Radiation Biology: Ch. 7 pg. 122-136

what is the target theory

• DNA is irreplaceable master molecule which serves as the target

• each cell is believed to contain a sensitive master cell or key molecule which maintains normal cell function

• necessary for the survival of the cell

what type of effects can the target be struck by

direct or indirect effects, radiation does not seek out to destroy it but interacts with molecule only by chance

for the cell to die, the _____ must be inactivated

target (can be single or multiple hits)

six adverse effects of irradiation:

1. instant death

2. reproductive death

3. apoptosis or programmed cell death

4. mitotic, or genetic death

5. mitotic delay

6. interference of function

when does instant death occur

when a large number of cells are irradiated with a dose of about 1000Gyt in a period of seconds or few minutes

what happens when instant death occurs in a cell

• causes gross disruption of cells form and function

• DNA macromolecules break up

• cellular proteins coagulate

what does dose does reproductive death occur at

cellular dose between 1-10 Gy

what happens to the cell when reproductive death occurs

• the cell does not die, it permanently looses its ability to reproduce, it will try and fail

• the cell continues to live and metabolize and synthesis nucleic acids and proteins

why does reproductive death occur

prevents the transmission of damage to future generations of cells

apoptosis was formerly called:

“programed cell death”

when does apoptosis occur

when a cell that has been irradiated dies without attempting division during interphase

what governs the dose required to cause apoptosis

the radiosensitivity of the cell

when does mitotic or genetic death occur

• when a cell dies after one or more divisions after irradiation

• can be caused by small doses of radiation

how much dose is required to cause mitotic delay

0.01Gyt of ionizing radiation

T or F: after mitotic delay the cell can return to normal mitotic function

True

what is interference of function

• permanent or temporary interference of cellular function independent of the cells ability to divide

• if repair enzymes can fix damage, the cell can recover and continue to function

a classic method of displaying the sensitivity of a particular type of cell to radiation, usually demonstrates both high and low LET radiation exposures

cell survival curves

the ease with which living tissue can be damaged by radiation

cell radiosensitivity

immature cells are _______ radiosensitive than mature cells

more radiosensitive

non specialized, undifferentiated, undergo rapid cell division

immature cells

specialized in their function, highly differentiated, divide at slow rate or do not divide at all

mature cells

oxygenation increases or decreases radiosensitivity?

increases

states the radiosensitivity of cells is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation

Law of Bergonie and Tribondeau

what does the Law of Bergonie and Tribondeau mean:

• stem cells are most radiosensitive

• more mature cells are more radio-resistant

• the younger the tissue and organs, the more radiosensitive they are

• the higher the rate of metabolic activity, the greater the radiosensitivity

• the greater the proliferation of cells, the greater the radiosensitivity

high radiosensitive cells

• lymphocytes/erythrocytes

• erythroblasts

• intestinal crypt cells

• basal skin cells

intermediate radiosensitive cells:

• endothelial cells

• osteoblasts

• spermatids

• fibroblasts

low radiosensitive cells:

• nerve

• brain

• muscle

what dose will decrease blood count within a few days

0.25Gyt (whole body)

how does radiation affect blood cells

adversely effects blood cells by depressing the number of cells in the peripheral circulation

what does will produce measurably hematologic depression within a few days

0.25Gyt

where are most blood cells manufactured

bone marrow

which types of cells rad exposure lessens with age and as they age lose their nucleus making it mature

red blood cells “erythrocytes”

function to transport oxygen and carbon dioxide through the blood stream

red blood cells

depletion as a result of radiation exposure can cause _____

anemia

_________ are among the most sensitive of the human tissues

erythrocytes

LD stands for:

lethal dose

what is the LD 50/30

LD 50/30 is the dose that produces 50% cell death of subjects within 30 days

-top number represents the percentage of the population that will die

-bottom number represents within how many days

human beings have a whole body dose of _______ without treatment

3.0-4.0 Gyt

defends against disease, only live for 24 hours (shortest life span of blood cells)

lymphocytes

are the most radiosensitive blood cells in the body

lymphocytes

what happens when a significant number of lymphocytes are damaged

the body looses its natural ability to combat infection and becomes susceptible to bacterial and viral antigens

at ____ Gyt the number of lymphocytes decreases slightly, at a dose of ____ the lymphocyte count will decrease to 0 within a few days

<0.25Gyt, 0.5-1Gyt

another form of WBC, helps fight infection

neutrophils

____Gyt will noticeably reduce the number of neutrophils circulating in the blood, ____Gyt will decrease number to less than 10% within a few weeks

0.5Gyt, 2-5Gyt

also known as platelets, initiate blood clotting and prevent hemorrhage, have a life span of 30 days

thrombocytes

____Gyt will lessen the number of platelets, at ____ Gyt cells only begin to regain their number after 2 months

0.5Gyt, 1-10Gyt

lines and covers body tissue, lie close together with little or no substances between them, and contains no blood vessels

epithelial tissue

how does epithelial tissue regenerate

mitosis

where is epithelial tissue found

lining of intestines, mucous lining of respiratory tract, in pulmonary alveoli, lining blood and lymphatic vessels

is epithelial tissue high or low radiosensitive

high

highly specialized cells that do not divide, insensitive to radiation

muscle tissue

where is nervous tissue found

in brain and spinal cord

does nervous tissue divide

no

what happens to nervous tissue when the nucleus is destroyed

cell will die and is never restored

what happens to nervous tissue when the nucleus is damaged

the cell may still function, but may be impaired

exposure of ____ Gyt can lead to death within a few hours or days in nervous tissue

50Gyt

when are nervous tissues the most critical

during organogenesis, when the nerve cells of the brain and spinal cord are developing

what type of congenital abnormalities can be caused by nervous tissue damage

spina bifida, hydrocephalus, microcephaly, and intellectual disability

what is the window of maximal sensitivity for nervous tissue damage in an embryo

8-15 weeks

how much fetal EqD is associated with as much as 4% of risk of intellectual disability

0.1 Sv fetal EqD

do human germ cells have high or low radiosensitivity

high

why do human germ cells sensitivity depend on if they are male or female

vary with the process of development from immature to mature cells

T or F: male germ cells contain both immature and mature cells

True

dose of _____ may cause temporary sterility (as long as 12 months) in male germ cells

2Gyt

dose of ____ may cause permanent sterility in male germ cells

5-6Gyt

dose as low as ____ may depress the number of sperm population

0.1Gyt

why must procreation be delayed for at least a few months after exposure to male germ cells

dose of 0.1Gyt or more may cause genetic mutation in future generations, prevents mutations from being passed down

what type of germ cell does not divide continuously

ova (female)

mature ovum is expelled every_____ days and have very ____radiosensitivity

28-36, little

after exposure a mature ovum can unite with a male germ cell, but it may contain ________

damaged chromosomes

a dose of ___ can cause temporary sterility in female germ cells

2 Gyt

a dose of ___ generally causes permanent sterility in female germ cells

5 Gyt

dose of ___ may cause menstrual irregularities such as a delay or suppression

0.1 Gyt

after an exposure of 0.1Gyt, what are women advised to do

postpone attempting conception for 30 days or more to allow the damage immature ova to be expelled

T or F: female germ cells sensitivity is age dependent

True

women between the ages of ___ and ___ are at the lowest level of sensitivity

20 and 30

why do women over the age of 30, until menopause, ovum have the greatest net sensitivity

there are no new ova to replace those being destroyed