|1.||any of the membranous air-filled extensions of the lungs of birds, which increase the efficiency of gaseous exchange in the lungs|
|2.||any of the thin-walled extensions of the tracheae of insects having a similar function|
air sac n.
A tiny, thin-walled, capillary-rich sac in the lungs where the exchange of oxygen and carbon dioxide takes place. Also called alveolar sac.
any of the air-filled extensions of the breathing apparatus of many animals. Air sacs are found as tiny sacs off the larger breathing tubes (tracheae) of insects, as extensions of the lungs in birds, and as end organs in the lungs of certain other vertebrates. They serve to increase respiratory efficiency by providing a large surface area for gas exchange. See also pulmonary alveolus.
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