Concept
Version 8
Created by Boundless
Mammalian Systems and Protective Mechanisms
Alveolar structure
Terminal bronchioles are connected by respiratory bronchioles to alveolar ducts and alveolar sacs. Each alveolar sac contains 20 to 30 spherical alveoli and has the appearance of a bunch of grapes. Air flows into the atrium of the alveolar sac, then circulates into alveoli where gas exchange occurs with the capillaries. Mucus glands secrete mucus into the airways, keeping them moist and flexible.
Source
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:
"OpenStax College, Systems of Gas Exchange. October 17, 2013."
http://cnx.org/content/m44792/latest/Figure_39_01_09.jpg
OpenStax CNX
CC BY 3.0.