acinus

https://doi.org/10.1351/goldbook.10328
  1. Small sac-like cavity in a gland, surrounded by secretory cells.
  2. Terminal region of the airways of the lung where gas exchange occurs.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 716 (https://doi.org/10.1515/pac-2015-1202)