How Does Copd Develop: Smoking Cessation
Content provided by the Faculty of the Harvard Medical School
How does COPD develop?
Chronic obstructive pulmonary disease (COPD) develops gradually over many years, as the airways become narrowed and the lungs lose their ability to expand and contract effectively when you breathe. In most people with the disease, these problems stem from inflammation that occurs when something — most often cigarette smoke — irritates the respiratory tract intermittently over many years. The irritant can damage the cells that line the airways and can cause changes in the glands and cells that normally produce small amounts of mucus to lubricate the airway walls. In response, the body unleashes a flood of inflammatory cells, which start a chemical cascade that further damages the airways and degrades lung tissue.
Inflammatory cells, such as macrophages, neutrophils, and lymphocytes, are the soldiers of your body's defense system; they carry out your body's attack against the irritants. In the course of their search and destroy mission, these cells infiltrate the walls of the airways and trigger the production of mucus inside the airways, leaving less room for air to pass.
As they try to defend the airways and the lung tissue against inhaled toxins such as cigarette smoke, these inflammatory cells release a variety of chemicals and enzymes called proteases, which aid in the fight against infection and injury. An overabundance of these chemicals and enzymes, however, is harmful and can contribute to emphysema and possibly to chronic bronchitis (see "The biology of chronic bronchitis," below, and "The biology of emphysema"). In some people, a genetic defect is to blame for the particularly harmful effects of one type of destructive protease (see "Genetic factors").
Chronic bronchitis or asthma?Is chronic bronchitis like asthma? These two conditions seem in many ways to be the same: Both involve inflammation of the airways, difficulty breathing, and often wheezing. But they are really distinct illnesses with key differences. For one thing, people with chronic bronchitis have increased mucus production and may have trouble breathing just about all the time, whereas people with asthma have bouts of breathlessness and wheezing that interrupt periods when they feel fine. Another difference is that asthma symptoms are often triggered by bronchospasm, the spasmodic contraction of the airways that chokes off airflow. But bronchospasm is not typical of chronic bronchitis. The two illnesses also start and progress in different ways. Asthma affects people of all ages, and when it starts in childhood it often improves over the years. But chronic bronchitis develops in middle age, usually in people who have smoked. The causes of these two conditions are different, too. The main cause of chronic bronchitis is smoking. Doctors don't fully understand what causes asthma, but they know that asthma attacks have a wide range of triggers, which may include allergens, exercising in cold air, air pollution, and respiratory tract infections. |
| Last updated: | May 23, 2007 |
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Medical content reviewed by the Faculty of the Harvard Medical School. Harvard Health Publications, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved. Used with permission of StayWell.
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