We take in oxygen and not other gases because oxygen is what is needed to maintain bodily functions. When we inhale, a mix of gases enters the lungs, containing oxygen, nitrogen, carbon(IV)oxide, water vapour and a little noble gases. The air then goes to the lungs together but only the oxygen is diffused into the blood stream. The rest of it is sent back out along with some carbon(IV)oxide that diffuses out. This oxygen is then transported around the body to
1) aid in the break down of food to release energy
2)keep the body oxidized.
These are things that can only be achieved with oxygen and as such, the body takes it in and not the other gases