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Bird Brains and Bird Breath 

Bird Brains and Bird Breath
Chapter:
Bird Brains and Bird Breath
Author(s):

James R. Munis

DOI:
10.1093/med/9780199797790.003.0016
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date: 09 May 2021

To begin with, the bird lung is invested with a series of hollow air channels, not dead-end alveoli. These air channels are connected to a network of thoracic air sacs. When the air sacs contract and relax in coordination, they force inspired air through the air channels in an almost continuous, unidirectional flow. The air channels contact the pulmonary vessels in an architectural array that looks suspiciously like a countercurrent exchange device. Countercurrent exchange also is engineered into blood infusion devices to rapidly warm intravenous fluid or blood for patients with extensive hemorrhage. Countercurrent exchange takes advantage of the concept that 2 media will exchange properties between themselves more efficiently if they are very close to each other and flowing in opposite directions. There is also crosscurrent exchange. In a crosscurrent arrangement, one material divides into multiple parallel branches, and each of these branches crosses over the other material at multiple points. Although crosscurrent exchange looks similar, it is not quite as efficient as countercurrent exchange. There was controversy about whether the bird lung used crosscurrent or countercurrent gas exchange.

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