Smoking and Health
Smoking and Health
Smoking cigarettes sets into motion a chain reaction of changes that set the stage for infection, degenerative diseases, cardiovascular disease, and cancer. Smoke contains thousands of chemicals, but it is nicotine that causes the powerful addiction that compels a person to continually deliver the other harmful chemicals to the respiratory system. Nicotine binds to receptors on certain nerve cells in the brain, causing the cells to release dopamine, which produces the associated pleasurable sensations. Addiction happens when a person seeks the good feelings and wants to avoid withdrawal symptoms.
Many of the health problems associated with cigarette smoking stem from impairment of the ability of the respiratory tract to cleanse itself. Each inhalation slows the beating of the cilia that line the tract, so that they cannot move mucus and particles out of the respiratory system. Eventually, the cilia are lost. Accumulating mucus causes smoker's cough, which can develop into chronic bronchitis. In addition, the mucus entraps pathogens , increasing the likelihood of respiratory infections. Meanwhile, the bronchiole linings thicken, and breathing becomes strained. As the bronchioles lose elasticity, the respiratory tract cannot resist the pressure changes that coughing produces, and the microscopic alveoli (air sacs) may burst. This leads to emphysema. Symptoms include difficulty taking a deep breath, worsening cough, wheezing, and fatigue that results from impaired oxygen delivery to tissues. Smokers face a fifteen times greater likelihood of developing emphysema than nonsmokers. Chronic bronchitis and emphysema are the two most common forms of chronic obstructive pulmonary disease (COPD), which is a general term for conditions that block the airways.
Smoking cigarettes accounts for 85 percent of lung cancer cases. The process begins years before a person notices symptoms. First, cells of the bronchial linings begin to divide more often than normal, which displaces the ciliated cells. If smoking continues, these errant cells break through to lung tissue, where they grow into a tumor. Lung cancer can also begin within a single alveolus. Smoking also increases the risk of cancers of the mouth and throat. In one case, a man who repeatedly placed chewing tobacco on his ear developed a skin cancer in that location. Smoking raises serum cholesterol, and can contribute to diseases of the blood vessels. About 21 percent of cases of coronary heart disease and 18 percent of strokes are directly related to smoking.
If a pregnant woman smokes cigarettes, the fetus is at greater risk of premature delivery or low birth weight. Spontaneous abortions and stillbirth are also more likely. Fetal growth becomes stunted because carbon monoxide in cigarette smoke crosses the placenta and binds to fetal hemoglobin molecules, blocking oxygen delivery. Other chemicals in cigarette smoke prevent nutrients from reaching a fetus.
A person can regain health if smoking ceases before too much damage has occurred. Although emphysema cannot be reversed and cancer or cardiovascular disease must be treated, the ciliated cells that are the guideposts of the respiratory system can regrow, and the cough and susceptibility to infection abate.
see also Cancer; Cardiovascular Diseases; Heart and Circulation; Oncogenes and Cancer Cells; Psychoactive Drugs; Respiration
Kleinman, Lowell, et al. Complete Idiot's Guide to Quitting Smoking. Indianapolis, IN: Macmillan, 2000.
"Smoking and Health." Biology. . Encyclopedia.com. (August 17, 2018). http://www.encyclopedia.com/science/news-wires-white-papers-and-books/smoking-and-health
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