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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 Low Intermediate High Cell type nerve cell muscle cells osteoblast,endothelial cells,fibroblast,spermatids spermatogonia, lymphocytes, stem cells, 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. 2. 3. 4. 5. True False False True bone, liver, kidneys, muscles