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When we breathe in (inhale), air passes through the airways of our lungs and ends up in small lung compartments called alveoli. From here gases freely diffuse both into and out of our blood through the thin walls of the alveolar compartments. With each breath in, these compartments stretch open like tiny air balloons. As we relax the breathing muscles, the alveolar compartments deflate and help force air out of the lungs.
In less than eight seconds after taking a drag on a cigarette, nicotine has passed into the blood system through the alveoli, and is working in the brain. The smoke, tar, and nicotine destroy the alveolar air sacs and decrease the amount of blood flowing to the lungs.
The result is that, over time, the lung surface area available to exchange gases between the air and blood decreases. The blood supply also has less oxygen in it. Oxygen is required for all of the body's cells, especially cells that are working hard, such as muscle cells during exercise. With less oxygen, smokers are more easily winded and perform more poorly in physically demanding sports and other activities.
In addition, when the walls of the air sacs in the lungs break down, the air compartments become abnormally enlarged and lose their elasticity, hampering the ability to breathe out and causing labored breathing. This severe and irreversible damage is known as emphysema.
Napier, K. (1996). Cigarettes: What the warning label doesn't tell you. New York: American Council on Science and Health