Pulmonary alveolus
hollow cavity found in the lungs
A pulmonary alveolus (pl. alveoli; from Latin alveolus 'little cavity'), also called an air sac or air space, is one of millions of hollow, distensible cup-shaped cavities in the lungs where pulmonary gas exchange takes place. Oxygen is exchanged for carbon dioxide at the blood–air barrier between the alveolar air and the pulmonary capillary. Alveoli make up the functional tissue of the mammalian lungs known as the lung parenchyma, which takes up 90 percent of the total lung volume.
Alveoli are first located in the respiratory bronchioles that mark the beginning of the respiratory zone. They are located sparsely in these bronchioles, line the walls of the alveolar ducts, and are more numerous in the blind-ended alveolar sacs. The acini are the basic units of respiration, with gas exchange taking place in all the alveoli present. The alveolar membrane is the gas exchange surface, surrounded by a network of capillaries. Oxygen is diffused across the membrane into the capillaries and carbon dioxide is released from the capillaries into the alveoli to be breathed out.
Alveoli are particular to mammalian lungs. Different structures are involved in gas exchange in other vertebrates.
The public source identifies “Pulmonary alveolus” as hollow cavity found in the lungs. This brief keeps that definition visible, then builds a research path around Pulmonary, alveolus and hollow.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Jul 21, 2026. The linked authority identifier is Q191341. The Library of Congress control number is sh85108995. 1 of 1 selected statements include explicit references; 1 carry qualifiers and 0 use preferred rank.
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This entry incorporates text from “Pulmonary alveolus” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.