Without conscious effort, you breathe in and out 10 to 15 times each minute. When you are at rest and breathe normally, each breath lasts about 4 to 6 seconds and moves approximately 1.5 pints of air. During vigorous physical exertion you may take in as many as 5 or 6 pints of air per breath.
The Respiratory System
The air you breathe passes through your trachea (windpipe), which divides into two smaller tubes called bronchial tubes, each of which leads to one of the lungs.The bronchial tubes branch into smaller and smaller tubes called bronchioles.At the ends of the bronchioles are tiny clusters of air sacs called alveoli (inset), where oxygen is absorbed into the bloodstream and carbon dioxide is eliminated from the bloodstream.
Your diaphragm, the large muscle that forms the base of your chest cavity, does most of the work during normal breathing. It receives messages from your brain to contract, which expands the chest cavity and creates a negative pressure that results in inward air ﬂow. Stretch receptors in the lungs inform your brain that enough air has been taken in, and the diaphragm is instructed to relax, allow- ing the air to move out. Your brain alters the rate and depth of respiration based on the levels of oxygen and carbon dioxide in your blood. Visual, auditory, or other stimuli, such as fear, also can alter the breathing pattern.
Your lungs are very spongelike. The right lung has three sections, or lobes, and is slightly larger than the left lung, which has only two lobes. Air enters the lungs through the trachea (windpipe) and is drawn through the two large bronchi (the main airways that lead into each lung) into smaller airways called bronchi- oles. The bronchi and the bronchioles are lined with tiny hairs called cilia that catch and sweep out large dust particles and mucus that is secreted by glands in the bronchioles and coats the airways.
Gases are exchanged (carbon dioxide is removed from the bloodstream, and oxygen enters the bloodstream) in the highly folded and moist surfaces of air sacs (also called alveolar sacs) at the end of each bronchiole. Each alveolar sac is made up of up to 30 tiny pouches called alveoli. Alveoli have walls that are only one cell thick and are richly supplied with capillaries (the smallest blood vessels in the body) to facilitate gas exchange. Healthy lungs provide approxi- mately 850 square feet of surface area for this purpose. Only 10 percent of the lungs is solid tissue; the rest is air and blood.
Protecting Your Lungs
Lung cancer is the leading cause of cancer death among both men and women in the United States. Twice as many men as women die of chronic obstructive pul- monary disease (such as emphysema), and pneumonia is a more common cause of death among men than among women.
Lung disease is directly related to speciﬁc risk factors such as cigarette smok- ing and working in occupations that carry risks for developing lung disease. Plastics, wood, metal, and textile workers; bakers; millers; farmers; poultry han- dlers; miners; grain elevator workers; laboratory technicians; drug manufactur- ers; dry cleaners; and detergent manufacturers are all exposed to airborne agents that can cause occupational asthma, lung cancer, and other respiratory disorders.
Your lungs have a limited capacity to protect themselves against many dif- ferent types of irritants. For example, foreign substances trapped by the mucus that lines the airways can be voluntarily expelled (coughed up) as needed. Also, macrophages—scavenging white blood cells—on the inner surface of the alveoli ingest and destroy dust, soot, and other foreign particles, including air- borne bacteria.
You also can take steps on your own to protect your respiratory system. Not
smoking and avoiding exposure to tobacco smoke are critical to protecting your lungs. Cigarette smoke is the major cause of lung cancer, chronic bronchitis, and emphysema. Exposure to cigarette smoke also increases your risk of respiratory infection, including colds. In the lungs, tobacco smoke increases the production of mucus, constricts air passages, and causes infections that break down the walls of alveoli, reducing the surface area for gas exchange. Cancer-causing substances (carcinogens) in tobacco smoke can cause abnormal cells to develop, which may eventually grow into malignant tumors that can spread to other parts of the body.
If your job exposes you to airborne irritants, be sure to wear a protective mask or, if needed, a respirator to prevent inhalation of those hazardous substances. Be familiar with the information and recommendations (such as precautions and ﬁrst-aid measures) contained in the material safety data sheets for all of the haz- ardous substances you may be exposed to at work. Your employer should provide all necessary protective equipment, which should be in good working order. You should also monitor pollution warnings on television and radio before working or exercising outdoors.
Keep your home well ventilated to prevent the accumulation of carbon monoxide or other harmful gases and to prevent mold and fungi from growing inside. Clean air conditioners, humidiﬁers, dehumidiﬁers, and air puriﬁers regu- larly to reduce your exposure to dust, mold spores, and other irritants and aller- gens. Test your home for radon, a colorless, odorless radioactive gas that is the second most common cause of lung cancer in the United States. Install carbon monoxide detectors (which are available at hardware stores) on each ﬂoor of your home.
Symptoms of Lung Disease
Because you have plenty of reserve lung tissue, respiratory disorders may begin long before symptoms appear. Talk to your doctor about the following symptoms as soon as they occur:
• Cough. Pay particular attention to a cough that lasts more than a month, that brings up blood from your lungs, or that produces mucus (especially if it is yellowish, green, or brown).
• Shortness of breath or difﬁculty breathing. Except during physical exertion and at high altitude, breathing should not require noticeable effort or leave you feeling as though you cannot get enough air.
• Chest pain. You should not feel pain when taking deep breaths or coughing, nor should your lungs ache.
• Abnormal breathing noises. Wheezing or whistling noises that accompany breathing can indicate an obstruction of air ﬂow.
Disorders That Obstruct Air Flow
The ﬂow of air from the lungs can be limited or obstructed by a variety of struc- tural changes in the lungs. Chronic obstructive pulmonary disease (COPD), a major cause of disability and death in men, refers to asthma, chronic bronchitis, and emphysema. With COPD the airway obstruction is generally irreversible. With asthma the obstruction is reversible with treatment, although the disease itself may not be cured.