Here is a neat video that I watched at the David Bruce Undergraduate Poster session at the Experimental Biology conference last week. It describes the amazing physiology of the avian lung and was created by an undergraduate student researcher, Peter Luu for the Physiology Video Contest sponsored by the American Physiological Society. This video won the Viewer's Choice Award:
To see more of the submitted videos, visit the American Physiological Society website.
The other half of the story is that birds have a countercurrent gas exchange mechanism in their lungs. At the tail end of the lung, the air moving forward is rich in oxygen and poor in CO2. The blood in capillaries is moving in the other direction (head to tail) coming in rich in CO2 and poor in oxygen. At each point along the flows (air and blood in opposite directions) there is a concentration gradient which drives oxygen into the blood and CO2 into the breathed air. At the tail end of the lung, the blood leaving, like the air entering is rich in oxygen and poor in CO2. At the head end, the air leaving, like the blood entering is relatively poor in oxygen and rich in CO2.
Birds just breathe better than mammals.
And we think of birds as modern-day dinosaurs! I wonder if their reptilian ancestors had the same lung design.