Exposure of large areas of the body to even small doses of radiation may have devastating effects. Dosages less than 1 Sv produce minimal or no symptoms. Greater exposures, however, cause health effects known as acute radiation syndromes, which at progressively higher doses involve the hematopoietic system, GI system, and CNS. The syndromes associated with total-body exposure to ionizing radiation are summarized in
Table 8.8
RADIATIONINJURYdose levels and large exposure fields, severe lymphopedose levels and large exposure fields, severe lymphope
Ionizingradiationmayinjurecellsdirectlyorindirectlybygeneratingfreeradicalsfromwaterormolecularoxygen.
IonizingradiationdamagesDNA;therefore,rapidlydividingcellssuchasgermcells,andthoseinthebonemarrowandGItractareverysensitivetoradiationinjury.
DNAdamagethatisnotadequatelyrepairedmayresultinmutationsthatpredisposeaffectedcellstoneoplastictransformation.
Ionizingradiationmaycausevasculardamageandsclerosis,resultinginischemicnecrosisofparenchymalcellsandtheirreplacementbyfibroustissue.
Millions of people in developing nations starve or live on the cruel edge of starvation, whereas those in the developed world, and more recently in the developing world, struggle to avoid calories and the attendant obesity or fear that what they eat may contribute to atherosclerosis and
Mainsignsand—ModerateleukopeniaLeukopenia,hemorrhage,Diarrhea,fever,electrolyteAtaxia,coma,convulsions,symptoms epilation,vomitingimbalance,vomitingvomiting http://ebooksmedicine.net hypertension. So both the lack of nutrition and overnutrition are major health concerns.
A healthy diet provides (1) sufficient energy, in the form of carbohydrates, fats, and proteins, for the body’s daily metabolic needs; (2) essential (as well as nonessential) amino acids and fatty acids, used as building blocks for synthesis of structural and functional proteins and lipids; and (3) vitamins and minerals, which function as co-enzymes or hormones in vital metabolic pathways or, as in the case of calcium and phosphate, as important structural components. In primary malnutrition, one or all of these components are missing from the diet. By contrast, in secondary, or conditional, malnutrition, the dietary intake of nutrients is adequate, and malnutrition results from nutrient malabsorption, impaired use or storage, excess losses, or increased requirements. The causes of secondary malnutrition can be grouped into three general but overlapping categories: GI diseases, chronic wasting diseases, and acute critical illness.
Malnutrition is widespread and may be gross or subtle. Some common causes of dietary insufficiencies are listed here.
Poverty. Homeless people, elderly persons, and children of the poor often suffer from severe malnutrition as well as trace nutrient deficiencies. In poor countries, poverty, together with droughts, crop failure, and livestock deaths, creates the setting for malnourishment of children and adults.
Ignorance. Even the affluent may fail to recognize that infants, adolescents, and pregnant women have increased nutritional needs. Ignorance about the nutritional content of various foods also contributes to malnutrition, as follows: (1) iron deficiency often develops in infants exclusively fed artificial milk diets; (2) polished rice used as the mainstay of a diet may lack adequate amounts of thiamine; and (3) iodine often is lacking in food and water in regions removed from the oceans, unless supplementation is provided.