Emphysema is a chronic disorder of respiratory system, in which inflation or abnormal distension of alveolar wall occurs. Cigarette smoking and the inhalation of smoke or toxic substances over a time period causes the damaging of septa present between the alveoli, and its elastic tissue is replaced by the connective tissue in lungs.
Hence, decreases the respiratory surface and causes emphysema. It causes shortness of breath, production of sputum, chronic bronchitis, etc.