INTRODUCTION

• Smoking is the most prevalent preventable cause of human death.

• Tobacco smoke contains more than 7000 compounds.Among these are nicotine, which is responsible for tobacco addiction, and Potent carcinogens—mainly, polycyclic aromatic hydrocarbons, nitrosamines, and aromatic amines. Nicotine also has other adverse effects, particularly on fetal development, and is associated with preterm birth and stillbirth.

• Approximately 90% of lung cancers occur in smokers. Smoking is also associated with an increased risk of cancers of the oral cavity, larynx, esophagus, stomach, bladder, and kidney, leukemia, liver and colorectal cancer. Cessation of smoking reduces the risk of lung cancer.

• Smokeless tobacco use is an important cause of oral cancers. Tobacco consumption interacts with alcohol in multiplying the risk of oral, laryngeal, and esophageal cancer . Tobacco consumption also increases the risk of lung cancers from occupational exposures to asbestos,uranium, and other agents.

• Tobacco use is an important risk factor for development of atherosclerosis, myocardial infarction, peripheral vascular disease, and cerebrovascular disease.

In the lungs, in addition to cancer, it predisposes to emphysema, chronic bronchitis, and chronic obstructive pulmonary disease.

• Maternal smoking increases the risk of spontaneous abortion,premature birth, and intrauterine growth retardation.

Smoking is the most readily preventable cause of death in humans. The main culprit is cigarette smoking, but smokeless tobacco (e.g., snuff, chewing tobacco) is also harmful to health and an important cause of oral cancer.

The use of tobacco products not only creates personal risks, but passive tobacco inhalation from the environment (second hand smoke) can cause lung cancer in nonsmokers.

EPIDEMIOLOGY

More than 20 million US residents have died of smoking-related diseases since the 1964 Surgeon General’s report on the adverse effects of smoking. Of these, almost 2.5 million died as a result of inhalation of second-hand smoke.

Annually, tobacco is responsible for more than 400,000 deaths in the United States, one-third of these due to lung cancer. Indeed, tobacco is the leading exogenous cause of human cancers, including 90% of lung cancers.

Worldwide, two-thirds of smokers live in 10 countries, led by China, which accounts for nearly 30%, and India with about 10%, followed by Indonesia, Russia, the United States, Japan, Brazil, Bangladesh, Germany, and Turkey.

Constituents  of tobacco smoke..

Tobacco smoke contains a complex mixture of 7000 chemicals, more than 60 of which have been identified as carcinogens.

Nicotine, an alkaloid present in tobacco leaves, is strongly addictive. Nicotine binds to nicotinic acetylcholine receptors in the brain, and stimulates the release of catecholamines from sympathetic neurons. This activity is responsible for the acute effects of smoking, such as the increase in heart rate and blood pressure and the elevation in cardiac contractility .

Effects on the fetus, as nicotine, exposure affects fetal brain development and contributes to preterm birth and still birth.

PATHOLOGY OF TOBACCO…

SMOKING AND LUNG CANCER–

Agents in smoke have a direct irritant effect on the tracheobronchial mucosa, producing increased mucus production (bronchitis). Components of cigarette smoke, particularly polycyclic hydrocarbons and nitrosamines are directly involved in the development of lung cancer in humans.

CYPs (cytochrome P-450 phase I enzymes) and phase II enzymes increase the water solubility of the carcinogens,facilitating their excretion. However, some intermediates produced by CYPs are electrophilic and form DNA adducts that are repaired by error-prone mechanisms, leading to potentially oncogenic mutations .

The risk of developing lung cancer is related to the number of pack-years or cigarettes smoked per day .

Moreover, smoking increases the risk of other carcinogenic influences. Witness the 10-fold higher incidence of lung carcinomas in asbestos workers and uranium miners who smoke over those who do not smoke and the interaction between tobacco consumptionand alcohol in the development of oral and laryngeal cancers .

Smoking and other diseases..

smoking is linked to many other malignant and nonmalignant disorders that affect numerous organ systems.

• Cigarette smoking is associated with cancers of the esophagus,pancreas, bladder, kidney, cervix, and bone marrow and the carcinomas of the liver and colon the latter is the second most common cause of cancer deaths.

• The toll taken by nonmalignant conditions associated with smoking is even more terrible. Agents in smoke have a direct irritant effect on the tracheobronchial mucosa, producing inflammation and increased mucus production (bronchitis).

• Cigarette smoke also causes the recruitment of leukocytes to the lung, with increased local elastase production and subsequent injury to lung tissue, leading to emphysema, chronic bronchitis, and chronic obstructive pulmonary disease. Smoking exacerbates asthma and increases the risk for pulmonary tuberculosis.

• Cigarette smoking is strongly linked to the development of atherosclerosis and its major complications, myocardial infarction and stroke.

• The causal mechanisms probably relate to several factors including increased platelet aggregation, decreased myocardial oxygen supply(because of significant lung disease coupled with the hypoxia related to the CO content of cigarette smoke) accompanied by increased myocardial oxygen demand and a decreased threshold for ventricular fibrillation.
•  Smoking has a multiplicative effect on the incidence of myocardial infarction when combined with hypertension and hypercholesterolemia.

In pregnant  females….

• Smoking also harms the developing fetus. Maternal smoking increases the risk of spontaneous abortions and preterm births and results in intrauterine growth retardation. Birth weights of infants born to mothers who stopped smoking before pregnancy are, however,normal.

– Smoking increases the risk of type 2 diabetes, rheumatoid arthritis, age-related macular degeneration, ectopic pregnancy, and erectile dysfunction.

• Exposure to environmental tobacco smoke (passive smoke inhalation) –

is associated with some of the same detrimental effects that result from active smoking. It is estimated that the relative risk of lung cancer in nonsmokers exposed to environmental smoke is about 1.3 times higher than that of nonsmokers who are not exposed to  smoke.

• Studies report that every year 30,000 to 60,000 cardiac deaths in the United States are associated with exposure to passive smoke.
• Children living in a household with an adult who smokes have an increased frequency of respiratory illnesses such as asthma.
• Passive smoke inhalation in nonsmokers can be estimated by measuring the blood levels of cotinine( a metabolite of nicotine)

However, passive exposure to tobacco smoke in the home remains a major public health concern, particularly for children. It is clear that the transient pleasure of smoking comes with a heavy long-term price.

• Electronic cigarettes (e-cigarettes),

e- cigarettes devices that simulate cigarette smoking by delivering vaporized nicotine and flavorings, are rising in popularity. The use of flavorede-cigarettes, called “vaping,” has been on the increase in recent years, especially among young adults. While for several years after the introduction of e-cigarettes nosignificant untoward effects were recorded, starting in the summer of 2019 an outbreak of vaping-associated acute lung injury occurred in the United States.

• By the end of 2019 close to 2000 cases had been reported to the CDC,with 42 fatalities. The pathogenesis of this outbreak is under intense investigations.