Why do habitual smokers feel the urge to smoke every hour?
Nicotine has a half life of 60 minutes in your blood stream. In lay man terms it is filtered out of your blood stream in a matter of 60 minutes approximately. Your liver takes care of the filtering; once it is filtered it is sent along with other impurities to kidney from where it is discharged out of your body. If you are addicted to nicotine you will start feeling uncomfortable as soon as the levels of nicotine start dropping in your blood stream. Your brain feel craved for nicotine and finds it difficult of concentrate on anything till its craving is fed.
Nicotine level reduction causes craving
It is unfortunate that nicotine has such a small half life but there are chain smokers around who smoke a couple of cigarettes every 10 minutes or so. I used to be one of them. I used to smoke involuntarily almost without a craving signal from the brain. This behavior is induced more out of habit than craving. The usual smoker would feel a craving signal from his brain while he is at work or involved in an activity, if he/she addicted they would involuntarily head for the nearest smoking section to fed their craving.
Moodiness and irritability
These are sensations which result in a pleasurable experience. People who start out smoking get back to lighting up just to experience this feeling, they are not addicted but just feel like experiencing the sensation. Once a person is hooked or becomes a habitual smoker he/she reaches out for a cigarette almost involuntarily, these sensation are not felt so strongly. For a habitual smoker the first cigarette he smokes, usually first thing after getting up in the morning, is the most pleasurable one. Nicotine is the chemical which gives you this sensation. Depending upon the brand you smoke nicotine content may be low or high in the tobacco used. Strong cigarettes have higher nicotine content and induce an immediate sensation, several smokers smoke strong for this very reason.
The criming chemical: nicotine
Nicotine is one of the thousand or so chemicals present in tobacco. It is primarily responsible for the sensations produced by tobacco consumed in any form. The reason for the potency of nicotine lies in the fact that it can easily diffuse into the blood stream via your skin membrane, mucous membrane (in your nose) or through lungs. Once it enters the blood stream it reaches the brain almost instantly. The effect is has on the nerves of the brain leads to all the sensational feelings you experience while smoking. From there is traverses via blood to different parts of the body and finally filtered out of the blood by the liver.
Nicotine and the blood stream
The quickest way known to inject nicotine into your blood stream is via inhaling tobacco smoke. When the smoke enters your air sacs present in your lung, the primary function of the air sacs is to ensure gas exchange. Basically it is supposed to diffuse oxygen and other chemicals present in the air you breath into the bloodstream. So when you inhale cigarette smoke the 4000 or so chemicals, 43 of them proven cancer inducing agents, have access to your blood stream. Nicotine being on the chemicals enters your bloodstream via the lungs. This blood is then pumped by the heart to your brain and hence nicotine reaches your brain, the spot where it does its magic.
It usually takes only 10-15 seconds for nicotine to show its magic when induced via smoking. Once your brain gets used to the magic it gets addicted. With time the brain finds it difficult to live without experiencing the sensations of nicotine, hence the withdrawal pains. The nicotine thus claims its victim. It usually takes only a few months for a person to get addicted to the nicotine effects. Your brain becomes your enemy, this is the sole reason why addiction is so difficult to quit. Your brain can easily trick you into indulging in the addiction by playing mind games, you will be surprised at the excuses it can come up with just to have a puff. To fight against your own brain is the toughest battle you will encounter, the only way to win the battle is to realize “you are not your mind”. If you become totally related with your mind it's impossible to quit.
Smoking is a tough addiction to break if you live in your mind, but its far easier to quit smoking than to break a addiction with narcotics like cocaine or heroin. For your information tobacco is a drug just like cocaine. Its just that tobacco is legally available, by no means does it become less potent as a addictive agent which can have the same ruination effects as any other narcotic.