Breathing takes oxygen in and carbon dioxide out of the body. Aerobic organisms require oxygen to create energy via respiration, in the form of the metabolism of energy-rich molecules such as glucose. The medical term for normal relaxed breathing is eupnea.
Breathing is only part of the processes of delivering oxygen to where it is needed in the body and removing carbon dioxide waste. The process of gas exchange occurs in the alveoli by passive diffusion of gases between the alveolar gas and the blood passing by in the lung capillaries. Once in the blood the heart powers the flow of dissolved gases 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.
Breathing is one of the few bodily functions which, within limits, can be controlled both consciously and unconsciously.
Conscious control
Conscious control of breathing is common in many forms of meditation, specifically forms of yoga for example pranayama unlike anapana which is only awareness of breath. In swimming, cardio fitness , speech or vocal training, one learns to discipline one's breathing, initially consciously but later sub-consciously, for purposes other than life support. Human speech is also dependent on conscious breath control.
Unconscious control
Unconsciously, breathing is controlled by specialized centers in the brainstem, which 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. Lactic acid produced by anaerobic exercise also lowers pH. The drop in the blood's pH stimulates chemoreceptors in the carotid and aortic bodies in the blood system to send nerve impulses to the respiration centre in the medulla oblongata and pons in the brain. These, in turn send nerve impulses through the phrenic and thoracic nerves to the diaphragm and the intercostal muscles, increasing the rate of breathing. Even a slight difference in the bloods normal pH, 7.4, could cause death , so this is an important process.
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This definition is part of a series that covers the topic of Breathing . The Official Guide to Breathing is Nancy Zi . Nancy Zi is the author of The Art of Breathing. She is an internationally known classical singer and voice teacher. American born, raised in China, and with a bi-cultural education, Zi weaves together the best of ancient Eastern disciplines with modern Western techniques.
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