Age Changes in Renal Function 



243 



Alving (1938) found some evidence that with increasing age 

 there is an accumulation of urea nitrogen in the blood. Their 

 data show a sUght rise in the fifth decade, but no significant 

 change during the sixth and seventh decades, with a rather 

 sharp increase after the 70th year. Most of the total rise from 

 a mean of 12-9 mg. urea N/100 ml. blood in the 30-40 age 



20 



30 



40 



50 



60 



70 



80 



90 



AGE YEARS 



Fig. 13, Total blood volumes, ml. per kg., and plasma volumes, 

 ml. per kg., in 105 males. □ total blood volume determinations 

 from Gibson and Evans (1937). | plasma volume (Gibson and 

 Evans), Q total blood volume, plasma volume (Cohn and 

 Shock). 



(From: Cohn and Shock, 1949). 



group to a mean of 21-2 mg. per cent in the 85-89-year-olds 

 occurred after the age of 70. It therefore appears that there is 

 some impairment in the excretion of nitrogenous substances 

 in the aged kidney, although capacity for maintaining electro- 

 lyte concentrations under resting conditions is still adequate. 

 With increasing age there is a reduction in the concentrating 

 ability of the kidney. The maximum specific gravity attained 



