Major surfactant is ?
**Core Concept**
Surfactants play a crucial role in reducing surface tension in the lungs, thereby facilitating easier expansion and contraction of alveoli. They are essential for maintaining lung compliance and preventing atelectasis.
**Why the Correct Answer is Right**
The major surfactant in the lungs is produced by type II pneumocytes and is composed of phospholipids, primarily dipalmitoylphosphatidylcholine (DPPC). This surfactant reduces the surface tension at the air-liquid interface, allowing for easier lung expansion during inspiration. The surfactant film is also stabilized by surfactant-associated proteins (SP-A, SP-B, SP-C, and SP-D).
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify a surfactant protein or a phospholipid. While surfactant proteins are essential for surfactant function, they are not the major surfactant component.
* **Option B:** This option is incorrect because it is not a known surfactant. The correct answer is a specific phospholipid, while this option is a distractor.
* **Option C:** This option is incorrect because it is a surfactant protein, not the major surfactant component. While surfactant proteins are essential for surfactant function, they are not the primary surfactant component.
**Clinical Pearl / High-Yield Fact**
Respiratory distress syndrome (RDS) in preterm infants is often caused by a deficiency of surfactant, leading to increased surface tension and difficulty in lung expansion.
**Correct Answer: D. Dipalmitoylphosphatidylcholine (DPPC)**