Respiratory system of Birds. “Double breath”

Respiratory system

The respiratory system is formed by the airways and lungs with air sacs. Air passes through the nostrils into the respiratory tract: the nasal cavity, larynx, trachea, bronchi – and further into the lungs and air sacs.


  • nasal cavity;
  • larynx (upper and lower (singing), performing the function of the vocal apparatus);
  • trachea;
  • bronchi.


Gas exchange occurs in the branching bronchioles of the lungs.
The lungs of birds are distinguished by a complex spongy structure.
The bronchi, entering the lungs, repeatedly branch and end in cavities, and some, leaving the lungs, expand, forming air sacs.

Air bags

Some bronchi end with air sacs that go into the cavities between the internal organs, in the cavity of the bones, between the muscles.

Air bag functions:

  • participate in breathing during flight (double breathing);
  • provide cooling of the body in flight;
  • reduce body density (and weight).

Double breathing

When the bird is at rest (not in flight), breathing occurs without the participation of air sacs.
In flight, air saturated with oxygen passes through the lungs of birds 2 times – during inhalation and during exhalation (during exhalation, it moves into the lungs from the air sacs). This breathing mechanism in birds is called double breathing.

Air movement pattern during double breathing of birds: trachea – bronchi – posterior air sacs – lungs (gas exchange!) – anterior air sacs – trachea – air outlet.

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