Breathing transports oxygen into the body and carbon dioxide out of the body. Aerobic organisms require oxygen to create energy via respiration, in the form of energy-rich molecules such as glucose. The medical term for normal relaxed breathing is eupnoea.
Mechanics
Breathing in, or inhaling, is usually an active movement, with the contraction of the diaphragm muscles needed. At rest, breathing out, or exhaling, is normally a passive process powered by the elastic recoil of the chest, similar to a deflating balloon.
Gas exchange
Breathing is only part of the process of delivering oxygen to where it is needed in the body. The process of gas exchange occurs in the alveoli by passive diffusion of gasses between the alveolar gas and the blood passing by in the lung capillaries. Once in the blood, the heart powers the flow dissolved gasses around the body in the circulation.
As well as carbon dioxide, breathing also results in loss of water from the body. Exhaled air has a relative humidity of 100% because of water diffusing across the moist surface of breathing passages and alveoli.
Control of breathing
Breathing is one of the few bodily functions which, within limits, can be controlled both consciously and unconsciously. Conscious attention to breathing is common in many forms of meditation, specifically anapana and other forms of yoga.
Relationship to death
Breath is sometimes used as a metaphor for life itself, and often "last breath" is the most obvious sign that death has occurred. The association between the end of life and breathing is not absolute, however. As modern treatment can now take over the process of breathing by mechanical ventilation, or cardiopulmonary resuscitation (CPR), breathing can be restarted if it stops. Because of this, modern deaths are now better defined in terms of brain dysfunction.
Respiratory rate
Humans typically breathe between 12 and 20 times per minute, with a cell.
Composition of air
The air we inhale is roughly 78% nitrogen, 21% oxygen and 1% argon, helium, carbon dioxide, and other gases. (% by volume)
Not all of the oxygen breathed in is converted into carbon dioxide, around 13% of what we breathe out is still oxygen, this is what makes resuscitation possible. Also our reliance on this relatively small amount of oxygen can cause overactivity or euphoria in pure or oxygen rich environments.
Gas exchange
The process of gas exchange occurs in the alveoli by passive diffusion of gasses between the alveolar gas and the blood passing by in the lung capillaries. Once in the blood, the heart powers the flow dissolved gasses around the body in the circulation.
Cultural significance
In Tai Chi Chuan aerobic training is combined with breathing to exercise the diaphram muscles, and to train effective posture, which both make better use of the bodies energy. In music, breath is used to play wind instrument wind instruments and many aerophones. Laughter, physically, is simply repeated sharp breaths. Hiccups and yawns are other breath-related phenomena.
Control of breathing
Specialized centers in the brainstem automatically regulate the rate and depth of breathing depending on the body’s needs at any time. When carbon dioxide levels increase in the blood, it reacts with the water in blood, producing carbonic acid. The drop in the blood's pH will then cause the medulla oblongata signalling centre in brain to send nerve impulses to the diaphragm and the intercostal muscles, increasing the rate of breathing. While exercising, the level of carbon dioxide in the blood increases due to increased cellular respiration by the muscles, and so breathing rate increases. During rest, the level of carbon dioxide is lower, so breathing rate is lower. This ensures an appropriate amount of oxygen is delivered to the muscles and other organs. This automatic control of respiration can be impaired in premature babies, or by drugs or disease.
It is not possible for a healthy person to voluntarily stop breathing. If we do not inhale, the level of carbon dioxide builds up in our blood, and we experience overwhelming air hunger. This irrepressible reflex is not surprising given that without breathing, the body's internal oxygen levels drop dangerously low within minutes, leading to permanent brain damage followed eventually by death.
If a healthy person were to voluntarily stop breathing (ie. hold his or her breath) for a certain amount of time, he or she would lose consciousness, but the body will resume breathing on its own.
The buildup of carbon dioxide making the blood acidic is what makes one desperate for a breath rather than lack of oxygen. Hyperventilating causes an influx of oxygen that lowers blood acidity to trick the brain into thinking it has more oxygen.
References
- Parkes M (2006). "Breath-holding and its breakpoint". Exp Physiol. 91 (1): 1–15. PMID 16272264. Full text
Yellowcard Breathing, a song from the Yellowcard album "Ocean Avenue"
See also
- Agonal breathing
- Cheyne-Stokes respiration
- Biot's respiration
- Mouth breathing
- Pneuma
- Prana
- Qi
- Respiratory rate
- Spirit
- Halitosis
Yellowcard Breathing, a song from the Yellowcard album "Ocean Avenue"