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

• 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

• 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

• 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

Inversely proportional to degree of differentiation

• 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