The act of breathing brings fresh air into your body and eliminates the waste carbon dioxide gas produced by your metabolism. Ventilation, the flow of air into and out of your lungs, involves not only the lungs, but your respiratory passageways, respiratory muscles, ribcage and parts of your nervous system all working in concert.
Airflow During Lung Ventilation
The process of breathing involves the inhalation of air into your lungs, the exchange of oxygen and carbon dioxide gasses between your lungs and blood and the exhalation of air out of your lungs. As air moves into your lungs, it passes through your nasal or oral cavity, then through your pharynx and larynx into your trachea. It goes from the trachea into your lungs via the bronchi and bronchioles. This pathway is reversed as air flows back out during exhalation. This process occurs at the rate of about 18 cycles per minute.
The Physics of Airflow During Lung Ventilation
The driving force that pushes air into and out of your lungs with each respiratory cycle is pressure. Air will flow into your lungs if the air pressure within your lungs is lower than the air pressure in the atmosphere. As the volume of your chest and lungs increase, the air pressure within your lungs will decrease. This decreased pressure will then pull air into your lungs, causing you to breathe in. Interestingly, your chest doesn't expand because your lungs have filled with air; rather, your lungs fill with air because your chest first expands. As your chest compresses during exhalation, the internal air pressure rises and air is forced out.
Mechanics of Breathing
The changes in air pressure that force airflow into and out of your lungs are created by the expansion and contraction of your chest. These movements are brought about by contraction of the muscles of respiration, which include the intercostal muscles and the diaphragm. The intercostal muscles alternatively raise and lower your ribs, increasing and then decreasing your chest volume. The diaphragm, a muscle separating your chest and abdominal cavities, changes your chest volume as it moves up or down.
Control of Breathing
The muscle contractions that change the volume of your chest when driving airflow in and out during a respiratory cycle are controlled by nerves. These nerves are influenced by the amount of carbon dioxide and oxygen in your blood, which is measured by sensory receptors in your carotid and aortic arteries and in the medulla of your brain. When oxygen levels fall and carbon dioxide levels rise, your respiratory muscles will initiate a respiratory cycle.
References
- "Exercise Science"; Warren Rosenberg, Ph.D., and Ciaran Cullen, D.C.; 2009
