Which law relates intra-alveolar pressure to surface tension and radius of an alveolus?

Which law relates intra-alveolar pressure to surface tension and radius of an alveolus?

• A. Graham's law
• B. Beer’s law
• C. Newton's law
• D. Laplace's law

Answer: (D)

Relating pressure to surface tension and radius is described by Laplace's law. For a spherical surface like an alveolus, the pressure difference across the surface equals 2 times the surface tension divided by the radius (ΔP = 2γ/R). This means smaller alveoli would need a higher internal pressure to remain open, which would tend to collapse them into larger ones if not for surfactant. Surfactant lowers the surface tension more effectively when the radius is small, stabilizing very small alveoli and preventing collapse. Because this specific relationship between intrapulmonary pressure, surface tension, and radius is Laplace's law, that is the correct association. Other options describe diffusion rates, light absorption, or general motion, none of which govern the pressure–surface tension–radius relationship in alveoli.

Relating pressure to surface tension and radius is described by Laplace's law. For a spherical surface like an alveolus, the pressure difference across the surface equals 2 times the surface tension divided by the radius (ΔP = 2γ/R). This means smaller alveoli would need a higher internal pressure to remain open, which would tend to collapse them into larger ones if not for surfactant. Surfactant lowers the surface tension more effectively when the radius is small, stabilizing very small alveoli and preventing collapse. Because this specific relationship between intrapulmonary pressure, surface tension, and radius is Laplace's law, that is the correct association. Other options describe diffusion rates, light absorption, or general motion, none of which govern the pressure–surface tension–radius relationship in alveoli.