are conducting airways lined with mucus and cilia, not sites of surfactant production, and the pleura is a serous membrane with pleural fluid. Therefore, surfactant is found in the alveoli.