LYCOS RETRIEVER 
Emphysema: Alveoli
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Emphysema is a condition in which the walls between the alveoli or air sacs within the lung lose their ability to stretch and recoil. The air sacs become weakened and break. Elasticity of the lung tissue is lost, causing air to be trapped in the air sacs and impairing the exchange of oxygen and carbon dioxide. Also, the support of the airways is lost, allowing for airflow obstruction.
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Emphysema is a severe lung disease in which the tiny air sacs (alveoli) in the lungs become damaged. Normal, healthy lungs look like upside down branches of a tree with many thousands of these tiny air sacs at the ends of those branches. Lungs with emphysema have fewer, larger sacs.
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Emphysema is traditionally a disease suffered by miners, particularly coal miners, as the fine dust that results from mining attacks the alveoli over a period of time. Most miners suffer from emphysema to some degree after a lifetime "down in the pit." In fact, emphysema is sometimes referred to as miner's lung or black lung.
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Emphysema results from permanent enlargement of the alveoli and damage to the walls of the air sacs. The walls of the alveoli lose the ability to expand and contract properly (similar to an overstretched balloon), the air sacs become weak, and air flow in the lungs is reduced. Emphysema affects the body's oxygen supply and makes breathing difficult.
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Emphysema can be classified into two types: Primary and Secondary. Primary emphysema can be subdivided into panacinary and centroacinary. Panacinary emphysema is related to the destruction of alveoli, because of an inflammation or deficiency of alfa-1-antitripsine. It is found more in young adults who do not have chronic bronchitis. Centroacinary emphysema is due to destruction of terminal bronchioli muchosis, due to chronic bronchitis. This is found mostly in elderly people with a long history of smoking.
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Emphysema is almost always caused by cigarette smoking. In normal lungs, tiny air sacs called alveoli support the small airways, called the bronchioles, and hold the airways open. With emphysema, smoke causes an overproduction of an enzyme that destroys the walls of the alveoli, so the bronchioles no longer have any support. When the bronchioles collapse, the airway becomes permanently narrowed.
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