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Rad Protection Ch.7
Molecular & Cellular Radiation Biology
| Question | Answer |
|---|---|
| Radiation Biology | The branch of biology concerned with the effects of ionizing radiation on living systems. |
| LET | - The amount of energy transferred on average by incident radiation to an object per unit length of track through the object. - It is expressed in units of keV/um (kiloelectron volts per micron). |
| Low LET Radiation | - X-rays and gamma rays are considered low LET. - Does not ionize much tissue. - Causes damage through indirect action. - Repair enzymes can usually repair damage caused from ____________ radiation. |
| Low LET | For an electron, several interactions may occur in the vicinity of a DNA strand, creating a risk of damage to the DNA. |
| High LET Radiation | - Alpha particles, ions of heavy nuclei, charged particle released from interactions between neutrons and atoms and low energy neutrons, which carry no electrical charge are examples. - More destructive than low LET. |
| High vs. Low | - Radiations with high LET can not penetrate deeply, but cause substantial damage over a short distance. - High LET energies produce MUCH more ionization per unit of distance traveled. |
| High LET | Because so many interactions may occur in the vicinity of a DNA strand, some damage is likely. |
| What kind of LET does x-rays have? | - X-rays and gamma rays are considered low LET. - Does not ionize much tissue. - Causes damage through indirect action. |
| Relative Biologic Effectiveness (RBE) | Describes the relative capabilities of radiation with differing LET's to produce a particular biologic reaction. |
| RBE = | Dose in Gy from 250 kVp x-ray (reference radiation). OVER Dose in Gy of test radiation. |
| Oxygen Enhancement Ratio (OER) | A ratio of the radiation dose required to cause a particular biologic response of cells or organism in any oxygen-deprived environment to the radiation dose required to cause an identical response under normally oxygenated conditions. |
| What is the significance of OER? | - When oxygen is present in the cell, free radicals can be produced. - Cause oxygen fixation. |
| Oxygen Fixation | When oxygen is present, the damage created can not be repaired. |
| Are cells more radio-resistant in the presence of oxygen? | No, oxygen makes cells more radiosensitive. |
| Molecular effects of irradiation | In living systems biologic damage resulting from exposure to ionizing radiation may be observed on three levels: - Molecular. - Cellular. - Organic. |
| Somatic cells | - Cells in the body with the exception to male and female germ cells. - Radiation may cause a disturbance in the cell's chemical balance and the way the body operates. |
| Germ Cells | - Male and female reproductive cells. - Radiation may affect future generations by passing on mutations in cells. |
| Direct Action | Interaction with DNA molecules. |
| Indirect Action | Interaction with water molecules. |
| Radiolysis of Water | - Ionization of water molecules. - Production of free radicals. - Production of undesirable chemical reactions and biologic damage. - Production of cell-damaging substances. - Organic free radical formation. |
| Indirect Action | The effect of free radicals created by the interaction of radiation with water molecules. Cell death can result. |
| Effects of Ionizing Radiation on DNA: | - Single strand breaks. - Double strand breaks. - Double strand break in the same rung. - Mutation. - Covalent cross links. |
| Single | - Strand Break in the ladder-like DNA molecular structure. - Called a point mutation. |
| Double | - Strand break in the ladder-like DNA molecular structure. - Strand break in the same rung of the DNA laddler-like molecular structure. - Causes complete chromosome breakage resulting in a cleaved or broken chromosome.. |
| Mutation | Changes in genes caused by the loss or change of a base in the DNA chainn |
| Covalent Cross-Links | - Chemical unions created between atoms by the single sharing of one or more pairs of electrons. - Molecules link where they should not. |
| Effects of Ionizing Radiation on Chromosomes: | - Radiation-induced chromosome breaks. - Chromosomal fragments. - Chromosome anomalies. - Chromosome aberrations. - Chromatid aberrations. - Structural changes in biologic tissue. |
| Which type of interaction is more deadly to the cell, Direct or Indirect? | - Direct will cause cell death more readily. - Indirect action may cause cell death however cells are equipped to repair themselves after certain typed of indirect actions. |
| Target Theory: Master, or Key, Molecule | A master, or key, molecule that maintains normal cell function is believed to be present in every cell. |
| Target Theory | - Master, or key, molecule is necessary for the survival of the cell. - Target theory may be used to explain cell death and nonfatal cell abnormalities caused by exposure to radiation. |
| Instant Death | Occurs when a volume is irradiated with an x-ray or gamma dose of about 1000 Gy in a period of seconds or a few minutes. It causes cell DNA to break up. Much higher than x-ray energy. |
| Reproductive Death | - Results from exposure of cells to moderate doses of 1 to 10 Gy or 100 to 1000 rad). - Cell does not die just loses its ability to procreate. - Prevents transmission of damage to future generations. |
| Apoptosis, or Programmed Cell Death | - Occurs spontaneously in normal tissue and tumors. - Cells do not attempt to divide. - Certain types of cells die for the good of the organism. |
| Mitotic, or Genetic, Death | - It may retard or inhibit mitotic process. - Cell death follows permanent inhibition. - Death occurs when a cell dies after one or more divisions. - Small doses of radiation can cause this. |
| 1.Mitotic Delay | - Failure of the cell to start dividing on time. - After delay cell may resume normal function reasons for delay. ~ Irradiation causes an alteration of the mitotic chemicals. |
| 2.Mitotic Delay | ~ Proteins required for division are not synthesized. ~ A change in the rate of DNA synthesis. |
| Interference with function | - Radiation can cause permanent or temporary interference of cellular function independent of the cell's ability to divide. - If repair enzymes can fix the damage, the cell can recover and continue to function. |
| Cell Maturity and Specialization | Immature cells (undergo rapid division) are more sensitive than mature cells (highly differentiated). |
| Cell Radiosensitivity | - Cell maturity and specialization. - The human body is composed of different types of cells and tissues, which vary in their degree of radiosensitivity. |
| Reproductive Cells | - Relatively radiosensitive. - Mature spermatogonia-insensitive. - Immature spermatogonia-extremely radiosensitive. - Mature female germ cells-ova- insensitive. - Immature ova-radiosensitive. |
| LET | As _______ increases the ability of the radiation to cause biologic effects also increases. |
| OER | The more oxygen present, the more radiosensitive the cell is. |
| Law of Bergonie and Tribondeau | Radiosensitivity of cells is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation. |
| Which types of cells are more radiosensitive? | - Cells that are rapidly dividing. - Cells that are immature. |
| Hematologic Depression | Radiation depresses the number of cells in the peripheral circulation. |
| Depletion of Immature Blood Cells | Radiation causes a decrease in the number of immature blood cells produced in the bone marrow and hence a reducation of the number of mature blood cells. |
| Repopulation after a period of recovery | If blood cells have not been completely destroyed, they can recover and repopulate after a period of time. |
| Neutrophils | - White blood cell responsible for fighting infection. - 0.5 Gy (50 rads) can cause a reduction with months of recovery. |
| Granulocytes | - A scavenger type of white blood cell that fight bacteria. - They only remain circulating in blood a few days with months of recovery. |
| Thrombocytes | - Type of white blood cell that initiate blood clotting and prevents hemorrhage. - 30 day life span. Normal platelet count is 150,000 to 350,000. .5Gy (50 rads) affects number with months of recovery. |
| Radiation exposure during diagnostic radiologic procedures | Most damage is from circulating lymphocytes that receive radiation. |
| Monitoring of patients undergoing radiation therapy treatment | Radiation therapy can cause the white blood count to decrease, the patient must be monitored. |
| Occupational radiation exposure monitoring | Blood counts may be performed if indicated. |
| Epithelial Tissue | - Lines and covers body tissue. - Highly radiosensitive. |
| Muscle Tissue | Not very radiosensitive b/c highly differentiated. |
| Nervous Tissue | Adult - not radiosensitive. Fetus - more radiosensitive. |
| Reproductive Cells | Spermatogonia & Ova. |
| Consequences to the Cell from Structural Changes Within the Nucleus: | - Restitution. - Deletion. - Broken-end rearrangement producing grossly misshapen chromosomes. - Broken-end rearrangement without visible damage to the chromatids. |
| Indirect Action | Means damage that is done to areas other than the DNA such as free radical production of hydrogen peroxide. Mostly in the cytoplasm. |
| Apoptosis | A non-mitotic or non division form of cell death that occurs when cells die without attempting division during the interphase portion of the cell life cycle. Also known as programmed cell death (formerly called interphase death). |
| Cell Survival Curve | Amethod of displaying the sensitivity of a particular type of cell to lethal effects of radiation. |
| Chromosome Breakage | The breaking of one or both of the sugar-phosphate chains of a DNA ladder-like structure, which is a potential outcome when ionizing radiation interacts with a DNA molecule. |
| Free Radicals | Solitary atoms, or most often a combination of atoms, that are very chemically reactive as a result of the presence of unpaired atoms. |
| Oxygen Enhancement Ratio Point Lesion (OER | The ratio of the radiation dose required to cause a particular biologic response of cells or organisms in any oxygen-deprived environment to the radiation dose required to cause an identical response under normally oxygenated conditions. |
| Radiation Weighting Factor (WR) | Adimensionless factor (a multiplier) that was chosen for radiation protection purposes to account for differences in biologic impact among various types of ionizing radiations. This factor places risks associated with biologic effects on a common scale. |
| Wave-Particle Duality | Electromagnetic radiation can travel and interact with matter in the form of a wave or a particle. For this reason, x-rays may be described as both waves and particles. |
| The _______________ is the most radiosensitive to all radiographic procedures. | Embryo. |
| 1.Hematopoietic System | Stem cells are the primary cells affected. Erythrocytes are most sensitive, but they have such a big population with a long life span that a decrease in these does not cause death. |
| 2.Hematopoietic System | Death is usually caused from an infection not fought well by the immune system or internal hemorrhage. |
| 1.Lymphocytes | They defend the body against antigens by producing antibodies to fight disease. |
| 2.Lymphocytes | They only live 24 hours, that is the shortest life span of all blood cells. Most radiosensitive blood cells in body. .25 Gy (25 rads) depresses the number. Normal wBC count is 5000 to 10000/mm3 of blood. Full recovery takes several months. |
| 1.Brain and Spinal Cord: | - 50 Gy (5000 rads) - Fetus may lead to central nervous system anomalies. - A lower level risk remains until week 25. |
| 2.Brain and Spinal Cord: | - Highly specialized in the adult . - Nerve cells contain a nucleus, so if one is destroyed the cell dies and is never restored. |
| 1.Because the mature spermatogonia are specialized and do not divide: | -They are insensitive to radiation. - To prevent mutations from being passed on to offspring, males receiving this level of testicular radiation dose should refrain from unprotected sex for a few months after exposure. |
| 2.Because the mature spermatogonia are specialized and do not divide: | -Immature are unspecialized and divided rapidly and are extremel radiosensitive. - 2 Gy (200rads) may cause temporary sterility for 12 months 5 or 6 Gy (500 to 600 rads) may cause permanent sterility. |
| 1.Ova mature female germ cells | -Do not divide constantly. -Post puberty one of two ovaries expel a mature ovum about every 28 to 36 days. -Radiation can cause female sterility. Temporary sterility 2 Gy (200 rads) to the ovaries. |
| 2.Ova mature female germ cells | - Advised to postpone attempting conception for 30 days or more to allow the immature ova to be expelled. - All the _____ a woman will ever possess are present at birth until the time they are fertilized or expelled. |
| Chromosome Aberrations | Lesions that result when irradiatoin occurs early in interphase, before DNA synthesis takes place. |
| Chromatid Abberations | Lestions that results when irradiation of individual chromatids occurs later in interphase, after DNA synthesis has taken place. |
| Oxygen Fixation Hypotheses | When oxygen is present, the damage created can not be repaired. |
| Free Radicals | A solitary atom or a combination of atoms that behaves as an extremely reactive single entity as a result of the presence of an unpaired electrons. They increase the amount of biological damage that may be produced. |
| High LET Radiation | Do not travel far because they loose all of their energy in the length they do travel. |
| Low LET Radiation | Travel a long way but do not cause much damage. |
| Restitution | Whereby the breaks rejoin in their original configuration with no visible damage. |
| Deletion | A part of the chromosome or chromatid is lost at the next cell division, thus creating an aberration known as an eccentric fragment and results in a cell mutation. |
| Broken-End Arrangement | A grossly misshapen chromosome may be produced. This results in a cell mutation. Ex) ring chromatids, dicentric chromosomes, anaphase bridges, and chromatids. |
| Broken-End rearrangement without visible damage to the chromatids | The chromatid's genetic material has been rearranged even though the chromatid appears normal. This results in a cell mutation. Ex) translocations. |
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