Breathing is a mechanical process that humans perform automatically, meaning the muscles involved perform the action without conscious effort. Breathing is performed by the respiratory system, which consists of the lungs, trachea, bronchi and diaphragm. The University of Virginia Health System reports that human take approximately 15 to 20 breaths per minute which is more than 21,600 breaths in a day. There are three main steps to breathing which are all equally important for sustaining life.
Inhalation
The first step to breathing is inhalation. Inhalation occurs when oxygen-rich air is sucked into the body. The diaphragm, a sheet of muscles that separates the chest cavity from the abdomen, initiates inhalation by contracting the muscles. As the muscles contract, the chest cavity becomes larger. With the larger cavity the lungs do not feel pressure from the outside. As the air is pulled into the body, the pressure is again equalized.
The air enters the mouth and nose and travels through the trachea, the tube that enters the chest cavity. The trachea branches off into two smaller tubes known as the bronchi. The left bronchial leads to the left lung while the right bronchial leads to the right lung. The bronchi branch into thousands of smaller tubes called the bronchioles. At the end of each bronchiole are alveoli, tiny balloon-like sacs that are able to expand with air.
Gas Exchange
Each lung contains approximately 300 million alveoli, according to information provided by Cedars-Sinai. As the air enters the body through the bronchioles, the alveoli expand. The alveoli are surrounded by capillaries that are filled with blood. Because the air-blood barrier is very thin as described by the Merck Manual, the oxygen is able to pass easily into the blood. At the same time, the carbon dioxide, a waste product produced by the body, flows from the blood into the air in the alveoli. This type of gas exchange is known as diffusion because it requires no energy or effort from the body.
Exhalation
Once the oxygen is in the blood and ready to be pumped throughout the body, the final step of exhalation must be completed. To exhale, the muscles of the diaphragm relax which adds pressure to the chest cavity and forces air from the alveoli into the bronchioles. The air continues to move through the tubes reaching the bronchi. The air containing the carbon dioxide then travels through the trachea and back out the mouth or nose.
