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When smelling, your nose detects the smells by absorbing them.

Does this mean that, if you were in an enclosed space, you could smell so much all the smell goes, and there is none of that molecule left to smell?

Would it take so long it would never happen in reality, or does it happen?

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  • $\begingroup$ It seems unlikely purely in terms of the amount of air which comes into contact with the nasal epithelium - the tissue which contains olfactory receptors. $\endgroup$ – Watercleave Feb 16 '15 at 17:51
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    $\begingroup$ Nose doesn't really absorb it. THe odorant molecules bind to olfactory recpetors that transduce that signal as action potentials. Even if some amount of odorant actually is irreversibly absorbed that would hardly affect its concentration in the air. $\endgroup$ – WYSIWYG Feb 16 '15 at 18:06
  • $\begingroup$ Besides, the odor rapidly diffuses across the entire available space - in your case this would be the room - so it is not possible to get rid of the odor until the source is removed and all the air recycled $\endgroup$ – One Face Feb 17 '15 at 8:27
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On the contrary, your olfactory epithelium - the bit that does the smelling up at the top of your nasal cavity - doesn't absorb smells. The olfactory receptors bind small molecules reversibly.

However, the olfactory epithelium has a coating of mucus, and so small molecules dissolve in the mucus in order to meet the receptors. Molecules will also evaporate off this mucus, but some vanishingly small fraction of the odorant in a room may stay in the mucus of the nose and the upper respiratory tract long enough to be moved by cilia to the stomach.

I think that for water-soluble molecules, the surface area of mucus lining the airways that odorant can reach is a more relevant factor than the number of a particular receptor (which is very low); but depleting a room of an odorant (which is concentrated enough for you to sense in the first place) by breathing would surely take an extremely long time; as the concentration dropped the remaining molecules would become 'harder to catch', and you'd suffocate first in this enclosed space.

Interestingly, hydrophobic molecules that do not readily dissolve in mucus may be bound by soluble 'shuttle'-like proteins which bridge the gap to the receptors: http://www.ncbi.nlm.nih.gov/pubmed/12044155 These odorant-binding-proteins probably contribute to the diversity of molecules we can smell, and presumably also bind odorants reversibly and may release them back in to the nasal cavity.

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