Tobacco Smoking

Tobacco smoking is the practice where tobacco is burned and the vapors either tasted or inhaled. The practice began as early as 5000–3000 BC. Many civilizations burnt incense during religious rituals, which was later adopted for pleasure or as a social tool and religious ceremonies. Tobacco was introduced to Eurasia in the late 16th century where it followed common trade routes. The substance was met with frequent criticism, but became popular nonetheless.

German scientists formally identified the link between smoking and lung cancer in the late 1920s leading the first anti-smoking campaign in modern history. The movement failed to reach across enemy lines during the Second World War, and quickly became unpopular thereafter. In 1950, health authorities again began to suggest a relationship between smoking and cancer. Scientific evidence mounted in the 1980s, which prompted political action against the practice. Rates of consumption from 1965 onward in the developed world have either peaked or declined. However, they continue to climb in the developing world.

Smoking is the most common method of consuming tobacco, and tobacco is the most common substance smoked. The agricultural product is often mixed with other additives and then pyrolyzed. The resulting vapors are then inhaled and the active substances absorbed through the alveoli in the lungs. The active substances trigger chemical reactions in nerve endings, which heightens heart rate, memory, alertness, and reaction time. Dopamine and later endorphins are released, which are often associated with pleasure. As of 2000, smoking is practiced by some 1.22 billion people. Men are more likely to smoke than women, though the gender gap declines with younger age.

Many smokers begin during adolescence or early adulthood. Usually during the early stages, smoking provides pleasurable sensations, serving as a source of positive reinforcement. After an individual has smoked for many years, the avoidance of withdrawal symptoms and negative reinforcement become the key motivations to continue.

Consumption

Cigars are tightly rolled bundles of dried and fermented tobacco which are ignited so that smoke may be drawn into the smoker's mouth. They are generally not inhaled because the high alkalinity of the smoke, which can quickly become irritating to the trachea and lungs. The prevalence of cigar smoking varies depending on location, historical period, and population surveyed, and prevalence estimates vary somewhat depending on the survey method. The United States is the top consuming country by far, followed by Germany and the United Kingdom; the US and Western Europe account for about 75% of cigar sales worldwide. As of 2005 it is estimated that 4.3% of men and 0.3% of women smoke cigars.

Cigarettes, French for "small cigar", are a product consumed through smoking and manufactured out of cured and finely cut tobacco leaves and reconstituted tobacco, often combined with other additives, which are then rolled or stuffed into a paper-wrapped cylinder. Cigarettes are ignited and inhaled, usually through a cellulose acetate filter, into the mouth and lungs.

Passive smoking is the involuntary consumption of smoked tobacco. Second-hand smoke (SHS) is the consumption where the burning end is present, environmental tobacco smoke (ETS) or third-hand smoke is the consumption of the smoke that remains after the burning end has been extinguished. Because of its negative implications, this form of consumption has played a central role in the regulation of tobacco products.

Pipe smoking typically consists of a small chamber (the bowl) for the combustion of the tobacco to be smoked and a thin stem (shank) that ends in a mouthpiece (the bit). Shredded pieces of tobacco are placed into the chamber and ignited. Tobaccos for smoking in pipes are often carefully treated and blended to achieve flavour nuances not available in other tobacco products.

Roll-Your-Own or hand-rolled cigarettes, often called 'rollies', are very popular particularly in European countries. These are prepared from loose tobacco, cigarette papers and filters all bought separately. They are usually much cheaper to make.

Physiology

The active substances in tobacco, especially cigarettes, are administered by burning the leaves and inhaling the vaporized gas that results. This quickly and effectively delivers substances into the bloodstream by absorption through the alveoli in the lungs. The lungs contain some 300 million alveoli, which amounts to a surface area of over 70 m² (about the size of a tennis court). This method is inefficient as not all of the smoke will be inhaled, and some amount of the active substances will be lost in the process of combustion, pyrolysis. Pipe and Cigar smoke are not inhaled because of its high alkalinity, which are irritating to the trachea and lungs. However, because of its higher alkalinity (pH 8.5) compared to cigarette smoke (pH 5.3), unionized nicotine is more readily absorbed through the mucous membranes in the mouth. Nicotine absorption from cigar and pipe, however, is much less than that from cigarette smoke.

The inhaled substances trigger chemical reactions in nerve endings. The cholinergic receptors are often triggered by the naturally occurring neurotransmitter acetylcholine. Acetylcholine and Nicotine express chemical similarities, which allows Nicotine to trigger the receptor as well. These nicotinic acetylcholine receptors takes are located in the central nervous system and at the nerve-muscle junction of skeletal muscles; whose activity increases heart rate, alertness, and faster reaction times. Nicotine acetylcholine stimulation is not directly addictive. However, since dopamine-releasing neurons are abundant on nicotine receptors, dopamine is released. This release of dopamine, which is associated with pleasure, is reinforcing and may also increase working memory. Nicotine and cocaine activate similar patterns of neurons, which supports the idea that common substrates among these drugs.

When tobacco is smoked, most of the nicotine is pyrolyzed. However, a dose sufficient to cause mild somatic dependency and mild to strong psychological dependency remains. There is also a formation of harmane (a MAO inhibitor) from the acetaldehyde in tobacco smoke. This seems to play an important role in nicotine addiction—probably by facilitating a dopamine release in the nucleus accumbens as a response to nicotine stimuli. Using rat studies, withdrawal after repeated exposure to nicotine results in less responsive nucleus accumbens cells, which produce dopamine responsible for reinforcement.

Health

Tobacco use leads most commonly to diseases affecting the heart and lungs, with smoking being a major risk factor for heart attacks, strokes, chronic obstructive pulmonary disease (COPD), emphysema, and cancer (particularly lung cancer, cancers of the larynx and mouth, and pancreatic cancer). Cigarette smoking increases the risk of Crohn's disease as well as the severity of the course of the disease. It is also the number one cause of bladder cancer.

The World Health Organization estimate that tobacco caused 5.4 million deaths in 2004 and 100 million deaths over the course of the 20th century. Similarly, the United States Centers for Disease Control and Prevention describes tobacco use as "the single most important preventable risk to human health in developed countries and an important cause of premature death worldwide."

Rates of smoking have leveled off or declined in the developed world. Smoking rates in the United States have dropped by half from 1965 to 2006 falling from 42% to 20.8% in adults. In the developing world, tobacco consumption is rising by 3.4% per year. Passive smoking presents a very real health risk. 603,000 deaths were attributable to second-hand smoke in 2004.

Smoking cessation, referred to as "quitting" is the action leading towards abstinence of tobacco smoking. There are a number of methods such as cold turkey, nicotine replacement therapy, antidepressants, hypnosis, self-help, and support groups.


Reference: http://en.wikipedia.org/wiki/Tobacco_smoking
Images: http://commons.wikimedia.org/wiki/Category:Tobacco_smoking