The Aging Kidney: Physiological Changes

Age-associated loss of kidney function has been recognized for decades. With aging, many subjects exhibit progressive decreases in glomerular filtration rate and renal blood flow, with wide variability among individuals. The fall in glomerular filtration rate is because of reductions in the glomerular capillary plasma flow rate and the glomerular capillary ultrafiltration coefficient. In addition, a primary reduction in afferent arteriolar resistance is associated with an increase in glomerular capillary hydraulic pressure. These hemodynamic changes occur in concert with structural changes, including loss of renal mass; hyalinization of afferent arterioles and in some cases, development of aglomerular arterioles; an increase in the percentage of sclerotic glomeruli; and tubulointerstitial fibrosis. Aging is associated with altered activity and responsiveness to vasoactive stimuli, such that responses to vasoconstrictor stimuli are enhanced, whereas vasodilatory responses are impaired. Changes in the activity of the renin–angiotensin and nitric oxide systems appear to be particularly important, as is the modulating effect of gender. These changes may predispose the older kidney to acute kidney injury, including normotensive ischemic nephropathy, as well as progressive chronic kidney disease.