Study guide
Study guide

Fick's Laws of Diffusion

Clinical relevance

The components of this equation are fundamental to understanding how gases, ions, and drugs move throughout the body.

Passive diffusion of a substance across a semipermeable membrane (e.g. a cell membrane) obeys Fick's Laws of Diffusion.

The rate of diffusion can be expressed as an equation.

J=A/T×sol/MW×(P1−P2)J = A/T \times \text{sol}/\sqrt{MW} \times (P_1-P_2)
  • JJ is the diffusive flux, a measure of the quantity diffused per unit of time
  • membrane characteristics
    • AA is the surface are of the membrane. More surface area → more diffusion.
    • TT is the thickness of the membrane. Thicker membrane → less diffusion.
  • solute characteristics
    • sol\text{sol} refers to the solubility of the substance diffusing across the membrane.
    • MWMW is the molecular weight of the substance. Bigger → less diffusion.
  • gradient
    • P1−P2P_1-P_2 refers to the partial pressure (of a gas) or concentration gradient (of a solute) across the membrane.
    • Bigger gradient → more diffusion.