Though it might seem easy to understand, that our lungs get rid of waste - the carbon dioxide that our bodies don't need, how this is done is a process that is as amazing as it is intricate. Our autonomic nervous system sends a signal that triggers our diaphragm, a large muscle below our lungs, to contract or relax. The diaphragm along with the rib cage push against our lungs to either release or take in oxygen. The oxygen quickly travels down our trachea through our nose or mouth and enters into both lungs via the bronchi. The bronchi divide into even smaller tree-like branches of air tubes call bronchioles, with a tiny air sac at each end. The air sac, better known as an alveolus, is wrapped in tiny blood vessels (capillaries) that absorb the oxygen into the blood and is then carried throughout the body in the blood stream. When the blood absorbs the oxygen in the air sac, it releases carbon dioxide in a process called diffusion. Diffusion occurs when gas moves from one location to another location of differing pressure. Carbon dioxide is a gas that is naturally produced by our cells as they work. Think of it as cell sweat. That cell sweat is switched out for clean, fresh oxygen in the alveoli (air sac) then release back to nature when we exhale.