Lungs are organs occupying the chest cavity which are responsible for oxygenating the blood supply.
Anatomy and Medicine
Lungs are made of a stetchy, spongy tissue which can expand and contract, forcing air in and out of the lungs. The air then follows narrower and narrower tubes, called bronchioles, until it reaches small air sacs called alveoli.
Within each air sac, oxygen passes (or diffuses) across the alveolar membrane into the pulmonary capillary. At the beginning of the pulmonary capillary, the hemoglobin in the red blood cells has carbon dioxide bound to it and very little oxygen. The oxygen binds to hemoglobin and the carbon dioxide is released. Carbon dioxide is also released from sodium bicarbonate dissolved in the blood of the pulmonary capillary. The concentration of carbon dioxide is high in the pulmonary capillary, so carbon dioxide leaves the blood and passes across the alveolar membrane into the air sac. This exchange of gases occurs rapidly (fractions of a second). The carbon dioxide then leaves the alveolus during exhalation and the oxygen-enriched blood returns to the heart for circulation around the body.