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ON THE IMAGE (Acute Radiation Syndromes).
There have been few instances of human disease caused by whole-body
irradiation, and most of our information has been derived from studies of
Japanese atom bomb casualties.
Further information have been obtained from study of the survivors of the
much smaller sample of people exposed in the accident at the Chernobyl
nuclear power plant in the USSR in 1986.
Since by definition the same dose of radiant
energy is transmitted to all organs in whole-body irradiation, the
development of the different acute radiation syndromes clearly reflects
only the dissimilarities in the vulnerbility of the target tissues.
At a dose of approximately
300 rads, a syndrome characterized by hematopoietic failure
develops within 2 weeks. Since all hematopoietic precursor elements are
highly sensitive to radiant energy, a pancytopenia typically characterizes
the hematopoietic whole-body irradiation syndrome. Following an initial
depression of circulating lymphocytes, a progressive decrease in formed
elements of the blood eventually leads to bleeding, anemia and infection.
The last is often the cause of death.
With more intense radiation,
about 1000 rads, the principal cause of death is related to the
gastrointestinal system. While gastrointestinal symptoms characterizes the
entire dose range of whole-body exposure, at higher levels severe
destruction of the entire epithelium of the gastrointestinal tracts occur
within 3 days, the time that corresponds to the normal life span of the
villous and crypt cells. As a result the fluid homeostasis of the bowel
is disrupted and severe diarrhea and dehydration ensue. Moreover, the
epithelial barrier to intestinal bacteria is breached, and bacteria invade
and disseminate throughout the body. Shock and septicemia kill the victim.
With exposure to whole-body doses of 2000 rads and
greater, central nervous system damage causes death within hours. In most
cases, endothelial injury resulting in cerebral edema and loss of the
integrity of the blood-brain barrier predominates, but with extreme doses
radiation necrosis of neurons can be expected. Convulsions, coma, and
death follow.
The effects of whole-body irradiation on the human
fetus have been documented in studies of the survivors of the atom bomb
explosions in Japan.
Pregnant women exposed to doses of 25 rads or greater
gave birth to infants with reduced head size, diminished overall growth ,
and mental retardation. [
Intrauterine
exposure to radiation at Nagasaki was significantly less teratogenic than
at Hiroshima. This disparity has been attributed to a difference in the
quality of the radiation in the two cities. The bomb dropped on Hiroshima
produced far greater fast-neutron radiation (20% as opposed to 1% of the
total energy released), which is lower in energy than comparable doses of
gamma rays and, therefore, produce greater biologic damage.]
In studies
of the clinical status of children who were exposed to therapeutic doses
of radiation in utero, the most likely time for the production of growth
retardation and microcephaly was between third and twentieth week of
gestation.
Other effects of irradiation in utero include hydrocephaly,
microphthalmia, chorioretinitis , blindness, spina bifida, cleft palate,
club feet, and genital abnormalities.
Data derived from experimental and
human studies strongly support the conclusion that major congenital
malformations are highly unlikely with doses less than 20 rads after 14
days of pregnancy.
This does not mean that lower doses cannot produce subtle
effects, but these have not been documented.
To protect against such a
possibility, the established maximum permissible dose to the fetus from
exposure of the expectant mother is far below the known teratogenic dose.
The potential genetic effects of radiation have been the source of
considerable public concern.
After
long-term follow-up, even the survivors of Hiroshima and Nagasaki have
failed to manifest evidence of genetic damage in the form of either
congenital abnormalities or hereditary diseases in subsequent offspring or
their descendants.
The finding that rodents exposed to whole-body
radiation have a shortened life span led to the suggestion that radiation
accelerates the aging process.
The
effects or ionizing radiation on mortality are specific and focal, and
there is no reason to believe that premature aging in humans or
radiation-induced carcinogenesis is due to a general acceleration of
aging.
Environmental Pathology - Radiation : click here
Localized Radiation Injury Associated with
Radiotherapy: click here
Radiation and Cancer: click here
Cutaneous lesions after exposure to Radiation: click
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