How Your Respiratory System Works
To understand how smoking damages your respiratory system, you must understand how the system works. When you breathe in through the nose or mouth, you are taking in oxygen-rich air, which will eventually supply your body with the oxygen it needs to function.
Before the oxygen gets to your heart to be pumped throughout your body, it has to pass through your airways. It passes down your throat, through your larynx and trachea. The trachea divides into two smaller tubes, called the bronchi, which then divide into even smaller bronchial tubes. Your bronchial tubes lead directly into your lungs, where they divide into thousands of smaller-yet-again bronchioles.
At the end of each bronchiole is a delicate air sac called an alveolus, which is covered in capillaries--tiny blood vessels connected to arteries and veins. Capillaries on the alveoli allow the transfer of oxygen into the bloodstream and the waste product, carbon dioxide, out of the bloodstream and into the lungs. The same airways that brought in the oxygen carry out the carbon dioxide.
Tiny mucus-coated hairs called cilia line all your airways, except in parts of your nose and your mouth. The cilia trap particles and germs that may come into your body in the air you breathe. The cilia sweep the particles back up into your nose or mouth to be swallowed, coughed or sneezed from your body, according to the National Heart, Lung and Blood Institute.