The surface tension exerted by alveolar fluid is decreased by the presence of what?
a) Air
b) O2
c) CO2
d) Surfactant
The correct answer and explanation is:
The correct answer is d) Surfactant.
Surfactant is a substance produced by the cells in the alveoli of the lungs, primarily by type II alveolar cells. It is composed of lipids and proteins, with dipalmitoylphosphatidylcholine being the most important lipid component. Surfactant plays a crucial role in reducing surface tension within the alveoli.
Surface tension is a force that pulls the molecules of a liquid at the surface toward the liquid, and in the case of alveolar fluid, this force makes the lungs less compliant and more difficult to inflate. In the absence of surfactant, the surface tension of the alveolar fluid would be high, and the lungs would collapse more easily due to the difficulty in overcoming this tension during inhalation.
Surfactant decreases the surface tension by disrupting the intermolecular forces between water molecules. This allows the alveoli to expand more easily during inhalation, and prevents them from collapsing during exhalation. This function is vital for maintaining efficient gas exchange in the lungs, as the alveoli must remain open to allow oxygen to diffuse into the blood and carbon dioxide to diffuse out.
In premature infants, surfactant production is often insufficient, leading to respiratory distress syndrome (RDS), a condition where the alveoli collapse due to inadequate surfactant, making it difficult for the infant to breathe. In these cases, surfactant replacement therapy is sometimes used to help reduce surface tension and improve lung function.
In summary, surfactant is critical for reducing the surface tension in the lungs, improving lung compliance, and ensuring effective respiration.