Which structure primarily assists with the maintenance of alveolar stability?

• A. Pneumocytes
• B. Surfactant
• C. Bronchial smooth muscle
• D. Lamina propria

Answer: (B)

Surfactant is a substance secreted by type II alveolar cells (pneumocytes) that plays a crucial role in maintaining alveolar stability. It is composed primarily of phospholipids and proteins and acts to reduce surface tension at the air-liquid interface within the alveoli. This reduction in surface tension is vital because it prevents the collapse of the alveoli during exhalation, ensuring that they remain open and available for gas exchange.

In addition to reducing surface tension, surfactant helps to equalize pressure among alveoli of different sizes, preventing smaller alveoli from collapsing into larger ones, a phenomenon known as atelectasis. By maintaining alveolar stability, surfactant facilitates efficient gas exchange, as the alveoli can remain optimally inflated and thereby increase the surface area for oxygen and carbon dioxide exchange.

While pneumocytes are the cells that produce surfactant, the primary role in stabilizing the alveoli belongs to the surfactant itself. Bronchial smooth muscle contributes to the regulation of airway diameter and resistance but does not directly impact alveolar stability. The lamina propria, a connective tissue layer, supports various structures in the respiratory system but is not directly involved in the stabilization of the alveoli.