+An **alveolus** (plural: alveoli) is a microscopic air sac, a delicate bubble nestled deep within the [Lung](/wiki/lung). Here, across its incredibly thin walls, life's essential [Gas Exchange](/wiki/gas_exchange) occurs, allowing oxygen to enter the bloodstream.
+## See also
+- [Respiration](/wiki/respiration)
+- [Capillary](/wiki/capillary)
+- [Bronchiole](/wiki/bronchiole)