Pulmonary alveolus

A pulmonary alveolus (plural: alveoli, from Latin alveolus, "little cavity") is a hollow cup-shaped cavity found in the lung parenchyma where gas exchange takes place. Lung alveoli are found in the acini at the beginning of the respiratory zone. They are located sparsely in the respiratory bronchioles, line the walls of the alveolar ducts, and are more numerous in the blind-ended alveolar sacs. Alveoli are an important part of the respiratory system whose function it is to exchange oxygen and carbon dioxide molecules to and from the bloodstream.