PPT 4/3 Pt 1

Two Basic Cell Types

1. Genetic

2. Somatic

Genetic

Reproductive cells (germ cells)

Somatic

All other cells, non-reproductive cells

Basic Cell Structure

A. Nucleus

B. Cytoplasm

Nucleus

Contains DNA. The DNA is at risk when a cell is exposed to ionizing radiation.

Cytoplasm

80% water. It can undergo changes when struck by ionizing radiation.

Response of cells to radiation

• No damage. radiation may pass through cell without doing any damage.

• Damage may occur but be repaired.

• The damaged cell may reproduce in its damaged form. Ex. Cancer

• The cell may die.

Theories for Cellular Absorption of Ionizing Radiation

1. Direct Hit Theory

2. Indirect Hit Theory

Direct Hit Theory

Direct ionization of the DNA molecule, which may result in genetic damage.

Indirect Hit Theory

Radiation ionizes water which causes free radicals to form. Free radicals attack targets such as DNA. Much more common in x-ray and gamma. “Reggie”.

*In Xray most of the cell damage is the result of Indirect hits*

Target Theory of Absorption of Radiation

• applies to both Direct and Indirect hits

• All cells have key molecules to survive

• A cell with several key molecules will recover from radiation damage

• The cell w/ less key molecules will not have replacements to continue its normal function.

• The “target” is a critical molecule (nucleus of the cell) that has undergone some interaction w/ radiation (directly or indirectly)

• The key molecule is assumed to be DNA.

Law of Bergonie and Tribondeau

• est 1906

• The sensitivity of cells to radiation is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation.

Cell Sensitivity to Radiation Depends On

1. Differentiation

2. Age

3. Metabolic Rate

4. Mitotic Rate

Differentation

Complex cells are less sensitive (nerve cells) than stem cells (blood cells).

Age

The younger cells in tissues and organs, the more radiosensitive than older cells. Embryos, fetuses, and children.

Metabolic Rate

If the level of metabolic activity is high, radio-sensitivity is high than those with slower metabolism. GI cells and mouth tissue.

Mitotic Rate

Cells that multiply faster are highly sensitive to radiation than those cells that divide slowly. Children tissues vs. adult tissue.

Effects of Ionizing Radiation on Human Cells

• Blood Cells

• Epithelial Tissue

• Muscle Tissue

• Nervous Tissue

• Reproductive cell/Germ cells

Blood Cells

Hematopoietic or the blood forming system leukocytes/erythrocytes are the most sensitive of human tissues

Epithelial Tissue

Line and covers body tissue. This type of tissue is constantly regenerating therefore is highly radiosensitive.

Muscle Tissue

Highly specialized and do not divide. They are relatively insensitive to radiation.

Nervous Tissue

Highly specialized. Do not divide. They’re highly resistant to radiation.

Reproductive Cell/Germ Cells

HIGHLY sensitive