Air is 78% of nitrogen. When we inhale air, we inhale large amounts of nitrogen when compared to oxygen. How is nitrogen not exchanged? How is it exhaled?

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    – Carey Gregory
    Apr 2, 2020 at 14:06
  • 1
    Why do you even think that it isn't exchanged? Apr 2, 2020 at 14:13
  • Yes It should not be exchanged but there is some underlying thing which prevents this exchange.
    – RaMathuzen
    Apr 2, 2020 at 14:42
  • Have you heard of "the bends" or en.wikipedia.org/wiki/Decompression_sickness in the context of diving? Nothing prevents nitrogen exchange.
    – Bryan Krause
    Apr 2, 2020 at 15:55
  • Yes But it Happens at such a High pressure. But how nitrogen is prevented in normal conditions
    – RaMathuzen
    Apr 2, 2020 at 16:28

1 Answer 1


There is no specific mechanism to carry nitrogen in blood, it is carried in a dissolved form unlike oxygen which uses the protein haemoglobin which is contained in red cells.

Animals can not utilize atmospheric nitrogen so there is very little exchange between inhaled nitrogen and dissolved nitrogen. Any nitrogen inhaled is exhaled again as it can not be dissolved further in blood to be removed from the inhaled air.

The composition of environmental air is approximately 78% nitrogen, 21% oxygen, 1% argon, and trace percentages of carbon dioxide, neon, methane, helium, krypton, hydrogen, xenon, ozone, nitrogen dioxide, iodine, carbon monoxide, and ammonia. Therefore, at sea level where atmospheric pressure is known to be 760 mm Hg, the partial pressures of the various gases can be estimated to have partial pressures of approximately 593 mm Hg for nitrogen, 160 mm Hg for oxygen, and 7.6 mm Hg for argon.


At 0.78 atmospheres of pressure, at sea level, the nitrogen content of blood is therefore 0.488 mmol/L. At standard conditions, that nitrogen would occupy a volume of 15ml.

That is 15ml of nitrogen for every litre of blood. There would obviously be more if the gas mixture were under pressure, eg. where the diver was in the depths of the sea, breathing a highly pressurised mixture of oxygen and nitrogen. One can imagine a 70kg gentleman with 5 litres of blood becoming extremely uncomfortable as several hundred millilitres of nitrogen suddenly fizz up out of their bloodstream like a shaken-up coke bottle.




  • This means some nitrogen is carried ?
    – RaMathuzen
    Apr 3, 2020 at 1:54
  • there is nitrogen in the blood but it's not actively exchanged with atmospheric nitrogen. Apr 3, 2020 at 1:57
  • I know that our source of nitrogen is from food not through respiration ,so which means atmospheric nitrogen is not used and because of that when we inhale , the oxygen &Co2 is exchanged due to partial pressure solubility etc and like this there should be a thing or factor that prevents the exchange of Nitrogen and so it mayn't be used that is what I asked
    – RaMathuzen
    Apr 3, 2020 at 2:37
  • It's already in equilibrium so doesn't need to be exchanged Apr 3, 2020 at 2:50
  • Yes Therefore it should be the reason and this implies the blood has dissolved nitrogen equivalent to as present in lungs
    – RaMathuzen
    Apr 3, 2020 at 3:01

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