What lines the alveolus and plays a role in preventing collapse?

Surfactant is a substance that lines the alveoli in the lungs and plays a critical role in preventing alveolar collapse, particularly during the process of breathing. It is a complex mixture of lipids and proteins produced by the type II alveolar cells. The primary function of surfactant is to reduce surface tension at the air-liquid interface within the alveoli. High surface tension can cause alveoli to collapse, especially during exhalation when the lung volume decreases.

By lowering the surface tension, surfactant helps to keep the alveoli open, ensuring that they remain inflated and ready for the next inhalation. This is particularly important at the end of exhalation, where the risk of collapse is greatest. The presence of surfactant allows for easier expansion of the alveoli during inhalation, facilitating gas exchange between the air and blood.

In contrast, serum, pleural fluid, and interstitial fluid do not play this specific role in the alveoli. Serum is primarily the liquid component of blood, pleural fluid serves to lubricate the pleural cavity, and interstitial fluid is found in the spaces between cells in tissues. Therefore, surfactant is uniquely adapted to fulfill the essential function of maintaining alveolar stability and enhancing