Some science behind the scenes
Breathing is an automatic function of the body regulated by our need for energy. As we become active – and this can be both physical activity or mental activity - the need for energy increases and our lungs take in more air. If the air is ‘thin’ or mixed with gases we cannot use [smoke, pollution, car fumes] , they work harder to take in yet more air so that oxygen can be extracted. If we are at sea level or the air is more ‘pure’ , there is less to do because the air is not as ‘thin’ and we can more easily extract the oxygen we need.
Dry air contains roughly (by volume) 80% nitrogen, 20% oxygen, 1% argon, 0.04% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%.
The air enters our lungs and oxygen is extracted by the alveoli and enters the blood stream. There is actually an exchange here as oxygen is taken up by the haemoglobin in the blood and the carbon dioxide is expelled and we breathe out carbon dioxide and water.
The oxygen in our blood stream is then pumped round by our heart and taken to our cells where it is used to produce ‘usable energy’ that powers our cells.
The trachea, bronchi and their branches are, surprisingly, not well adapted for gaseous exchange. At the end of exhalation these tubes contain ‘used’ air and when a person inhales, this used air is drawn back into the lungs. Therefore out of 0.5 dm3 of air inhaled only about 0.35 dm3 of fresh air enters the lungs. The dead space makes up about one third of ‘tidal volume’ at rest [tidal volume is the volume of air breathed into or out of the lungs per breath]. But if we exercise lightly or breathe more deeply, more oxygen or ‘fresh air’ enters the body.
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