How do our lungs know which gas to inhale or exhale from a number of gases present in the atmosphere ?

How do our lungs know which gas to inhale or exhale from a number of g

1.	How do our lungs know which gas to inhale or exhale from a number of gases present in the atmosphere ?
Answer» How do our lungs know which gas to inhale or exhale from a number of gases present in the atmosphere ?