Question

II The small capillaries in the lungs are in close contact with the alveoli. A red blood cell takes up oxygen during the 0.5s that it squeezes through a capillary at the surface of an alveolus. What is the diffusion time for oxygen across the 1-um thick membrane separating air from blood? Assume that the diffusion coefficient for oxygen in tissue is .2x10^-11m^2/s Give your answer to 1 significant figure.

Answer 1

The diffusion time of the red blood cell to take oxygen through the membrane is 25uS.

The small capillaries in the lungs are in close contact and it takes a red blood cell 0.5 seconds to squeeze through the capillary.

The diffusion time for the oxygen across the 1 um thick membrane separating the air is given by,

t = x²/2D

Where,

t is the diffusion time,

x is the thickness of the membrane,

D is the diffusion coefficient.

Putting values,

t = (1 x 10⁻⁹)²/2 x 2 x 10⁻¹¹

t = 10⁻⁷/4

t = 25 x 10⁻⁹ seconds.

t = 25 uS.

so, the diffusion time is 25uS.

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