air sac

air sac

noun
1.
a sac containing air.
2.
alveolus ( def 2 ).
3.
any of certain cavities in a bird's body connected with the lungs.
4.
a saclike dilation of the wall of a trachea in many insects.

Origin:
1820–30

Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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Collins
World English Dictionary
air sac
 
n
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

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Medical Dictionary

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.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
air sac  
  1. An air-filled space in the body of a bird that forms a connection between the lungs and bone cavities and aids in breathing and temperature regulation.

  2. See alveolus.

  3. A saclike enlargement in the trachea of an insect.

  4. A baglike piece of skin or tissue below the jaw of certain animals, such as the bullfrog and orangutan, that can be inflated to increase sound production.


The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica
Encyclopedia

air 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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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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