1. The process of taking air into the lungs is called inspiration or inhalation.
2. During inspiration, the sternum is pushed up and outward and the diaphragm is pulled down.
3. This increases the volume of the thoracic cavity and the pressure decreases.
4. The air outside the body flows into the lungs. Here exchange of gases takes place between the air and the blood.
5. The process of expelling air from the lungs is called expiration or exhalation. Upon exhalation, the lungs recoil to force the air out of the lungs.
6. The intercostal muscles relax, returning the chest wall to its original position. During exhalation, the diaphragm also relaxes, moving higher into the thoracic cavity.
7. This increases the pressure within the thoracic cavity relative to the environment.
8. Air rushes out of the lungs due to the pressure gradient. This movement of air out of the lungs is a passive event.
