Information AboutRadiosensitivity |
| CATEGORIES ABOUT RADIOSENSITIVITY | |
| radiobiology | |
| radioactivity | |
| radiation health effects | |
| oncology | |
|
" X-rays are more effective on cells which have a greater reproductive activity." From their observation, they concluded that quickly dividing Tumor Cell s are generally more sensitive than the majority of body cells. This is not always true. Tumor cells can be Hypoxic and therefore less sensitive to X-rays that mediate most of their effects through Free Radical s produced by ionizing oxygen. Later it has been shown that the most sensitive cells are those that are Undifferentiated , well nourished, divide quickly and are highly Metabolically active. Amongst the body cells, the most sensitive are Spermatogonia and Erythroblast s, Epidermal Stem Cell s, Gastrointestinal Stem Cell s. The least sensitive are Nerve Cell s and Muscle Fiber s. Very sensitive cells are also Oocyte s and Lymphocyte s, although they are Resting Cell s and do not meet the criteria described above. The reasons for their sensitivity are not clear. The damage of the cell can be lethal (the cell dies) or '''sublethal''' (the cell can repair itself). The effects on cells can be, according to ICRP , deterministic and stochastic. Deterministic effects have a threshold of irradiation under which they do not appear and are the necessary cosequence of irradiation. The damage they cause depends on the dose: they are sublethal from 0,25 to 2 Sv (a less pronounced form of disease), lethal from 2 to 5 Sv (a certain percent of population dies in 60 days), above 5 Sv the majority of people die in 60 days and above 6 to 7 all people die. Of course, these effect depend also on many other factors, like age, sex, health etc. Stochastic effects are coincidental and cannot be avoided. They don't have a threshold. These can be divided into somatic and genetic. Among the '''somatic''' ones, the Cancer is the most important. It develops because radiation causes DNA Mutation s directly and indirectly. Direct effects are those caused by ionizing particles and rays themselves, while the indirect are those that are caused by free radicals, generated especially in Water and Oxygen Radiolysis . The '''genetic''' confer the predisposition to cancer to the offspring. They are not very well understood. SEE ALSO
REFERENCE
|
|
|