The diaphragm contracts and air moves through the windpipes to the lungs during inspiration. This initiates the process of enriching the body's blood supply with the oxygen that keeps the entire organism alive. Excessive and deficient inflation of the lungs are both problematic.
When a person inhales, the diaphragm tightens and moves down. This increases the space in the chest cavity into which the lungs expand. The intercostal muscles between the ribs contract to move the rib cage up and down during inspiration.
Air then enters the mouth or nose and travels through the windpipe into the lungs. From there, the air goes to the bronchial tubes and reaches its final destination at the alveoli, or air sacs. From here, oxygen travels to nearby capillaries, aided in its motion by the red blood cell protein hemoglobin.
While this happens, carbon dioxide from the capillaries goes into the alveoli, traveling from the right side of the heart to the pulmonary artery.
A network of capillaries carries oxygen-enriched blood to the pulmonary vein, which in turn sends this blood to the left side of the heart. The left side of the heart pumps blood into the surrounding tissue and subsequently to the rest of the body.
Mucus, inflammation and swelling block the body's airways and inhibit inspiration. A condition known as hyperinflation has the opposite effect by abnormally filling the alveoli.