Respiratory Infections and Lung Disorders
Pathogens frequently spread from one individual to another by way of the respiratory tract. Droplets from a single sneeze may be loaded with billions of bacteria or viruses. The mucous membranes are protected by mucus production and by the constant beating of the cilia, but if the number of infective agents is large and/or the individual's resistance is reduced, an upper respiratory infection can result. Lower Respiratory Tract Infections and Disorders
Acute bronchitis, pneumonia, and tuberculosis, three infections of the lungs, formerly caused a large percentage of deaths in the United States but are now controlled by antibiotics. Other illnesses, such as emphysema and lung cancer, are not due to infections but, in most instances, to cigarette smoking.
Bronchitis
Bronchitis can be acute or chronic. Acute bronchitis is usually caused by a secondary bacterial infection of the bronchi, resulting in a heavy mucus discharge with persistent coughing. Acute bronchitis usually responds to antibiotic therapy.
Chronic bronchitis is not necessarily due to infection, but rather to a constant irritation of the lining of the bronchi. The irritation causes the bronchi lining to become inflamed and undergo degenerative changes, with the loss of cilia preventing normal cleansing action. The affected individual coughs frequently and is more susceptible to upper respiratory infections. Chronic bronchitis most often affects cigarette smokers.
Asthma
Asthma is a disease of the bronchi and bronchioles that is marked by wheezing, breathlessness, and sometimes cough and expectoration of mucus. The airways are unusually sensitive to specific irritants, which can include a wide range of allergens such as pollen, animal dander, dust, cigarette smoke, and industrial fumes. Even cold air, however, can be an irritant. When exposed to the irritant, the smooth muscle in the bronchioles undergoes spasms. It now appears that chemical mediators given off by immune cells in the bronchioles result in the spasms. Most asthma patients have some degree of bronchial inflammation that reduces the diameter of the airways and contributes to the seriousness of an attack. Asthma is not curable but is treatable. There are inhalers that control the inflammation and hopefully prevent an attack, but there are also inhalers that stop the muscle spasms should an attack occur.
Pneumonia
Most forms of pneumonia are caused by bacteria or viruses that infect the lungs. The demise of AIDS patients is usually due to a particularly rare form of pneumonia caused by the protozoan Pneumocystis carinii. Sometimes, pneumonia is localized in specific lobes of the lungs, which become inoperative as they fill with fluid. The more lobes involved, the more serious the infection.
Pulmonary Tuberculosis
Tuberculosis is caused by the tubercle bacillus. Exposure to tuberculosis is detected by the use of a skin test in which a highly diluted extract of the bacilli is injected into the patient's skin. A person who has never been in contact with the bacilli will show no reaction, but one who has developed immunity to the organism will show an area of inflammation that peaks in about 48 hours.
If bacilli invade the lung tissue, tissue cells build a protective capsule around the bacilli, isolating them from the rest of the body. This tiny capsule is called a tubercle. If body resistance is high, the imprisoned organisms may die, but if resistance is low, the organisms may eventually be liberated. If a chest X ray detects the presence of tubercles, the individual is put on appropriate drug therapy to ensure the localization of the disease and the eventual destruction of any live bacterial organisms.
Tuberculosis killed about 100,000 people a year in the United States before the middle of the 20th century, when antibiotic therapy brought it largely under control. In recent years, however, the incidence of tuberculosis has risen, particularly among AIDS patients, the homeless, and the rural poor. Worse, the new strains are resistant to the usual antibiotic therapy. Therefore, some physicians would like to again quarantine patients in sanitoriums.
Emphysema
Emphysema refers to the destruction of lung tissue, with accompanying ballooning or inflation of the lungs due to trapped air. The problems of emphysema stem from the destruction and collapse of the bronchioles. When this occurs, the alveoli are cut off from renewed oxygen supply, and the air within them is trapped. The trapped air often causes alveolar walls to rupture, and a loss of elasticity also makes breathing difficult. The victim is breathless and may have a cough. Since the surface area for gas exchange is reduced, not enough oxygen reaches the heart and the brain. Even so, the heart works furiously to force more blood through the lungs, which can lead to a heart condition. Lack of oxygen to the brain can make the person feel depressed, sluggish, and irritable. Chronic bronchitis and emphysema, two conditions most often caused by smoking, together are called chronic obstructive pulmonary disease (COPD).
Pulmonary Fibrosis
Inhaling particles such as silica (sand), coal dust, and asbestos can lead to pulmonary fibrosis, in which fibrous connective tissue accumulates in the lungs. Breathing capacity can be seriously impaired, and cancer can develop. In the past, asbestos was widely used as a fireproofing and insulating agent, resulting in unwarranted exposure.
Lung Cancer
For many years, lung cancer was more prevalent in men than in women, but recently, it has surpassed breast cancer as a cause of death in women. This can be linked to an increase in the number of women who smoke today. Autopsies on smokers have revealed the progressive steps by which the most common form of lung cancer develops. The first event appears to be thickening and callusing of the cells lining the bronchi. (Callusing occurs whenever cells are exposed to irritants.) Then, a loss of cilia makes it impossible to prevent dust and dirt from settling in the lungs. Following this, cells with atypical nuclei appear in the callused lining. A tumor consisting of disordered cells with atypical nuclei is considered to be cancer in situ (at one location). A final step occurs when some of these cells break loose and penetrate other tissues, a process called metastasis. Now the cancer has spread. The tumor may grow until the bronchus is blocked, cutting off the air supply to that lung. The entire lung then collapses, the secretions trapped in the lung spaces become infected, and pneumonia or a lung abscess (localized area of pus) results. The only treatment that offers a possibility of cure is to remove a lobe or the lung completely before secondary growths have had time to form. This operation is called pneumonectomy.
The incidence of lung cancer is over 20 times higher in individuals who smoke than in those who do not. In addition, current research indicates that passive smokingsimply breathing in air filled with cigarette smoke-can also cause lung cancer and other illnesses associated with smoking. If a person stops smoking, and if the body tissues are not already cancerous, they usually return to normal over time.
Acute bronchitis. pneumonia. and tuberculosis are caused by bacteria. Chronic bronchitis. emphysema. and lung cancer occur more frequently in smokers than in nonsmokers.
