: How is nitrogen not exchanged in respiration? 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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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.

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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.
www.ncbi.nlm.nih.gov/books/NBK493219/ https://www.nature.com/scitable/knowledge/library/the-nitrogen-cycle-processes-players-and-human-15644632/ derangedphysiology.com/main/cicm-primary-exam/required-reading/respiratory-system/Chapter%20002/partial-pressure-and-solubility-gases-biological-systems