Lecture_2.pptx

Radiobiology & Protection RMI 212 Lecture 2 CELLULAR EFFECTS OF RADIATION Slide 1 fchs.ac.ae Review of Cell Biology Cell structure: The cell can be divided onto two major sections: the nucleus and the cytoplasm surrounded by the ce...

Radiobiology & Protection RMI 212 Lecture 2 CELLULAR EFFECTS OF RADIATION Slide 1 fchs.ac.ae Review of Cell Biology Cell structure: The cell can be divided onto two major sections: the nucleus and the cytoplasm surrounded by the cell membrane. The cytoplasm is the site of metabolism, but the nucleus supervises and coordinates cytoplasmic activities. fchs.ac.ae Review of Cell Biology Cytoplasmic organelles : Cell membrane. Endoplasmic reticulum. Ribosomes. Mitochondria. Lysosomes. Golgi complex. Nuclear structures: Nuclear envelope. Chromosomes. DNA fchs.ac.ae Review of Cell Biology Cytoplasmic organelles : Cell membrane. Endoplasmic reticulum. Ribosomes. Mitochondria. Lysosomes. Golgi complex. Nuclear structures: Nuclear envelope. Chromosomes. fchs.ac.ae Review of Cell Biology fchs.ac.ae Review of Cell Biology fchs.ac.ae Cell Division: : It is the multiplication process, whereby one cell forms two or more cells. There are two types of cell division: A. Mitosis: the method by which somatic cells divide. B. Meiosis: the method by which germ cells (gametes) divide. fchs.ac.ae Mitosis It is divided into four phases: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase fchs.ac.ae  Meiosis It is a specialized type of cell division that reduces the number of chromosomes in the oocyte and spermatozoa from the diploid number (2n) to the haploid number (n). It has the same phases as in mitosis. At the end of telophase, the original “parent” germ cell has formed two daughter cells with 2n number of chromosomes. These daughter cells now undergo a second division, and the consequence is four gametes, each containing the haploid number of chromosomes. fchs.ac.ae Meiosis fchs.ac.ae Course: FRD1011 Radiologic Physics & Radiation Protection Lecture 1: Essential Concepts of Radio Slide 11 fchs.ac.ae Course: FRD1011 Radiologic Physics & Radiation Protection Lecture 1: Essential Concepts of Slide 12 fchs.ac.ae Course: FRD1011 Radiologic Physics & Radiation Protection Lecture 1: Essential Concepts of Radio Slide 13 fchs.ac.ae DNA Deoxyribonucleic acid DNA: is a molecule that encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses. The two DNA strands are known as polynucleotides since they are composed of simpler units called nucleotides. Each nucleotide is composed of a nitrogen- containing nucleobase—either guanine (G), adenine (A), thymine (T), or cytosine (C)—as well as a monosaccharide sugar called deoxyribose and a phosphate group. fchs.ac.ae  DNA The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. According to base pairing rules (A with T and C with G), hydrogen bonds bind the nitrogenous bases of the two separate polynucleotide strands to make double-stranded DNA. Within cells, DNA is organized into long structures called chromosomes. During cell division these chromosomes are duplicated in the process of DNA replication, providing each cell its own complete set of chromosomes fchs.ac.ae DNA Effects Single strand break Double-Strand Break Double-Strand Break in Same Rung of DNA Mutation fchs.ac.ae  Single-Strand Break This type of injury to DNA is called a point mutation Point mutations commonly occur with low-LET radiations cell are capable of reversing this damage. fchs.ac.ae Double-Strand Break Double-strand breaks occur more commonly with densely ionizing (high-LET) fchs.ac.ae Double-Strand Break in Same Rung of DNA the result is a cleaved or broken chromosome This will culminate in the death or impaired functioning of the new daughter cell. fchs.ac.ae DNA Damage fchs.ac.ae  Cell Radiosensitivity Radiosensitivity is the relative susceptibility of cells, tissues, organs, organisms, or other substances to the injurious action of radiation. In general, it has been found that cell radiosensitivity is directly proportional to the rate of cell division and inversely proportional to the degree of cell differentiation. In short, this means that actively dividing cells or those not fully mature are most at risk from radiation. As stated previously in the Law of Bergonie and Tribondeau. Immature cells are significantly more radiosensitive than are mature cells. fchs.ac.ae The most radio-sensitive cells are those which: 1. have a high division rate 2. have a high metabolic rate 3. are of a non-specialized type 4. are well nourished fchs.ac.ae The Relative Radiosensitivity Of The Cells In The Body Fully differentiated, functional and non-dividing cells (e.g, nerve cells, muscle cells) are radioresistant Partially differentiated cells that can be called upon to divide again (e.g., liver cells, glandular cells) are somewhat less radio resistant Cells which can divide but lend support to the other cells in a tissue (e.g. endothelial cells lining the blood vessels, fibroblasts of the connective tissue) are intermediate in radio sensitivity fchs.ac.ae  Relative cell Radiosenstivity Dividing cells which start to differentiate (e.g., myelocytes, spermatocytes) are fairly radiosensitive. Continuously dividing stem cells (such as found in the bone marrow, the intestine, the skin, and the testes) are very radiosensitive. If not killed, these stem cells can rapidly allow the tissue and organ to recover. Two cell types not in the last category, but which are very radiosensitive, are the oocyte and the small lymphocyte (whose death will have immediate negative impact on the immune system) fchs.ac.ae  Radioresistant cells  Bone  Liver  Kidney  Cartilage  Muscle  Nervous tissue fchs.ac.ae Radiosensitive cells  Germinal cells  Lymphoid tissues fchs.ac.ae  Cell Radiosensitivity Examples of various tissues and their relative radiosensitivities are listed below: High Radiosensitivity Lymphoid organs, bone marrow, blood, testes, ovaries, intestines Fairly High Radiosensitivity Skin and other organs with epithelial cell lining (cornea, oral cavity, esophagus, rectum, bladder, vagina, uterine cervix, ureters) Moderate Radiosensitivity Optic lens, stomach, growing cartilage, fine vasculature, growing bone Fairly Low Radiosensitivity Mature cartilage or bones, salivary glands, respiratory organs, kidneys, liver, pancreas, thyroid, adrenal and pituitary glands Low Radiosensitivity Muscle, brain, spinal cord fchs.ac.ae