The principle component of surfactant that reduces surface tension in the alveoli and keeps them inflated and non-collapsed?
**Core Concept**
The reduction of surface tension in the alveoli is crucial for maintaining lung volume and preventing atelectasis. This is achieved through the action of surfactant, a complex mixture of phospholipids and proteins produced by type II pneumocytes.
**Why the Correct Answer is Right**
The primary component of surfactant responsible for reducing surface tension is dipalmitoylphosphatidylcholine (DPPC). DPPC molecules are amphipathic, meaning they have both hydrophobic and hydrophilic regions. When DPPC molecules are present at the air-liquid interface of the alveoli, their hydrophobic tails interact with the air, reducing the surface tension and making it easier for the alveoli to remain inflated. This is known as the "film pressure" effect.
**Why Each Wrong Option is Incorrect**
* **Option A:** Pulmonary surfactant is composed of several components, but DPPC is the primary phospholipid responsible for reducing surface tension.
* **Option B:** Surfactant protein B (SP-B) is a crucial component of surfactant, but it is not the primary phospholipid that reduces surface tension.
* **Option D:** Surfactant protein A (SP-A) plays a role in surfactant function, but it is not directly responsible for reducing surface tension.
**Clinical Pearl / High-Yield Fact**
Respiratory distress syndrome (RDS) can occur in premature infants due to a lack of surfactant production, leading to high surface tension and alveolar collapse. Treatment with surfactant replacement therapy can significantly improve lung function in these patients.
**Correct Answer: C. Dipalmitoylphosphatidylcholine (DPPC)**