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Tobacco is made from the dried leaves of the tobacco plant. Tar is the name given to the yellow-brown substance that stains smokers’ teeth, fingers and lungs. Many of these chemicals are known carcinogens (cancer causing), and tobacco smoke itself is carcinogenic.

Ya… It’s exactly!  Over the last decades environmental factors have been accepted as predominant causes of human cancer, largely on the strength of epidemiological [The study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems], studies showing that cancer incidence varied widely depending on geographical factors, and the immigrants tended to acquire the cancer risk of their new adopted location. Inherited factors have been largely explored in rare familial cancer syndromes(a group of symptoms that together arecharacteristic of a specific disorder, disease, or the like), and genes identified from the study of such families, have made major contributions to the understanding of cancer and to biology in general. Yet such high-penetrance genes contribute little to inherited susceptibility to the common cancers, though they are frequently the subject of cancer causing somatic mutations (genetic problems in DNA). However, advances in molecular biology over the last have resulted in increasing experimental support for the role of  low-penetrance genetic variants     (polymorphisms) in determining the risk of cancer development, and have provided a molecular explanation for gene–environment interactions in the pathogenesis of cancer. Notably, the demonstration of genetic linkages in breast cancer families strongly supports the role of inherited genetic factors  in a common cancer. Together with the study of inherited cancer syndromes, the study of  viruses in tumor production has also had a disproportionately large impact on cancer biology. Thus, although few human cancers are caused by viruses, the study of virus-induced cancers in animal models and of those few human examples  has contributed substantially to the discovery of several important oncogenes  (cancer causing gene ) and also tumor suppressors. Major concerns still exist about how much  weight can be placed on animal models of  carcinogen-exposure-induced cancer. In general, the levels in these studies greatly exceed those to which most humans will ever be  exposed and moreover, in this studies almost invariably address single carcinogens (cancer causing chemicals or radiations ), whereas humans will be exposed often to complex mixtures. Even tobacco smoke is believed to contain upwards of 50 different carcinogenic compounds

– the effects this mixtures are poorly understood. Improved understanding of the mechanisms underlying the toxic effects of carcinogens and how such lesions are recognized and repaired is also often incomplete. This information would increase our ability to determine the minimal levels of carcinogen exposure needed to cause cancer, and thereby to set safe thresholds for these factors in the environment.

Inter individual variability in susceptibility to carcinogens and other cancer-contributing factors  is also an important issue. With this in mind, we must continue to explore the interactions between susceptibility and resistance genes targeted by carcinogens or influencing the consequences of exposure to carcinogens. The ability to incorporate large numbers of genes and lifestyle factors into the accurate calculation of risk will result from our increasing ability to understand the clinical implications of human DNA sequence variability.  Advances in cancer biology, bioinformatics, systems biology, and mathematics may finally allow us to exploit the results of the Human Genome Project in order to improve the accuracy of cancer risk evaluation and benefit the patient by the implementation of tailored chemo preventative, screening, and lifestyle strategies.

  Smoking is harmful for not just the smoker, but also for those around, who are known as the victims of passive smoking

 When you smoke, you are not cool. In the end, however, you are extinct

 Smoking is like paying someone to kill you. They’re rich; you’re dead

 If God had wanted us to smoke, he would have given us a separate hole for it

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