We breathe in about 35 pounds of air through 20,000 breaths each day [source: Spokane Regional Clean Air Agency]. The blood carries oxygen directly to the heart, and the heart sends that oxygen-rich blood throughout the body. Every cell in our body needs oxygen to function, so you can see why proper lung function is so important. It delivers oxygen in its trucks, or red blood cells. Inside the pulmonary capillaries, the hemoglobin has carbon dioxide bound to it and very little oxygen at first. The carbon dioxide then leaves the alveolus when you exhale, and the oxygen-rich blood returns to the heart.
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http://health.howstuffworks.com/wellness/drugs-alcohol/smoking-starve-the-heart-of-oxygen.htm#mkcpgn=kaw1
