Oxygen and carbon dioxide crossing between blood and air in the lungs must pass through cells of the following types:

Question

Quizplus · Accepted Answer

Type I pneumocytes and endothelial cells form the barrier between the air in the lungs and the blood vessels. Oxygen and carbon dioxide molecules can diffuse across the thin walls of both cell types to move between the blood and air. Type II pneumocytes secrete surfactant, which helps keep the lungs inflated, but they do not play a direct role in gas exchange. Clara cells are non-ciliated secretory cells found in the bronchioles that secrete substances to protect the airway and are not involved in gas exchange.

Oxygen and Carbon Dioxide Crossing Between Blood and Air in the Lungs