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  • Artikel: DFG Deutsche Nationallizenzen  (2)
  • Hypoxia  (1)
  • List of MAK and BAT values  (1)
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  • Artikel: DFG Deutsche Nationallizenzen  (2)
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  • 1
    ISSN: 1432-1335
    Schlagwort(e): Key words Chemical carcinogens ; List of MAK and BAT values ; Cancer risk ; carcinogen classification
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Carcinogenic chemicals in the work area were previously classified into three categories in section III of the German List of MAK and BAT values (the list of values on maximum workplace concentrations and bio‐logical tolerance for occupational exposures). This classification was based on qualitative criteria and reflected essentially the weight of evidence available for judging the carcinogenic potential of the chemicals. In the new classification scheme the former sections IIIA1, IIIA2, and IIIB are retained as categories 1, 2, and 3, to correspond with European Union regulations. On the basis of our advancing knowledge of reaction mechanisms and the potency of carcinogens, these three categories are supplemented with two additional categories. The essential feature of substances classified in the new categories is that exposure to these chemicals does not contribute significantly to the risk of cancer to man, provided that an appropriate exposure limit (MAK value) is observed. Chemicals known to act typically by non-genotoxic mechanisms, and for which information is available that allows evaluation of the effects of low-dose exposures, are classified in category 4. Genotoxic chemicals for which low carcinogenic potency can be expected on the basis of dose/response relationships and toxicokinetics and for which risk at low doses can be assessed are classified in category 5. The basis for a better differentiation of carcinogens is discussed, the new categories are defined, and possible criteria for classification are described. Examples for category 4 (1,4-dioxane) and category 5 (styrene) are presented.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Annals of hematology 49 (1984), S. 427-439 
    ISSN: 1432-0584
    Schlagwort(e): Hematopoiesis ; Stem cells ; Mathematical model ; Hypoxia ; Posthypoxia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary A previously described mathematical model of the hematopoietic stem cell system has been extended to permit a detailed understanding of the data during and after hypoxia. The model includes stem cells, erythroid and granuloid progenitors and precursors. Concerning the intramedullary feedback mechanisms two basic assumptions are made: 1) The fraction “a” of CFU-S in active cell cycle is regulated. Reduced cell densities of CFU-S, progenitors or precursors lead to an accelerated stem cell cycling. Enlarged cell densities suppress cycling. 2) The self renewal probability “p” of CFU-S is also regulated. The normal steady state is described by p=0.5, indicating that on statistical average each dividing mother stem cell is replaced by one daughter stem cell, while the second differentiates. Diminished cell densities of CFU-S or enlarged densities of progenitors and precursors induce a more intensive self renewal (p〉0.5), such that the stem cell number increases. The self renewal probability declines (p〈0.5) if too many CFU-S or too few progenitors and precursors are present. The model reproduces bone marrow data for CFU-S, BFU-E, CFU-C, CFU-E, 59 Fe-uptake and nucleated cells in hypoxia and posthypoxia. Although the ratio of differentiation into the erythroid and granuloid cell lines is kept constant in the model, a changing ratio of CFU-E and CFU-C results. The model suggests that stem cells and progenitor cells are regulated by a regulatory interference of erythropoiesis and granulopoiesis.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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