Biology of radiation Flashcards
Sources of radiation?
1-Background (natural)
2-Manmade (artificial)
Dental radiation makes how much % of all manmade radiation?
0.26%
what is radiation biology?
a branch of biology that is concerned with the effects of ionizing radiation on living tissues and organisms.
who are the irradiated study populations?
1-atomic bomb survivors
2-workers exposed to radioactive materials (radium watch dial painters)
3-nuclear power plants accidents (Chernobyl)
4-patient undergoing radiation therapy (they are less because the radiation is area specific and not whole body)
recent studies show that radiation workers in nuclear industries who have suffered low doses of radiation approximated to that of CT scan, and atomic bomb survivors who received low doses approximate to those from CT scans
interaction of radiation with atoms?
9%= no interaction
7% coherent scattering (nowadays it is filtered)
27%=photoelectric effect
57%= Compton scattering
mechanism of radiation injury are?
1-direct action
2-indirect action
what happens to atom in direct action of radiation?
the ionized atom has a positive charge and it is chemically active trying to replace the missing electron..
what happens if the ionized atom is a part of a larger molecule?
it will cause braking of the molecular bonds
what will happen if enough molecules are damaged in direct action of radiation?
1-loss of cell function
2-didruption of cell organelles
3-death of cell
what is the (critical biomolecular target) for radiation?
the DNA
So by breaking molecular bonds, radiation has a DIRECT EFFECT on the cell
what is the percentage of direct action of radiation?
20%
what is the chemical effect of indirect radition?
radiolysis of water
-mechanism is mostly via chemical effect
in the indirect action, which by product of the chemical reaction is the most dangerous?
H2O2 caused by free radicals
hydrogen peroxide.
what are free radicals?
atoms, molecules or ions which is not combined to anything and carries unpaired electron
why are free radicals dangerous?
they are highly reactive and become stable through breaking part or joining of molecules
what is the effect of free radicals on DNA
they join with DNA molecule to producec damage
so, in Indirect action, produced chemical reaction that indirectly harms the cell by leading to formation of the chemical that cause the damage.
which part of the cell is the most radiosensitive?
the nucleus (it contains the DNA)
what is the effect of radiation on the nucleus?
1-chromosomal aberrations (damage)
2-mitotic delay
3-cell death
a dead cell is better than one with a chromosomal aberration, which may lead to?
cancer or genetic defect
sequence of radiation injury?
exposure->injury->repair
what is the latent period?
time period between exposure to radiation and appearance of observable clinical signs
range of latent period
from few days to years
repair is inversely proportional to ?
1-degree of exposure
2-rate of exposure
what is the cumulative effect?
each radiation exposure adds to this residual damage
critical organs
1-lens of the eyes
2-gonads
3-fetus
4-bone marrow
5-thyroid glans
6-skin
difference between somatic and genetic damage?
somatic (all cells)
-damage if to the exposed individual only
genetic (occytes and spermatogonia?)
-damage in inherited from one generation to the next
what are the types of dose response?
1-deterministic
2-stochastic
what is deterministic dose effect?
increase in dose ->increase in severity
-there is a threshold that must be crossed.
examples?
1-epilation
2-erythema
3-cataract
4-sterility
difference between deterministic and stochastic?
deterministic requires a large dose to produce serious damage.
stochastic meaning?
increase in dose -> increase CHANCE only
the severity is unrelated to magnitude of dose
examples
1-genetic mutation
2-tumor induction
what are the determinants of radiation injury? the radiation factors
1-type of radiation (alpha, beta…etc)
2-total dose (dental less than medical
3-quality of beam (superfacial vs deep tissue)
4-acute vs chronic (chronic has less efect because the tissue has time to repair themselves= similar to dental radiographic exposure
5-local vs whole body
6-dose rate
what are the determinants of radiation injury? the host factors
1-species (mammals are more sensitive)
2-intrinsic resistance (cannot be predicted)
3-type of tissue (is it radiosensitive or not?)
4-rate of cell division
what is hormesis?
low doses of radiation may have beneficial effect on tissue, through
1-stimulation of cellular repair
2-and immune system
radioresistant tissue?
1-mature bone
2-muscle
2-nerves
deterministic effect on oral cavity, include?
1-mucositis
2-taste loss
3-xerostomia
4-radiation caries
5-osteoradionecrosis
6-muscle trismus
