Module 2 Biological Effects
In general, the larger the area of the body that receives a
dose, the greater the biological effect.
Extremities are less sensitive than blood forming and
other critical organs. That is why the annual dose limit
for extremities is higher than for a whole body dose that
irradiates internal organs.
The most sensitive cells are those that are rapidly
dividing. Examples include blood cells, hair follicles,
and the cells lining the gastrointestinal tract.
Some individuals are more sensitive to environmental
factors such as ionizing radiation.
The developing embryo/fetus is the most sensitive, and
children are more sensitive than adults.
In general, the human body becomes relatively less
sensitive to ionizing radiation with increasing age. The
exception is that elderly people are more sensitive than
middle-aged adults due to the inability to repair damage
as quickly (less efficient cell repair mechanisms).
Prenatal Radiation Exposure
EO8 State the potential
Although no effects were seen in Japanese children conceived
effects associated with
after the atomic bomb, there were effects seen in some
prenatal radiation dose.
children who were in the womb when exposed to the atomic
bomb radiation at Hiroshima and Nagasaki. Some of these
children were born with a slightly smaller head size, lower
average birth weight, and increased incidence of mental
retardation. Some later showed lower IQ test scores and
slower scholastic development, smaller physical size, and
increased incidence of behavioral problems.
Sensitivity of the fetus
Embryo/fetal cells are rapidly dividing, which makes
them sensitive to many environmental factors including
ionizing radiation. The embryo/fetus is most
susceptible to developing adverse health effects if
exposed during the time period of 8 - 15 weeks after
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