Emphysema
Emphysema, when applied to the lung, means distension of the alveoli - the air sacs at the end of the terminal bronchioles where oxygen and carbon dioxide are exchanged across the capillary walls. As the disease progresses there is destruction of the walls of the terminal bronchioles and the air space expands to produce blebs called bullae. Since these cannot contract they play no part in respiration and there is progressive shortness of breath - part of Chronic Obstructive Pulmonary Disease. There are two distinct types of emphysema: by far the commonest is that caused by smoking, which affects the upper lobes of the lungs; the much rarer type caused by a genetic deficiency of an enzyme called alpha 1 antitrypsin (which also affects the liver) affects mainly the lower lobes.
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