Questions: What prevents the lungs from collapsing?

The answer is the first one: pulmonary surfactant and pressure differences.

Explanation for each option:

• Pulmonary surfactant and pressure differences: This is the correct answer. Pulmonary surfactant is a substance produced by the cells in the alveoli of the lungs that reduces surface tension, preventing the alveoli from collapsing. Additionally, the pressure difference between the inside of the lungs and the pleural cavity (intrapleural pressure) helps keep the lungs inflated.

• Smoking: This is incorrect. Smoking can damage the lungs and lead to diseases such as emphysema and chronic obstructive pulmonary disease (COPD), but it does not prevent the lungs from collapsing.

• Rib fracture: This is incorrect. A rib fracture can actually increase the risk of lung collapse (pneumothorax) if the sharp edges of the broken rib puncture the lung or pleura.

• Pneumothorax: This is incorrect. Pneumothorax refers to the presence of air in the pleural space, which can cause the lung to collapse. It is a condition that leads to lung collapse, not something that prevents it.

In summary, pulmonary surfactant and pressure differences are the key factors that prevent the lungs from collapsing.