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Biological Diffusion Processes, Allen R. Killpatrick, Norman J. Chonacky

Physical Science Modules for Bioscience Students

What happens in the lung is that air meets blood. Figure 1 shows the lung's architecture. Focus your attention upon the smallest scale structures which are the termini of the air passages. These are the alveolar air sacs or, simply, alveoli. The inhalation/exhalation actions of the lung, alternately, flood these alveoli with atmospheric air and expel its oxygen-poor/carbon dioxide-rich replacement. Figure (2a) depicts, in a somewhat simplified manner, these alveoli with their appended venous blood suppliers, the pulmonary arteries. Figure {2b} shows the structure of the blood distribution system over a small, typical portion of the alveolar surface in much …