534 UNIT VIII RENAL AND UROLOGICAL DISORDERS
African Americans have the greatest incidence of CKD. African Americans make up 13% of the U.S. popula- tion but constitute 35% of persons with kidney failure. Between 1990 and 2015, the incidence of end-stage renal disease (ESRD) increased by almost 100% within the population. Nearly 786,000 Americans have kidney failure, 558,000 (71%) are on dialysis, and approximately 228,000 (29%) live with a functioning kidney transplant. Basic Concepts of Renal Function Renal function begins with blood flow to the renal vas- culature. The kidneys receive 20% to 25% of the body’s cardiac output. It is filtered at a rate of approximately 90 to 120 mL/min. The renal blood filtered per unit of time, known as the glomerular filtration rate (GFR) , is directly related to renal perfusion (see Fig. 22-1). Disease processes that decrease blood pressure and renal perfusion result in a decreased GFR. As an indi- vidual ages, the normal GFR rate of 90 to 120 mL/ minute diminishes. Peak function of the kidneys occurs at age 30 years; for each year after, GFR decreases by 1 mL/minute until by age 70 years, normal GFR is 70 mL/min. This reduction in GFR in the older adult can cause accumulation of toxins, particularly drug metabolites, in the blood.
Excretory Functions The basic unit of the kidney is the nephron, a sequence of tubes that filters the blood of waste and conserves the fluid and electrolytes that the body needs. Each neph- ron is surrounded by blood vessels, where the exchange of water and electrolytes between the blood and the tubule fluid occurs. At the glomerular capillaries, the major mechanisms of the nephron—waste removal and water recycling—begin. The different sections of the nephron perform various functions to form the final product, which is concentrated urine. Urine must con- tain all the waste products, electrolytes, metabolites, and nitrogenous compounds for excretion. At the same time, urine needs to be sparing of water; the kidney needs to conserve the water the body needs. The Nephron Renal blood flow through the glomerulus, a tuft of cap- illaries within Bowman’s capsule, requires high hydro- static pressure to push blood through the filtration process. The kidneys autoregulate renal blood flow to maintain sufficient pressure to push blood through the glomeruli, regardless of whether blood volume is high or low. As blood flows through the glomerulus and a mem- branous cap called Bowman’s capsule, water and
Left kidney
Right kidney
Renal tubules
Ureter
Renal pelvis
Bladder
Urine
Urethra
Prostate
Penis
FIGURE 22-1. Kidney and urological anatomy.
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