Since the question of cilia and coughing and lung damage comes up often I figured I would try to show some illustrations as to what happens in the lungs from smoking. In this string I am going to concentrate at the microscopic level, in the lining tissue of the bronchus.
On the top we see the cilia, labeled (H). They are attached to columnar cells, labeled (I). The cilia sweep the mucous produced in the goblet cells, labeled (J) as well as mucous coming from deeper glands within the lungs and the particulate matter trapped in the mucous. The bottom layer of cells, labeled (L) are the basal cells.
The above picture is representative of a healthy non-smokers lung. Below we start to see the changes that occur as people begin to smoke. You will see that the columnar cells are starting to be crowded out and displaced by additional layers of basal cells. Not only are fewer cilia present but the ones that are still functioning are doing so at a much lower level of efficiency. Many chemicals in tobacco smoke are toxic to cilia, first slowing them down, soon paralyzing them all together and then destroying them.
As you see with the cilia actions being diminished, mucous starts to build up in the small airways making it harder for the smoker to breath and causing the characteristic smokers cough in order to clear out the airways.
Eventually though, the ciliated columnar cells are totally displaced. As can be seen below ominous changes have taken place. Not only is the smoker more prone to infection from the loss of the cleansing mechanism of the cilia, but these abnormal cells (O) are cancerous squamous cells. These cells will eventually break through the basement membrane wall and invade into underlying lung tissue and often spread throughout the body long before the person even knows they have the disease.
If a smoker quits before cancer actually starts, even if the cells are in a precancerous state, the process is highly reversible. Cilia regeneration starts in about 3 days once smoking stops. Even if cilia has been destroyed and not present for years, the lining tissue of the windpipe will start to repair. Even the precancerous cells will be sloughed off over time, reversing the cellular process to the point where the lining tissue goes back to normal. But if a smoker waits too long and cancer starts, it may be too late to save his or her life.
You just don't know which cigarette was going to be the one to start an irreversible process. To reduce your risk you must stop the deposit of the thousands of chemicals, especially the 43 known carcinogens that come in with every puff of a cigarette you take. To stop this process thus reducing your risk cancer, as well as helping to keep your lungs clean of other irritants by allowing the healing of the cilia, you must always remember and practice the simple treatment of knowing to never take another puff!
Commentary added 2-2-09
We now have the ability to edit our old posts. Since I am going to refer to this post often when questions of cilia are raised, I am going to enhance the first post in this string by combining some of the latter posts to this first post in the string. This is a commentary added in the eighth response to this string:
The above string explains how the healing process can cause cold like symptoms. As the cilia starts to break up and sweep out mucous, coughing and congestion can follow. On top of this there is regeneration of nerve cells that were also destroyed from the chronic abuse of smoking on the lungs and trachea. But life goes on without smoking, and people still can get infections after cessation. So while cold and flu like symptoms can often be attributed to initial cessation, there is also always the possibility that a cold or flu is also responsible. Symptoms should be treated with the same caution as you would normally exercise when you were a smoker. If long enough or severe enough, getting checked out is a prudent course to follow.
Always know the best way to help prevent such problems in the future, and even more serious lung diseases that don't just have a short course of a week or two with a return to normal, is to keep your lung from ever being assaulted again from the thousands of chemicals, hundreds of poisons and 43 known carcinogens in tobacco smoke. The only way to stop this assault is to never take another puff!
The following video discusses the nerve regeneration issue: