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🔴 High Sensitivity

Lymphocytes (WBCs)

Erythroblasts (immature RBCs)

Bone marrow cells (hematopoietic stem cells) – highly mitotic; produce all blood cells

Oocytes (immature female cells) – developing germ cells

Spermatogonia (male stem cells) – divide continuously to form sperm

Epithelial cells (ex. skin)

Skin basal cells - regenerate the epidermis

🟠Moderate Sensitivity

Endothelial cells - line blood vessels

Neutrophils (type of WBCs)

Thrombocytes (platelets)

Glands (ex. thyroid, pancreas)

Osteoblasts (bone forming)

🔵Low Sensitivity

Ova (mature female cells)

Spermatozoa (mature male cells)

Erythrocytes (mature RBCs)

Muscle cells

Adult Nerve cells

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Hematopoietic Stem Cells (In bone marrow)

Very radiosensitive

Rapidly dividing throughout life

Undifferentiated precursor cells

High metabolic rate because of the continuous cell turnover

Repopulation after exposure:

<1 Gy --> a few weeks

1-10 Gy --> much longer

WBD 5 Gy --> death of the individual within 30-60 days

Erythrocytes (RBC)

Carries O2 to tissues & organs

Cells live for 120 days

Mature cells have no nucleus

Low metabolic rate

Radioresistant

Lymphocytes

Most radiosensitive blood cell

Cells live for 24 hours

Whole body dose (WBD)

0.25 Gy --> noticeable decrease in cells --> recovery possible shortly after exposure

0.5 to 1 Gy --> cell count goes to zero in days --> recovery in months

Significant reduction to these cells --> body more susceptible to infection

Neutrophils

Type of WBC; help w/ fighting infections

WBD of 0.5 Gy reduces # of cells

2-5 Gy reduce to 10% or less within weeks - takes months to return to original #

Thrombocytes (platelets)

Involved in blood clotting

Limited metabolic activity

>0.5 Gy reduces # of platelets

1-10 Gy significantly affects #s - takes 2 months to repopulate - clotting function compromised

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Primordial follicle --> mature follicle --> corpus luteum --> ovum

Mature female germ cell - Don't divide & lower metabolic rate

Radiosensitivity varies considerably throughout the lifetime of the germ cell

Immature ova --> very radiosensitive

Mature ova --> more radiosensitive

Fetal & child cells are immature and sensitive

20–30-year-old females have cells that are the most radioresistant

Damage to chromosomes in these cells --> potential mutations for future generations

Single 2 Gy dose --> temporary sterility

Single 5 Gy dose --> permanent sterility

Low LET 0.1 Gy --> menstrual irregularities

Fractionated dose of up to 20 Gy --> repair still possible

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Spermatogonia (male stem cell) --> spermatocyte --> spermatid --> sperm

Immature cells --> very radiosensitive

Mature cells --> more radioresistant

Constantly dividing w/ a high metabolic rate

0.1 Gy --> reduces sperm #s --> may have mutations for future generations

2 Gy --> 12 months of temporary sterility

5 -6 Gy --> permanent sterility

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Adults

Highly specialized

Don't divide & low metabolic rate

Radioresistant

Exposure to nucleus --> destruction or damage --> cell death or impairment

Embryo/Fetus

Much more radiosensitive than adult nerve cells

Nerve cells are maturing and dividing & higher metabolic rate

Exposure to embryo --> CNS anomalies, microcephaly & intellectual disabilities

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Highly specialized

Don't divide --> low mitotic rate

Moderate metabolic rate

Radioresistant

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The Law of Bergonie & Tribondeau

4 Tenets

1. Age

Mature cells vs. immature cells

Immature cells more radiosensitive

2. Differentiation

Undifferentiated cells more radiosensitive

3. Mitotic Rate

- High mitotic rate --> rapidly dividing --> more radiosensitive

4. Metabolic Rate

- High metabolic activity --> use energy rapidly --> more radiosensitive

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How radiosensitive a cell is depends on its metabolic state

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Directly proportional to reproductive activity

Inversely proportional to degree of differentiation

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Law applied initially to germ cells but true for all types.

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Found in: skin, intestinal lining

Rapidly dividing

Metabolically active (continuous cell turnover)

Highly radiosensitive