Function of the Chronically Diseased Kidney
The Adaptive Nephron
Adaptive morphological and functional changes in the chronically diseased kidney are described in historical perspective and their correlation is stressed. The consequences of decreased glomerular filtration rate (GFR) in the presence of unchanged dietary intake on the mechanisms of excretion of substances passively reabsorbed, actively reabsorbed, and secreted are reviewed. Under these circumstances the plasma concentrations of creatinine and urea are necessarily elevated, but not that of electrolytes with regulated tubular transport. In the case of sodium, fractional excretion and GFR are reciprocally related in order to maintain unchanged rates of excretion and plasma concentration. With phosphate, regulated tubular reabsorption can prevent an increase in plasma concentration provided the GFR does not fall below approximately 25 ml/min. In the case of potassium, tubular secretion becomes apparent at marked decreases in filtration rate.
These adaptive regulatory changes are considered predictable and necessary in order for the patient to survive, and are supported by compensatory morphological changes in some of the surviving nephrons. Heterogeneity in size of the surviving nephrons, particularly the proximal tubules and glomeruli, is documented and the prediction is made that these structural changes are associated with appropriate changes in rates of transport. Data are presented demonstrating marked heterogeneity of nephron filtration rates and proximal tubular transit times in experimentally diseased kidneys. The necessity of utilizing appropriate methods of study to obtain data on individual nephrons is stressed, as is the lack of knowledge concerning the mechanisms that lead to the compensatory structural and functional changes.
It is concluded that the adaptive changes exhibited by the kidney with chronic renal disease are another and a special example of adaptive growth and, therefore, that it is more appropriate to think in terms of "adaptive nephrons" and not "intact nephrons".
- creatinine clearance
- urea clearance
- sodium excretion
- potassium excretion
- phosphate excretion
- renal disease
- tubular transport
- electrolyte concentration
- © 1971 American Heart Association, Inc.