The respiratory system, which includes the nose, throat, windpipe and lungs, brings air into the body when you breathe. In the lungs, the oxygen from each breath is transferred to the bloodstream and sent to all of the body’s cells in order for them to function (otherwise they would just stop working and die). This is one of the most important systems in the body, not just in a physiological way, but it is also directly connected to the mind and is able to promote relaxation and focus.