Biological Systems MCAT Practice Exam

What ensures the alveoli do not collapse due to surface tension during respiration?

1. Respiratory epithelium

2. Surfactant

3. Goblet cells

4. Interstitial fluid

The correct answer is: Surfactant

The prevention of alveolar collapse during respiration is primarily due to the action of surfactant. Surfactant is a lipoprotein complex secreted by type II alveolar cells in the lungs. It reduces surface tension at the air-liquid interface in the alveoli by disrupting cohesive forces between water molecules. This reduction in surface tension is crucial for maintaining alveolar stability, especially during exhalation when alveoli would otherwise be prone to collapse. When the lungs inflate, the surfactant spreads out and coats the alveoli, ensuring that they remain open even at low lung volumes. This allows for easier inflation of the alveoli during breathing and helps to prevent atelectasis (the collapse of lung structures). Additionally, surfactant plays a role in improving lung compliance, making it easier for the lungs to expand with each breath, further supporting effective gas exchange. The other options, such as respiratory epithelium, goblet cells, and interstitial fluid, serve different functions in the respiratory system. The respiratory epithelium primarily functions as a protective barrier and is involved in the exchange of gases, while goblet cells are responsible for producing mucus to trap particles and pathogens. Interstitial fluid helps to provide a medium for nutrient and gas