chapter 5 Flashcards
x rays have the ability to detach and remove electric charges from the complex atoms that make up the molecules of body tissues; delicate balance of structure is altered, and a cell may be damaged or destroyed
ionization
what are the two theories for how radiation damages biological tissues
direct and indirect
one third of biological alterations from x radiation exposure result from a direct effect; most dental x ray photons probably pass through a cell with little or no damage
direct theory
x ray photons collide with important cell chemicals and break them apart by ionization, causing critical damage to large molecules; a healthy cell can repair any minor damage that might occur
direct theory
based on the assumption that radiation can cause chemical damage to a cell by ionizing the water within it; before it enters the cell
indirect theory
two thirds of biological alterations from x radiation exposure result from___ effects
indirect
radiolysis of water
indirect theory
indicates threshold amount of radiation, below which no biological response would be expected
threshold dose response curve
indicates that any amount of radiation, no matter how small, has the potential to cause a biological response
non threshold dose response curve
As low as reasonably achievable
ALARA
sequence of events following radiation exposure
latent period , period of injury recovery period
following initial radiation exposure, and before the first detectable effect occurs
latent period
follows latent period stoppage of mitosis breaking or clumping chromosomes abnormal mitosis formation of multinucleated cells associated with cancer(giant cells; large tissue clumped together, could be cancerous)
period of injury
following exposure to radiation, recovery can take place(short term effects);
may be a certain amount of damage from which no recovery occurs(later or long term effects)
recovery period
greater dose, more severe the probable biological effect
total dose
a given dose will produce less effect if it is divided than if it is given in a single exposure
dose rate
larger exposure area, greater injury
area exposed
LD50/30
the lethal dose, dose required to kill 50 % of the individuals in a large population in a 30 day period
most sensitive to radiation
lymphocytes and blood forming cells reproductive cells
moderately sensitive to radiation
GI tract, skin cell, and lens of the eye
least sensitive to radiation
mature bone, cartilage, nerve, brain, and muscle cells
when the severity of the change is dependent on the dose
deterministic(nonstochastic) effect
when a biological response is based on the probability of occurence rather then the severity of the change; when dose of radiation is increased, the probability of the stochastic effect occurring increases, but not its severity
stochastic effect
occurs when a biological change or damage occurs in the irradiated individual, but is not passed along to offspring(all except reproductive cells)
somatic effect
describes changes in hereditary tissues that do not manifest in the irradiated individual, but show up in the individuals offspring
genetic effect
when a very large dose of radiation is delivered in a very short period of time, the latent period is____
short
ARS
acute radiation syndrome
symptoms for ARS
erythema, nausea vomiting diarrhea hemorrhage hair loss
primary risk from dental radiography is a ____ effect
stochastic
critical tissues for dental radiography
skin of head and neck
bone marrow in mandible
thyroid gland
