An Alveolus
The alveoli are the site of oxygen and carbon dioxide exchange in the lungs.
This diagram of an alveolus indicates the capillary beds, connective tissue, alveolar sacs, alveolar duct, mucous gland, mucosal lining, pulmonary vein, pulmonary artery, and atrium.
Source
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:
"File:Alveolus diagram.svg - Wikimedia Commons."
http://commons.wikimedia.org/w/index.php?title=File:Alveolus_diagram.svg&page=1
Wikimedia
CC BY-SA.
