In a preterm baby with respiratory distress syndrome, which type of cell is deficient?
**Core Concept**
Respiratory distress syndrome (RDS) in preterm babies is primarily caused by a deficiency of surfactant, a substance that reduces the surface tension of the air-liquid interface in the lungs. This deficiency leads to alveolar collapse and impaired gas exchange, resulting in respiratory distress. Surfactant is produced by type II pneumocytes in the alveoli.
**Why the Correct Answer is Right**
Type II pneumocytes are responsible for producing and secreting surfactant, a complex mixture of phospholipids and proteins. The main component of surfactant is dipalmitoylphosphatidylcholine (DPPC), which reduces surface tension in the alveoli. In preterm babies, the surfactant production is immature, leading to a deficiency. This deficiency causes the alveoli to collapse, making it difficult for the baby to breathe.
**Why Each Wrong Option is Incorrect**
* **Option A:** Macrophages are involved in the clearance of surfactant from the alveoli, but they are not responsible for producing surfactant.
* **Option B:** Alveolar type I pneumocytes are involved in gas exchange, but they do not produce surfactant.
* **Option D:** None of the other options are correct.
**Clinical Pearl / High-Yield Fact**
Preterm babies with respiratory distress syndrome often require surfactant replacement therapy, which can significantly improve their outcome. This therapy involves administering synthetic surfactant directly into the lungs.
**Correct Answer:** C. Type II pneumocytes.