Gas Exchange in the Lungs
The lungs contain about 3 x 108 alveoli (little sacs) in which air and blood are brought close together so that gas exchange can occur. The principal gases exchanged are O 2, which is picked up by the blood and CO 2, which leaves the blood stream and enters the air spaces of the lung. These gases need to cross the thin alveolar—capillary membrane; this occurs by diffusion. In normal circumstances, the alveolar—capillary membrane presents so slight a barrier to diffusion that the blood in the alveolar capillaries achieves equilibrium with the alveolar air before leaving the capillaries.
KeywordsPartial Pressure Alveolar Ventilation Arterial Partial Pressure Perfusion Ratio Alveolar Capillary
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This Chapter is strongly influenced by the following book, which emphasizes the importance of the ratio of ventilation to perfusion
- West, J.B.: Ventilation/Blood Flow and Gas Exchange, Blackwell, Oxford, UK, 1965.Google Scholar
The following paper also addresses the specific issue of optimal gas transport, which is the dominant theme of this Chapter
- Evans, J.W., Wagner, and West, J.B.: Conditions for reduction of pulmonary gas transfer by ventilation—perfusion inequality. Journal of Applied Physiology, 36, 535–567, 1974.Google Scholar