A drug molecule with diffusion coefficient is carried by blood along a capillary long at

PHYSICS · Multi-part · Fermi University Physics · Biophysics & Medical Physics · Physical foundations of the living cell · Physical foundations of the living cell

Life at Thermal Energy, Ch Random walks, diffusion and the crowded cell

Problem

A drug molecule with diffusion coefficient D=5.0×10−10 m2 s−1D = 5.0\times10^{-10}\,\mathrm{m^2\,s^{-1}} is carried by blood along a capillary 1.0 mm1.0\,\mathrm{mm} long at 0.50 mm s−10.50\,\mathrm{mm\,s^{-1}}. After leaving the capillary it must cross a 10 μm10\,\mathrm{\mu m} gap of tissue, through which fluid seeps at about 1.0 μm s−11.0\,\mathrm{\mu m\,s^{-1}}. ((a)) Calculate the Peclet number along the capillary, and say whether flow or diffusion carries the drug there. ((b)) Calculate the Peclet number across the tissue gap, and say which process carries it there. ((c)) At the seepage speed, over what distance would flow and diffusion be equally effective?

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