1. Mouth & Nose The nose is the main external opening for the respiratory system.   Air (oxygen) enters and exits the body.  The mouth is also used for taking in and expelling air.

2. Trachea
The trachea is also known as the windpipe.  It connects the larynx (voice box) to the lungs.  It is made of rings of cartilage.

3. Bronchus Bronchi are the main passageway into the lungs
Bronchus Bronchi are the main passageway into the lungs.  They become smaller and are called bronchioles inside the lungs.  They then evolve into air sacs called alveoli.

4. Lungs
The primary organ of the respiratory system.  They take in oxygen and expels carbon dioxide.  They are inflated and deflated by the action of the diaphragm.

5. Diaphragm
The most important muscle in the respiratory system.  It expands and contracts forcing air in and out of the lungs.  Spasms of the muscle cause hiccups.

6. Alveoli Tiny sacs in the lungs that allow oxygen and carbon dioxide to move between the lungs and the bloodstream.