Nose is the outermost opening of this system. There are 2 nostrils through which air is inhaled and exhaled.
The air passing through the nose is filtered by the hair inside and it is warmed and moisturized by contact with the inner curved surfaces. Through the throat, the air enters the trachea or vent pipe, which is further divided into two main branches called Bronchus. The Bronchus is further divided in to sub branches in the Thoracic Cavity. This cavity is extended to the Diaphragm at the bottom and is covered by the ribs from the side. The inhaled air passing through Bronchus reaches at terminal bronchiole and finally in the alveoli where the exchange of oxygen and Carbon dioxide takes place and air is exhaled out of the body through the same passage.