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CHAPTER 38

CHAPTER 38

This chapter is concerned with renal function, including glomerular filtration and the factors affecting it, tubular reabsorption and secretion and their control, and the function of the ureters and bladder. The endocrine functions of the kidney are also reviewed. The material in the chapter should help students to—

Describe the morphology of a typical nephron and its blood supply.

Define autoregulation, and list the major theories advanced to explain autoregulation in the kidneys.

List the hormones secreted by the kidneys and tell what each one does.

Outline the functions of the renal nerves.

Define glomerular filtration rate, describe how it can be measured, and list the major factors affecting it.

Define and discuss tubuloglomerular feedback and glomerulotubular balance.

Discuss tubular reabsorption and secretion of glucose and K+.

Outline tubular handling of Na+.

Summarize tubular handling of Cl-, HCO3-, urea, and uric acid in terms of amounts filtered, secreted, reabsorbed, and excreted in urine.

Describe how the countercurrent mechanism in the kidney operates to produce a hypertonic or hypotonic urine.

Outline the processes involved in the secretion of H+ into the tubules, and discuss the significance of these processes in the regulation of acid-base balance.

List the major classes of diuretics and how each operates to increase urine flow.

Describe the voiding reflex and draw a cystometrogram.

General Questions

1. Why, when the Tm of a substance that is secreted by the tubules is reached, does clearance of the substance decrease as its plasma concentration increases?

2. Why is the renal medulla especially sensitive to hypoxic damage?

3. What is the physiologic role of the mesangial cells in the glomeruli, and how do they carry it out?

4. Compare the cellular mechanisms responsible for H+ secretion in the proximal tubule with those in the distal tubule and those in the gastric mucosa.

5. Discuss the mechanisms responsible for the adaptation of NH4+ excretion that develops over a period of days in prolonged acidosis.

6. Why is acidosis a common complication of chronic renal disease? How would you treat it?

7. The following observations were made on a patient:

Plasma HCO3-: 20 meq/L

GFR: 125 mL/min

24-hour urine volume: 1500 mL

Urinary HCO3-: 25 meq/L

Urinary NH4+: 75 meq/L

Urinary titratable acidity: 50 meq/L

(A) Approximately how much HCO3- is being reabsorbed per 24 hours?

(B) How much Na+ is being reabsorbed with the HCO3-?

(C) How much H+ is being secreted by the renal tubules per 24 hours?

Multiple-Choice Questions

In questions 1-17, select the single best answer. In questions 1-5, which refer to Table 38-A, match the disease or condition in each question with the lettered pattern of laboratory findings in Table 38-A that is most closely associated with it. Each lettered pattern may be selected once, more than once, or not at all.

1. Diabetes insipidus

2. Nephrosis

3. Fasting

4. Dehydration

5. Diabetes mellitus

6. In the presence of vasopressin, the greatest fraction of filtered water is absorbed in the

(A) proximal tubule

(B) loop of Henle

(C) distal tubule

(D) cortical collecting duct

(E) medullary collecting duct

7. In the absence of vasopressin, the greatest fraction of filtered water is absorbed in the

(A) proximal tubule

(B) loop of Henle

(C) distal tubule

(D) cortical collecting duct

(E) medullary collecting duct

8. If the clearance of a substance which is freely filtered is less than that of inulin

(A) there is net reabsorption of the substance in the tubules

(B) there is net secretion of the substance in the tubules

(C) the substance is neither secreted nor reabsorbed in the tubules

(D) the substance becomes bound to protein in the tubules

(E) the substance is secreted in the proximal tubule to a greater degree than in the distal tubule

9. Glucose reabsorption occurs in the

(A) proximal tubule

(B) loop of Henle

(C) distal tubule

(D) cortical collecting duct

(E) medullary collecting duct

10. On which of the following does aldosterone exert its greatest effect?

(A) Glomerulus

(B) Proximal tubule

(C) Thin portion of the loop of Henle

(D) Thick portion of the loop of Henle

(E) Cortical collecting duct

11. What is the clearance of a substance when its concentration in the plasma is 10 mg/dL, its concentration in the urine is 100 mg/dL, and urine flow is 2 mL/ min?

(A) 2 mL/min

(B) 10 mL/min

(C) 20 mL/min

(D) 200 mL/min

(E) Clearance cannot be determined from the information given

12. As urine flow increases during osmotic diuresis

(A) the osmolality of urine falls below that of plasma

(B) the osmolality of urine increases because of the increased amounts of nonreabsorbable solute in the urine

(C) the osmolality of urine approaches that of plasma because plasma leaks into the tubules

(D) the osmolality of urine approaches that of plasma because an increasingly large fraction of the excreted urine is isotonic proximal tubular fluid

(E) the action of vasopressin on the renal tubules is inhibited

Questions 13-15 refer to the data in Table 38-B, which were obtained in a normal woman.

13. The glomerular filtration rate in the experimental period is

(A) four times that in the control period

(B) twice that in the control period

(C) the same as in the control period

(D) one-half that in the control period

(E) one-quarter that in the control period

14. The clearance of urea in the experimental period is

(A) increased, probably because the urine flow is increased

(B) increased, probably because the urine glucose concentration is increased

(C) the same as in the control period

(D) decreased, probably because the urine flow is increased

(E) decreased, probably because the amount of urea filtered is decreased

15. The Tm for glucose in this woman

(A) is 100 mg/min

(B) is 130 mg/min

(C) is 200 mg/min

(D) is 290 mg/min

(E) cannot be calculated from the data given

16. To produce a concentrated urine, vasopressin

(A) introduces the movement of aquaporin from the cytoplasm to the cell membrane of proximal tubule cells

(B) increases the movement of aquaporin-2 from the cytoplasm to the cell membrane of collecting duct cells

(C) has no effect on molecular motors in proximal tubule cells

(D) has no effect on molecular motors in collecting duct cells

(E) increases Na+ reabsorption in the thick ascending limb of Henle

17. A gain-of-function mutation in the gene for which of the following proteins is associated with increased Na+ retention and hypertension with a normal or low plasma aldosterone level (Liddle’s syndrome)?

(A) Aldosterone synthase

(B) An inward rectifier K+ channel

(C) 11β-Hydroxylase

(D) V2 receptor

(E) Epithelial Na+ channel

Questions 18-22 refer to Figure 38-A. Select the letter or letters identifying the appropriate part of the nephron. Each lettered item may be selected once, more than once, or not at all. Note that in some instances, the correct answer may be more than one letter.

Figure 38-A. Juxtamedullary nephron.

18. Site(s) at which furosemide acts

19. Site(s) at which thiazides act

20. Site(s) at which tubular fluid osmolality exceeds that of plasma by the greatest amount

21. Site(s) at which Na+ is actively reabsorbed

22. Site(s) at which K+ is secreted

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