Ingenious solutions employed by free-diving penguins
Posted By Erik Seedhouse on 16 June 2003
When the penguin inhales again the sequence of events described above begins again but this is still not the end of the story since air still in the lungs travels further along the system to the anterior air sacs. On reaching this stage the muscles of the abdomen contract, the penguin exhales again and air is forced through the system. Air that remains in the anterior air sacs is funneled into the interclavicular air sacs - essentially a part of the trachea -- and air is expelled via the trachea. This final stage represents the final part of the respiration 'loop'.
Diagram 3. Penguin respiratory system
Diagrammatically it is possible to see the structures that facilitate the circular respiration pattern. This design essentially ensures a continuous flow of air is passed through the lungs, allowing a constant supply of fresh oxygen. The reason the oxygen is fresh is because the oxygen-blood exchange membrane always has oxygen flowing over it, unlike the human situation that is reliant upon an in-out movement.
The structure of the penguins respiratory system also explains why this species do not suffer nitrogen narcosis. While descending the air sacs do not resist pressure but become compressed. The air is in these sacs and NOT in the lungs so there is not too much air in the lungs and no bubbles (the ones that lead to the 'bends') can be formed under increasing water pressure. Just to be on the safe side however, penguins do not employ vertical free ascents when free-diving, choosing instead to veer at an oblique angle, thus significantly slowing their ascent. This allows time for any nitrogen that might be under lower pressure to return to the air inside their body cavities.
One more surprise design feature of this avian free-diving species is the interclavicular sac, an air pocket that is continuous with bone, allowing penguins to fill bone cavities thereby creating an extra air reservoir -- a possible challenge for genetic engineers seeking to design a human free-diving hybrid maybe?
The complete physiology of penguins is still unknown. For example, researchers do not know whether penguins are able to consciously control or limit blood flow or if this occurs automatically. Whatever the science, these birds have evolved some impressive solutions since abandoning the skies over 50 million years ago.
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