Post by Ann on Oct 26, 2005 13:25:44 GMT -5
How Nicotine Works
by Ann Meeker-O'Connell
Nicotine comes from the leaves of the tobacco plant.
For thousands of years, people have smoked or chewed the leaves of the tobacco plant, Nicotiana tabacum. Tobacco was first found and cultivated in the Americas, perhaps as early as 6000 B.C. Following the discovery and colonization of North and South America, the tobacco plant was exported widely, to continental Europe and the rest of the civilized world. Even in its early days, tobacco use was controversial. Some hailed its medicinal properties. For example, tobacco was supposed to be protective against the ravages of the Plague! As early as the 1600s, people speculated that there might be a link between diseases, like cancer, and tobacco use. Since then, modern research methods have provided evidence of this link, and public service announcements that warn of tobacco's health risks and addictive nature are seen regularly on TV.
What is it about tobacco that makes people so compelled to use it despite all of the admonitions? Smoking or chewing tobacco makes people feel good, even mildly euphoric. While there are thousands of chemicals in the tobacco plant (not to mention those added by cigarette manufacturers), one, nicotine, produces all the good feelings that draw people back for another cigarette or plug of tobacco. In this article, we'll examine nicotine and how it affects the human body.
What is Nicotine?
Structure of nicotine
Nicotine (C10H14N2) is a naturally occurring liquid alkaloid. An alkaloid is an organic compound made out of carbon, hydrogen, nitrogen and sometimes oxygen. These chemicals have potent effects on the human body. For example, many people regularly enjoy the stimulating effects of another alkaloid, caffeine, as they quaff a cup or two of coffee in the morning.
Nicotine normally makes up about 5 percent of a tobacco plant, by weight. Cigarettes contain 8 to 20 milligrams (mg) of nicotine (depending on the brand), but only approximately 1 mg is actually absorbed by your body when you smoke a cigarette.
Nicotine in the Body
As with most addictive substances, humans have devised a number of ways of delivering nicotine to their bodies. Nicotine readily diffuses through:
Skin
Lungs
Mucous membranes (such as the lining of your nose or your gums)
Nicotine moves right into the small blood vessels that line the tissues listed above. From there, nicotine travels through your bloodstream to the brain, and then is delivered to the rest of your body.
The most common (and the most expedient way) to get nicotine and other drugs into your bloodstream is through inhalation -- by smoking it. Your lungs are lined by millions of alveoli, the tiny air sacs where gas exchange occurs. These alveoli provide an enormous surface area -- 90 times greater than that of your skin -- and thus provide ample access for nicotine and other compounds. Once in your bloodstream, nicotine flows almost immediately to your brain. Although nicotine takes a lot of different actions throughout your body, what it does in the brain is responsible for both the good feelings you get from smoking, as well as the irritability you feel if you try to quit (see the section on addiction and withdrawal for details). Within 10 to 15 seconds of inhaling, most smokers are in the throes of nicotine's effects.
Nicotine doesn't stick around your body for too long. It has a half-life of about 60 minutes, meaning that six hours after a cigarette, only about 0.031 mg of the 1 mg of nicotine you inhaled remains in your body.
How does your body get rid of nicotine? Here's the process:
About 80 percent of nicotine is broken down to cotinine by enzymes in your liver.
Nicotine is also metabolized in your lungs to cotinine and nicotine oxide.
Cotinine and other metabolites are excreted in your urine. Cotinine has a 24-hour half-life, so you can test whether or not someone has been smoking in the past day or two by screening his or her urine for cotinine.
The remaining nicotine is filtered from the blood by your kidneys and excreted in the urine.
Different people metabolize nicotine at different rates. Some people even have a genetic defect in the enzymes in their liver that break down nicotine, whereby the mutant enzyme is much less effective at metabolizing nicotine than the normal variant. If a person has this gene, their blood and brain nicotine levels stay higher for longer after smoking a cigarette. Normally, people keep smoking cigarettes throughout the day to maintain a steady level of nicotine in their bodies. Smokers with this gene usually end up smoking many fewer cigarettes, because they don't constantly need more nicotine.
Effects of Nicotine
Nicotine changes how your brain and your body function. The net results are somewhat of a paradox: Nicotine can both invigorate and relax a smoker, depending on how much and how often they smoke. This biphasic effect is not uncommon. Although the actions of nicotine and ethanol in the body are quite different, you also see dose-dependent effects when you drink alcoholic beverages. Your first drink may loosen your inhibitions and fire you up, but after several drinks, you're usually pretty sedate.