CHAPTER 3

Sensitivity of Various Organs of the Body

LEARNING OUTCOMES

At the end of the lesson, the student should be able to:-

• Explain factors which affect organ sensitivity.

• Explain cellular components

The Cell

• Three Main Parts: 1. Cell Membrane 2. Cytoplasm 3. Nucleus

• Cell Membrane – Protects the cell, holds water/nutrients and is semipermeable.

• Cytoplasm – Composed mostly of water, Conducts cell metabolism, and contains organelles.

Organelles 1. Centrosomes – Participate in cell division.

2. Ribosomes – Synthesize protein.

3. Lysosomes – Intracellular digestion.

4. Mitochondria – Produce energy.

5. Golgi Apparatus – Combines proteins & carbohydrates.

6. Endoplasmic Reticulum – Moves food/molecules in cell.

• Nucleus – Contains DNA and RNA – DNA controls cell function.

Law of Bergonie’ and Tribondeau

It was developed in 1906 by two French radiobiologist, Bergonie’ and Tribondeau

It offers a prediction about the relative sensitivity of two different types of cells or tissues to radiation

Law of Bergonie’ and Tribondeau

It states that the radiosensitivity of cell is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation.

Cells most active in reproducing themselves and cells not fully mature will be most harmed by radiation.

The more mature and specialized in performing functions as cell is, the less sensitive it is to radiation.

More radiosensitive cells

Cells that have a high division rate

Cells that have a high metabolic rate

Cells that are of a non-specialized type

Cells that are well nourished

Sensitivity – Cell Cycle Phase

Cells are most sensitive to radiation during mitosis (M phase) and RNA synthesis (G2 phase)

Less sensitive during the preparatory period for DNA synthesis (G1 phase)

Least sensitive during DNA synthesis (S phase)

During mitosis (M), the metaphase is the most sensitive

Radioresistant cells

Bone

Liver

Kidney

Cartilage

Muscle

Nervous tissue

Radiosensitive cells

Germinal cells

Lymphoid tissues

basal cells

Hematopoietic tissues

Epithelium of the GI tract

Gonads are very radiosensitive

Females

Temporally sterility 1.5 Gy (150 rad)

Permanent sterility 5 Gy (500 rad)

Males

Temporally sterility 2.5 Gy (250 rad)

Permanent sterility 6 Gy (600 rad)

Pregnancy and minors

Children could be expected to be more radiosensitive than adults

fetuses more radiosensitive than children and embryos even more in the first weeks of pregnancy when organs are forming

Radiosensitivity of various cell types

Radiosensitivity Cell type

Low nerve cell

muscle cells

Intermediate osteoblast,endothelial

cells,fibroblast,spermatids

spermatogonia,

lymphocytes, stem cells,

High intestinal mucosa cells and

erythroblast

Questions

1. The law of Bergonie and tribondeau states that the radiosensitivity of cell is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation.

2. Those cells with a low metabolic rate are more radiosensitive.

3. Cells are more sensitive during meiosis phase.

4. Gonads are very radiosensitive cells

5. List four of the radioresistant cells.

Answer

1. True

2. False

3. False

4. True

5. bone, liver, kidneys, muscles