Smoking is the leading cause of lung disease in the United States. Among the direct causes of death are pneumonia, influenza, bronchitis, emphysema, and chronic airway obstruction. Smoking increases mucus production in the airways and deadens the respiratory cilia, the tiny hairs that sweep debris out from the lungs. Without the action of the cilia, bacteria and inhaled particles from cigarette smoke are free to damage the lungs.
In the smaller airways of the lungs—the tiny bronchioles that branch off from the larger bronchi—chronic inflammation is present in smokers which causes airway to constrict causing cough, mucus production, and shortness of breath. Eventually, this inflammation can lead to chronic obstructive pulmonary disease (COPD), a condition in which oxygen absorption by the lungs is greatly reduced, severely limiting the amount of oxygen transported to body tissues.
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