Thursday, March 11, 2010

American Alligator


American Alligator, originally uploaded by dpfunsun.
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Alligators have one-waybreathing similar to that in birds, new research shows. The finding, reported in the Jan. 15 Science, could explain how ancestors of birds, reptiles and dinosaurs rose to prominence.

"It's absolutely transformational," comments Adam Summers of the University of Washington's Friday Harbor Laboratories on San Juan Island. "It really makes us think hard about our interpretations of anatomy."

In mammals, air flows through branching tubes called bronchi, which culminate in small cul-de-sac chambers where blood vessels exchange oxygen. Air then exits the lungs via the same path.

But in birds' lungs, air makes a single circuit before being exhaled. This unidirectional flow is much more efficient - air can zip right past the blood vessels that need oxygen and then be on its way.

Conventional wisdom has held that only birds can do this because they have air sacs thought to steer air in one direction. "Alligators don't have air sacs, so no one ever looked," says C.G. Farmer of the University of Utah in Salt Lake City, a coauthor of the new study. But Farmer noticed a similarity in the way bird and alligator bronchi branch.


"If you look at the alligator lung, it's not hard to see how small modifications in this design could potentially lead to an avian lung," she says.

Farmer and coauthor Kent Sanders, "also of the University of Utah, measured the speed and direction air moved in lungs of six living gators and, using pumps, five dead ones. The primary-bronchi each split into an inner, first branch and an outer, second branch shortly after the point where air enters the lung. Surprisingly, air moved through the inner branch in each lung in the same direction whether the gator was inhaling or exhaling

Farmer thinks that air skips past the inner bronchial branch, which forms a hairpin turn, and enters the outer branch instead. Air then passes through small tubes called parabronchi, where oxygen is traded for carbon dioxide. Finally, air flows from the parabronchi into the inner branch and out through the trachea.

The finding may mean one-way breathing is far older than suspected and could have helped archosaurs, forebearers of birds, reptiles and dinosaurs, dominate millions of years ago. Efficient one-way breathing may have given archosaurs a boost: Work shows oxygen levels in their time were about half of today's, lower than available at the top of Mount Everest.

Source Citation
Grossman, Lisa. "Gator breath is a one-way street: looping airflow may be older than reptiles and dinosaurs." Science News 13 Feb. 2010: 11. Academic OneFile. Web. 11 Mar. 2010.
Document URL

Gale Document Number:A219581278

Disclaimer:This information is not a tool for self-diagnosis or a substitute for professional care.

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