16.7. Name principal causes of malignant tumours occurrence.

There are three groups of the etiological factors: chemical (carcinogenic substances), physical (ionizing radiation, ultra-violet radiation, a heat, mechanical influence), biological (oncogenic viruses).

16.8. Who and how for the first time has proved a role of chemical factors in occurrence of malignant tumours?

In 1775 English doctor P. Pott for the first time has assumed, that chemical compounds can cause a cancer. It was caused by his supervision of numerous cases of a cancer of a skin of scrotum of young men some years later after work as chimney sweeps in the children's age. Thus connection between cancer of chimney sweeps and pollution of a skin by soot and pitch has been noted.

However only in 1915 the Japanese scientists Ishikava and Jamagiva have confirmed this conclusion in experiment. For the first time they have reproduced a malignant tumour (a cancer of skin) by long, during 6 months rubbing of coal pitch in a skin of an ear of rabbits.

At the beginning of 30th years has been allocated 3,4-benzpyrene from coal pitch - substance with which action the carcinogenic effect of products of incomplete combustion of coal has been connected.

16.9. How are chemical carcinogens classified?

Chemical carcinogens are the substances, capable to cause development of malignant tumours.

I. By origin natural and artificial carcinogens are distinguished.

II According to the chemical structure carcinogens can be presented by: polycyclic aromatic hydrocarbons (PAH); aromatic amines; nitrozo-compaunds; mycotoxynes; heterocyclic hydrocarbons; aminonitrose substances, simple substances (asbestos, etc.).

III. In relation to an organism chemical carcinogens can be exogenous and endogenous.

IV. On the mechanism of carcinogenic influence carcinogens of direct action and carcinogens of indirect action are distinguished.

16.10. Give the examples of carcinogens of a natural and artificial origin.

Products of metabolism of some mushrooms concern to carcinogens of a natural origin (mycotoxines) and products of volcanic activity.

Sources of an artificial origin carcinogens are: 1) emissions of the industrial enterprises; 2) exhaust gases of automobiles; 3) a tobacco smoke; 4) products of wrong culinary processing of food (use of the overroasted fats, violation of technology of smoking, etc.).

Violation of technology of cooking can lead to formation of carcinogenic substances.

16.11. Characterize carcinogenic action of polycyclic aromatic hydrocarbons (pah).

PAH are substances which have in structure of the molecules some interfaced benzol circles. The most widespread and studied are such compounds, as 3,4-benzpyrene, dimethylbenzantracene. They are found out in products of volcanic activity, emissions of the industrial enterprises, exhaust gases of cars, a tobacco smoke, foodstuff at their wrong smoking, etc.

The main feature of carcinogenic influence of PAH consists in their local action. It means, that they cause development of tumours in those organs and tissues to which they contact. So, at rubbing in a skin there is a cancer of a skin, at hypodermic introduction - a sarcoma, at inhalation - cancer of lungs; at receipt with food - a cancer of a gullet, a stomach and guts, at allocation with milk - a cancer of mammary glands.