Biology / Unit 13 Bio 3153 short lesson, about 20 seconds
Avian Flow-Through Lungs and Air Sacs
Captions available
The idea
Bird lungs connect to air sacs that keep air flowing through in one direction on both inhalation and exhalation, unlike a mammal's in-and-out flow.
In practice
One-directional airflow lets a bird's lung contact fresh air continuously, supporting flight at low-oxygen altitude.
Where people slip
One-directional flow needs two full breathing cycles to move one volume of air completely through.
Your place on the trail
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