Effects of Ionizing Radiation on Cells

Radiation is thought to damage the cells by producing ionization in them. Water which forms the largest part of the cell mass is ionized and decomposed with formation of very unstable oxidizing free radical such as hydroxyl and perhydroxyl (HO2-) and of oxidizing compounds like H2O2 and organic peroxides. Presence of oxygen increase while anoxia and the presence of reducing agents like cysteine decreases the lethal effects of radiation.
Radiation has been shown to exert the following effects on cells:

  1. Brief exposure of the cells of skin to soft x-rays leads to a reddening or erythema that is followed by a slight tanning. More prolonged exposure, however, leads to skin damage.
  2. Radiation interferes with cell division. This is mainly due to an inhibitory effect on DNA synthesis. This is thought to be due to a damage to DNA template or Kornberg’s enzyme (DNA-polymyrase). The reproductive capacity of a cell is much more sensitive to radiation than are its other function on account of the content of DNA. The nuclei of cells which contain DNS are more sensitive to radiation than the cytoplasm.
  3. Certain kinds of cells are specially sensitive to ionized radiations. These include lymphocytes, proliferating cells and synthetically active cells. The blood forming cells are selectively destroyed. As a result of this there is a change in the number and the proportion of the various types of blood cells. The undifferentiated malignant tumor cells, being actively proliferating, are more readily affected than the normal differentiated cells. For this reason ionizing radiation has been specially useful in inhibiting the growth of malignant tumors.

The gametogenic cells, even though deep in gonads, are selectively affected by radiation. With smaller doses, mutation are induced in gametes later formed; therefore radiation are much used in genetic experiments. For the same reason an indiscriminate use of x-rays whether for diagnosis or for treatment should be avoided. Radiation can also cause cancer. For example, before the carcinogenic action of x-rays was known, many surgeons who used to manipulate fractured limbs directly under x-rays developed cancer of bone of the hand. Many girls using radium to paint the watch dials also suffered from cancer. The survivors of Hiroshima and Nagasaki who were exposed to radium had a much higher incidence of leukemias than the unexposed population. Dosages of radiation greater than mutagenic completely inhibit gametogenesis thereby sterilizing the organism.