by Melody St. John

Created on: July 25, 2011   Last Updated: July 28, 2011

Emphysema is one of several respiratory diseases which are collectively known as chronic obstructive pulmonary disease (COPD). It is primarily caused by smoking and is characterized by a gradual destruction of the air sacs in the lungs. Otherwise called alveoli (1), these air sacs are the ultimate branches of the respiratory tree. They are spherical in shape and clustered together like bunches of grapes. The alveoli serve as the primary gas exchange units of the lung where oxygen enters the circulation and carbon dioxide enters the lungs to be exhaled.

To understand the disease mechanism of emphysema as well as its associated signs and symptoms, it is important to take a look at the basic anatomy of the alveoli and how the process of gas exchange takes place. The alveoli and the pulmonary capillaries (small blood vessels in the lungs) play major roles in this process. Inside the alveoli is the oxygen that needs to enter the circulation via the pulmonary capillaries; while the pulmonary capillaries contain carbon dioxide to be released via the alveoli.

Lying between the alveoli and the pulmonary capillaries is the so-called gas-blood barrier which is composed of an extremely thin layer of alveolar epithelial cells (covering the alveoli), a thin interstitial space, and the capillary endothelium (covering the capillaries). Gas exchange occurs when the oxygen within the alveolar space diffuses through the gas-blood barrier into the capillaries while the carbon dioxide in the capillaries diffuses through the opposite direction into the alveoli.

When the spherical alveoli or air sacs are damaged gradually, emphysema occurs. As the condition progresses, the air sacs become large, irregular pockets with wide open holes in their inner walls. This causes a decrease in the surface area of the lungs which in turn, lowers the oxygen entering the blood stream. As a result, the amount of oxygen delivered into the various organs in your body is decreased. In addition, the elastic fibers that hold open the minute airways leading to the air sacs are slowly destroyed. This damage causes the airways to collapse when you breathe out, preventing the air in your lungs from being released.

You can have emphysema for a long time without noticing any signs or symptoms. But because oxygen supply becomes inadequate in this condition, you can experience shortness of breath, which is the main symptom of emphysema. This symptom usually has a gradual onset and is manifested when you engage

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