The lungs are made up of approximately 350 million tiny sacs called alveoli, where carbon dioxide from the body is exchanged for oxygen from the air. Various diseases that affect the lungs either destroy the alveoli directly, as does emphysema, or impair the alveoli’s ability to exchange gases. This picture shows the effects of emphysema (caused by smoking) on lung tissue.
The lungs are subject to a number of disorders, with symptoms that may include difficulty in breathing, chest pain, coughing, and wheezing. Lung cancer, most commonly caused by smoking tobacco, is the deadliest lung disease, and each year it kills more Americans than any other kind of cancer. Smoking tobacco may also lead to emphysema, which is caused by wholesale destruction of alveoli. Other lung disorders include pneumonia, or inflammation of the lungs, which is usually caused by viruses or bacteria; pneumothorax, or collapse of the lung; pulmonary edema, or fluid in the lung; and pleural effusion, or fluid on the pleura. Pulmonary embolism occurs when a blood clot or other foreign substance lodges in the lungs and blocks the major pulmonary arteries.