Biological effects of ionizing radiation THE INITIAL STAGES

Biological effects of ionizing radiation

THE INITIAL STAGES OF THE DEVELOPMENT OF RADIATION INJURY The main property of ionizing radiation causes its biological (including lethality) action - the ability to penetrate into various tissues, cells and subcellular structures, causing a transition to the excited state of the atoms and molecules biosubstrate up to their ionization.

At the core of the primary radiation-chemical changes in molecules based on two mechanisms: Direct action, when the molecule is damaged by direct interaction with radiation. Indirect action when the molecule gains energy by transferring from another molecule. Damaging effect depends on the penetrating power, the amount of absorbed energy and its distribution

Spontaneous decay of nuclei Observed in elements with large atomic mass nuclei in the capture of slow neutrons. In this same nucleus fission fragments to form different pairs - of new elements which are also usually radioactive

Biological effect ionizing radiation should be understood its ability to cause structural and functional changes in metabolic and at different levels of biological objects: molecular, tissue, organism.

Characteristics of the biological effects of ionizing radiation Ionizing radiation may interact with any of the atoms and molecules. Instant absorption of ionizing radiation energy of atoms and molecules.

Of simultaneous actions on different body structures (cells, tissues, organs) due penetrating ionizing radiation. Exceptional disparity between the extremely low value of the absorbed energy and extremely pronounced reaction to irradiation of biological objects.

Biological effect depends on: §Radiation dose; Type and energy of radiation; Dose distribution in time and scope.

On dose distribution in the amount of body decided to allocate Uniform - irradiation of the whole body; Uneven - (preferential exposure of individual body parts). In situations where the distribution of energy in the body remains unknown to assess the overall biological effect is extremely difficult.

Dose distribution in time With decreasing dose rate irradiation with prolonged or increasing the time interval between periods of radiation exposure dose fractionation decreases affecting the ability of ionizing radiation.

Radiation damage cells The main radiobiological law applies to all cells. Most radiosensitive cell structure is the nucleus. Most radiosensitivity of cells in mitosis phase

The cellular effects of radiation Each biological species, the type of cells and tissues characterized by its own measure of sensitivity or resistance to the action of ionizing radiation - its radioresistance or radiosensitivity.

Relative radiosensitivity of mammalian cells (Rubin, Casarett) Class 1 - vegetative cells intermitotic: multipotent progenitor cells, intestinal crypt cells, epidermal cells, spermatogonia and oogonia, and lymphocytes. Class 2 - differentiating intermito-cal cells: B spermatogonia and oogonia, maturing hematopoietic cells.

Class 3 - multipotent connective cells: endothelium, fibroblasts and mesenchymal cells. Class 4 - resting postmitotic cells: the epidermal cells of the liver, pancreas and lungs, reticular cells of hematopoietic tissue, parenchymal cells in the sweat glands. Class 5 - fixed post-mitotic cells: mature nerve and muscle cells, sperm cells, red blood cells.

Types of cell death Interphase cell death which is based not only damage the chromatin, but membranes. Reproductive death (mitotic and post-mitotic) - associated with not repair or wrongly to repair DNA damage.

Types of post nuclear DNA damage Changes in each of the chains that do not violate its spatial continuity (single-strand breaks, damaged bases). Damage, leading to the breakdown of spatial continuity (double-stranded, double breaks). Violations of the secondary structure and supramolecular organization.

Repair of radiation DNA damage Most biomolecules are presented in a large number of copies of the cell, so the elimination of damaged copies may not affect cell viability. Elimination of damaged DNA molecules can not be indifferent, so there are mechanisms repair of damaged nuclear DNA.

repair mechanisms Excision repair type - endo-exonuclease and provide direct removal of the damaged portion. DNA polymerases involved in the substitution reparative wherein the matrix is an intact DNA strand. Less studied postreplikation repair, recombinational repair of double breaks, etc.

DNA damage, observed after irradiation, some are not unique. They occur in all dividing cells. Enzymatic repair systems are the normal activities of a special system of maintaining genetic stability of the cells. To carry out DNA repair requires the same enzymes and nucleotides as for the percolation of replicative synthesis in dividing cells.

THEORY BLAIR-DAVIDSON Radiation exposure is developed proportionally to the intensity of irradiation and recovery processes are at a rate which is proportional to the injury. In this part remains in permanent injury (10%), which is proportional to the value of the total cumulative dose.

Basic radiation syndromes Bone marrow hematopoietic or in a dosage range from 1 to 10 Gy. hemorrhagic syndrome infectious syndrome Intestinal - from 10 to 80 Gy. Cerebral - more than 80 Gy due to neuronal death.

radiotoxicity nuclides Radiotoxicity characterizes the degree of radiation damage in the incorporation of radioactive substances. In nuclear medicine all radionuclides as sources of internal radiation is usually divided into four groups according to the lowest toxicity much my activity in the workplace.

Factors contributing to the degree of radiotoxicity nuclides: Type of radioactive decay; The half-life; The decay scheme; Type of radiation; Radiation energy; Route of exposure;

Duration of; Nature of the decay in the body; Path of excretion; Prezent time in the body.