Laplace’s Law describes the relationship between pressure, surface tension, and radius in curved surfaces like bubbles, blood vessels, or alveoli in the lungs.
For a spherical structure | For a cylindrical structure |
P = 2T / r P = pressure inside the sphere (alveoli) T = surface tension r = radius of the sphere | P = T / r P = pressure inside the cylinder (blood vessel) T = wall tension r = radius of the cylinder |
Smaller alveoli would collapse because pressure is higher. The body prevents this using surfactant, which reduces surface tension. | If a vessel radius increases (like in aneurysm), wall tension increases, making rupture more likely. |
Simple summary-
• Inspiration:
Alveoli expand, radius (r) increases → pressure decreases. INICET May 2025
• Expiration:
Alveoli shrink, radius (r) decreases → pressure increases.
