Porth's Essentials of Pathophysiology, 4e

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Kidney and Urinary Tract Function

U N I T 7

creatinine of 2.5 mg/dL. He complains that he has been urinating more frequently than usual. His first morning urine specimen reveals a dilute urine with a specific gravity of 1.010. A. Explain the elevation of serum creatinine in terms of a decrease in renal function. B. Explain the inability of persons with early renal failure to produce a concentrated urine as evidenced by the frequency of urination and the low specific gravity of his first morning urine specimen. Hall JE. Guyton & Hall Textbook of Medical Physiology . 12th ed. Philadelphia, PA: Elsevier Saunders; 2011:303–378. Inker LA, Schmid CH, Tighiouart H, et al. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med. 2012;367(1):20–29. National Kidney Foundation. Cystatin C: What’s is its role in estimating GFR. 2008. www.kidney.org/professionals/tools/pdf/ cystatinC.pdf. Accessed May 20013. Nielson S, Kwon TH, Fenton RA, et al. Anatomy of the kidney. In: Taal MW, Chertow GM, Marsden PA, et al. Brenner and Rector’s The Kidney . 9th ed. Philadelphia, PA: Elsevier Saunders; 2012:31–92. Ross GI, Pawlina W. Histology: A Text and Atlas . 6th ed. Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams & Wilkins; 2011:698–723. Sherwood L. Human Physiology: From Cells to Systems . 8th ed. Belmont, CA: Brooks/Cole; 2013:505–547. Simon J, Amode M, Poggio EG. Interpreting the estimated glomerular filtration rate in primary care: benefits and pitfalls. Clev Clinic J Med. 2011;78(3):189–195. Smith H. From Fish to Philosopher . Boston, MA: Little, Brown; 1953:4. Stanton BA, Koepen BM. Elements of renal function and solute and water transport along the nephron: Tubular function. In: Koeppen BM, Stanton BA, eds. Berne & Levy Physiology . 6th ed. Philadelphia, PA: Mosby Elsevier; 2010:557–618. Stevens LA, Levey AS. Measurement of kidney function. Med Clin North Am. 2005;89:457–473. Tanner GA. Kidney function. In: Rhoades RA, Bell DR, eds. Medical Physiology . 2nd ed. Philadelphia, PA: Wolters Kluwer Health/ Lippincott Williams & Wilkins; 2013:399–406. B I B L I O G R A P H Y

SUMMARY CONCEPTS

R E V I EW E X E R C I S E S 1. A 32-year-old woman with diabetes is found to have a positive result on a urine dipstick test for microalbuminuria. A subsequent 24-hour urine specimen reveals an albumin excretion of 50 mg (an albumin excretion >30 mg/day is abnormal). A. Use the structures of the glomerulus in Figure 24-5 to provide a possible explanation for this finding. Why specifically test for the albumin rather than the globulins or other plasma proteins? B. Strict control of blood sugars and treatment of hypertension have been shown to decrease the progression of kidney disease in persons with diabetes. Explain the physiologic rationale for these two types of treatments. 2. A 10-year-old boy with enuresis (bed-wetting) was placed on an ADH nasal spray at bedtime as a means of treating the disorder. A. Explain the rationale for using ADH to treat bed-wetting. 3. A 54-year-old man, seen by his physician for an elevated blood pressure, was found to have a serum creatinine, is also influenced by protein intake, gastrointestinal bleeding, and hydration status. ■■ Urinalysis and urine specific gravity is used to assess the kidneys’ ability to concentrate urine. Dipstick and 24-hour urine tests for proteinuria and microalbuminuria are used to detect abnormal filtering of albumin in the glomeruli. ■■ The composition of urine and blood samples provides valuable information about kidney function. ■■ Blood tests that measure serum levels of pH, electrolytes, and by-products of metabolism provide information about renal function. Creatinine, a product of creatine metabolism in muscles, is freely filtered in the glomeruli and neither reabsorbed nor secreted into the tubules; therefore, serum creatinine levels are commonly used to estimate the GFR. Urea is formed in the liver as a by-product of protein metabolism and is eliminated entirely by the kidneys; thus, blood urea nitrogen (BUN) is related to the GFR but, unlike

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