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Extrapulmonary gas exchange enhances brain oxygen in pigeons
Science (New York, N.Y.)
|November 2, 1984
Summary
Birds use mouth, nose, and eye blood evaporation to cool the brain via a vascular heat exchanger. This system also enhances brain oxygen supply during exercise and high altitude.
Area of Science:
- Physiology
- Comparative Anatomy
- Thermoregulation
Background:
- Birds possess a cephalic vascular heat exchanger, the ophthalmic rete, involved in thermoregulation.
- Evaporative cooling of blood in head tissues is a known mechanism in some birds.
Purpose of the Study:
- To investigate the dual role of the ophthalmic rete in thermoregulation and gas exchange in birds.
- To determine if blood involved in evaporative cooling also facilitates oxygen and carbon dioxide exchange.
Main Methods:
- Studied unanesthetized domestic pigeons (Columba livia).
- Monitored blood flow and temperature in the cephalic vascular system.
- Analyzed gas exchange in blood perfusing evaporative surfaces and the ophthalmic rete.
Main Results:
- Blood cooling via evaporation in head tissues was confirmed.
- Evidence suggests gas exchange occurs between air and blood at evaporative surfaces.
- The ophthalmic rete facilitates counter-current heat exchange and appears to mediate gas exchange, increasing arterial oxygen and decreasing carbon dioxide toward the brain.
Conclusions:
- The ophthalmic rete functions as a heat sink, cooling arterial blood supplying the brain.
- This vascular system enhances brain oxygenation by facilitating gas exchange, crucial for high-demand activities and hypoxic conditions.