The exchange surface
The respiratory membrane.
A thin, extensive interface designed to move gas rapidly between alveolar air and pulmonary capillary blood.
I
Alveolar airGas reaches the exchange surface.
II
Thin barrierDistance is kept to a minimum.
III
Capillary bloodFlow preserves the pressure gradient.
Area ↑More exchange surface increases diffusion.
Thickness ↓A shorter path accelerates gas movement.
Gradient ↑A larger pressure difference increases flow.
Diffusion ↑The membrane performs when all three align.
Fick's law
V̇gas ∝ (A / T) × D × ΔP
FibrosisThickness rises, so diffusion falls.
EmphysemaSurface area falls, so reserve is lost.
ExerciseShorter transit time can expose limitation.