HELP---anatomy and physiology

[callie3056]

Cancer-causing agents (carcinogens) usually act on cells that are dividing. Which of the four tissues would carcinogens most influence? Least influence?

[dundurn]

I think you need to tell us which 4 tissues the questioner gave you!

[theprof]

The four tissues are undoubtedly muscle, nerve, epithelial and connective. All tissues in an animal body belong to one of these categories.

Epithelial tissues are most susceptible to carcinogens whilst connective tissues are least susceptible.

[theprof]

Incidentally, if you're looking for figures, the percentages are very roughly 85-90% epithelial, less than 1%, connective and the balance divided between muscle and nerve tissues.

[dundurn]

Is this because epithelial tissues form the external layers of the organism including the gut and the circulatory system, and therefore are most likely to come into (first) contact with carcinogens, or because the epithelial layers are shed more frquently and thus have a relatively high rate of cell division or a combination of the two?

[theprof]

We're not entirely certain about this but it's thought that epithelial tissue is more susceptible to carcinogens and cancer because epithelial tissue is for the most part,either lacking a blood supply and lymphatic system or poorly supplied by them. Oxygen and nutrients for the cells are obtained from capillaries in adjacent connective tissue via diffusion. The fact that epithelium tissue is very slightly acidic due to a rich carbon dioxide content in comparison to the three other tissues is also thought to promote carcinogenesis via a very complex process.

You're right in thinking that epithelial tissue is more susceptible to cancer because they are more exposed to carcinogens. Chemical carcinogenesis relies a great deal upon this exposure both inside and outside the body. The rate of cell replacement and division does influence carcinogenesis - the greater the division, the greater the rate of development of the carcinoma or adenocarcinoma