http://www.ck12.org Chapter 1. Human Biology
1.31 Respiration
- Describe how breathing works.
Why do you breathe?
We breathe because we need oxygen. Breathing also releases carbon dioxide from our bodies into the air. The
respiratory system is the body system that brings air containing oxygen into the body and releases carbon dioxide
into the atmosphere.
How We Breathe
Most of the time, you breathe without thinking about it. Breathing is mostly an involuntary action that is controlled
by a part of your brain that also controls your heart beat. If you swim, do yoga, or sing, you know you can control
your breathing, however. Taking air into the body through the nose and mouth is calledinhalation. Pushing air
out of the body through the nose or mouth is calledexhalation. The woman pictured below is exhaling before she
surfaces from the pool water (Figure1.55).
How do lungs allow air in? As mentioned above, air moves into and out of the lungs by the movement of muscles.
The most important muscle in the process of breathing is thediaphragm, a sheet of muscle that spreads across the