Download Cell Biology and Radiation Genetics

Cell Biology and Radiation
Genetics
Dr.Sayed abbas
NMT 232
L7
• Mechanisms of Damage
• Injury to living tissue results from the transfer
of energy to atoms and molecules in the
cellular structure. Ionizing radiation causes
atoms and molecules to become ionized or
excited. These excitations and ionizations can:
• Produce Damage molecules that regulate vital
cell processes (e.g. DNA, RNA, proteins).
Tissue Sensitivity
In general, the radiation sensitivity of a tissue is:
• proportional to the rate of proliferation of its cells
inversely proportional to the degree of cell
differentiation
Most Sensitive: Blood-forming organs
• Reproductive organs
• Skin
• Bone and teeth
• Muscle
• Least sensitive: Nervous system
Radiosensitivities of various tissues
Prompt Effects
• High doses delivered to the whole body of
healthy adults within short periods of time
can produce effects such as blood component
changes, fatigue, diarrhea, nausea and death.
These effects will develop within hours, days
or weeks, depending on the size of the dose.
The larger the dose, the sooner a given effect
will occur.
Prompt Effects
Effect
Dose
Blood count changes
50 rem
Vomiting (threshold)
100 rem
Mortality (threshold)
150 rem
LD50/60* (with minimal supportive care)
320 – 360 rem
LD50/60 (with supportive medical treatment)
480 – 540 rem
100% mortality (with best available treatment)
800 rem
Delayed Effects of Radiation Exposure
These acute effects apply only when the whole
body is relatively uniformly irradiated.
Cataracts:
induced when a dose exceeding approximately
200-300 rem is delivered to the lens of the eye.
Cancer:
associated with high doses. include leukemia,
multiple myeloma, breast cancer, lung cancer,
and skin cancer. take 10 - 15 years or more to
appear.
Genetic Effects
Prenatal Radiation Exposure:
radiation exposure can produce developmental
problems, particularly in the developing brain, when
an embryo/fetus is exposed prenatally effects are
include low birth weight, microcephaly, mental
retardation, and other neurological problems.
The threshold dose for developmental effects is
approximately 10 rems.
Bergonie and Tribondeau Law
Radiosensitivity is based on the metabolic state
of the tissue being irradiated
• The radiosensitivity of a tissue depends on:
1- The excess amount of less-differentiated cells
in the tissue.
2- The excess amount of active mitotic cells.
3- The duration of active proliferation of the
cells.
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• According to the Bergonie and Tribondeau law, the
effect of radiation on undifferentiated divided cells
with high mitotic activity is much greater than the
effect of radiation on undivided differentiated cells .
Undifferentiated :
cell that has not assumed the morphologic and
functional characteristics it will later acquire .
Differentiated :
Is a cell in a multicellular organism that is
specialized in its function
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