Prevention of Alveolar Collapse

Collapse of alveolar sacs is prevented by:

Correct Answer: Surfactant

Pulmonary surfactant (DPPC) prevents the collapse (atelectasis) of alveolar sacs by reducing surface tension at the air-liquid interface of the alveoli.

Why Surfactant is Essential

• Alveoli are small bubble-like structures lined by a fluid layer. Without surfactant, surface tension would cause them to collapse on expiration (La Place's Law: smaller radius = higher collapsing pressure).
• Surfactant reduces surface tension → alveoli remain open → stable gas exchange.

Surfactant Deficiency

• Neonatal Respiratory Distress Syndrome (NRDS): Premature infants lack mature surfactant → alveolar collapse → severe breathing difficulty → treated with exogenous surfactant therapy.

Cells Producing Surfactant

• Mammals: Type II pneumocytes (type II alveolar cells)
• Birds: Granular cells