In the meantime your air tubes have also been getting smaller and smaller until they reach the end of the road where tiny bunches of air sacs (the alveoli) hang together like clusters of microscopic grapes.
In the very deepest part of the lungs, the tiny air sacs and the narrow blood vessels are so tightly woven together that they more or less share common walls. A blood molecule has only a fraction of a second to offload its oxygen, pick up its spent load of carbon dioxide and continue along its way. This exchange through the walls of the alveoli is what keeps you alive and kicking.
The gas exchange at this exact point in your chest is incredibly delicate and complicated. This is not an area that was designed to defend itself well. That would be like expecting a brilliant brain surgeon to do security duty at the front desk at the same time he is operating on a patient.
Remember that you have wonderful defense systems further “upstream.” Do your best to keep the bad stuff from getting past the defenses of your nose, throat and upper chest into your sanctum sanctorum.
Be well. Breathe beautifully.
