Which one of the following acts as lung surfactant:
**Core Concept**
Lung surfactant is a complex mixture of phospholipids and proteins that reduces the surface tension within the alveoli, facilitating easier lung expansion during inspiration.
**Why the Correct Answer is Right**
Pulmonary surfactant is primarily composed of dipalmitoylphosphatidylcholine (DPPC), a type of phospholipid, along with other surfactant-associated proteins (SP-A, SP-B, SP-C, and SP-D). These molecules are produced by type II pneumocytes in the alveolar lining and play a crucial role in maintaining lung compliance and preventing alveolar collapse.
**Why Each Wrong Option is Incorrect**
**Option A:** This choice is not provided.
**Option B:** Although surfactant proteins are crucial for surfactant function, they do not directly act as lung surfactant.
**Option C:** This option is not provided.
**Clinical Pearl / High-Yield Fact**
Lung surfactant deficiency or dysfunction can lead to conditions such as respiratory distress syndrome (RDS) in preterm infants and acute respiratory distress syndrome (ARDS) in adults.
**Correct Answer: C. Dipalmitoylphosphatidylcholine (DPPC)**