Stability of alveoli is maintained by
**Core Concept**
The stability of alveoli is crucial for effective gas exchange in the lungs. This is maintained by the balance between surface tension forces and the elastic recoil of the lung tissue. The surfactant system plays a key role in reducing the surface tension at the air-liquid interface, thereby stabilizing the alveoli.
**Why the Correct Answer is Right**
Surfactant, a complex mixture of phospholipids and proteins, is secreted by type II pneumocytes and spreads across the alveolar surface. It reduces the surface tension by increasing the distance between the alveolar walls, thus preventing alveolar collapse during expiration. This is achieved through the formation of a monolayer of phospholipid molecules, primarily dipalmitoylphosphatidylcholine (DPPC), which reduces the interfacial tension between the air and the alveolar fluid.
**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect as it does not directly relate to the maintenance of alveolar stability. While lung compliance is an important property of the lung, it is not directly responsible for maintaining alveolar stability.
**Option B:** This option is incorrect as it refers to the process of gas exchange, which is a separate function of the alveoli. While gas exchange is crucial for the overall function of the lungs, it is not directly related to the stability of the alveoli.
**Option C:** This choice is incorrect as it refers to the process of airway closure, which is a separate phenomenon from alveolar stability. Airway closure can occur due to various factors, including surfactant deficiency, but it is not the primary mechanism for maintaining alveolar stability.
**Clinical Pearl / High-Yield Fact**
A deficiency in surfactant, such as in respiratory distress syndrome (RDS) in premature infants, can lead to alveolar instability and collapse, resulting in impaired gas exchange and respiratory failure.
**Correct Answer: C. Elastic recoil of lung tissue.**