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Science 2 November 1984:
Vol. 226. no. 4674, pp. 564 - 566
DOI: 10.1126/science.6436975
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Articles

Science, Vol 226, Issue 4674, 564-566
Copyright © 1984 by American Association for the Advancement of Science

articles

Extrapulmonary gas exchange enhances brain oxygen in pigeons

MH Bernstein, HL Duran, and B Pinshow

Blood in mouth, nose, and eye tissues of birds cools by evaporation, then flows to a cephalic vascular heat exchanger, the ophthalmic rete. There, acting as a heat sink, blood from the evaporative surfaces cools arterial blood flowing counter-current to it toward the brain. The brain thus remains cooler than the body core. Data for unanesthetized domestic pigeons (Columba livia) suggest that in addition to losing heat, blood perfusing the evaporative surfaces also exchanges oxygen and carbon dioxide with air. In the heat exchanger, this blood apparently gives up oxygen to, and gains carbon dioxide from, arterial blood. The consequent increase in oxygen and decrease in carbon dioxide in the brain's arterial blood enhance diffusion of these gases in, and oxygen supply to, the brain. Such events may help birds maintain the brain's oxygen supply during the high systemic demand of exercise and at the reduced oxygen availability of high altitude.


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Science. ISSN 0036-8075 (print), 1095-9203 (online)