Which cells line the alveolar walls for gas exchange, and what other alveolar cell type is present?

Which cells line the alveolar walls for gas exchange, and what other alveolar cell type is present?

• A. Type II pneumocytes line alveolar walls; Type I pneumocytes secrete surfactant.
• B. Type II pneumocytes line alveolar walls; Type I pneumocytes secrete surfactant.
• C. Alveolar walls are lined by club cells; Type I pneumocytes secrete mucus.
• D. Type I pneumocytes line alveolar walls; Clara cells secrete surfactant.

Answer: (C)

Gas exchange in the alveoli relies on very thin, flat cells that cover the alveolar walls—these are the Type I pneumocytes, forming the main diffusion barrier. The other alveolar cell type present is the Type II pneumocyte, which is cuboidal and produces surfactant to lower surface tension and prevent collapse; these cells also serve as progenitors that can regenerate Type I pneumocytes after injury. Club (Clara) cells are located in the bronchioles, not the alveolar walls, and they are not responsible for surfactant production or gas exchange. They play a different protective/detoxifying role in the conducting airways. So the correct concept is: alveolar walls lined by Type I pneumocytes for gas exchange, with Type II pneumocytes present to secrete surfactant.

Gas exchange in the alveoli relies on very thin, flat cells that cover the alveolar walls—these are the Type I pneumocytes, forming the main diffusion barrier. The other alveolar cell type present is the Type II pneumocyte, which is cuboidal and produces surfactant to lower surface tension and prevent collapse; these cells also serve as progenitors that can regenerate Type I pneumocytes after injury.

Club (Clara) cells are located in the bronchioles, not the alveolar walls, and they are not responsible for surfactant production or gas exchange. They play a different protective/detoxifying role in the conducting airways. So the correct concept is: alveolar walls lined by Type I pneumocytes for gas exchange, with Type II pneumocytes present to secrete surfactant.