Respiration is the process in which human beings ingest oxygen from the surrounding environment and excrete carbon dioxide. The lungs are instrumental in the this process, but it is the brain and nervous system which are responsible for controlling the rate of breathing, “The principal nervous center for controlling the rate and depth of respiration is in the respiratory section of the vagus nucleus in the medulla oblongata. The cells of the nucleus are sensitive to the acidity of the blood, which reflects higher and lower concentrations of carbon dioxide in the blood plasma. When the acidity of the blood is high, as is usually the caused by an excess of carbon dioxide, the respiratory center stimulates the respiratory muscles to greater activity. When the carbon dioxide concentration is low, breathing is depressed” (Encarta 1). The respiratory system must function properly to help the body receive the oxygen it needs while helping it eliminate potentially lethal carbon monoxide. The respiratory system is also responsible for helping ward off infection, like pneumonia. Many parts of the respiratory system act as filters to help keep harmful particles from reaching the lungs, like nostril hair which acts as a filter. Mucous is also secreted in order to keep temperature regulated, for example when one smokes. The toxins in cigarettes are often responsible for many respiratory diseases, like emphysema. In habitual smokers, toxins often form free radicals which deposit themselves in the lungs because they are too big to pass through the alveoli. It is these deposits which can form cancerous cells. The constant heat and abrasion from cigarette smoke can also cause mouth and throat cancers. There is a great deal of research to support not only the fact that smoking is the principal cause of lung cancer, but also that it contributes to the development of respiratory disease in those non-smokers who exp
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