Alveoli are tiny air sacs in your lungs that take up the oxygen you breathe in and keep your body going. Although they’re microscopic, alveoli are the workhorses of your respiratory system ...

Figure 3 - Schematic diagram of lung anatomy with cross-sections of bronchi, bronchioles alveolar ducts, and alveoli. From the following article. Anatomy, development, and physiology of the lungs.