Take a deep breath, really. Wonder at the engineering of our respiratory system. From nose hairs filtering large particles, to the mouth and infection-fighting lymph tissue ring at the front of the throat, into the windpipe, and branching out from substantial to smaller branches with cilia to flush out fine particles and viruses. Our pulmonary system is like an upside down tree. At the ends of the branches are the alveoli, the "leaves". There, if all is well, effective delivery of oxygen and removal of carbon dioxide occur at the lung-blood supply filter system. When our breathing system is healthy, we take it for granted; like a good umpire at a baseball game. When the system is damaged, we have trouble catching our breath.