Which structure primarily prevents the collapse of alveoli?

Which structure primarily prevents the collapse of alveoli?

• A. Alveolar ducts
• B. Surfactant
• C. Bronchioles
• D. Trachea

Answer: (B)

The primary structure that prevents the collapse of alveoli is surfactant. Surfactant is a substance composed of lipids and proteins secreted by the type II alveolar cells in the lungs. It plays a crucial role in reducing surface tension within the alveoli, which are the small air sacs where gas exchange occurs.

When the surface tension is high, the alveoli can become prone to collapse, especially at lower lung volumes. By significantly lowering this surface tension, surfactant ensures that the alveoli remain open and can expand efficiently during inhalation. This not only facilitates effective gas exchange but also aids in maintaining the structural integrity of the alveoli during the different phases of the breathing cycle.

Other structures listed, such as alveolar ducts, bronchioles, and trachea, have essential roles in the respiratory system, including conducting air and supporting overall lung architecture. However, they do not specifically address the prevention of alveolar collapse caused by surface tension. Surfactant is unique in its function and is vital for ensuring the proper functioning of the alveoli.