What substance lowers the surface tension to prevent alveolar collapse?

Surfactant is the substance that lowers surface tension in the alveoli, thereby preventing their collapse. It is a complex mixture of lipids and proteins secreted by the type II alveolar cells in the lungs. The primary role of surfactant is to reduce the surface tension at the air-liquid interface within the alveoli. By doing so, surfactant stabilizes the alveoli and allows them to remain open during exhalation, which is crucial for maintaining adequate gas exchange and preventing atelectasis, or the collapse of lung tissue.

In the absence of sufficient surfactant, surface tension increases, leading to difficulty in inflating the lungs and an increased risk of alveolar collapse, particularly in conditions such as neonatal respiratory distress syndrome. This is why surfactant is vital for lung function, especially in premature infants who may not have developed adequate levels of surfactant.

The other substances listed do not serve this specific role. Hemoglobin is responsible for oxygen transport in the blood and does not influence alveolar surface tension. Interstitial fluid is the liquid that surrounds cells and does not play a role in alveolar stability or surface tension reduction. Albumin is a protein found in plasma that helps maintain osmotic pressure in the circulatory