THE ROLE OF THE KIDNEY IN ELECTROLYTE 

 AND WATER REGULATION IN THE AGED 



N. W. Shock 



Gerontology Branch, National Heart Institute, National Institutes 



of Health, PHS, D.H.E. & W., Bethesda, and the Baltimore City 



Hospitals, Baltimore, Maryland 



The kidney is the first line of defence in maintaining appro- 

 priate concentrations of water and electrolytes in the internal 

 environment of all the cells in the body. Although there are 

 other avenues through which salts and water may be lost 

 from the body, and other factors which may enter into the 

 regulation of concentrations in local areas, it is the kidney 

 which carries the major burden of electrolyte and water 

 regulation. The kidney responds to a multitude of stimuli and 

 is blessed with large reserve capacities. It is the purpose of 

 this report to describe briefly some of our findings with 

 regard to age changes in renal function, to discuss the possible 

 mechanisms of these changes, and to discuss their relation to 

 the maintenance of certain physiological constants in the 

 aged. 



In order for the kidney to serve its functions of regulating 

 water and electrolyte concentrations, as well as the volume of 

 extracellular fluid, blood must be delivered to it in adequate 

 amounts, glomerular filtrate must be formed, and the tubular 

 cells must selectively reabsorb and excrete substances in 

 accordance with a variety of stimuli to which the kidney must 

 respond. The application of clearance techniques makes it 

 possible to assess the nature of age changes in discrete renal 

 functions. The studies to be reported are based on ambulatory 

 male subjects between the ages of 20 and 90 years who were 

 found to be free from clinical evidence of renal disease as 

 judged by clinical laboratory tests and medical history. All 



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