Effects of radiation Flashcards
what is non-ionising radiation
radiation in the part of the electromagnetic spectrum where there is insufficient energy to cause ionisation
what is ionising radiation
radiation which carries sufficient energy to remove an electron from its orbit around a nucleus i.e it causes the atom to become ionised
effects of non-ionising radiation (2 things)
1) carries a risk of damage, particularly to the skin and eyes
2) sources include electric and magnetic fields, radiowaves, microwaves, infrared, lasers, ultraviolet and visible radiation
example of non-ionsing radiation: excessive exposure to UV light sources such as the sun, sunbeds
Acute effects- sunburn and cornea inflammation
Long term effects- skin cancer, skin thickening, premature aging of the skin, cataracts
ionising radiation comes in two main sources:
man-made and natural
what are man made sources of ionising radiation
mainly arises from Radiology/Radiotheraphy and also the nuclear industry and warfare
what are natural sources of ionising radiation
arises from certain rocks, radon gas, cosmic radiation (radiation doses increases with altitude as the protective function of the atmosphere diminishes)
Effects of ionising radiation (2 main)
1) direct ionisation of DNA
2) Radiolysis of cell water
what happens during direct ionisation of DNA
- occurs when radiation interacts with the strands of the DNA molecule
- Can be single strand breaks after which there is usually complete repair, or double strand breaks where there is a greater chance of repair error
- a repair error passed onto another cell is a mutation
what happens during radiolysis of cell water
- occurs when radiation interacts with the cell water molecules (roughly 80% of a cells composition)
- the energy causes the water molecules to split leading to the formation of free radicals
- these can also lead to alteration in the base sequences (coding) in the DNA molecule
Possible effects on the cell of changes to DNA sequence (8 examples)
1) no noticeable effect
2) altered cell growth
3) altered cell development
4) inability to divide
5) Loss of control of cell division
6) changes in biochemistry (production of proteins)
7) Changes in respiration (due to effects in mitochondria)
8) cell death
possible effects on exposed individuals (somatic effects)
5 examples
1) no noticeable effect (even if cells are affected)
2) altered cell growth- tumour formation
3) excessive cell killing- impaired organ function
4) altered biochemistry- impaired body function
5) beneficial effects
possible effects on future generations (hereditary effects)
these effects will only occur due to mutations in germinal tissue i.e. due to irradiation of parents’ gonads
- no noticeable effect
- genetic/chromosomal disorders- lethal effects/malformations/cancers
what is radio sensitivity
the relative susceptibility of cells, tissues, organs and organisms to the harmful action of raiation
what is cell raiosensitivity irectly proportional to
the rate of cell division- this means that actively dividing cells or those not fully mature are most at risk from radiation
example of high radiosensitivity
lymphoid organs, bone marrow, blood, testes, ovaries, intestines
examples of moderate radiosensitivity
optic lens, stomach, growing cartilage, fine vasoculture, growing bone
examples of low radiosensitivity
muscle, brain, spinal cord
biological effects- due to 6 factors
1) type of radiation involved
2) size of does received
3) rate the dose is received
4) part of the body exposed
5) the age of the individual
6) biological differences
type of radiation involved
per unit of absorbed dose, alpha particles are far more harmful than x/ gamma rays/ beta particles
size of the dose received
for STOCHASTIC effects the higher the dose the greater the risk
for DETERMINISTIC effects increasing the dose increases the effect only after a threshold has been reached
rate the dose is received
tissue can receive the same dose of radiation over different periods of time. If the dosage occurs over a number of days or weeks, the results are often not as serious if a similar dose was received in a matter minutes
part of the body exposed
radiosensitivity is greater where the cells are most rapidly dividing
the age of the individual
cell division slows with age and the effects of radiation are less damaging than when cells were rapidly dividing
biological differences
Some individuals are more sensitive to the
effects of radiation than others. Studies have not
been able to conclusively determine the reason why
somatic
occur to the individual who receives the radiation
genetic (hereditary)
occur to future generations of the person receiving the radiation following irradiation of the gonads of one or both of the parents e.g. mutations
stochastic
effects for which the probability of occurrence increases with the dose received, with NO DOSE THRESHOLD. They usually have a long latent period of years e.g. cancers and their severity is not dose related
deterministic
effects for which there is A DOSE THRESHOLD at which they are certain to occur. Further dose above the threshold increases the severity of the effect. Generally shorter latent period (hours or days) e.g. skin reddening, radiation sickness
examples of stochastic
- cancer induction
- leukemia
- genetic effects
examples of deterministic
- skin erythema
- nercrosis (death of tissue)
- epilation (hair loss)
- radiation sickness
two main sources of evidence
1) experiments
2) epidemiology
what are experiments
in-vitro cell cultures and in-vivo animal experiments provide evidence of mechanisms of damage, repair, mutation rates etc
what is epidemology
observational studies provide evidence of types of effects in living persons, risk factors and latent periods
atomic bomb survivors
- main source of data on risk factors and latent periods
- established association between acute high doses of radiation and leukaemias and some solid tumors
- also some deterministic in-utero effects
radiation effects in the embryo and fetus (5 effects)
1) lethal effect in the embryo- occur around time of implantation- dose greater than 11mGy
2) malformations- type dependent upon when the dose is received
3) mental retardation- 8 to 15 weeks
4) childhood cancers and leukaemias
5) hereditary effects
