What is the primary purpose of surfactant in the lungs?

Surfactant plays a critical role in the lungs by decreasing surface tension in the alveoli, which are the tiny air sacs where gas exchange occurs. This reduction in surface tension is vital because it prevents the alveoli from collapsing during exhalation. By keeping the alveoli stable and open, surfactant enhances lung compliance and facilitates efficient gas exchange.

In the absence of adequate surfactant, the alveoli would struggle to remain inflated, leading to respiratory difficulties, such as those seen in conditions like neonatal respiratory distress syndrome.

The other options do not accurately represent the primary function of surfactant. For instance, surfactant does not expand blood vessels, nor does it directly increase the respiratory rate or filter harmful particles from the air entering the lungs. Instead, its main job is to ensure optimal surface tension within the alveoli, thereby playing a crucial role in maintaining effective lung function.