When we inhale air, all the other gases present in it also enter our lungs. We have no selective mechanism to inhale only oxygen. In the terminal region of lungs, the alveoli, an exchange of gases takes place. The Haemoglobin in RBCs has an affinity for this oxygen present(Due to the iron contained in the Haemoglobin) in the inhaled air and it is immediately absorbed. The remaining gases are inert (with respect to the blood\’s constituents) which are sent out during exhalation.
There are many gasses in the atmosphere , but the hair in our nose will purify the air and allow only oxygen to enter our respiratory system