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 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 their 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.

Nicotine and the Body
Nicotine initially causes a rapid release of adrenaline, the "fight-or-flight" hormone. If you've ever jumped in fright at a scary movie or rushed around the office trying to finish a project by your deadline, you may be familiar with adrenaline's effects:

• Rapid heartbeat
• Increased blood pressure
• Rapid, shallow breathing

Adrenaline also tells your body to dump some of its glucose stores into your blood. This makes sense if you remind yourself that the "fight-or-flight" response is meant to help you either defend yourself from a hungry predator or hightail it out of a dangerous situation -- running or brawling both require plenty of energy to fuel your muscles.

Nicotine itself may also block the release of the hormone Insulin tells your cells to take up excess glucose from your blood. This means that nicotine makes people somewhat hyperglycemic, having more sugar than usual in their blood. Some people think that nicotine also curbs their appetite so that they eat less. This hyperglycemia could be one explanation why: Their bodies and brain may see the excess sugar and down-regulate the hormones and other signals that are perceived as hunger.

Nicotine may also increase your basal metabolic rate slightly. This means that you burn more calories than you usually would when you are just sitting around. However, losing weight by smoking doesn't give you any of the health benefits that you'd get if you were losing weight by exercising -- it actually does the opposite! Over the long haul, nicotine can increase the level of the "bad" cholesterol, LDL, that damages your arteries. This makes it more likely that you could have a heart attack or a stroke.