Tópico: Crocodilos têm respiração com fluxo de ar unidirecional, como pássaros

[Buckaroo Banzai]

Science 15 January 2010:
Vol. 327. no. 5963, pp. 338 - 340
DOI: 10.1126/science.1180219
   
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Reports
Unidirectional Airflow in the Lungs of Alligators
C. G. Farmer1,* and Kent Sanders2

The lungs of birds move air in only one direction during both inspiration and expiration through most of the tubular gas-exchanging bronchi (parabronchi), whereas in the lungs of mammals and presumably other vertebrates, air moves tidally into and out of terminal gas-exchange structures, which are cul-de-sacs. Unidirectional flow purportedly depends on bellowslike ventilation by air sacs and may have evolved to meet the high aerobic demands of sustained flight. Here, we show that air flows unidirectionally through parabronchi in the lungs of the American alligator, an amphibious ectotherm without air sacs, which suggests that this pattern dates back to the basal archosaurs of the Triassic and may have been present in their nondinosaur descendants (phytosaurs, aetosaurs, rauisuchians, crocodylomorphs, and pterosaurs) as well as in dinosaurs.

1 Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112, USA.
2 Department of Radiology, Musculoskeletal Division, 50 North Medical Drive, Room 1A71, University of Utah Health Sciences Center, Salt Lake City, UT 84132, USA.

http://www.sciencemag.org/cgi/content/short/327/5963/338





http://www.newscientist.com/article/dn18392-alligators-bird-breath-may-explain-dinosaurs-triumph.html

[Buckaroo Banzai]

Computerized tomographic (CT) X-ray images of side and top views of a 24-pound American alligator, with 3-D renderings of the bones and of airways or bronchi within the lungs. The windpipe and first-tier of bronchi are not shown. A University of Utah study found that air flows in one direction through a gator's lungs. It flows from the first-tier bronchi through second-tier bronchi (blue), then through tube-like third-tier parabronchi (not shown) and then back through other second-tier bronchi (forest green). (Credit: C.G. Farmer and Kent Sanders, University of Utah.)

http://www.sciencedaily.com/releases/2010/01/100114143014.htm

[Panthera]

Wow! "Um caráter basal compartilhado entre todos os "não-dinossauros" bem como os dinossauros."

Quanta coisa pra se descobrir sobre esses bichos!

[Zeichner]

Não sou biólogo e não entendi direito.
O jacaré não expira?

Sai peidando o ar que entra, já que vai numa direção só?

[Panthera]

Sim, expira.

É que no caso de mamífero, é um tipo de sistema "vai-e-volta": chega ao pulmão, pelos brônquios e volta pelo mesmo lugar.

Nas aves, o ar faz um ciclo, e é necessário 2 movimentos inspiração/expiração para o ar entrar e sair. Porque?
O ar inspirado vai pra um conjunto de sacos aéreos, para depois passar pelos bronquiolos:

Referir-se a unidirecional ou não, é em relação ao movimento ao ar passando pelos bronquíolos.  

No desenho:

Redondos: sacos aéreos
Linhas retas entre eles: bronquíolos



No crocodilo, o ar segue passando por diferentes brônquios, como mostrado na figura que o Buck postou.  

[Zeichner]

Obrigado.

[Buckaroo Banzai]

Achei uma animação:

During exhalation, air moves out of the posterior air sacs into and through the parabronchi and, simultaneously,  out of the anterior air sacs and out of the body via the trachea.

<a href="http://people.eku.edu/ritchisong/554images/Struthio-Release/angular-airflows.swf" target="_blank" class="new_win">http://people.eku.edu/ritchisong/554images/Struthio-Release/angular-airflows.swf</a>
  During inhalation, all air sacs expand as inhaled air enters the posterior air sacs and lungs and, simultaneously, air moves out of the lungs  and into the anterior air sacs.  During exhalation, the air sacs diminish in
  volume as air moves (1) from the posterior air sacs through the lungs and (2) from the anterior air sacs and out of the body via the trachea.

http://people.eku.edu/ritchisong/birdrespiration.html

[Buckaroo Banzai]

   Ultra-Low Oxygen Could Have Spurred Bird Breathing System -- Recent evidence suggests that oxygen levels were suppressed worldwide 175 - 275 million years ago, low enough to make breathing the air at sea level feel like respiration at high altitude. Peter Ward, a University of Washington paleontologist, theorizes that low oxygen and repeated short but substantial temperature increases because of greenhouse warming sparked two major mass-extinction events. In addition, he believes the conditions spurred the development of an unusual breathing system in Saurischian dinosaurs. Rather than having a diaphragm to force air in and out of lungs, the Saurischians had lungs attached to a series of thin-walled air sacs that appear to have functioned something like bellows to move air through the body. This breathing system, still found in today's birds, made the Saurischian dinosaurs better equipped than mammals to survive the harsh conditions in which oxygen content of air at the Earth's surface was only about half of today's 21%. "The literature always said that the reason birds had sacs was so they could breathe when they fly. But I don't know of any brontosaurus that could fly," Ward said. "However, when we considered that birds fly at altitudes where oxygen is significantly lower, we finally put it all together with the fact that the oxygen level at the surface was only 10 - 11% at the time the dinosaurs evolved. That's the same as trying to breathe at 14,000 feet. If you've ever been at 14,000 feet, you know it's not easy to breathe," he said.

Ward presented his ideas at the 2003 annual meeting of the American Geological Society  in Seattle. See:

http://www.nature.com/nsu/031103/031103-7.html & http://www.washington.edu

Ainda do mesmo site:

http://people.eku.edu/ritchisong/birdrespiration.html