Birds are way cool. In this podcast from The American Physiological Society, Dr. John West at the University of California in San Diego discusses the unique adaptations of the avian respiratory system. In mammals, the movement of air in and out of the lungs in a bidirectional fashion is called ventilation. This air fills the small air sacs (alveoli) which are surrounded by capillaries to aid in gas exchange between the blood and air. In birds, ventilation (controlled by air sacs) is unidirectional and occurs separately from gas exchange, which takes place in the air capillaries of the parabronchi. The pulmonary blood capillaries are quite rigid because they are surrounded by air capillaries. Dr. West is currently examining whether this capillary morphology has an impact on the pressure of the pulmonary arteries during flight. Click here to to listen to the interview.