From normal lung function to COPD: what causes COPD?
Frequent coughing, excess phlegm, and shortness of breath are all symptoms of chronic obstructive pulmonary disease, or COPD - one of the top 10 causes of death in the United States.
COPD is not one disease but two: chronic bronchitis and emphysema. Both are long-term problems that obstruct breathing, and both share a main cause - smoking. You do not need both conditions to have COPD, but many people with one also have the other.
Symptoms of both vary from person to person and usually worsen as the condition advances. The good news is that treatments and lifestyle changes can help greatly.
What causes COPD?
COPD develops gradually over many years, as the airways narrow and the lungs lose their ability to expand and contract effectively. In most people with the disease, the trouble begins with inflammation triggered when something - most often cigarette smoke - irritates the respiratory tract on and off over many years. The irritant damages the cells lining the airways.
It also alters the airway lining that normally produces small amounts of mucus to lubricate the airway walls. Your body does not stand idly by: the immune system unleashes a flood of inflammatory cells - macrophages, neutrophils, and lymphocytes. Unfortunately, this defense ultimately makes the problem worse.
These inflammatory cells, the soldiers of your defense system, attack the irritants. On their search-and-destroy mission they infiltrate the airway walls and trigger extra mucus production inside the airways, leaving less room for air to pass.
The cells also release various chemicals, including enzymes called proteases. Proteases act like molecular scissors, snipping apart proteins and tissues the body wants to break down - useful in fighting infection and injury.
But an overabundance of these chemicals is harmful and can contribute to emphysema and possibly chronic bronchitis. In some people, a genetic defect is behind the especially destructive effects of one such protease, neutrophil elastase.
