الفهرس 
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Abstract
Aging is a biological process from which no living being is exempt, and a universal effect of aging is the gradual loss of functioning cells from organs and tissues. (Anderson and Brenner, 1986).
Thus nephrons being have no ability to divide, are gradual!iy lost during a normal life time and cell loss contributes to the reduction in their physioloqic reserve capacity (Shock, 1982). So changes in renal function during normal aging are among the most dramatic of any organ system, so that the glomerular filtration rate of healthy octagenarians is only half to two thirds that measured in yoUng adults (Davies and Shock, 1950 and Rowe et al., 1976). Concurrent with the age related decrease in Glomerular Filtration Rate (GFR), there was, in general, progressive increase in urine volume and decrease in the concentration of urine creatinine (Kiebzak and Sacktor, 1986). Also, the average creatinine clearance in men in their eighth and ninth decades was approximately 50% of that in men in their fourth decade (orwoll and Meier, 1986). Also, Beck and Yu (1982), showed that the renal blood flow decreases progressively at the age of 40 years so that the mean renal plasma flow of 600 ml per minute is lowered to 300 ml/minute at age of 85 years. Similarly, the normal GFR of 120 mI/minute at age of 40 years declines to 60 to 70 ml/minute at age of 85 years (Papper, 1973). The capacity of the proximal tubular cells to secrete diodrast (or para—amino hipufate.) is some index of tubular mass. These decline are comparable fashion to RBF or GFR (Bulletin, 1969). However, Lindeman et al., (1966), showed that with aging there is reduced maximum rate of urine flow and formation of solute-free water while urinary concentration fails to become as dilute as in the young. These demonstrated limitations in diluting ability correlate quantitatiieLy with the observed decrease in GFR and the total solute secretion (Papper, 1973). In added to, the ability of the kidney to readjust acid base balance is markedly diminished with aging (for example pH and bicarbonate adjustment to either 20 grams of sodium bicarbonate or 10 grams of ammonium chloride occurs in 8 to 10 hours in the young and in 24 to 48 hours in the aged (Adler et al., 1968).
The aim of the present work is to study the effect of age on some kidney functions, including creatinine clearance and renal conservation of phosphates and calcium in albino rats.