Matching Flows Across Exchange Surfaces

Examples occur in any organ, but the human lung is a "best" example, as air flowing to and from alveoli must match blood flowing through the capillaries around the alveoli. At large and smaller resolutions we can visualize the patterns of these distributions graphically, and using our graphs we can create our models. But first what constitutes flow matching in the lung?

In a closed circulation supplying an organ such as a liver or lung from a blood supply entering and leaving the organ through a single portal, one problem of distribution is how to divide up the flows internally so that all regions of the organ receive adequate blood. Liver or heart muscles seen at one resolution contain cells that occupy the volume inside the organ almost homogeneously. Blood flow backs up rarely. The alveolar surface of the lung shows a similar match-up, but because we can easily visualize our lung as a two-dimensional surface, we shall use the lung as our example of a flow matched to need situation.

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