234 N. W. Shock 



90 years. The regression equation is : Twlq = 432 • 8 — 2 • 604 X 

 age (in years). The maximum capacity for both a reabsorptive 

 and excretory mechanism in the renal tubules showed ap- 

 proximately the same percentage decrement with age. 



The average inulin clearance per unit of Tm remains con- 

 stant between the ages of 20 and 90 years (Fig. 6). This 

 finding lends support to the hypothesis that a nephron loses 

 its function as a unit. In contrast, the diodrast clearance per 



o 

 z 

 < 



-J 

 o 



T \ 1 \ \ 1 \ 1 \ \ 1 \ ^ 1 T 



'• • • - ••_ 



J__J \ \ \ I \ I I I i I \ \ L 



- 10 20 30 40 50 60 70 80 90 



AGE YEARS 



Fig. 6. Change in rate of glomerular filtration per unit of diodrast Tm. 

 O O average values. 



(From: Shock, 1952). 



unit of Tm decreases from an average value of 12-6 at age 

 30-39 to 9-7 at age 80-89 (Fig. 7). This steady decline in the 

 effective renal plasma flow per unit of tubular excretory 

 capacity indicates that the average amount of blood delivered 

 to each tubule, and by implication each nephron, declines with 

 age. Since we have been able to demonstrate a significant 

 reduction in resting cardiac output with age (Brandfonbrener, 



