Pathway of air in inhalation 1) nose 2) __ 3) __ 4) __ 5) __ 6) Alveoli

When a mammal breathes in air, the pathway it takes is

1. Nose


2. Nasopharynx/oral pharynx


3. Trachea (the "windpipe")


4. Bronchi


5. Bronchioles


6. Alveoli

After air enters the nose (or mouth) it passes into the pharynx, which is a passage for both breathing and eating. The epiglottis, a flap of tissue, keeps food from entering the trachea. Air travels easily through the trachea due to cartilage rings that keep it open. The trachea divides into smaller airways called bronchi, which enter the lungs. These further divide into smaller and smaller bronchioles. They eventually become extremely small alveoli, which is where gas exchange takes place between the alveoli and the capillaries of the circulatory system. Oxygen and carbon dioxide diffuse through the membranes of the capillaries and alveoli from their areas of relatively higher concentration to the relatively lower concentration. Oxygen from the air breathed in diffuses into the capillaries, and carbon dioxide moves from the capillaries to the alveoli.