The lungs are a vital organ because of their ability to take in oxygen and release other gases, such as carbon dioxide. This function makes the lungs indispensable for survival, as the body requires oxygen for efficient use of energy. By working with the heart, the lungs ensure that a constant supply of oxygen is available for all tissues in the body.
Inhalation and Exhalation
The lungs are able to either inhale or exhale as a result of changing pressures, the Anesthetist explains. When the body inhales, the diaphragm and other muscles move to expand the lungs' volume. This change in volume causes the pressure inside the lungs to be less than the pressure of the atmosphere, which causes air to enter. Similarly, exhalation is achieved by muscles contracting to shrink the lung volume, which increases the lungs' pressure and forces air out through the mouth and nose.
Alveoli
Many small cells called alveoli line the lungs, according to a 2006 article in GI Motility Online ("Anatomy, development and physiology of the lungs"). Alveoli are very thin cells that are responsible for the exchange of gases such as oxygen and carbon dioxide. The approximately 300 million alveoli give the lungs an extensive surface area (roughly 90 square meters), which allows for the rapid intake of oxygen and expelling of carbon dioxide.
Gas Exchange
The alveoli are the cells that allow oxygen from the air to be transferred to the blood. This occurs as the result of a process known as diffusion. Alveoli are connected to very thin blood vessels called capillaries. When the alevoli fill with air, oxygen is able to travel to the blood where it binds to red blood cells via a protein called hemoglobin. Using the same process, carbon dioxide in the blood is then able to travel into the air, where it can be exhaled.
Protection
Because the lungs are exposed to the outside world, they need to have a system that eliminates foreign particles (such as dust) and bacteria. The bronchioles (airway) are lined with small mucous-covered cells called cilia, which, according to the CDC, catch dust, dirt and other foreign particles and propel them upward. Mucous within the lungs can also catch foreign particles, which can then be expelled via coughing. The alveoli are also surrounded by small immune cells called macrophages, which destroy bacteria and other potentially harmful molecules.
Control
Inhalation and and exhalation are under both voluntary and involuntary control, the Anesthetist explains. This means that it is possible for people to consciously control their breathing, which allows them to increase or decrease their rate of respiration. The lungs are also under unconscious control, which means that breathing occurs without a person having to think about it. The brain stem regulates the muscle movements that cause inhalation and exhalation, allowing breathing to continue while a person is asleep or otherwise not thinking about his lungs.
