The respiratory system, sometimes called the respiratory tract, works with the circulatory system to provide oxygen to the body's cells and to remove carbon dioxide, the waste product of cellular metabolism. All of the body's cells need oxygen to function and maintain life.
The exchange of oxygen and carbon dioxide between the atmosphere and the body's cells is the process known as respiration. In a healthy body at rest, nerve impulses stimulate the breathing process, or ventilation, every three to five seconds. Ventilation moves air through a series of passages into and out of the lungs.
Ventilation is followed by external respiration, which is the exchange of gases between the lungs and the blood. The blood then transports the gases to and from the tissue cells throughout the body. The exchange of oxygen and carbon dioxide between the blood and tissue cells is called internal respiration.
Finally, each cell uses the oxygen for its own specific activity, a process known as cellular metabolism or cellular respiration.
The respiratory system is divided into the upper respiratory tract and the lower respiratory tract. The upper respiratory tract includes:
- The nose and mouth
- Nasal cavities
- Paranasal sinuses
- The pharynx, or throat, and
- The larynx, or voice box
The lower respiratory tract includes:
- The trachea, or windpipe
- The bronchi and bronchial tree, and
- The lungs
Several muscles, including the diaphragm, intercostal muscles, and abdominal muscles, also play a role in the process of respiration.