1. Eighth lecture

2. Radiation syndromes and stages in human A syndrome is a combination of symptoms resulting from a single cause and occurring together so as to constitute a single clinical picture. Large acute whole-body exposures in man may result in one of the three radiation syndromes: i-Hematopoietic syndrome. ii-Gastrointestinal tract syndrome. iii-Central nervous system syndrome.

3. Hematopoietic system syndrome. Progress of the hematopoietic system syndrome: i-Prodromal stage: following dose of 2-10 Gy. NVD will occur within 1-5 days. ii-Latent phase: will last 1-3 weeks. iii-Illness: NVD, fatigue, anemia, fever, epilation, anorexia & petechial hemorrhaging on skin. iv-Death: occurs within 2-6 weeks. the most probable causes of death will be : hemorrhage and infection.

4. Gastrointestinal tract syndrome Progress of the GIT syndrome: i-Prodromal stage: following dose of 10-50 Gy. It lasts 1-3 days, within 2 hrs loss of appetite, upset stomach & apathy. Several hrs later, NVD will occur. ii-Latent phase: will last 1-7 days after prodromal St. iii-Illness: NVD, fever, apathy, anorexia & loss of wt. iv-Death: occurs within 3-12 days. the causes of death include fluid and electrolyte losses (circulatory collapse)

5. Central nervous system syndrome Is produced by acute whole-body exposures above 50 Gy Survival is impossible. Death results from respiratory failure and/or brain edema caused from direct damage to brain or indirect damage mediated by effects on the blood vessels of the brain. Within hrs, symptoms become very severe; they include V&D, apathy, disorientation & tremors. The victim is likely to fall into a coma.

6. The effects of radiation on biological systems: Tissues Hematopoietic System Are the cells of the hematopoietic system and related lymphoid system. Are highly sensitive to radiation killing. Most sensitive cells are: i-The stem cells of the bone marrow. ii-The lymphoid tissues found in the spleen, liver, lymph nodes and thymus.

7. Hematopoietic system Circulating lymphocytes are quite sensitive to radiation. 10 cGy can show a measurable drop in the circulating small lymphocyte population. Of particular resistance are the mature circulating red blood cells and platelets. The effect is pan-cytopenia (depression of all cell types), resulting in hemorrhage (platelet reduction), infection (white-cell depression), and the effect of anemia from plummeting red cells.

8. Gastrointestinal system The GIT is highly sensitive to radiation. The first changes seen occur in the epithelium lining of the villi. Radiation causes mitotic arrest of the crypt cells followed by eventual denudation of the villi, ulceration of the wall, and septic infiltration.

9. Gastrointestinal system Effects on the large intestine cause functional impairment resulting in fluid and electrolyte loss, and diarrhea. Effects on the upper GI tract include vomiting, depression of acid, and pepsin secretion. Destruction of the epithelium lining of the pharynx and esophagus results in dryness, soreness, and petechia (capillary rupture).

10. Central nervous system CNS & PNS are resistant to radiation effects. Very high doses are required to cause substantial effects on the brain and nervous system. Effects on the vessels cause breakdown of the blood capillaries, interstitial edema, and the breakdown of the blood-brain barrier. The spinal cord exhibits radiation effects including thickening of the vessels, dissolution of white matter