4. We need to breathe.

5. Organs of the respiratory system.

6. Breathing air.

7. Motion of breathing.

11. Trachea

12. Bronchi

13. Bronchioles

14. Lungs

15. Alveoli

17. Travels down through the trachea ( windpipe ).

18. Goes into the lungs through two tubes called bronchi .

19. They divide into smaller tubes called bronchioles .

20. These ones end in tiny air sacs called alveoli .

22. When we breathe out, the air goes out and the lungs empty.