Much of the respiratory system is just for moving air in and out of the lungs. This is called the conducting zone. Here are some the organs involved the conduction zone.
1) The nose is the only part of the respiratory system that you can see. Air enters the nostrils into the nasal cavity where it is warmed, made moist, filtered, cleaned, and scents are detected.
2) Next it passes through the pharynx, which is just a passageway, but it is ringed by tonsils that trap and kill bacteria that enter with the air.
3) The larynx is a doorway. When food is passing through the pharynx, the larynx closes. When we inhale air, it is open and passes through toward the lungs. The larynx also has the vocal cords that make sound for speech.
4) After air passes through the larynx, they enter the trachea. The trachea or windpipe is about 4 inches long (12cm) and is kept open by tiny rings of stiff cartilage. The last ring of cartilage is called the carina and is covered by sensitive tissue. If you inhale anything but air, when it touches the carina, you cough violently until it is gone. This protects the lower airways from being blocked.
5) The trachea splits at the bottom to become the two bronchi, one for each lung. The right and left bronchi enter the lungs and branch many times into smaller and smaller airways: secondary bronchi, tertiary bronchi and finally, tiny bronchioles. Until now the air has just passed through the conducting zone. No gas exchange has occurred. Now it enters the respiratory zone from the bronchioles down to the tiny alveoli, where oxygen exchange occurs.
6) True respiration begins in the smallest bronchioles – the respiratory bronchioles. They branch into alveolar ducts and finally into alveoli. Alveoli look like clusters of tiny grapes. This is where gas exchange occurs. The capillaries that carry oxygen lie right up against the alveoli and form the respiratory membrane. Across this membrane, respiration occurs, when oxygen is traded for carbon dioxide.
