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-blasts vs -cytes varies in radiosensitivity

Osteoblasts (undifferentiated)=highly radiosensitive, osteocytes (differentiated)=lower radiosensitivity

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Contains fibers that affect movement of an organ or part of the body

Since muscle tissue cells are highly specialized and do not divide, they are relatively insensitive to radiation

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Younger cells are more radiosensitive than older cells:

Immature Ova and Spermatogonia=MORE radiosensitive

Sex Cells= Spermatogonia (undifferentiated)=Highly radiosensitive, Spermatozoa (highly differentiated)=Lower radiosensitivity

Fetal nerve cells= maximum window of sensitivity is 8-15 weeks of gestation= MORE radiosensitive the younger they are

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Directly Proportional to Reproductive Activity

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Directly Proportional to Reproductive Activity

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Those that divide and multiply (reproduce) more rapidly are more radiosensitive.

Epithelial Cells= Continuously replaces at a rate of 2% per day (constantly regenerating)= More radiosensitive

Mature (developed) spermatazoa=do not divide so they are relatively insensitive to ionizing radiation

Young (immature) spermatogonia=divide rapidly and are extremely radiosensitive

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Inversely Proportional to Degree of Differentiation

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Inversely Proportional to Degree of Differentiation

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Simple cells (undifferentiated) cells are more radiosensitive than complex ones:

Nerve Cell=Highly differentiated=LEAST radiosensitive

Muscle Cell=differentiated=Low radiosensitivity

Erythrocyte=Differentiated=Lower radiosensitivity

Bone Cells=Osteoblasts (undifferentiated)=highly radiosensitive, osteocytes (differentiated)=lower radiosensitivity

Epithelial cell=Undifferentiated=intermediate radiosensitivity

Sex Cells= Spermatogonia (undifferentiated)=Highly radiosensitive, Spermatozoa (highly differentiated)=Lower radiosensitivity

Lymphocytes=Undifferentiated=MOST radiosenstive

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Those that use energy more rapidly are more radiosensitive.

Epithelial Cells= Continuously replaces at a rate of 2% per day (constantly regenerating)= Use more energy

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Male vs. Female germ cells differ in radiosensitivity

Male testes contain mature and immature spermatogonia

Since the mature (developed) spermatazoa are specialized and do not divide, they are relatively insensitive to ionizing radiation

The “young” immature spermatogonia are unspecialized and divide rapidly and are extremely radiosensitive

0.1Gy dose can depress sperm count and there is potential for genetic mutations

Dose of 2Gy may cause sterility for up to 12 months

Dose of 5-6Gy can cause permanent sterility

Mature female reproductive cells don’t divide constantly

Sensitivity varies throughout the lifetime of the germ cell

If fertilization of an ovum with  damaged chromosomes occur, hereditary damage can be passed onto the child=congenital abnormalities

Fetus/young child are very radiosensitive (stem cells and immature ova) and this decreases with age

20-30 years old is the least sensitive time in life

After 30, the overall sensitivity of the ovaries increases constantly until menopause because the new ova being destroyed are not replenished

Doses of 0.1Gy = menstrual irregularity

Doses of 2Gy = temporary sterility

Doses of 5Gy delivered in a single dose = permanent sterility

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Found in the brain and spinal cord

Relay messages to and from the brain (a message enters the nerve cell through the dendrites and passes through the cell body and exits the cell through the axon=message transmitted across a synapse leading to next nerve cell in the chain)

Radioresistant because they are highly specialized in adults, and do not divide or multiply

If nucleus destroyed = cell death and not replaced

If nucleus damaged = cell can function but it is impaired

If damage to dendrite/axon = disruption to communication and control in part of body (can be temporary or permanent)

Caveat=Fetal nerve cells are more radiosensitive than mature nerve cells of adults and can lead to congenital defects (maximum window of sensitivity is 8-15 weeks after gestation)

After this a lower level of elevated risk remains until week 25

0.1-Sv fetal EqD is associated with as much as a 4% chance of intellectual disability

A dose in excess of 50Gy of ionizing radiation may lead to death within a few hours or days

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Lines and covers body tissues

Highly radiosensitive= constantly regenerating

Continually renewing (interstitial lining renews appx 50% each day)

Crypts of Lieberkuhn (intestinal lining precursor cell) = Highly sensitive

Epidermis=Lowest layer basal cells=damage is first in the basal cells

Dermis=Hair follicles, sebaceous glands, sweat glands

Subcutaneous Layer=Fatty connective tissue

Continuously replaces at a rate of 2% per day

Relatively radiosensitive

Skin Response to radiation:

Erythema=Sunburn like reddening, damage to basal cells, moderate doses (2-10Gy), radiodermatitis

Desquamation=Ulceration, denudation, follows erythema at high doses, moist desquamation then dry

Skin Damage:

Epilation=Hair loss, temporary at low doses, can be permanent at high doses

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Thrombocytes (platelets) initiate blood clotting and have a life span of appx 30 days (prevent hemorrhage)

A dose of 0.5Gy or greater of ionizing radiation lessens the number of platelets in the circulating blood

A dose of 1Gy to 10Gy of ionizing radiation and these cells may become significantly depleted

Takes appx 2 months after being irradiated to go back to their original number (during this period wound clotting will be highly compromised)

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Neutrophils are another type of WBC and play an important role in fighting infection

A dose of 0.5Gy of ionizing radiation will reduce the number of neutrophils in circulating blood making a person susceptible to infection

When larger doses 2 to 5Gy are received these cells decrease in number to 10% or less within a few weeks of irradiation

Requires several months after exposure for the number of neutrophils to return to their original value

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Lymphocytes live only for 24 hours are manufactured in the bone marrow and are the most radiosensitive blood cells in the human body

Radiation doses as low as 0.25Gy is sufficient to depress the number of lymphocytes and doses from 0.5-1Gy can completely wipe out these cells and recovery can take months (count decreases to 0 in days)

When significant numbers are damaged by radiation exposure, the body loses its natural ability to combat infection and becomes susceptible to bacterial and viral antigens

GRANULOCYTES are scavenger WBC’s that live for less than a week, rapid drop and then a slower drop after ionizing radiation, recovery takes about 2 months

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Radiosensitivity varies greatly (cells are created, grow, divide and differentiate in bone marrow)

Erythroblasts are extremely radiosensitive, erythrocytes=LEAST radiosensitive of blood cells

Ionizing radiation adversely affects blood cells by depressing the number of cells in peripheral circulation (1st response)

A whole body dose of 0.25Gy delivered within a few days produces a measurable decrease in blood count

Radiation causes a decrease in the number of immature blood cells produced in bone marrow, hence a reduction in the number of mature blood cells in the bloodstream

Decrease # of immature blood cells --> less mature blood cells circulating

As older cells die, they are not replaced

Body had decreased ability to fight infections and blood clotting

The higher the radiation dose received by the bone marrow, the greater the severity will be of the resulting cell depletion

Due to the high number of circulating red blood cells and their long life span, depletion of red blood cells is usually not the cause of death in high dose irradiation

Death is typically caused by infection that cannot be overcome by the immune system because of the destruction of myeloblasts and internal hemorrhage

Can take weeks for recovery with exposure < 1Gy

Higher doses take longer

In extremely high doses, if the victim survives, the blood count may never return to normal

Humans who receive whole body +5Gy may die within 30-60 days because of the effects related to the initial depletion of the stem cells of the hematopoietic system

RBCs that have a 120 day life span (the longest life span of all blood cells) and that are the least sensitive of blood cells

Depletion of erythrocytes does not show up immediately

Lethal whole body dose for humans is generally estimated to be 3.0 to 4.0 Gy