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Breathing is the process that moves air in and out of the lungs, or oxygen through other respiratory organs such as gills. For organisms with lungs, breathing is also called ventilation, which includes both inhalation and exhalation. Breathing is one part of physiological respiration required to sustain life. Aerobic organisms of birds, mammals, and reptiles—require oxygen to release energy via cellular respiration, in the form of the metabolism of energy-rich molecules such as glucose. Breathing is only one of the processes that deliver oxygen to where it is needed in the body and remove carbon dioxide. Another important process involves the movement of blood by the circulatory system. Gas exchange occurs in the pulmonary alveoli by passive diffusion of gases between the alveolar gas and the blood in lung capillaries. Once these dissolved gases are in the blood, the heart powers their flow around the body (via the circulatory system). The medical term for normal relaxed breathing is eupnea. In addition to removing carbon dioxide, breathing 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. When a person exhales into very cold outdoor air, the moisture-laden atmosphere from the lungs becomes chilled to the point where the water condenses into a fog, making the exhale visible by anyone. ==Mechanics== In mammals, breathing in, or inhaling, is due to the contraction and flattening of the diaphragm, a domed muscle that separates thorax and abdomen. If the abdomen is relaxed, this contraction causes the abdomen to bulge outwards, expanding the volume of the body. This increased volume causes a fall in pressure in the thorax, which causes the expansion of the lungs. When the diaphragm relaxes, air leaves largely by elasticity of the lung. This is quiet, relaxed breathing needing little energy. When need increases, the abdominal muscles resist expansion. The increased abdominal pressure then tilts the diaphragm and ribcage upwards with an increase in volume and the entry of air. Expiration follows relaxation of diaphragm and abdominal muscles, but can be increased by downward action of abdominal muscles on the rib cage. This forced expiration increases pressure across the airway's walls and may lead to narrowing and perhaps to wheezing. Speech depends on the balance between the two forms of breathing, and in humans conscious change often modifies autonomous reaction to need. The pattern can vary with fear in anticipation of need, and so with anxiety, and may be conditioned to experience such as the loss of an inhaler. It is also affected by loss of lung elasticity in age or pulmonary disease, of abdominal expansion from obesity, or of muscle power to resist expansion or to pull the ribcage down. Ten muscles are used for inspiration:〔(All You Need to Know About Inspiratory Muscles Part I | Swimming Science )〕 Diaphragm, Intercostal Muscles, Scalenes, Pectoralis Minor, Serratus Anterior, Sternocleidomastoid, Levator Costarum, Upper / Superior Trapezius, Latissimus Dorsi, and Subclavius. Eight are used for forced expiration:〔(All You Need to Know About Inspiratory Muscles Part II ) 〕 Internal intercostal, Obliquus Internus, Obliquus Externus, Levator Ani, Triangularis Sterni, Transversalis, Pyramidalis, and Rectus Abdominus. In amphibians, the process used is positive pressure breathing. Muscles lower the floor of the oral cavity, enlarging it and drawing in air through the nostrils (which uses the same mechanics - pressure, volume, and diffusion - as a mammalian lung). With the nostrils and mouth closed, the floor of the oral cavity is forced up, which forces air down the trachea into the lungs. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Breathing」の詳細全文を読む スポンサード リンク
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