Surfactant is made up of which of the following:
**Core Concept**
Surfactant is a complex mixture of phospholipids and proteins that lines the alveoli, reducing surface tension and preventing alveolar collapse during expiration. This property is crucial for maintaining lung volume and facilitating gas exchange.
**Why the Correct Answer is Right**
The correct answer is a combination of phospholipids, specifically dipalmitoylphosphatidylcholine (DPPC), and proteins, such as surfactant protein B (SP-B) and surfactant protein C (SP-C). These components work together to reduce surface tension, allowing for easier lung expansion and preventing alveolar collapse.
*Phospholipids, particularly DPPC, have a hydrophobic tail and a hydrophilic head, which allows them to form a monolayer at the air-liquid interface, reducing surface tension.*
*Surfactant proteins, SP-B and SP-C, play a crucial role in surfactant function by facilitating the formation of a stable, condensed surfactant film and regulating the release of surfactant lipids.*
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately represent the composition of surfactant.
**Option B:** This option is incorrect because it is a component of cell membranes, not surfactant.
**Option C:** This option is incorrect because it is a type of lung cancer, not a component of surfactant.
**Clinical Pearl / High-Yield Fact**
Surfactant deficiency or dysfunction can lead to respiratory distress syndrome (RDS) in premature infants, highlighting the importance of surfactant in maintaining lung function.
**Correct Answer:** D.