Breath Reflexes

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(Tagged October 2005)

Breathing transports oxygeninto the body and carbon dioxideout of the body. Aerobicorganismsrequire oxygen to create energy via respiration, in the form of energy-rich moleculessuch as glucose.

Humans typically breathe between 12 and 20 times per minute, with children breathing faster than adults. Babies may breathe as much as 40 times per minute. Adults normally breathe about 500-700ml of air at a time. An average 14 year old takes around 30,000 breaths per day.

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 CPR, breathing can be restarted if it stops. Because of this, in modern times death is now better defined in terms of brain function.

Breathing is only part of the process of delivering oxygen to where it is needed in the body. Breathing in, or inhaling, is usually an active movement, with the contraction of chestand diaphragmmuscles 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. 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 waterfrom 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 consciouslyand unconsciously. Conscious attention to breathing is common in many forms of meditation, specifically anapana. In music, breath is used to play windand brassmusical instrumentsand many aerophones. Laughter, physically, is simply repeated sharp breaths. Hiccupsare another still-mysterious breath-related phenomenon.

Specialized centers in the brainstemautomatically 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 (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, some drugs and other disease processes.

It is not possible for a healthy person to voluntarily stop breathing. If we do not inhale, and the level of carbon dioxide builds up in our blood, the urge to breathe generally becomes overwhelming. This irrepressible reflex is not surprising given that without breathing the bodies internal oxygen levels drop dangerously low within minutes leading to permanent brain damage and then death.

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Breath

Control of Breathing

See also