Jan 24 2009
Changes in Kidney Function with Increasing Age
Kidney function is very immature at birth. The kidney of a newborn lacks the ability to concentrate urine and are less efficient in handling electrolytes. No new nephrons are formed in the kidneys after the fetal period; however, the nephrons and kidneys continue to grow in size until maturity is reached. Thereafter renal weight, blood flow, and glomerular filtration decline, especially after age 50. These changes are most marked when they are standardized to body surface area, and less marked when lean body mass is used. As a person ages, the kidneys can maintain the homeostasis of the plasma constituents, but they are slower to respond to changes in load.
When one kidney experiences loss of function, the remaining kidney is capable of considerable compensatory hypertrophy because there are a large number of rserve nephrons that can enlarge and increase their function. However, the number of reserve nephrons declines with age, and renal parenchyma is replaced by fibrous tissue; consequently, the ability to hypertrophy is reduced in older individuals.