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35 Cards in this Set
- Front
- Back
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in what ways does radiation interact with living tissues
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- direct effects
- indirect effects |
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what are direct effects
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occur when the energy of a photon ionizes biological macromolecules, resulting in an unstable free radical.
PHOTON ---------> RH ---> R· + H· |
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what are indirect effects
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occur when the photon is absorbed by the water in an organism, ionizing the water. the resultant ions create free radicals, which produce changes in biologic molecules
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what percentage of interactions of photons with tissues are direct actions
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25-30%
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what percentage of interactions of photons with tissues are indirect actions
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70%
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indirect actions work via __________
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radiolysis of water
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what are the possible free radicals made by H2O? which is the most dangerous?
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H·, OH·, HO2·
OH· is the most dangerous |
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in what ways can peroxides be formed
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OH· + OH·
HO2· + H· |
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possible DNA alterations by radiation
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- breakage of one or both DNA strands
- cross-linking of DNA strands within the helix, to other DNA strands or proteins - change or loss of a base - disruption of H bonds between DNA strands |
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what determines the effects of radiation on a cell
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the point in cell division during which the cell is exposed to radiation
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what happens if the cell is exposed to radiation before s phase
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double arm (chromosome) abberation
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what happens if the cell is exposed to radiaiton after the s phase
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single arm (chromatid) abberation
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what is the main form of cancer caused by radiation
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leukemia
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name the 2 categories of biological effects of radiation
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- deterministic effects
- stochastic effects |
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deterministic effects
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severity of response is proportional to the dose
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stochastic effects
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the probability of the occurance of a change, rather than its severity, is dose-dependent
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examples of deterministic effects
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skin/oral changes in response to radiation therapy
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which type of biological effects has a threshold level
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deterministic effects
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example of stochastic effects
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radiation induced cancer
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which type of biological effects of radiation are all-or-none
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stochastic effects
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5 classifications of cell types based on radio-sensitivity
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1- vegetative intermitotic
2- differentiating intermitotic 3- multipotential connective tissue cell 4- reverting post mitotic 5- fixed post mitotic |
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vegetative intermitotic cells
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- divide regularly
- undifferentiated - |
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examples of intermitotic cells
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stem cells, spermatogenesis cells, basal cells
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differentiating intermitotic cells
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- divide less often
- some differentiation |
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examples of differentiating intermitotic cells
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cells of inner enamel epithelium, hematopoietic cells, spermatocytes, oocytes
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multipotential connective tissue cells
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divide irregularly in response to a need
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examples of multipotential connective tissue cells
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fibroblasts, vascular endothelial cells, mesenchymal cells
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reverting post mitotic cells
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- becoming radio-resistant
- divide infrequently - specialized cells - have reached a fair amount of maturity |
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examples of reverting post mitotic cells
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salivary glands - acinar, ductal cells, parenchyma - cells of the pancreas, kidney, liver, thyroid
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fixed post mitotic cells
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- don't divide
- fully differentiated - totally mature |
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examples of post mitotic cells
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skeletal muscle cells, neurons, mature keratinocytes, red blood cells
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organs that have a high susceptibility to radiation
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- lymphatics
- bone marrow - testes - mucous membranes |
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organs that have moderate suscepitibility to radiaiton
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- fine vasculature
- growing cartilage and bone - salivary glands - lungs - liver - kidney |
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organs that have a low susceptibility to radiation
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- optic lens
- red blood cells - skeletal muscle - neurons |
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what is worse: administer 5 g of radiation over one minute or over time in increments of 5 mg/min? why?
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5 g in one minute - if you do it in increments of smaller doses, you give the cells time to prepare themselves
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