FUNCTIONAL CHANGES INDUCED BY RADIATIONS 



SKIN 



493 



Renewal 



Maturation 



I Progenitive or 

 1 Stem Cells 



(Maturation 

 ^ I Product (Squama) 



Gastrointestinal 

 Tract 



Thymus, Lymph Nodes, Spleen, 

 Bone Marrow 



Spermatic 

 Tubule 



Stem Cells 



© ^0 



Secretory 

 Cells 



Lymphocyte — Erythrocyte 



Neutrophil 

 Platelet 



Fig. 3. Progenitive tissue renewal and maturation. 



from irradiated cells that survived. Whereas regrowth of progenitive ele- 

 ments may be essentially complete, it has been found that the surviving 

 tissues do not perform as well in later life as do similar tissues which did 

 not receive irradiation. In this connection, it is important to consider 

 whether nen-ous system components, while nonproliferative in adult life 

 and less affected by radiation so far as cell-killing is concerned, are able to 

 perform as well after irradiation. 



The 200 r dose may cause significant destruction of progenitive tissue 

 elements, but damage is rarely (if ever, in humans) sufficient to cause death. 

 In the descending scale of exposure, therefore, the range between 2,000 and 

 200 r is of particular significance, inasmuch as we become confronted with 

 organisms that have recovered from substantial proliferative tissue loss, but 

 nevertheless show earlier deterioration of function in later life. Studies to 

 detect modified nervous system function following 200 to 2,000 r exposures 

 are in preliininary stages, but some positive findings have been reported. 



