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Overview of the Respiratory System

Author(s): Nancy Moreno, PhD, Barbara Tharp, MS, and Judith Dresden, MS.
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The Science of Breathing

Breathing is the drawing in and expelling of air. Students observed the following properties of air during this activity. 

Volume changes in the chest cavity cause air to move in and out of the lungs. Breathing is partially a passive process controlled (by the brain) and involves changing the volume of the chest cavity. 

The work of breathing is accomplished by the diaphragm (a thin layer of muscle at the base of the chest cavity) and muscles in the walls of the chest. The diaphragm is responsible for about 75% of the air flow in breathing. At rest, it is relaxed and bulges upward. 

When we are about to take a breath, the diaphragm muscles tighten, move downward, and increase the space available (and decrease total pressure) within the chest. Outside air rushes in to fill this space. As we exhale, the muscles of the chest and diaphragm relax, the space in the chest cavity contracts, and air is forced out of the lungs.