If you are familiar with the human lungs, you know there is a trachea, two mainstem bronchi and two lungs.That's basically it. Right away you can see that there are several other components to the penguin pulmonary system.  With the expansion of the abdomen, air is drawn into the trachea, which is continuous with the oral cavity via the oropharynx and the larynx. Air travels through the cartilaginous trachea. As it passes through the trachea, it runs through a distended portion known as the syrinx. The syrinx is the elaboration of the trachea that enables a penguin to make the numerous vocalizations that you hear like the ecstatic display or the trumpeting you might here when mates greet each other. The syrinx is also the site of the tracheal bifurcation, or site where the trachea splits into two channels. Each of these channels connects the syrinx to each lung. However, air first entering the respiratory system immediately flows into the posterior air sacs. All this occurs during the first inhalation. 

    When the penguin exhales, air situated in the posterior air sacs flows into the lungs via the ventrobronchi and dorsobronchi. As air flows through these two bronchi, they travel out into smaller bronchi called parabronchi. You've read about this in the histology section, so you know this is where oxygen exchanges with the air and the blood. Unlike human lungs, the air doesn't stop here; it keeps flowing onward.

    When the penguin inhales for the second time, all the above starts over again. However, the air still in the lungs is pushed further along the respiratory system. Air in the lungs, parabronchi, ventrobronchi, and dorsobronchi is delivered to the anterior air sacs. At this point the penguin exhales one more time. The muscles of the abdomen contract and air is pushed throughout the system once more. Air sitting in the anterior air sacs is throttled into the interclavicular air sac, which is continuous with the trachea. Air flows out the trachea. The cycle of respiration is complete and it begins again.

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