Which biomechanical effect underlies efficient oxygen extraction from air sacs during avian flight?

💡 Explanation

When air flows through avian parabronchi, countercurrent exchange occurs because blood capillaries flow in the opposite direction of airflow, which maintains a high oxygen concentration gradient. Therefore, countercurrent exchange maximizes oxygen extraction, rather than reliance on hemoglobin affinity, diffusion, ventilation, requiring different mechanisms.

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