Outline the physiological factors that affect the diffusion of oxygen and carbon
dioxide within the lung.
Good answers to this question were those that included a definition of diffusion; an outline of
Fick’s Law of Diffusion and then a further description how each of the variables in the this Law
affect the diffusion of oxygen and carbon dioxide in the lung; and an outline of the other factors
that affect diffusion not covered by the above. Most candidates included Fick's Law in their
answers and at least briefly expanded on the associated variables.
Few candidates defined the process of diffusion. The other common omissions were the
factors that affect diffusion that aren't directly encompassed in Fick's Law, such as cardiac
output, capillary transit time, carbonic anhydrase (conversion of HCO3 to CO2) and
combination of oxygen with haemoglobin
Diffusion of a gas is a process by which a net transfer of molecules takes place from a zone in which the gas exerts a high partial pressure to a zone in which it exerts a lower partial pressure.
Diffusion of respiratory gases through the alveolar membrane is determined by
Factors which influence the diffusion of gases in the lung are:
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