Emphysema
Emphysemais a chronic lung disease caused by loss of elasticity of the lung tissue. The
surfaces of healthy alveoli are springy and elastic. They stretch out a little when full of air
andrelaxwhenairleavesthem. Butthebreakdownofthetissuesthatsupportthealveoliand
the capillaries that feed the alveoli cause the alveoli to become hard and stiff. Eventually
the walls of the alveoli break down and the alveoli become larger. When alveoli become
larger, the amount of oxygen that can enter the blood with each breath is reduced. Much of
the oxygen that gets into the large alveoli cannot be absorbed across the alveoli walls into
the blood. Symptoms of emphysema include shortness of breath on exertion (usually when
climbing stairs or a hill). Damage to the alveoli, which can be seen inFigure19.9, is not
curable. Smoking is a leading cause of emphysema.
Figure 19.9: The lung of a smoker who had emphysema (left); the black areas are enlarged
alveoliandtar,asticky,blacksubstancefoundintobaccosmokeisevident,and(right)COPD
(Chronic obstructive pulmonary disease), a tobacco-related disease that is characterized by
emphysema. ( 18 )
Causes of Respiratory Diseases
Pathogens
Many respiratory diseases are caused by pathogens. Apathogenis an organism that causes
disease in another organism. Certain bacteria, viruses, and fungi are pathogens of the
respiratory system. The common cold and flu are caused by viruses. The influenza virus that
causes the flu is shown inFigure19.10. Tuberculosis, whooping cough, and acute bronchitis
are caused by bacteria. The pathogens that cause colds, flu, and TB can be passed from
person to person by coughing, sneezing, and by spitting.
Pollution
Air quality is related to several respiratory diseases. Asthma, heart and lung diseases,
allergies, and several types of cancers are all linked to air quality. Air pollution can be
caused by outdoor pollution or indoor pollution. Outdoor air pollution can be caused by car
exhaust fumes, smoke from factories and forest fires, volcanoes, and animal feces. Some of