Assume the alveolar radii are 0.05 and 0.07 mm towards the end of exhalation. Knowing that air flows from high to low pressures, calculate the pressure difference between the alveoli and justify why the smaller alveolus does not collapse. (Assume surface tension of alveolar wall due to surfactant is 25 mN/m)

Explanation:

Using Laplace's law of surface tension:

where:

P = pressure

T = surface tension

r = radius

In the longer alveoli with radius of  0.07 mm = ; we have:

P =  

P =

In the smaller alveoli with radius 0.05 mm = ; we have:

P =

P =

The pressure difference can now be calculate as follows:

Pressure difference =

Pressure difference =

a 20-cm-long, cylindrical graphite (pure carbon) rod is inserted into an oxidizing atmosphere at 1145 k and 1.013 x 105 pa pressure. the oxidizing process is limited by the diffu- sion of oxygen counterflow to the carbon monoxide that is formed on the cylindrical surface.