Questions & Answers
1. A hyperosmotic solution of urea, a nontoxic substance, is injected intravenously (IV). Urea readily permeates most cell membranes via uniporters. After it has distributed throughout the body fluids,
A. both intracellular (ICF) and extracellular fluid (ECF) volumes will be decreased.
B. ECF volume will be decreased.
C. the osmolality of ICF and ECF will be increased.
D. the osmolality of the ICF will be decreased.
E. ICF volume will be increased.
2. Which is the main factor that determines the amount of water, and therefore volume, of the ECF compartment?
A. Na+ concentration
B. Na+ content
E. Cl− concentration
3. If a patient hemorrhages 1 L of blood in 5 minutes, you would restore the body fluid balance by giving 1 L of which of the following?
A. 5% glucose IV
B. 5% glucose intraperitoneally
C. 0.9% NaCl IV
D. 4.5% NaCl IV
E. Distilled water IV
4. During severe exertion in a hot environment, a person may lose 4 L of hyposmotic sweat per hour. This would result in
A. decreased plasma volume.
B. decreased plasma osmolality.
C. decreased plasma ADH.
D. decreased plasma aldosterone.
E. decreased plasma renin.
5. Renal autoregulation of blood flow and glomerular filtration rate (GFR) require
A. autonomic innervation.
E. no action of extrarenal factors.
6. The following data are provided for a substance X. These data are consistent with X being which substance?
Plasma concentration of X = 0.02 mg/100 mL
Urine concentration of X = 12 mg/mL
Urine flow rate = 1 mL/min
GFR = 125 mL/min
B. Para-aminohippuric acid (PAH)
C. Sodium ions
7. A patient with a serum creatinine of 0.8 mg/dL submits a 12-hour urine collection containing 400 mg of creatinine. What is his creatinine clearance in mL/min? (Note: Answering this question requires some unit conversions.)
A. 50 mL/min
B. 69 mL/min
C. 100 mL/min
D. 145 mL/min
E. 800 mL/min
8. After a patient has a renal transplant, the serum creatinine is 0.6 mg/dL. Six months after the transplant, it rises to 1.2 mg/dL. This last change is most likely due to
A. a significant decrease in the GFR.
B. the daily fluctuation of serum creatinine within the normal range.
C. a rise in creatinine production.
D. impairment of protein synthesis due to corticosteroids (for immunosuppression).
E. increase in efferent arteriolar resistance.
9. If ouabain, a drug that inhibits Na+−K+ ATPase, is infused into the renal artery,
A. urine flow will decrease.
B. there will be an osmotic diuresis.
C. renal glucose reabsorption will not be affected.
D. the [Na+] within proximal tubular cells will decrease.
E. K+ reabsorption will increase.
10. Given the data below, what is the rate of excretion of substance X in the urine? Substance X is freely filtered.
GFR = 125 mL/min
Plasma concentration of X = 2 mg/mL
Tubular reabsorption of X = 30 mg/min
Tubular secretion of X = 60 mg/min
A. 160 mg/min
B. 220 mg/min
C. 250 mg/min
D. 280 mg/min
E. 340 mg/min
11. Filtered Cl− is reabsorbed by a multiporter with K+ and Na+ in the
A. proximal tubule.
B. proximal tubule and descending limbs of the loop of Henle.
C. proximal tubule and ascending limb of the loop of Henle.
D. ascending limb of the loop of Henle.
E. distal tubule and collecting duct.
12. Which action serves to conserve blood volume?
A. Suppression of ADH secretion
B. Increased renin secretion
C. Increased renal filtration fraction
D. Increased GFR
E. Increased renal medullary blood flow
13. A 49-year-old woman complains of weakness, easy fatigability, and loss of appetite. During the past year, she lost 15 lb. Her blood pressure is 80/50 mm Hg, her serum [Na+] is 130 mEq/L (normal 135−145 mEq/L), and her serum [K+] is 6.5 mEq/L (normal 3.5 to 5.0 mEq/L). This patient is diagnosed as having Addison disease (decreased levels of adrenal corticosteroids). One possible cause for her hyperkalemia is
A. decreased K+ secretion by the cortical collecting duct.
B. increased K+ reabsorption by the proximal tubule.
C. increased Na+ reabsorption by the collecting duct.
D. increased volume flow rate of tubular fluid along the nephron.
E. increased levels of serum aldosterone.
14. During administration of aldosterone, you expect
A. elevated plasma renin concentration.
B. reduced 24-hour urinary Na+.
C. reduced plasma volume.
D. reduced blood pressure.
E. increased urine volume.
15. A 45-year-old man with a blood pressure of 150/90 mm Hg for the past 6 months is stabilized on a diet with 200 mEq Na+ per day. One day after a dose of a short-acting powerful diuretic drug, you would expect
A. reduced plasma renin concentration,
B. elevated urinary Na+.
C. reduced plasma volume.
D. elevated blood pressure.
E. increased urine volume.
16. A healthy adult with a creatinine clearance of 110 mL/min has a K+ clearance of 65 mL/min. After administration of a new drug, K+ clearance increases to 130 mL/min with no change in creatinine clearance. The drug could have produced this change in K+ clearance by
A. stimulating K+ reabsorption in the proximal tubule.
B. inhibiting aldosterone secretion.
C. stimulating K+ reabsorption in the distal nephron.
D. inhibiting K+ secretion in the distal nephron.
E. stimulating K+ secretion in the distal nephron.
17. The most significant contribution of the loop of Henle to the process of urine concentration and dilution is
A. the production of hyperosmotic tubular fluid.
B. serving as the site where ADH controls water reabsorption.
C. acting as a countercurrent exchanger that establishes the medullary osmotic gradient.
D. actively reabsorbing Na+ and Cl−.
E. reabsorption of urea.
18. ADH conserves water by
A. constricting afferent arterioles, thereby reducing the GFR.
B. increasing water reabsorption by the proximal tubule.
C. stimulating active reabsorption of solutes in the descending limb of the loop of Henle.
D. increasing water permeability of the collecting duct.
E. blocking urea secretion in the loop of Henle.
19. Which of the following actions of a drug is possible if treatment of a patient causes formation of a large volume of urine with an osmolality of 300 mOsm/kg H2O?
A. Inhibition of renin secretion
B. Increase of ADH secretion
C. Increased permeability to water in distal nephron and collecting ducts
D. Decreased active Cl− reabsorption by the ascending limb of the loop of Henle
E. Inhibition of aldosterone secretion
20. A 60-year-old man was brought unconscious to the emergency room. A neighbor states that the patient has not felt well over the past week and looks as though he has lost weight lately. Which diagnosis fits if his plasma Na+ and plasma osmolality are reduced, and his kidneys excrete concentrated urine?
B. Excessive production/release of ADH
C. Water intoxication
D. Diabetes insipidus
E. Diabetes mellitus
21. The kidney excretes acid loads mainly by
A. excreting filtered HCO3−.
B. secreting titratable acid
C. a high urinary content of free H+.
D. raising urine pH via H+ secretion.
E. excreting NH4+.
For questions 22 and 23, a patient suffering from chronic lung disease has an arterial pH of 7.37 and an arterial Pco2 of 54 mm Hg.
22. His condition is a primary
A. respiratory acidosis.
B. respiratory alkalosis.
C. metabolic acidosis.
D. metabolic alkalosis.
E. normal acid–base status.
23. One would expect that his arterial
A. plasma HCO3− is lower than normal.
B. plasma HCO3− is higher than normal.
C. plasma H+ is lower than normal.
D. plasma dissolved CO2 concentration is lower than normal.
E. total CO2 is lower than normal.
24. Renal compensation for respiratory acidosis
A. is a result of decreased plasma Pco2.
B. includes hyperventilation.
C. requires renal generation of HCO3−.
D. is a rapid process that keeps up in time with changes in Pco2.
E. does not affect urinary [NH4+] excretion.
25. Which of the following values characterizes uncompensated respiratory alkalosis?
26. The primary factor that usually determines the long-term (over days) output of urine via the kidney is
A. arterial blood pressure.
B. cardiac output (CO).
C. plasma concentration of antidiuretic hormone (ADH).
D. central venous pressure.
E. the volume of total fluid intake.
Answers and Explanations
1. C. The urea distributes at equal concentrations in the ICF and ECF and increases osmolality in both compartments (D) (p. 156).
A,B,E Assuming the injected volume is not significant, the volumes of the compartments do not change because there is no shift of water from one to the other.
2. B. Because the osmolality of the body fluids is held nearly constant, the status of Na+ balance determines the volume of the ECF. Volume = amount of solute/osmolality (p. 155).
A Na+ concentration is normally controlled within a narrow range even as Na+ content varies considerably.
C,D Potassium is the major intracellular electrolyte.
E Chloride is distributed close to its equilibrium between intra- and extracellular compartments. Because of the negative membrane potential, intracellular chloride concentration is much lower than extracellular chloride concentration.
3. C. Hemorrhage is isosmotic volume depletion. Isotonic NaCl (0.9%) restores both water and ions (p. 156).
A,B Glucose is metabolized, so it does not restore ion concentrations.
D A large amount of concentrated NaCl would cause a shrinkage of cells.
E Water alone is not given IV because it causes lysis of red blood cells.
4. A. Sweat contains K+, Na+, and Cl−. Therefore, there is a net loss of water, K+, Na+, and Cl−. Plasma volume would be smaller (p. 156). B,C Because the loss of water is relatively greater than the loss of solute, there would be an increase in plasma osmolality stimulating the release of ADH.
D,E Net Na+ and volume loss will result in increased plasma levels of renin and aldosterone.
5. E. Renal autoregulation is an intrinsic property of the kidney. Afferent arterioles change their resistance proportionally to blood pressure, so renal blood flow and glomerular filtration rate change only slightly (p. 158).
A–D The other answer choices are not requirements for GFR and renal autoregulation.
6. B. Clearance of X = (1 mL/min × 12 mg/mL)/0.02 mg/mL = 600 mL/min. Because the volume of plasma being cleared of X is greater than the GFR, the substance must have been secreted into the tubule and so could be PAH (pp. 159, 161).
A The clearance of insulin is equal to its GFR.
C–E These are reabsorbed.
7. B. Clearance = excretion rate/plasma concentration. Creatinine excretion/min = 400 mg/(12 h × 60 min/h) = 0.55 mg/min. Plasma creatinine concentration = 0.8 mg/dL = 0.008 mg/mL. Creatinine clearance = 0.55 mg/min/0.008 mg/mL = 69 mL/min (pp. 159–160).
8. A. Deterioration in the GFR by about half doubles serum creatinine (p. 160).
B The normal range of daily fluctuation is much less than a change by a factor of 2.
C Creatinine production will rise only if there is an increase in muscle mass. For serum creatinine to double, the person must have doubled his muscle mass, an unlikely situation.
D Serum creatinine is not related to protein synthesis.
E An increase in resistance of efferent arterioles increases the GFR, which would lower the serum creatinine.
9. B. Ouabain, a glycoside poison, binds to and inhibits the action of the Na+−K+ pump in the cell membrane. Blocking reabsorption of Na+ will leave excess Na+ and water in the proximal tubule, which will be passed along to the rest of the nephron and produce an osmotic diuresis (p. 162).
A Urine flow will increase.
C This will stop reabsorption of organic substances, including glucose, that depend on secondary active transport.
D The concentration of [Na+] within proximal tubular cells will increase because it is not pumped out.
E Reabsorption of K+ in the proximal tubule will decrease because it depends on the reabsorption of water to increase its luminal concentration.
10. D. Amount excreted = filtered load + amount secreted – amount reabsorbed. Filtered load = GFR × plasma concentration. Thus, 125 mL/min × 2 mg/mL + 60 mg/min − 30 mg/min = 280 mg/min.
11. D. The Na+−K+−2Cl− (NKCC) multiporter is expressed abundantly in the ascending limb of the loop of Henle (p. 166).
A − C Some Cl− is reabsorbed actively in the proximal tubule via a different process.
E Cl− is not reabsorbed actively in the collecting ducts.
12. B. Renin stimulates production of angiotensin II and aldosterone, which reduce salt and water excretion (p. 168).
A Less ADH secretion increases excretion of water.
C,D Increased GFR or increased filtration fraction lead to greater excretion, and therefore decreased blood volume.
E Increased medullary blood flow reduces medullary osmolality and leads to greater water excretion.
13. A. K+ secretion is decreased by a decrease in plasma aldosterone, causing retention of K+ and hyperkalemia (p. 172).
B Urinary K+ excretion is determined mostly by K+ secretion into the cortical collecting duct, not by proximal K+ reabsorption.
C Reduced aldosterone also decreases Na+ reabsorption.
D Low blood pressure and loss of volume will reduce flow rate.
E Aldosterone is a corticosteroid, and its secretion is decreased in Addison disease.
14. B. Aldosterone causes Na+ retention, so urine Na+ is reduced (p. 168).
A Renin output is slightly suppressed by hypervolemia, or high blood volume.
C,D Plasma volume expands due to Na+ retention, and blood pressure rises.
E Aldosterone, by causing increased Na+ reabsorption, reduces water excretion.
15. C. The diuretic causes loss of Na+ and contraction of plasma volume, resulting in slightly reduced blood pressure (not D) (p. 169). A,B,E Once the diuretic is no longer acting, the kidneys reabsorb more Na+. Urinary Na+ and water excretion now decrease, and the renin level rises.
16. E. A rise in K+ clearance without a change in creatinine clearance indicates increased secretion of K+, not a decrease (D). K+ is secreted in the distal nephron, not reabsorbed in the proximal tubule or distal nephron (A,C) (pp.171–173).
B Less aldosterone decreases K+ secretion in the distal nephron.
17. D. The loop of Henle as a whole actively removes salt from the tubular fluid and deposits it in the outer medullary interstitium (pp. 178–179).
A The tubular fluid that leaves the loop of Henle is hyposmotic.
B ADH controls water reabsorption in the collecting ducts.
C Countercurrent exchange occurs in the vasa recta.
E Urea is secreted into the loop of Henle (urea recycling).
18. D. ADH increases permeability of the collecting duct to water (p. 178).
A,B ADH at normal levels has minimal effect on arterioles or the proximal tubule.
C Although the main action of ADH involves water reabsorption, it also stimulates salt reabsorption in the thick ascending limb.
E By stimulating urea reabsorption in the medullary collecting ducts, ADH promotes urea secretion in the loop of Henle.
19. D. Decreased Cl− reabsorption by the NKCC multiporter in the loop of Henle decreases dilution of the tubular fluid, reduces net solute reabsorption, and diminishes the corticomedullary osmotic gradient. The result is a diuresis with a nearly isosmotic urine (p. 179).
A,E Inhibition of renin and aldosterone secretion inhibits Na+ reabsorption, but not in the loop of Henle, so urine could still be hyper-osmotic.
B Increase of ADH secretion increases water reabsorption in the distal nephron and medullary collecting ducts, producing a concentrated urine.
C Increased permeability to water produces a concentrated urine.
20. B. Excessive ADH promotes excessive water reabsorption, so urine is concentrated, and plasma Na+ and osmolarity are reduced (p. 178).
A In dehydration, both plasma Na+ and osmolarity are elevated.
C,D In either diabetes insipidus or water intoxication, the urine is dilute.
E In diabetes mellitus, the plasma would be hyperosmotic due to the excess glucose.
21. E. Large acid loads are excreted primarily in the form of NH4+ (p. 188).
A When excreting acid loads, the kidneys reabsorb all filtered bicarbonate.
B Titratable acid is formed by protonating filtered base, not by secretion.
C Even with a low urinary pH, the amount of free, unbuffered H+ is trivial.
D H+ secretion lowers urine pH.
22. A. A high Pco2 could be either a primary respiratory acidosis or compensation for a primary metabolic alkalosis. Because the pH is toward the low end of normal, this indicates a respiratory acidosis that is well compensated (therefore B–D incorrect) (p. 190).
E Although the pH is toward the low end of normal, the Pco2 is above normal therefore the patient’s acid–base status is not normal.
23. B. Elevation of Pco2 causes a compensating increase in plasma HCO3− concentration, not a decrease (A) (p. 190).
C Plasma H+ is on the high side of normal.
D Physically dissolved CO2 is what determines Pco2 and is high.
E Total CO2 (dissolved CO2 + bicarbonate) is high.
24. C. Raising plasma [HCO3−] requires renal generation of HCO3− (p. 190).
A,B By definition, a respiratory acidosis is a high Pco2 that exists because of hypoventilation.
D Renal compensation requires hours to days.
E The generation of new bicarbonate requires increased acid excretion, which occurs primarily as NH4+.
25. C. Uncompensated respiratory alkalosis is characterized by an alkaline pH, reduced Pco2, and slightly reduced HCO3− (pp. 192–193). A This is compensated respiratory acidosis.
B This is respiratory acidosis.
D This is metabolic alkalosis.
E This is metabolic acidosis.
26. E. In a steady state, fluid intake must equal fluid output, and regulatory systems adjust output to match input.
A Urine output is not affected by the normal range of arterial pressures.
B CO has no direct influence on urine output.
C ADH is an important regulator that keeps plasma osmolality constant in the face of variable fluid intake.
D Central venous pressure is normally controlled within a small range, so it has little effect on urine output.