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Respiratory System

Respiratory Disorders

The respiratory system is open to airborne microbes and to outside pollution. It is not surprising that respiratory diseases occur, in spite of the body's defenses. Some respiratory disorders are relatively mild and, unfortunately, very familiar. We all experience the excess mucus, coughing, and sneezing of the common cold from time to time. The common cold is an example of rhinitis, an inflammation of the epithelium lining the nose and nasal cavity. Viruses, bacteria, and allergens are among the causes of rhinitis.

Since the respiratory lining is continuous, nasal cavity infections often spread. Laryngitis, an inflammation of the vocal cords, results in hoarseness and loss of voice. Swelling of the inflamed vocal cords interferes with or prevents normal vibration. Pathogens, irritating chemicals in the air, and overuse of the voice are causes of laryngitis.

Pneumonia, inflammation of the alveoli, is most commonly caused by bacteria and viruses. During a bout of pneumonia, the inflamed alveoli fill up with fluid and dead bacteria, and the external respiration rate drops. Patients come down with fever, chills, and pain, coughing up phlegm and sometimes blood. Sufferers of bronchitis, an inflammation of the bronchi, also cough up thick phlegm. There are two types of bronchitis, acute and chronic. Acute bronchitis can be a complication of a cold or flu. Bacteria, smoking, and air pollution can also cause acute bronchitis. This type of bronchitis clears up in a short time.

Chronic bronchitis and emphysema are termed chronic obstructive pulmonary disease (COPD), in which the airways are obstructed and the respiratory surface is diminished. COPD patients do not improve without treatment. Air pollution and cigarette smoking are the main causes of COPD. Nonsmokers who inhale the smoke of others—passive smokers—are also at risk. Smoking stimulates the lining cells in the bronchi to produce mucus. This causes the epithelium lining the bronchi and its branches to thicken and thereby narrow. Patients cough up phlegm and experience breathlessness as well as strain on the heart. In emphysema, also caused by smoking, the alveolar walls disintegrate and the alveoli blend together. They form large air pockets from which the air does not escape. This cuts down the surface area for gas exchange. It becomes difficult for the patient to exhale. The extra work of exhaling over several years can cause the chest to enlarge and become barrel-shaped. The body is unable to repair the damage to the lungs brought on by COPD, and the disease can lead to respiratory failure. During respiratory failure, the respiratory system does not supply sufficient oxygen to sustain the organism.

In addition to COPD, lung cancer also destroys lung tissue. The most common type of cancer in the United States, lung cancer is the leading cause of cancer death in men. It is the second leading cause of cancer death, after breast cancer, in women. Cigarette smoking is the main cause of lung cancer. Passive smokers are also at risk. Air pollution, radioactive minerals, and asbestos also cause lung cancer. The symptoms of the disease include a chronic cough from bronchitis, coughing up blood, shortness of breath, and chest pain. Lung cancer can spread in the lung area. Unchecked, it can metastasize (spread) to other parts of the body. Physicians use surgery, anticancer drugs, and radiation therapy to destroy the cancer cells and contain the disease.

See also Cigarette smoke.



Blaustein, Daniel. Biology: The Dynamics of Life. Westerville, OH: McGraw-Hill Companies, 1998.

Essenfeld, Bernice, Carol R. Gontang, and Randy Moore. Biology. Menlo Park, CA: Addison-Wesley Publishing Co., 1996.

Marieb, Elaine Nicpon. Human Anatomy & Physiology. 5th ed. San Francisco: Benjamin/Cummings, 2000.


Crapo, Robert O. "Pulmonary Function Testing." New England Journal of Medicine (July 7, 1994).

Martinez, F.D. "The Coming-of-age of the Hygiene Hypothesis." Respiratory Research no. 2 (March 2001): 129-132.


The Human Voice. VHS. Princeton, NJ: Films for the Humanities and Sciences, 1995.

Respiration. VHS. Princeton, NJ: Films for the Humanities and Sciences, 1995.

Bernice Essenfeld


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Alveolus (plural, alveoli)

—An air sac of the lung, in which oxygen and carbon dioxide exchange occurs.

Breathing centers

—Specialized areas in the medulla and pons that regulate the basic rate of breathing.

Bronchial tree

—Branching, air-conducting subdivisions of the bronchi in the lungs.


—Chronic obstructive pulmonary disease, in which the air passages of the lungs become narrower and obstructed. Includes chronic bronchitis and emphysema.

Gill filaments

—Finely divided surface of a gill of a fish or other aquatic animal where gas exchange takes place.


—Tubes in land arthropods that conduct air from opening in body walls to body tissues.

Additional topics

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