<Li> segmental bronchus (diameter 4.5 to 13 mm) <Ul> <Li> subsegmental bronchus (diameter 1 to 6 mm) <Ul> <Li> conducting bronchiole <Ul> <Li> terminal bronchiole <Ul> <Li> respiratory bronchiole <Ul> <Li> alveolar duct <Ul> <Li> alveolar sac <Ul> <Li> alveolus </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> <Ul> <Li> subsegmental bronchus (diameter 1 to 6 mm) <Ul> <Li> conducting bronchiole <Ul> <Li> terminal bronchiole <Ul> <Li> respiratory bronchiole <Ul> <Li> alveolar duct <Ul> <Li> alveolar sac <Ul> <Li> alveolus </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> <Li> subsegmental bronchus (diameter 1 to 6 mm) <Ul> <Li> conducting bronchiole <Ul> <Li> terminal bronchiole <Ul> <Li> respiratory bronchiole <Ul> <Li> alveolar duct <Ul> <Li> alveolar sac <Ul> <Li> alveolus </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> <Ul> <Li> conducting bronchiole <Ul> <Li> terminal bronchiole <Ul> <Li> respiratory bronchiole <Ul> <Li> alveolar duct <Ul> <Li> alveolar sac <Ul> <Li> alveolus </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul> </Li> </Ul>

Where does the respiratory system begin and end