Physiology Review Questions: The Body Fluids and Kidneys

55. The GFR of a 26-year-old man with glomerulonephritis decreases by 50% and remains at that level for one month. For which substance would you expect to find the greatest increase in plasma concentration? A) Creatinine B) K+ C) Glucose D) Na+ E) Phosphate F) H+

A) A 50% reduction of GFR would approximately double the plasma creatinine concentration because creatinine is not reabsorbed or secreted, and its excretion depends largely on glomerular filtration. Therefore, when GFR decreases, the plasma concentration of creatinine increases until the renal excretion of creatinine returns to normal. Plasma concentrations of glucose, potassium, sodium, and hydrogen ions are closely regulated by multiple mechanisms that keep them relatively constant even when GFR falls to very low levels. Plasma phosphate concentration is also maintained near normal until GFR falls to below 20% to 30% of normal.

79. Which change, compared with normal, would be expected to occur, under steady-state conditions, in a patient whose severe renal disease has reduced the number of functional nephrons to 25% of normal? A) Increased GFR of the surviving nephrons B) Decreased urinary creatinine excretion rate C) Decreased urine flow rate in the surviving nephrons D) Decreased urinary excretion of sodium E) Increased urine-concentrating ability

A) A reduction in the number of functional nephrons to 25% of normal would cause a compensatory increase in GFR and urine flow rate of the surviving nephrons and decreased urine concentrating ability. Under steady-state conditions, the urinary creatinine excretion rate and sodium excretion rate would be maintained at normal levels. (For further information, see TMP14, Table 32-6.)

83. In a person on a very low potassium diet, which part of the nephron would be expected to reabsorb the most potassium? A) A B) B C) C D) D E) E

A) About 65% of the filtered potassium is reabsorbed in the proximal tubule, and another 20% to 30% is reabsorbed in the loop of Henle. Although most of the daily variation in potassium excretion is caused by changes in potassium secretion in the distal and collecting tubules, only a small percentage of the filtered potassium load can be reabsorbed in these nephron segments. (For further information, see TMP14, Figure 30-2.)

24. If a person maintains a high (150 mmol/day) potassium diet, which part of the nephron would be expected to reabsorb the most potassium? Choose the appropriate nephron site in the figure below. A) A B) B C) C D) D E) E F) F

A) Approximately 65% of the filtered load of potassium is reabsorbed in the proximal tubule. Variations in renal excretion of potassium during change in potassium intake are achieved mainly by changes in potassium secretion in collecting tubules. With high potassium intake, the proximal tubule still reabsorbs a high fraction of the filtered load of potassium.

126. In a person with chronic respiratory acidosis who has partial renal compensation, you would expect to find which changes, compared with normal? ______ urinary excretion of NH4 +; ______ plasma concentration; and _____ urine pH. A) Increased, increased, decreased B) Increased, decreased, decreased C) No change in, increased, decreased D) No change in, no change in, decreased E) Increased, no change in, increased

A) Chronic respiratory acidosis is caused by insufficient pulmonary ventilation, resulting in an increase in PCO2. Acidosis, in turn, stimulates the secretion of hydrogen ions into the tubular fluid and increased renal tubular production of NH4 +, which further contributes to the excretion of hydrogen ions and the renal production of HCO3, thereby increasing plasma bicarbonate concentration. The increased tubular secretion of hydrogen ions also reduces urine pH.

119. Which of the following would you expect to find in a patient who has chronic diabetic ketoacidosis? A) Decreased renal HCO3 excretion, increased NH4 + excretion, increased plasma anion gap B) Increased respiration rate, decreased arterial PCO2, decreased plasma anion gap C) Increased NH4 + excretion, increased plasma anion gap, increased urine pH D) Increased renal HCO3 production, increased NH4 + excretion, decreased plasma anion gap E) Decreased urine pH, decreased renal HCO3 excretion, increased arterial

A) Diabetic ketoacidosis results in a metabolic acidosis that is characterized by a decrease in plasma bicarbonate concentration, increased anion gap (due to the addition of unmeasured anions to the extracellular fluid along with the ketoacids), and a renal compensatory response that includes increased secretion of NH4 +. There is also an increased respiratory rate with a reduction in arterial PCO2, as well as decreased urine pH and decreased renal HCO3 excretion.

127. Increases in both renal blood flow and GFR are caused by which mechanism? A) Dilation of the afferent arterioles B) Increased glomerular capillary filtration coefficient C) Increased plasma colloid osmotic pressure D) Dilation of the efferent arterioles

A) Dilation of the afferent arterioles leads to an increase in the glomerular hydrostatic pressure and therefore an increase in GFR, as well as an increase in renal blood flow. Increased glomerular capillary filtration coefficient would also raise the GFR but would not be expected to alter renal blood flow. Increased plasma colloid osmotic pressure or dilation of the efferent arterioles would both tend to reduce the GFR. Increased blood viscosity would tend to reduce renal blood flow and GFR.

70. A 22-year-old woman runs a 10-km race on a hot day and becomes dehydrated. Assuming that her ADH levels are very high and that her kidneys are functioning normally, in which part of the renal tubule is the most water reabsorbed? A) Proximal tubule B) Loop of Henle C) Distal tubule D) Cortical collecting tubule E) Medullary collecting duct

A) In normally functioning kidneys, approximately two thirds of the water filtered by the glomerular capillaries is reabsorbed in the proximal tubule. Although dehydration increases ADH levels and water reabsorption by the distal tubules, collecting tubules, and collecting ducts and this action contributes importantly to decreased water excretion in dehydration, the total amount of water that remains in these tubular segments is small compared with the amount of water in the proximal tubules.

113. Which change tends to increase urinary calcium (Ca2+) excretion? A) Extracellular fluid volume expansion B) Increased plasma parathyroid hormone concentration C) Decreased blood pressure D) Increased plasma phosphate concentration E) Metabolic alkalosis

A) In the proximal tubule, calcium reabsorption usually parallels sodium and water reabsorption. With extracellular volume expansion or increased blood pressure, proximal sodium and water reabsorption are reduced, and a reduction in calcium reabsorption also occurs, causing increased urinary excretion of calcium. Increased parathyroid hormone, increased plasma phosphate concentration, and metabolic alkalosis all tend to decrease the renal excretion of calcium.

129. An older adult patient reports muscle weakness and lethargy. A urine specimen reveals a Na+ concentration of 600 mmol/l and an osmolarity of 1200 mOsm/l. Additional laboratory tests provide the following information: plasma Na+ concentration = 167 mmol/l, plasma renin activity = 4 ng angiotensin I/ml/h (normal = 1 ml/h), plasma ADH = 60 pg/ml (normal = 3 pg/ml), and plasma aldosterone = 15 ng/dl (normal = 6 ng/dl). What is the most likely reason for this patient's hypernatremia? A) Dehydration caused by decreased fluid intake B) Syndrome of inappropriate ADH C) Nephrogenic diabetes insipidus D) Primary aldosteronism E) Renin-secreting tumor

A) In this example, the plasma sodium concentration is markedly increased but the urine sodium concentration is relatively normal, and urine osmolarity is almost maximally increased to 1200 mOsm/l. In addition, there are increases in plasma renin, ADH, and aldosterone, which is consistent with dehydration caused by decreased fluid intake. The syndrome of inappropriate ADH would result in a decrease in plasma sodium concentration, as well as suppression of renin and aldosterone secretion. Nephrogenic diabetes insipidus, caused by the kidneys' failure to respond to ADH, would also be associated with dehydration, but urine osmolarity would be reduced rather than increased. Primary aldosteronism would tend to cause sodium and water retention with only a modest change in plasma sodium concentration and a marked reduction in the secretion of renin. Likewise, a renin-secreting tumor would be associated with increases in plasma aldosterone concentration and plasma renin activity but only a modest change in plasma sodium concentration.

25. Which of the following would tend to cause hypokalemia by shifting potassium from the extracellular fluid into the intracellular fluid? A) Metabolic alkalosis B) Insulin deficiency C) Aldosterone deficiency D) Beta-adrenergic receptor blockade E) Increased extracellular fluid osmolarity

A) Metabolic alkalosis shifts potassium from the extracellular fluid into the cells and contributes to hypokalemia. Insulin deficiency, aldosterone deficiency, beta-adrenergic blockade, and increased extracellular fluid osmolarity all cause a shift of potassium from the cells to the extracellular fluid.

57. If the average hydrostatic pressure in the glomerular capillaries is 50 mm Hg, the hydrostatic pressure in the Bowman's space is 12 mm Hg, the average colloid osmotic pressure in the glomerular capillaries is 30 mm Hg, and there is no protein in the glomerular ultrafiltrate, what is the net pressure driving glomerular filtration? A) 8 mm Hg B) 32 mm Hg C) 48 mm Hg D) 60 mm Hg E) 92 mm Hg

A) The net filtration pressure at the glomerular capillaries is equal to the sum of the forces favoring filtration (glomerular capillary hydrostatic pressure) minus the forces that oppose filtration (hydrostatic pressure in Bowman's space and glomerular colloid osmotic pressure). Therefore, the net pressure driving glomerular filtration is 50 − 12 − 30 = 8 mm Hg.

84. Which part of the nephron normally reabsorbs the most water? A) A B) B C) C D) D E) E

A) The proximal tubule normally absorbs approximately 65% of the filtered water, with much smaller percentages being reabsorbed in the descending loop of Henle and in the distal and collecting tubules. The ascending limb of the loop of Henle is relatively impermeable to water and therefore reabsorbs very little water.

14. Which of the following occurs in type A intercalated cells of the collecting tubules? A) Secretion of H+, reabsorption of HCO3-, and reabsorption of K+ B) Secretion of H+, reabsorption of HCO3-, and secretion of K+ C) Secretion of K+, reabsorption of Na+, and reabsorption of HCO3- D) Reabsorption of H+, secretion of HCO3-, and secretion of K+ E) Reabsorption of H+, secretion of HCO3-, and reabsorption of K+

A) Type A intercalated cells of the collecting tubules secrete H+ by a hydrogen-ATPase transporter and by a hydrogen-potassium-ATPase transporter. They also reabsorb and K+

12. If glomerular filtration rate suddenly decreases by 50%, from 80 ml/min to 40 ml/min and tubular fluid reabsorption simultaneously decreases from 78 ml/min to 40 ml/min, which of the following changes in urinary excretion rate will occur (assuming that the changes in GFR and tubular fluid reabsorption are maintained)? A) Urine flow rate will decrease to zero B) Urine flow rate will not change C) Urine flow rate will decrease by 50% D) Urine flow rate will increase by 50%

A) Urine excretion rate is equal to glomerular filtration rate (GFR) minus tubular reabsorption rate. In this example, the final is 40 ml/min, and the tubular reabsorption rate is 40 ml/min. Therefore, the urine excretion rate is zero.

23. If creatinine clearance = 100 ml/min, urine flow rate = 1.0 ml/min, plasma Na+ concentration = 140 mmol/l, and urine Na+ concentration = 80 mmol/l, what is the approximate rate of Na+ excretion? A) 0.08 mmol/min B) 0.16 mmol/min C) 16 mmol/min D) 160 mmol/min E) Excretion rate of Na+ cannot be calculated from these data

A) Urine excretion rate of Na+ is equal to urine flow rate (1.0 ml/min or 0.001 l/min) multiplied by urine Na+ concentration (80 mmol/l), or 0.08 mmol/min.

107. Which change would you expect to find in a patient who developed acute renal failure after ingesting poisonous mushrooms that caused renal tubular necrosis? A) Increased plasma bicarbonate concentration B) Metabolic acidosis C) Decreased plasma potassium concentration D) Decreased blood urea nitrogen concentration E) Decreased hydrostatic pressure in Bowman's capsule

B) Acute renal failure caused by tubular necrosis would cause the rapid development of metabolic acidosis due to the kidneys' failure to rid the body of the acid waste products of metabolism. The metabolic acidosis would lead to decreased plasma HCO3 concentration. Acute renal failure would also lead to a rapid increase in blood urea nitrogen concentration and a significant increase in plasma potassium concentration due to the kidneys' failure to excrete electrolytes or nitrogenous waste products. Necrosis of the renal epithelial cells causes them to slough away from the basement membrane and plug up the renal tubules, thereby increasing hydrostatic pressure in Bowman's capsule and decreasing GFR.

Urine flow rate = 1 ml/min Urine inulin concentration = 100 mg/ml Plasma inulin concentration = 2 mg/ml Urine urea concentration = 50 mg/ml Plasma urea concentration = 2.5 mg/ml 36. What is the GFR? A) 25 ml/min B) 50 ml/min C) 100 ml/min D) 125 ml/min E) None of the above

B) GFR is equal to inulin clearance, which is calculated as the urine inulin concentration (100 mg/ml) × urine flow rate (1 ml/min)/plasma inulin concentration (2 mg/ml), which is equal to 50 ml/min.

77. Under conditions of normal renal function, which of the following statements is true of the concentration of urea in tubular fluid at the end of the proximal tubule? A) It is higher than the concentration of urea in tubular fluid at the tip of the loop of Henle B) It is higher than the concentration of urea in the plasma C) It is higher than the concentration of urea in the final urine in antidiuresis D) It is lower than plasma urea concentration because of active urea reabsorption along the proximal tubule

B) Approximately 30% to 40% of the filtered urea is reabsorbed in the proximal tubule. However, the tubular fluid urea concentration increases because urea is not nearly as permeant as water in this nephron segment. Urea concentration increases further in the tip of the loop of Henle because water is reabsorbed in the descending limb of the loop of Henle. Under conditions of antidiuresis, urea is further concentrated as water is reabsorbed and as fluid flows along the collecting ducts. Therefore, the final urine concentration of urea is substantially greater than the concentration in the proximal tubule or in the plasma.

38. In normal kidneys, which of the following is true of the osmolarity of renal tubular fluid that flows through the early distal tubule in the region of the macula densa? A) Usually isotonic compared with plasma B) Usually hypotonic compared with plasma C) Usually hypertonic compared with plasma D) Hypertonic, compared with plasma, in antidiuresis

B) As water flows up the ascending limb of the loop of Henle, solutes are reabsorbed, but this segment is relatively impermeable to water; progressive dilution of the tubular fluid occurs so that the osmolarity decreases to approximately 100 mOsm/l by the time the fluid reaches the early distal tubule. Even during maximal antidiuresis, this portion of the renal tubule is relatively impermeable to water and is therefore called the diluting segment of the renal tubule.

64. An adrenal tumor that causes excess aldosterone secretion would tend to __________ plasma K+ concentration, __________ plasma pH, __________ renin secretion, and __________ blood pressure. A) decrease, decrease, decrease, decrease B) decrease, increase, decrease, increase C) decrease, decrease, decrease, increase D) decrease, increase, increase, increase E) increase, increase, decrease, increase F) increase, decrease, decrease, increase

B) Excess aldosterone increases sodium reabsorption and potassium secretion by the principal cells of the collecting tubules, causing sodium retention, increased blood pressure, and decreased renin secretion while increasing excretion of potassium and tending to decrease plasma potassium concentration. Excess aldosterone also causes a shift of potassium from the extracellular fluid into the cells, further reducing plasma potassium concentration. Aldosterone excess also stimulates hydrogen ion secretion and bicarbonate reabsorption by the intercalated cells and tends to increase plasma pH (alkalosis). Therefore, the classic manifestations of excess aldosterone secretion are hypokalemia, hypertension, alkalosis, and low renin levels.

109. Which of the following is true of the tubular fluid that passes through the lumen of the early distal tubule in the region of the macula densa? A) It is usually isotonic B) It is usually hypotonic C) It is usually hypertonic D) It is hypertonic in antidiuresis E) It is hypertonic when the filtration rate of its own nephron decreases to 50% below normal

B) Fluid entering the early distal tubule is almost always hypotonic because sodium and other ions are actively transported out of the thick ascending loop of Henle, whereas this portion of the nephron is virtually impermeable to water. For this reason, the thick ascending limb of the loop of Henle and the early part of the distal tubule are often called the diluting segment.

81. A patient's urine is collected for 2 hours, and the total volume is 600 ml during this time. Her urine osmolarity is 150 mOsm/l, and her plasma osmolarity is 300 mOsm/l. What is her "free water clearance"? A) +5.0 ml/min B) +2.5 ml/min C) 0.0 ml/min D) −2.5 ml/min E) −5.0 ml/min

B) Free water clearance is calculated as urine flow rate (600 ml/2 h, or 5 ml/min) − osmolar clearance (urine osmolarity × urine flow rate/plasma osmolarity). Therefore, free water clearance is equal to +2.5 ml/min.

91. Which diuretic inhibits Na+-2Cl − -K+ co-transport in the loop of Henle as its primary action? A) Thiazide diuretic B) Furosemide C) Carbonic anhydrase inhibitor D) Osmotic diuretic E) Amiloride F) Spironolactone

B) Furosemide is a powerful inhibitor of the Na+-2Cl − -K+ co-transporter in the loop of Henle. Thiazide diuretics primarily inhibit NaCl reabsorption into the distal tubule, whereas carbonic anhydrase inhibitors decrease bicarbonate reabsorption in the tubules. Amiloride inhibits sodium channel activity, whereas spironolactone inhibits the action of mineralocorticoids in the renal tubules. Osmotic diuretics inhibit water and solute reabsorption by increasing osmolarity of the tubular fluid.

To evaluate kidney function in a 45-year-old woman with type 2 diabetes, you ask her to collect her urine for a 24-hour period. She collects 3600 ml of urine in that period. The clinical laboratory returns the following results after analyzing the patient's urine and plasma samples: plasma creatinine = 4 mg/dl, urine creatinine = 32 mg/dl, plasma potassium = 5 mmol/l, and urine potassium = 10 mmol/l. 100. What is this patient's approximate GFR, assuming that she collected all her urine in the 24-hour period? A) 10 ml/min B) 20 ml/min C) 30 ml/min D) 40 ml/min E) 80 ml/min

B) GFR is approximately equal to the clearance of creatinine. Creatinine clearance = urine creatinine concentration (32 mg/dl) × urine flow rate (3600 ml/24 h, or 2.5 ml/min) ÷ plasma creatinine concentration (4 mg/dl) = 20 ml/min.

72. A female patient has unexplained hypernatremia (plasma Na+ = 167 mmol/l) and reports frequent urination and large urine volumes. A urine specimen reveals that the Na+ concentration is 15 mmol/l (very low) and the osmolarity is 155 mOsm/l (very low). Laboratory tests reveal the following data: plasma renin activity = 3 ng angiotensin I/ml/h (normal = 1.0), plasma ADH = 30 pg/ml (normal = 3 pg/ml), and plasma aldosterone = 20 ng/dl (normal = 6 ng/dl). Which of the following is the most likely reason for her hypernatremia? A) Simple dehydration caused by decreased water intake B) Nephrogenic diabetes insipidus C) Central diabetes insipidus D) Syndrome of inappropriate ADH E) Primary aldosteronism F) Renin-secreting tumor

B) Hypernatremia can be caused by excessive sodium retention or water loss. The fact that the patient has large volumes of dilute urine suggests excessive urinary water excretion. Of the two possible disturbances listed that could cause excessive urinary water excretion (nephrogenic diabetes insipidus and central diabetes insipidus), nephrogenic diabetes insipidus is the most likely cause. Central diabetes insipidus (decreased ADH secretion) is not the correct answer because plasma ADH levels are markedly elevated. Simple dehydration due to decreased water intake is unlikely because the patient is excreting large volumes of dilute urine.

124. Which change would tend to increase Ca2+ reabsorption in the renal tubule? A) Extracellular fluid volume expansion B) Increased plasma parathyroid hormone concentration C) Increased blood pressure D) Decreased plasma phosphate concentration E) Metabolic acidosis

B) Increased levels of parathyroid hormone stimulate calcium reabsorption in the thick ascending loops of Henle and distal tubules. Extracellular fluid volume expansion, increased blood pressure, decreased plasma phosphate concentration, and metabolic acidosis are all associated with decreased calcium reabsorption by the renal tubules.

49. What would cause the greatest degree of hyperkalemia? A) Increase in potassium intake from 60 to 180 mmol/day in a person with normal kidneys and a normal aldosterone system B) Chronic treatment with a diuretic that inhibits the action of aldosterone C) Decrease in sodium intake from 200 to 100 mmol/day D) Chronic treatment with a diuretic that inhibits loop of Henle Na+-2Cl − -K+ co-transport E) Chronic treatment with a diuretic that inhibits sodium reabsorption in the collecting ducts

B) Inhibition of aldosterone causes hyperkalemia by two mechanisms: (1) shifting potassium out of the cells into the extracellular fluid and (2) decreasing cortical collecting tubular secretion of potassium. Increasing potassium intake from 60 to 180 mmol/day would cause only a very small increase in plasma potassium concentration in a person with normal kidneys and normal aldosterone feedback mechanisms. A reduction in sodium intake also has very little effect on plasma potassium concentration. Chronic treatment with a diuretic that inhibits loop of Henle Na+-2Cl − -K+ co-transport would tend to cause potassium loss in the urine and hypokalemia. However, chronic treatment with a diuretic that inhibits sodium reabsorption in the collecting ducts, such as amiloride, would have little effect on plasma potassium concentration.

120. Using the indicator dilution method to assess body fluid volumes in a 40-year-old man weighing 70 kg, the inulin space is calculated to be 16 l, and 125I-albumin space is 4 l. If 60% of his total body weight is water, what is his approximate interstitial fluid volume? A) 4 l B) 12 l C) 16 l D) 26 l E) 38 l F) 42 l

B) Interstitial fluid volume cannot be measured directly, but it can be calculated as the difference between extracellular fluid volume (inulin space = 16 l) and plasma volume (125I-albumin space = 4 l). Therefore, interstitial fluid volume is approximately 12 l.

128. A 55-year-old male patient with hypertension has had his blood pressure reasonably well controlled by administration of a thiazide diuretic. At his last visit (6 months ago), his blood pressure was 130/75 mm Hg, and his serum creatinine was 1 mg/100 ml. He has been exercising regularly for the past 2 years but recently has reported knee pain and began taking large amounts of a nonsteroidal antiinflammatory drug. When he arrives at your office, his blood pressure is 155/85 mm Hg, and his serum creatinine is 2.5 mg/100 ml. What best explains his increased serum creatinine level? A) Increased efferent arteriolar resistance that reduced GFR B) Increased afferent arteriolar resistance that reduced GFR C) Increased glomerular capillary filtration coefficient that reduced GFR D) Increased angiotensin II formation that decreased GFR E) Increased muscle mass due to the exercise

B) Nonsteroidal antiinflammatory drugs inhibit the synthesis of prostaglandins, which, in turn, causes constriction of afferent arterioles that can reduce the GFR. The decrease in GFR, in turn, leads to an increase in serum creatinine. Increased efferent arteriole resistance and increased glomerular capillary filtration coefficient would both tend to increase rather than reduce GFR. Increasing muscle mass due to exercise would cause very little change in serum creatinine.

28. Partial obstruction of a major vein draining a tissue would tend to __________ lymph flow rate, __________ interstitial fluid hydrostatic pressure, and __________ interstitial fluid protein concentration in the tissue drained by that vein. A) increase, increase, increase B) increase, increase, decrease C) increase, decrease, decrease D) decrease, decrease, decrease E) decrease, increase, increase F) decrease, increase, decrease

B) Partial obstruction of a major vein draining a tissue would increase capillary hydrostatic pressure in the tissue, which, in turn, would raise capillary fluid filtration and cause increases interstitial fluid volume, interstitial fluid hydrostatic pressure, and lymph flow. The increased lymph flow would "wash out" proteins from the interstitial fluid, decreasing interstitial fluid protein concentration.

10. If GFR = 60 ml/min, urine flow rate = 2.0 ml/min, plasma K+ concentration = 4.0 mmol/l, and urine K+ concentration = 80 mmol/l, what is the approximate rate of K+ excretion? A) 0.08 mmol/min B) 0.16 mmol/min C) 0.32 mmol/min D) 16 mmol/min E) 160 mmol/min F) Excretion rate of K+ cannot be determined from these data

B) Potassium excretion in this case is equal to urine concentration of K+ (80 mmol/l) multiplied by the urine flow rate (2.0 ml/min, or 0.002 l/min) which is 0.16 mmol/min.

65. Which of the following tends to increase potassium secretion by the cortical collecting tubule? A) A diuretic that inhibits the action of aldosterone (e.g., spironolactone) B) A diuretic that decreases loop of Henle sodium reabsorption (e.g., furosemide) C) Decreased plasma potassium concentration D) Acute metabolic acidosis E) Low sodium intake

B) Potassium secretion by the cortical collecting ducts is stimulated by (1) aldosterone, (2) increased plasma potassium concentration, (3) increased flow rate in the cortical collecting tubules, and (4) alkalosis. Therefore, a diuretic that inhibits aldosterone, decreased plasma potassium concentration, acute acidosis, and low sodium intake would all tend to decrease potassium secretion by the cortical collecting tubules. A diuretic that decreases loop of Henle sodium reabsorption, however, would tend to increase the flow rate in the cortical collecting tubule and therefore stimulate potassium secretion.

3. Calculate the approximate extracellular fluid volume of a patient after administration of 3.0 l of 5% glucose solution, assuming complete metabolism of the glucose, osmotic equilibrium, and no excretion of water or electrolytes. Also assume the following initial conditions prior to infusing the glucose solution: Body weight = 50 kg Plasma sodium concentration = 170 mmol/l Plasma osmolarity = 360 mOsm/l Intracellular fluid volume = 40% of body weight Extracellular fluid volume = 20% of body weight Molecular wt of glucose = 180 g/mole A) 8.0 l B) 10.7 l C) 11.7 l D) 130 l E) 20.3 l F) 21.3 l G) 30.0 l

B) The initial total body water would be 60% of body weight or ∼30 L. The initial total mOsm in the body fluids would be 30 l × 360 mOsm/l, or 10,800 mOsm. The initial extracellular fluid volume would be 20% of body weight, or ∼10 l. The initial total mOsm in the extracellular fluid would be 360 mOsm/l × 10 l, or 3600 mOsm. After adding the glucose solution, total body water would be 30 l + 2 l or 32 l. If we assume that all of the glucose is metabolized, the final mOsm would also be 10,800. Therefore, the extracellular and intracellular osmolarity would be 10,800 mOsm/32 l, or approximately 338 mOsm/l. The extracellular fluid would continue to have a total of 3600 mOsm. Therefore, the final extracellular fluid volume would be 3600 mOsm/338 mOsm per l, or ∼10.7 l.

68. A 48-year-old woman reports severe polyuria (producing about 0.5 l of urine each hour) and polydipsia (drinking two to three glasses of water every hour). Her urine contains no glucose, and she is placed on overnight water restriction for further evaluation. The next morning, she is weak and confused, her sodium concentration is 160 mEq/l, and her urine osmolarity is 80 mOsm/l. Which of the following is the most likely diagnosis? A) Diabetes mellitus B) Diabetes insipidus C) Primary aldosteronism D) Renin-secreting tumor E) Syndrome of inappropriate ADH

B) The most likely diagnosis for this patient is diabetes insipidus, which can account for the polyuria and the fact that her urine osmolarity is very low (80 mOsm/l) despite overnight water restriction. In many patients with diabetes insipidus, the plasma sodium concentration can be maintained relatively close to normal by increasing fluid intake (polydipsia). When water intake is restricted, however, the high urine flow rate leads to rapid depletion of extracellular fluid volume and severe hypernatremia, as occurred in this patient. The fact that she has no glucose in her urine rules out diabetes mellitus. Neither primary aldosteronism nor a renin-secreting tumor would lead to an inability to concentrate the urine after overnight water restriction. Syndrome of inappropriate ADH would cause excessive fluid retention and increased urine osmolarity.

45. The clinical laboratory returned the following values for arterial blood taken from a patient: plasma pH = 7.28, plasma HCO3 = 32 , and plasma partial pressure of carbon dioxide (PCO2) = 70 mm Hg. What is this patient's acid-base disorder? A) Acute respiratory acidosis without renal compensation B) Respiratory acidosis with partial renal compensation C) Acute metabolic acidosis without respiratory compensation D) Metabolic acidosis with partial respiratory compensation

B) This patient has respiratory acidosis because the plasma pH is lower than the normal level of 7.4, and the plasma PCO2 is higher than the normal level of 40 mm Hg. The elevation in plasma bicarbonate concentration above normal (∼24 mEq/l) is due to partial renal compensation for the respiratory acidosis. Therefore, this patient has respiratory acidosis with partial renal compensation.

8. A patient with diabetes mellitus has a glomerular filtration rate of 100 ml/min, a urine flow rate of 4.0 ml/min, and a urine glucose concentration of 2 mg/ml. If he has a kidney transport maximum for glucose of 200 mg/min, what would be his approximate rate of glucose excretion? A) 0 mg/min B) 8 mg/min C) 100 mg/min D) 180 mg/min E) 300 mg/min F) Urinary excretion rate of glucose cannot be determined from these data

B) With a glomerular filtration rate of 100 ml/min and a plasma glucose concentration of 4 mg/ml, the filtered load of glucose would be 400 mg/min. Since the transport maximum for glucose in this case is 200 mg/min, the maximum rate of glucose reabsorption is 200 mg/min. Glucose excreted rate is therefore the difference between the filtered load of glucose (400 mg/min) and the glucose reabsorption rate (200 mg/min), or 200 mg/min.

27. Which of the following solutions, when infused intravenously, would result in an increase in extracellular fluid volume, a decrease in intracellular fluid volume, and an increase in total body water after osmotic equilibrium? A) 1 l of 0.9% sodium chloride (NaCl) solution B) 1 l of 0.45% NaCl solution C) 1 l of 3% NaCl solution D) 1 l of 5% dextrose solution E) 1 l of pure water

C) A 3% NaCl solution is hypertonic, and when infused intravenously, it would increase extracellular fluid volume and osmolarity, thereby causing water to flow out of the cell. This action would decrease intracellular fluid volume and further increase extracellular fluid volume. The 0.9% NaCl solution and 5% dextrose solution are isotonic and therefore would not reduce intracellular fluid volume. Pure water and the 0.45% NaCl solution are hypotonic, and when infused, they would increase both intracellular and extracellular fluid volumes.

56. Which changes would you expect to find after administering a vasodilator drug that caused a 50% decrease in afferent arteriolar resistance and no change in arterial pressure? A) Decreased renal blood flow, decreased GFR, and decreased peritubular capillary hydrostatic pressure B) Decreased renal blood flow, decreased GFR, and increased peritubular capillary hydrostatic pressure C) Increased renal blood flow, increased GFR, and increased peritubular capillary hydrostatic pressure D) Increased renal blood flow, increased GFR, and no change in peritubular capillary hydrostatic pressure E) Increased renal blood flow, increased GFR, and decreased peritubular capillary hydrostatic pressure

C) A 50% reduction in afferent arteriolar resistance with no change in arterial pressure would increase renal blood flow and glomerular hydrostatic pressure, thereby increasing GFR. At the same time, the reduction in afferent arteriolar resistance would raise peritubular capillary hydrostatic pressure.

115. What would tend to decrease GFR by more than 20% in a normal kidney? A) Decrease in renal arterial pressure from 100 to 85 mm Hg B) 50% decrease in afferent arteriolar resistance C) 50% decrease in efferent arteriolar resistance D) 50% increase in the glomerular capillary filtration coefficient E) Decrease in plasma colloid osmotic pressure from 28 to 20 mm Hg

C) A 50% reduction in efferent arteriolar resistance would cause a large decrease in GFR—greater than 10%. A decrease in renal artery pressure from 100 to 85 mm Hg would cause only a slight decrease in GFR in a normal, autoregulating kidney. A decrease in afferent arteriole resistance, a decrease in plasma colloid osmotic pressure, or an increase in the glomerular capillary filtration coefficient would all tend to increase GFR.

4. A patient with cirrhosis experiences a doubling of his serum creatinine over a 6-month period after sustained heavy ingestion of a nonsteroidal antiinflammatory drug (NSAID) for his arthritis. Which of the following is the best explanation for his increased serum creatinine? A) Increased efferent arteriolar resistance which reduced glomerular filtration rate (GFR) B) Decreased Bowman's capsule pressure which reduced GFR C) Increased afferent arteriolar resistance which reduced GFR D) Increased glomerular capillary filtration coefficient which reduced GFR E) Increased renal prostaglandins due to the NSAID F) Increased nitric oxide formation due to the NSAID

C) A doubling of serum creatinine implies a reduction in glomerular filtration rate (GFR). Non-steroidal anti-inflammatory drugs (NSAIDS) inhibit prostaglandin synthesis, which would tend increase afferent arteriolar and reduce GFR.

34. Which of the following tends to decrease potassium secretion by the cortical collecting tubule? A) Increased plasma potassium concentration B) A diuretic that decreases proximal tubule sodium reabsorption C) A diuretic that inhibits the action of aldosterone (e.g., spironolactone) D) Acute alkalosis E) High sodium intake

C) Aldosterone stimulates potassium secretion by the principal cells of the collecting tubules. Therefore, blockade of the action of aldosterone with spironolactone would inhibit potassium secretion. Other factors that stimulate potassium secretion by the cortical collecting tubule include increased potassium concentration, increased cortical collecting tubule flow rate (as would occur with high sodium intake or a diuretic that reduces proximal tubular sodium reabsorption), and acute alkalosis.

69. Which substance is filtered most readily by the glomerular capillaries? A) Albumin in plasma B) Neutral dextran with a molecular weight of 25,000 C) Polycationic dextran with a molecular weight of 25,000 D) Polyanionic dextran with a molecular weight of 25,000 E) Red blood cells

C) The filterability of solutes in the plasma is inversely related to the size of the solute (molecular weight). Also, positively charged molecules are filtered more readily than are neutral molecules or negatively charged molecules of equal molecular weight. Therefore, the positively charged polycationic dextran with a molecular weight of 25,000 would be the most readily filtered substance of the choices provided. Red blood cells are not filtered at all by the glomerular capillaries under normal conditions.

A 65-year-old man had a heart attack and experiences cardiopulmonary arrest while being transported to the emergency department. Use the following laboratory values obtained from arterial blood to answer Questions 47 and 48. Plasma pH = 7.12 Plasma PO2 = 60 mm Hg Plasma HCO3 concentration = 19 mEq/l 47. Which of the following options best describes his acid-base disorder? A) Respiratory acidosis with partial renal compensation B) Metabolic acidosis with partial respiratory compensation C) Mixed acidosis: combined metabolic and respiratory acidosis D) Mixed alkalosis: combined respiratory and metabolic alkalosis

C) Because the patient has a low plasma pH (normal = 7.4), he has acidosis. The fact that his plasma bicarbonate concentration is also low (normal = 24 mEq/l) indicates that he has metabolic acidosis. However, he also appears to have respiratory acidosis because his plasma PCO2 is high (normal = 40 mm Hg). The rise in PCO2 is due to his impaired breathing as a result of cardiopulmonary arrest. Therefore, the patient has a mixed acidosis with combined metabolic and respiratory acidosis.

61. If distal tubule fluid creatinine concentration is 5 mg/100 ml and plasma creatinine concentration is 1.0 mg/100 ml, what is the approximate percentage of the water filtered by the glomerular capillaries that remains in the distal tubule? A) 5% B) 10% C) 20% D) 50% E) 80% F) 95%

C) Because water is reabsorbed by the renal tubules but creatinine is not reabsorbed, the concentration of creatinine in the renal tubular fluid will increase as fluid flows from the proximal to the distal tubule. An increase in the concentration from 1.0 mg/100 ml in the proximal tubule to 5.0 mg/100 ml in the distal tubule means that only about one fifth (20%) of the water that was in the proximal tubules remains in the distal tubule.

75. Which of the following would cause the most serious hypokalemia? A) A decrease in potassium intake from 150 mEq/day to 60 mEq/day D) An increase in sodium intake from 100 to 200 mEq/day C) Excessive aldosterone secretion plus high sodium intake D) Excessive aldosterone secretion plus low sodium intake E) A patient with Addison's disease F) Treatment with a beta-adrenergic blocker G) Treatment with spironolactone

C) Excess aldosterone and a high-salt diet could cause serious hypokalemia because aldosterone stimulates potassium secretion by the renal tubules (and therefore tends to increase potassium excretion), as well as causing a shift of potassium from the extracellular fluid into the cells. A high-salt diet would exacerbate the hypokalemia because this would increase collecting tubular flow rate, which would tend to further increase renal potassium secretion. Treatment with spironolactone or a beta-adrenergic blocker or Addison disease (adrenal insufficiency) would tend to increase plasma potassium concentration. Changes in sodium and potassium intakes over the ranges indicated would have minimal effects on plasma potassium concentration.

74. Juvenile (type 1) diabetes mellitus is often diagnosed because of polyuria (high urine flow) and polydipsia (frequent drinking) that occur because of which of the following? A) Increased delivery of glucose to the collecting duct interferes with the action of antidiuretic hormone B) Increased glomerular filtration of glucose increases Na+ reabsorption via the sodium-glucose co-transporter C) When the filtered load of glucose exceeds the renal threshold, a rising glucose concentration in the proximal tubule decreases the osmotic driving force for water reabsorption D) High plasma glucose concentration decreases thirst E) High plasma glucose concentration stimulates ADH release from the posterior pituitary

C) High urine flow occurs in type 1 diabetes because the filtered load of glucose exceeds the renal threshold, resulting in an increase in glucose concentration in the tubule, which decreases the osmotic driving force for water reabsorption. Increased urine flow reduces extracellular fluid volume and stimulates the release of ADH.

112. If the renal clearance of substance X is 300 ml/min and the glomerular filtration rate is 100 ml/min, it is most likely that substance X is A) Filtered freely but not secreted or reabsorbed B) Bound to plasma proteins C) Secreted D) Reabsorbed E) Bound to tubular proteins F) Clearance of a substance cannot be greater than the GFR

C) If the renal clearance is greater than the GFR, this implies that there must be secretion of that substance into the renal tubules. A substance that is freely filtered and not secreted or reabsorbed would have a renal clearance equal to the GFR.

125. A young man is found comatose, having taken an unknown number of sleeping pills an unknown time before. An arterial blood sample yields the following values: pH = 7.02, HCO3= 14 mEq/l, and PCO2= 68 mm Hg. Which of the following describes this patient's acid-base status most accurately? A) Uncompensated metabolic acidosis B) Uncompensated respiratory acidosis C) Simultaneous respiratory and metabolic acidosis D) Respiratory acidosis with partial renal compensation E) Respiratory acidosis with complete renal compensation

C) In this example, the acidosis is associated with a reduced plasma bicarbonate concentration, signifying metabolic acidosis. In addition, the patient also has an elevated , signifying respiratory acidosis. Therefore, the patient has simultaneous respiratory and metabolic acidosis.

114. Which change would you expect to find in a patient consuming a high-sodium diet (200 mEq/day) compared with the same patient on a normal-sodium diet (100 mEq/day), assuming steady-state conditions? A) Increased plasma aldosterone concentration B) Increased urinary potassium excretion C) Decreased plasma renin activity D) Decreased plasma atrial natriuretic peptide E) An increase in plasma sodium concentration of at least 5 mmol/l

C) Increasing sodium intake would decrease renin secretion and plasma renin activity, as well as reduce plasma aldosterone concentration and increase plasma atrial natriuretic peptide because of a mod est expansion of extracellular fluid volume. Although a high sodium intake would initially increase distal NaCl delivery, which would tend to increase potassium excretion, the decrease in aldosterone concentration would offset this effect, resulting in no change in potassium excretion under steady-state conditions. Even very large increases in sodium intake cause only minimal changes in plasma sodium concentration as long as the ADH-thirst mechanisms are fully operative.

A person with normal body fluid volumes weighs 60 kg and has an extracellular fluid volume of approximately 12.8 l, a blood volume of 4.3 l, and a hematocrit of 0.4; 57% of his body weight is water. Use this information to answer Questions 95-97. 97. What is the approximate interstitial fluid volume? A) 6.4 l B) 8.4 l C) 10.2 l D) 11.3 l E) 12.0 l

C) Interstitial fluid volume is calculated as the difference between extracellular fluid volume (12.8 l) and plasma volume (2.6 l), which is equal to 10.2 l.

A person with normal body fluid volumes weighs 60 kg and has an extracellular fluid volume of approximately 12.8 l, a blood volume of 4.3 l, and a hematocrit of 0.4; 57% of his body weight is water. Use this information to answer Questions 95-97. 95. What is the approximate intracellular fluid volume? A) 17.1 l B) 19.6 l C) 21.4 l D) 23.5 l E) 25.6 l

C) Intracellular fluid volume is calculated as the difference between total body fluid (0.57 × 60 g = 34.2 kg, or ∼34.2 l) and extracellular fluid volume (12.8 l), which equals 21.4 l.

62. Which change tends to increase peritubular capillary fluid reabsorption? A) Increased blood pressure B) Decreased filtration fraction C) Increased efferent arteriolar resistance D) Decreased angiotensin II E) Increased renal blood flow

C) Peritubular capillary fluid reabsorption is determined by the balance of hydrostatic and colloid osmotic forces in the peritubular capillaries. Increased efferent arteriolar resistance reduces peritubular capillary hydrostatic pressure and therefore increases the net force favoring fluid reabsorption. Increased blood pressure tends to raise peritubular capillary hydrostatic pressure and reduce fluid reabsorption. Decreased filtration fraction increases the peritubular capillary colloid osmotic pressure and tends to reduce peritubular capillary reabsorption. Decreased angiotensin II causes vasodilatation of efferent arterioles, raising peritubular capillary hydrostatic pressure, decreasing reabsorption, and decreasing tubular transport of water and electrolytes. Increased renal blood flow also tends to raise peritubular capillary hydrostatic pressure and decrease fluid reabsorption.

35. Because the usual rate of phosphate filtration exceeds the transport maximum for phosphate reabsorption, which statement is true? A) All the phosphate that is filtered is reabsorbed B) More phosphate is reabsorbed than is filtered C) Phosphate in the tubules can contribute significantly to titratable acid in the urine D) The "threshold" for phosphate is usually not exceeded E) Parathyroid hormone must be secreted for phosphate reabsorption to occur

C) Phosphate excretion by the kidneys is controlled by an overflow mechanism. When the transport maximum for reabsorbing phosphate is exceeded, the remaining phosphate in the renal tubules is excreted in the urine and can be used to buffer hydrogen ions and form titratable acid. Phosphate normally begins to spill into the urine when the concentration of extracellular fluid rises above a threshold of 0.8 mmol/l, which is usually exceeded.

A person with normal body fluid volumes weighs 60 kg and has an extracellular fluid volume of approximately 12.8 l, a blood volume of 4.3 l, and a hematocrit of 0.4; 57% of his body weight is water. Use this information to answer Questions 95-97. 96. What is the approximate plasma volume? A) 2.0 l B) 2.3 l C) 2.6 l D) 3.0 l E) 3.3 l

C) Plasma volume is calculated as blood volume (4.3 l) × (1.0 − hematocrit), which is 4.3 × 0.6 = 2.58 l (rounded up to 2.6).

16. Which of the following statements is incorrect? A) Urea transporters UT-A1 and UTA-3 in the collecting ducts are activated by antidiuretic hormone (ADH) B) Urea reabsorption in the inner medullary collecting duct is greater than in the distal tubule during dehydration C) Increased ADH markedly increases urea reabsorption by the cortical collecting tubule D) The inner medullary collecting tubule reabsorbs more urea during antidiuresis than the thick ascending limb of Henle's loop E) The cortical collecting tubule is less permeable to urea than is the inner medullary collecting duct during antidiuresis F) Passive diffusion of urea into the thin loops of Henle is facilitated by the urea transporter UT-A2

C) The cortical collecting tubule is relatively impermeable to urea, and very little reabsorption occurs in this tubular segment, even in the presence of ADH. All of the other statements are correct.

63. A 32-year-old man reports frequent urination. He is overweight (280 lb [127 kg], 5 feet 10 inches [178 cm] tall). After measuring the 24-hour creatinine clearance, you estimate his GFR to be 150 ml/min. His plasma glucose level is 300 mg/dl. Assuming that his renal transport maximum for glucose is normal, as shown in the figure above, what would be this patient's approximate rate of urinary glucose excretion? A) 0 mg/min B) 100 mg/min C) 150 mg/min D) 225 mg/min E) 300 mg/min F) Information provided is inadequate to estimate the glucose excretion rate

C) The filtered load of glucose in this example is determined as follows: GFR (150 ml/min) × plasma glucose (300 mg/dl) = 450 mg/min. The transport maximum for glucose in this example is 300 mg/min. Therefore, the maximum rate of glucose reabsorption is 300 mg/min. The urinary glucose excretion is equal to the filtered load (450 mg/min) minus the tubular reabsorption of glucose (300 mg/min), or 150 mg/min.

52. Which change tends to increase GFR? A) Increased afferent arteriolar resistance B) Decreased efferent arteriolar resistance C) Increased glomerular capillary filtration coefficient D) Increased Bowman's capsule hydrostatic pressure E) Decreased glomerular capillary hydrostatic pressure

C) The glomerular capillary filtration coefficient is the product of the hydraulic conductivity and surface area of the glomerular capillaries. Therefore, increasing the glomerular capillary filtration coefficient tends to increase GFR. Increased afferent arteriolar resistance, decreased efferent arteriolar resistance, increased Bowman's capsule hydrostatic pressure, and decreased glomerular hydrostatic pressure tend to decrease GFR.

29. A 36-year-old woman reports headaches and frequent urination. Laboratory values reveal the following information. Urine specific gravity = 1.003 Urine protein = negative Plasma sodium (Na+) = 165 mmol/l Plasma potassium (K+) = 4.4 mmol/l Plasma creatinine = 1.4 mg/dl Blood pressure = 88/40 mm Hg Heart rate = 115 beats/min What is the most likely cause of her elevated plasma Na+ concentration? A) Primary aldosteronism B) Diabetes mellitus C) Diabetes insipidus D) Simple dehydration caused by insufficient water intake and heavy exercise E) Bartter syndrome F) Liddle syndrome

C) The hypernatremia (plasma Na+ = 165 mmol/l) associated with a low blood pressure (88/44 mm Hg) suggests dehydration. The frequent urination and low urine specific gravity (1.003, which implies a urine osmolarity of about 100-120 mOsm/l) despite hypernatremia and dehydration suggests diabetes insipidus due to either insufficient secretion of ADH (central diabetes insipidus) or failure of the kidneys to respond to ADH (nephrogenic diabetes insipidus).

54. A patient has the following laboratory values: arterial pH = 7.13, plasma HCO3 = 15, plasma chloride concentration = 118 mEq/l, arterial PO2 = 28 mm Hg, and plasma Na+ concentration = 141 mEq/l. What is the most likely cause of his acidosis? A) Salicylic acid poisoning B) Diabetes mellitus C) Diarrhea D) Emphysema

C) The patient has a lower than normal pH and is therefore acidotic. Because the plasma bicarbonate concentration is also lower than normal, the patient has metabolic acidosis with respiratory compensation.

98. Which nephron segment is the primary site of magnesium reabsorption under normal conditions? A) Proximal tubule B) Descending limb of the loop of Henle C) Ascending limb of the loop of Henle D) Distal convoluted tubule E) Collecting ducts

C) The primary site of reabsorption of magnesium is in the loop of Henle, where about 65% of the filtered load of magnesium is reabsorbed. The proximal tubule normally reabsorbs only about 25% of filtered magnesium, and the distal and collecting tubules reabsorb less than 5%.

85. In a normally functioning kidney, which part of the tubule has the lowest permeability to water during antidiuresis? A) A B) B C) C D) D E) E

C) The thick ascending limb of the loop of Henle is relatively impermeable to water even under conditions of maximal antidiuresis. The proximal tubule and descending limb of the loop of Henle are highly permeable to water under normal conditions, as well as during antidiuresis. Water permeability of the late distal and collecting tubules increases markedly during antidiuresis because of the effects of increased levels of ADH.

17. In a dehydrated person with normal kidneys and high ADH levels, which part of the nephron normally reabsorbs the smallest amount of water (see figure below of a renal tubule)? A) A B) B C) C D) D E) E F) F

C) The thick ascending loop of Henle is relatively impermeable to water even in the presence of high levels of ADH. The other tubular segments reabsorb significant amounts of water.

30. After receiving a kidney transplant, a patient has severe hypertension (170/110 mm Hg). A renal arteriogram indicates severe renal artery stenosis in his single remaining kidney, with a reduction in glomerular filtration rate (GFR) to 25% of normal. Which of the following changes, compared with normal, would be expected in this patient, assuming steady-state conditions? A) A large increase in plasma sodium concentration B) A reduction in urinary sodium excretion to 25% of normal C) A reduction in urinary creatinine excretion to 25% of normal D) An increase in serum creatinine to about four times normal E) Normal renal blood flow in the stenotic kidney due to autoregulation

D) A severe renal artery stenosis that reduces GFR to 25% of normal would also decrease renal blood flow but would cause only a transient decrease in urinary creatinine excretion. The transient decrease in creatinine excretion would increase serum creatinine (to about four times normal), which would restore the filtered creatinine load to normal and therefore return urinary creatinine excretion to normal levels under steady-state conditions. Urinary sodium secretion would also decrease transiently but would be restored to normal so that intake and excretion of sodium are balanced. Plasma sodium concentration would not change significantly because it is carefully regulated by the ADH-thirst mechanism.

116. Acute metabolic acidosis tends to _____ intracellular K+ concentration and _____ K+ secretion by the cortical collecting tubules. A) Increase, increase B) Increase, decrease C) Decrease, increase D) Decrease, decrease E) Cause no change in, increase F) Cause no change in, cause no change in

D) Acute metabolic acidosis reduces intracellular potassium concentration, which, in turn, decreases potassium secretion by the principal cells of the collecting tubules. The primary mechanism by which increased hydrogen ion concentration inhibits potassium secretion is by reducing the activity of the sodium-potassium adenosine triphosphatase pump. This action then reduces intracellular potassium concentration, which, in turn, decreases the rate of passive diffusion of potassium across the luminal membrane into the tubule.

18. Acute metabolic alkalosis tends to ______K+ secretion by the cortical collecting tubules and ______ plasma K+ concentration. A) decrease, decrease B) decrease, increase C) increase, increase D) increase, decrease E) cause no change in, increase F) cause no change in, cause no change in

D) Acute metabolic alkalosis tends to shift K+ from the extracellular fluid into the cells, including the renal tubular cells, contributing to increased K+ secretion and decreased plasma K+ concentration (hypokalemia).

19. Which of the following statements is incorrect? A) Carbonic anhydrase inhibitors tend to cause metabolic acidosis. B) Thiazide diuretics inhibit the Na-Cl co-transporter in the distal tubules. C) Osmotic diuretics tend to increase potassium secretion. D) Aldosterone antagonists (e.g., spironolactone) tend to cause hypokalemia. E) Sodium channel blockers (e.g., amiloride) inhibit sodium transport across the luminal membrane of the collecting tubules. F) Loop diuretics (e.g., furosemide) tend to cause hypokalemia.

D) Aldosterone antagonists such as spironolactone tend to cause hyperkalemia rather than hypokalemia by shifting potassium from the intracellular to the extracellular fluid and by inhibiting potassium secretion in the principal cells of collecting tubules. All of the other statements are correct.

A 65-year-old man had a heart attack and experiences cardiopulmonary arrest while being transported to the emergency department. Use the following laboratory values obtained from arterial blood to answer Questions 47 and 48. Plasma pH = 7.12 Plasma PO2 = 60 mm Hg Plasma HCO3 concentration = 19 mEq/l 48. In this patient, which of the following laboratory results would be expected, compared with normal? A) Increased renal excretion of bicarbonate (HCO3 ) B) Decreased urinary titratable acid C) Increased urine pH D) Increased renal excretion of ammonia (NH4 +)

D) An important compensation for respiratory acidosis is increased renal production of NH4 + and increased NH4 + excretion. In acidosis, urinary excretion of HCO3 would be reduced, as would urine pH, and urinary titratable acid would be slightly increased as a compensatory response to the acidosis.

80. Which statement is correct? A) Urea reabsorption in the medullary collecting tubule is less than in the distal convoluted tubule during antidiuresis B) Urea concentration in the interstitial fluid of the renal cortex is greater than in the interstitial fluid of the renal medulla during antidiuresis C) The thick ascending limb of the loop of Henle reabsorbs more urea than the inner medullary collecting tubule during antidiuresis D) Urea reabsorption in the proximal tubule is greater than in the cortical collecting tubule

D) Approximately 40% to 50% of the filtered urea is reabsorbed in the proximal tubule. The distal convoluted tubule and the cortical collecting tubules are relatively impermeable to urea, even under conditions of antidiuresis; therefore, little urea reabsorption takes place in these segments. Likewise, very little urea reabsorption takes place in the thick ascending limb of the loop of Henle. Under conditions of antidiuresis, the concentration of urea in the renal medullary interstitial fluid is markedly increased because of reabsorption of urea from the collecting ducts, which contributes to the hyperosmotic renal medulla.

90. If a person has a kidney transport maximum for glucose of 350 mg/min, a GFR of 100 ml/min, a plasma glucose level of 150 mg/dl, a urine flow rate of 2 ml/min, and no detectable glucose in the urine, what would be the approximate rate of glucose reabsorption, assuming normal kidneys? A) Glucose reabsorption cannot be estimated from these data B) 0 mg/min C) 50 mg/min D) 150 mg/min E) 350 mg/min

D) In this example, the filtered load of glucose is equal to GFR (100 ml/min) × plasma glucose (150 mg/dl), or 150 mg/min. If there is no detectable glucose in the urine, the reabsorption rate is equal to the filtered load of glucose, or 150 mg/min.

7. Which of the following statements is incorrect? A) Creatinine concentration in the urine is normally higher than in the glomerular filtrate. B) Urea concentration in the urine is normally higher than in the glomerular filtrate. C) The proximal tubules normally reabsorb almost all of the glucose filtered by the glomerular capillaries. D) concentration in the urine is normally higher than in the glomerular filtrate. E) Organic acids and bases are secreted mainly by the proximal tubules. F) Sodium concentration remains relatively constant as tubular fluid flows along the proximal tubule.

D) Bicarbonate is more avidly reabsorbed in the proximal tubules than water, and therefore concentration decreases along the proximal tubules and has a lower concentration in the urine than in the glomerular filtrate. Approximately 85% of the filtered load of HCO3 is normally reabsorbed in the proximal tubules. All of the other statements are correct.

110. In a person with normal kidneys and normal lungs who has chronic metabolic acidosis, you would expect to find all of the following, compared with normal, EXCEPT: A) Increased renal excretion of NH4Cl B) Decreased urine pH B) Decreased urine HCO3- excretion D) Increased plasma HCO3- concentration E) Decreased plasma PCO2

D) Chronic metabolic acidosis is, by definition, associated with decreased plasma HCO3 concentration. Decreased excretion of NH4Cl and HCO3 occurs with renal compensation for the acidosis, and respiratory compensation for the acidosis increases the ventilation rate, resulting in decreased plasma PCO2.

73. Which change would you expect to find in a dehydrated person deprived of water for 24 hours? A) Decreased plasma renin activity B) Decreased plasma antidiuretic hormone concentration C) Increased plasma atrial natriuretic peptide concentration D) Increased water permeability of the collecting duct

D) Dehydration due to water deprivation decreases extracellular fluid volume, which in turn increases renin secretion and decreases plasma atrial natriuretic peptide. Dehydration also increases the plasma sodium concentration, which stimulates the secretion of ADH. The increased ADH increases water permeability in the collecting ducts. The ascending limb of the loop of Henle is relatively impermeable to water, and this low permeability is not altered by water deprivation or increased levels of ADH.

6. Given the following measurements, calculate the approximate filtration fraction: Glomerular capillary hydrostatic pressure = 60 mm Hg Colloid osmotic pressure in the glomerular capillaries = 30 mm Hg Bowman's space hydrostatic pressure = 20 mm Hg Glomerular capillary filtration coefficient (Kf) = 10 ml/min/mm Hg Renal plasma flow = 600 ml/min Hematocrit = 0.4 A) 10 mm Hg B) 100 ml/min C) 0.100 D) 0.167 E) 0.200 F) 0.333

D) Filtration fraction (FF) = glomerular filtration rate (GFR)/renal plasma flow. GFR = Kf x (PG - ΠC - PB) where Kf is the glomerular capillary filtration coefficient, PG is glomerular hydrostatic pressure, ΠC is glomerular capillary colloid osmotic pressure, and PB is Bowman's space hydrostatic pressure. Therefore, GFR= 10 × (60 − 20 − 10) = 100 ml/min. Since renal plasma flow is 600 ml/min, FF= 100 ml/min/600 ml/min = 0.167.

71. Furosemide (Lasix) is a diuretic that also produces natriuresis. Which of the following is an undesirable side effect of furosemide due to its site of action on the renal tubule? A) Edema B) Hyperkalemia C) Hypercalcemia D) Decreased ability to concentrate the urine E) Heart failure

D) Furosemide (Lasix) inhibits the Na+-2Cl − -K+ co-transporter in the ascending limb of the loop of Henle. This action not only causes marked natriuresis and diuresis but also reduces the urine-concentrating ability. Furosemide does not cause edema; in fact, it is often used to treat severe edema and heart failure. Furosemide also increases the renal excretion of potassium and calcium and therefore tends to cause hypokalemia and hypocalcemia rather than increasing the plasma concentrations of potassium and calcium.

46. The following laboratory values were obtained in a 58-year-old man: Urine volume = 4320 ml of urine collected during the preceding 24 hours Plasma creatinine = 3 mg/100 ml Urine creatinine = 50 mg/100 ml Plasma potassium = 4.0 mmol/l Urine potassium = 30 mmol/l What is his approximate GFR, assuming that he collected all of his urine in the 24-hour period? A) 20 ml/min B) 30 ml/min C) 40 ml/min D) 50 ml/min E) 60 ml/min F) 80 ml/min G) 100 ml/min

D) GFR is approximately equal to creatinine clearance, which is calculated as the urine creatinine concentration (50 mg/100 ml) × urine flow rate (3 ml/min)/plasma creatinine concentration (3 mg/100 ml), which is equal to 50 ml/min. Urine flow rate = 4320 ml/24 h = 4320 ml/1440 min = 3 ml/min.

117. Which statement is true? A) ADH increases water reabsorption from the ascending loop of Henle B) Water reabsorption from the descending loop of Henle is normally less than that from the ascending loop of Henle C) Sodium reabsorption from the ascending loop of Henle is normally less than that from the descending loop of Henle D) Osmolarity of fluid in the early distal tubule would be less than 300 mOsm/l in a dehydrated person with normal kidneys and increased ADH levels E) ADH decreases the urea permeability in the medullary collecting tubules

D) In a dehydrated person, osmolarity in the early distal tubule is usually less than 300 mOsm/l because the ascending limb of the loop of Henle and the early distal tubule are relatively impermeable to water, even in the presence of ADH. Therefore, the tubular fluid becomes progressively more dilute in these segments compared with plasma. ADH does not influence water reabsorption in the ascending limb of the loop of Henle. The ascending limb, however, reabsorbs sodium to a much greater extent than does the descending limb. Another important action of ADH is to increase the urea permeability in the medullary collecting ducts, which contributes to the hyperosmotic renal medullary interstitium in antidiuresis.

86. Which substances are best suited to measure interstitial fluid volume? A) Inulin and heavy water B) Inulin and 22Na C) Heavy water and 125I-albumin D) Inulin and 125I-albumin E) 51Cr red blood cells and 125I-albumin

D) Interstitial fluid volume is equal to extracellular fluid volume minus plasma volume. Extracellular fluid volume can be estimated from the distribution of inulin or 22Na, whereas plasma volume can be estimated from 125I-albumin distribution. Therefore, interstitial fluid volume is calculated from the difference between the inulin distribution space and the 125I-albumin distribution space.

41. When the dietary intake of K+ increases, body K+ balance is maintained by an increase in K+ excretion primarily by which of the following? A) Decreased glomerular filtration of K+ B) Decreased reabsorption of K+ by the proximal tubule C) Decreased reabsorption of K+ by the thick ascending limb of the loop of Henle D) Increased K+ secretion by the late distal and collecting tubules E) Shift of K+ into the intracellular compartment

D) Most of the daily variation in potassium excretion is caused by changes in potassium secretion in the late distal tubules and collecting tubules. Therefore, when the dietary intake of potassium increases, the total body balance of potassium is maintained primarily by an increase in potassium secretion in these tubular segments. Increased potassium intake has little effect on GFR or on reabsorption of potassium in the proximal tubule and loop of Henle. Although high potassium intake may cause a slight shift of potassium into the intracellular compartment, a balance between intake and output must be achieved by increasing the excretion of potassium during high potassium intake.

To evaluate kidney function in a 45-year-old woman with type 2 diabetes, you ask her to collect her urine for a 24-hour period. She collects 3600 ml of urine in that period. The clinical laboratory returns the following results after analyzing the patient's urine and plasma samples: plasma creatinine = 4 mg/dl, urine creatinine = 32 mg/dl, plasma potassium = 5 mmol/l, and urine potassium = 10 mmol/l. 101. What is the net renal tubular reabsorption rate of potassium in this patient? A) 1.050 mmol/min B) 0.100 mmol/min C) 0.037 mmol/min D) 0.075 mmol/min E) Potassium is not reabsorbed in this example

D) The net renal tubular reabsorption rate is the difference between the filtered load of potassium (GFR × plasma potassium concentration) and the urinary excretion of potassium (urine potassium concentration × urine flow rate). Therefore, the net tubular reabsorption of potassium is 0.075 mmol/min.

Urine flow rate = 1 ml/min Urine inulin concentration = 100 mg/ml Plasma inulin concentration = 2 mg/ml Urine urea concentration = 50 mg/ml Plasma urea concentration = 2.5 mg/ml 37. What is the net urea reabsorption rate? A) 0 mg/min B) 25 mg/min C) 50 mg/min D) 75 mg/min E) 100 mg/min

D) The net urea reabsorption rate is equal to the filtered load of urea (GFR [50 ml/min] × plasma urea concentration [2.5 mg/ml]) − urinary excretion rate of urea (urine urea concentration [50 mg/ml] × urine flow rate [1 ml/min]). Therefore, net urea reabsorption = (50 ml/min × 2.5 mg/ml) − (50 mg/ml × 1 ml/min) = 75 mg/min.

21. A patient has the following laboratory values: Arterial pH = 7.18 Plasma HCO3- = 10 mEq/l Plasma chloride concentration = 100 mEq/l Arterial PCO2 = 28 mm Hg Plasma Na+ concentration = 141 mEq/l What is the most likely cause of his acid-base disturbance? A) Emphysema B) Renal tubular acidosis C) Severe diarrhea D) Methanol poisoning E) Ingestion of excess sodium bicarbonate

D) The patient has a low pH (7.18) and a low plasma ,indicating metabolic acidosis. The plasma anion gap is 31. This is far above normal (8-16 mEq/l), indicating unmeasured anions and excess nonvolatile acids. Therefore, the most likely explanation for the patient's metabolic acidosis is methanol poisoning. Patients with emphysema would have respiratory acidosis. Patients with diarrhea or renal tubular acidosis would have metabolic acidosis due to bicarbonate loss and normal anion gap with hyperchloremia. Ingestion of excess sodium bicarbonate would cause metabolic alkalosis.

122. A 26-year-old construction worker is brought to the emergency department with a change in mental status after working a 10-hour shift on a hot summer day (average outside temperature was 97°F [36°C]). The man had been sweating profusely during the day but did not drink fluids. He has a fever of 102°F [39°C], a heart rate of 140 beats/min, and a blood pressure of 100/55 mm Hg in the supine position. Upon examination, he has no perspiration, appears to have dry mucous membranes, and is poorly oriented to person, place, and time. Assuming that his kidneys were normal yesterday, which set of hormone levels describes his condition, compared with normal? A) High ADH, high renin, low angiotensin II, low aldosterone B) Low ADH, low renin, low angiotensin II, low aldosterone C) High ADH, low renin, high angiotensin II, low aldosterone D) High ADH, high renin, high angiotensin II, high aldosterone E) Low ADH, high renin, low angiotensin II, high aldosterone

D) This patient is severely dehydrated as a result of sweating and lack of adequate fluid intake. The dehydration markedly stimulates the release of ADH and renin secretion, which in turn stimulates the formation of angiotensin II and aldosterone secretion.

13. Calculate the approximate total renal plasma flow given the following data: Urine PAH concentration = 200 μg/ml Urine flow rate = 2 ml/min Arterial plasma paraaminohippuric acid (PAH) concentration = 1.0 μg/ml Renal venous PAH concentration = 0.2 μg/ml Hematocrit = 0.4 A) 120 ml/min B) 200 ml/min C) 400 ml/min D) 500 ml/min E) 667 ml/min F) 833 ml/min

D) Total renal plasma flow (RPF) is equal to the clearance of paraaminohippuric acid (PAH) divided by the renal PAH extraction ratio (EPAH).

42. Which of the following would cause the greatest decrease in GFR in a person with otherwise normal kidneys? A) Decrease in renal arterial pressure from 100 to 80 mm Hg in a normal kidney B) 50% increase in glomerular capillary filtration coefficient C) 50% increase in proximal tubular sodium reabsorption D) 50% decrease in afferent arteriolar resistance E) 50% decrease in efferent arteriolar resistance F) 5 mm Hg decrease in Bowman's capsule pressure

E) A 50% decrease in efferent arteriolar resistance would cause a substantial decrease in GFR. A decrease in renal arterial pressure from 100 to 80 mm Hg in a normal kidney would cause only a slight reduction in GFR in a normal kidney because of autoregulation. All of the other changes would tend to increase GFR.

11. If the glomerular filtration rate (GFR) of a patient is reduced to 50% of normal and sustained at that level, you would expect to find __________ renal creatinine excretion rate, __________ renal creatinine clearance, and __________ serum creatinine concentration 6 weeks after the decrease in GFR compared with normal. Assume steady-state conditions and that the patient has maintained the same diet. A) Decreased, decreased, increased B) Decreased, no change, increased C) No change, increased, increased D) No change, no change, increased E) No change, decreased, increased F) Decreased, no change, decreased

E) A 50% reduction in glomerular filtration rate (GFR) would initially cause a reduction in creatinine excretion rate. However, within a few days, the filtered load and excretion of creatinine would return to normal as serum creatinine concentration increased to approximately twice the normal level under steady-state conditions (see figure in next column). Creatinine clearance is approximately equal to GFR and would also be reduced by approximately 50%.

22. Atrial natriuretic peptide causes which of the following effects? A) Reduced renal tubular sodium reabsorption B) Reduced renin secretion C) Increased renal sodium excretion D) Only A and C E) A, B, and C

E) Atrial natriuretic peptide decreases renal sodium reabsorption through direct effects on the renal tubules as well as indirectly by inhibiting renin secretion. Both of these effects contribute to increased renal sodium excretion.

92. A selective decrease in efferent arteriolar resistance would __________ glomerular hydrostatic pressure, __________ GFR, and __________ renal blood flow. A) increase, increase, increase B) increase, decrease, increase C) increase, decrease, decrease D) decrease, increase, decrease E) decrease, decrease, increase F) decrease, increase, increase

E) Decreased efferent arteriolar resistance would increase renal blood flow while reducing glomerular hydrostatic pressure, which, in turn, would tend to decrease the GFR.

82. In a patient with severe central diabetes insipidus caused by a lack of ADH secretion, which part of the tubule would have the lowest tubular fluid osmolarity? A) A B) B C) C D) D E) E

E) In the absence of ADH, the late distal tubule and collecting tubules are not permeable to water. Therefore, the tubular fluid, which is already dilute when it leaves the loop of Henle (∼ 100 mOsm/l), becomes further diluted as it flows through the late distal tubule and collecting tubules as electrolytes are reabsorbed. Therefore, the final urine osmolarity in the complete absence of ADH is less than 100 mOsm/l.

15. Which of the following statements is incorrect? A) Beta-adrenergic stimulation would tend to cause hypokalemia by shifting potassium from the extracellular fluid into the cells B) A powerful diuretic that inhibits proximal tubule or loop of Henle sodium reabsorption would tend to increase potassium secretion by the collecting tubules C) Injection of excess insulin into a patient would tend to cause hypokalemia D) Strenuous, sustained exercise may tend to cause significant hyperkalemia E) Increased extracellular fluid osmolarity would tend to cause hypokalemia

E) Increased extracellular fluid osmolarity would tend to cause hyperkalemia, rather than hypokalemia due to cell dehydration, which raise intracellular potassium concentration and promotes potassium diffusion into the extracellular fluid. All of the other statements are correct.

121. What would tend to decrease plasma potassium concentration by causing a shift of potassium from the extracellular fluid into the cells? A) Strenuous exercise B) Aldosterone deficiency C) Acidosis D) β-adrenergic blockade E) Insulin excess

E) Increased levels of insulin cause a shift of potassium from the extracellular fluid into the cells. All the other conditions have the reverse effect of shifting potassium out of the cells into the extracellular fluid.

1. All of the following changes would tend to cause interstitial fluid edema in a tissue EXCEPT one. Which one is the EXCEPTION? A) Increased venous resistance B) Increased venous pressure C) Decreased arteriolar resistance D) Increased capillary filtration coefficient E) Increased plasma protein concentration

E) Increased plasma protein concentration would reduce the net force favoring capillary filtration and would oppose edema formation. All of the other changes would increase capillary filtration rate and tend to cause edema.

108. Which of the following has similar values for both intracellular and interstitial body fluids? A) Potassium ion concentration B) Colloid osmotic pressure C) Sodium ion concentration D) Chloride ion concentration E) Total osmolarity

E) Intracellular and extracellular body fluids have the same total osmolarity under steady-state conditions because the cell membrane is highly permeable to water. Therefore, water flows rapidly across the cell membrane until osmotic equilibrium is achieved. The colloid osmotic pressure is determined by the protein concentration, which is considerably higher inside the cell. The cell membrane is also relatively impermeable to potassium, sodium, and chloride, and active transport mechanisms maintain low intracellular concentrations of sodium and chloride and a high intracellular concentration of potassium.

89. Which of the following would be expected to cause a decrease in extracellular fluid potassium concentration (hypokalemia) at least in part by stimulating potassium uptake into the cells? A) α-Adrenergic blockade B) Insulin deficiency C) Strenuous exercise D) Aldosterone deficiency (Addison disease) E) Metabolic alkalosis

E) Metabolic alkalosis is associated with hypokalemia due to a shift of potassium from the extracellular fluid into the cells (see table below). Beta-adrenergic blockade, insulin deficiency, strenuous exercise, and aldosterone deficiency all cause hyperkalemia due to a shift of potassium out of the cells into the extracellular fluid.

118. In a person on a high-potassium (200 mmol/day) diet, which part of the nephron would be expected to secrete the most potassium? A) Proximal tubule B) Descending loop of Henle C) Ascending loop of Henle D) Early distal tubule E) Collecting tubules

E) Most potassium secretion occurs in the collecting tubules. A high-potassium diet stimulates potassium secretion by the collecting tubules through multiple mechanisms, including small increases in extracellular potassium concentration, as well as increased levels of aldosterone.

2. Calculate the approximate extracellular fluid osmolarity of a patient after administration of 2.0 l of 5% glucose solution, assuming complete metabolism of the glucose, osmotic equilibrium and no excretion of water or electrolytes. Also assume the following initial conditions prior to infusing the glucose solution: Body weight = 50 kg Plasma sodium concentration = 170 mmol/l Plasma osmolarity = 360 mOsm/l Intracellular fluid volume = 40% of body weight Extracellular fluid volume = 20% of body weight Molecular wt of glucose = 180 g/mole A) 264 mOsm/l B) 282 mOsm/l C) 306 mOsm/l D) 319 mOsm/l E) 338 mOsm/l F) 355 mOsm/l G) 360 mOsm/l

E) The total body water would initially be 60% of body weight or ∼30 l. The initial total mOsm in the body fluids would be 30 l × 360 mOsm/l, or 10,800 mOsm. After adding the glucose solution, total body water would be 30 l + 2 l or 32 l. If we assume that all of the glucose is metabolized, the final mOsm would also be 10,800. Therefore, the extracellular and intracellular osmolarity would be 10,800 mOsm/32 l, or approximately 338 mOsm/l.

26. What is the theoretical maximum clearance rate possible for a substance X that is freely filtered, actively secreted by the renal tubules, and completely cleared from the plasma given the following data? Glomerular filtration rate = 100 ml/min Plasma concentration of a substance X = 2 mg/ml Urine flow= 5 ml/min Renal plasma flow = 800 ml/min A) 5 ml/min B) 100 ml/min C) 200 ml/min D) 500 ml/min E) 800 ml/min F) 1000 ml/min

E) Theoretically, if all of the plasma flowing through the kidneys was cleared of a substance, the clearance rate would be equal to the total renal plasma flow. In this example, renal plasma flow is equal to 800 ml/min.

9. As tubular fluid passes along a juxtamedullary nephron of a person with severe central diabetes insipidus and essentially no antidiuretic hormone, where is the osmolarity lowest? A) Bowman's capsule (glomerular filtrate) B) Fluid leaving the proximal tubule and entering the loop of Henle C) Fluid leaving the descending thin limb and entering the ascending thin limb of the loop of Henle D) Fluid leaving the thick ascending segment of the loop of Henle and entering the early distal tubule E) Fluid in the cortical collecting tubules F) Fluid leaving the collecting ducts (urine)

F) Fluid in the ascending loop of Henle becomes dilute as electrolytes are reabsorbed and water remains in the tubule. When antidiuretic hormone (ADH) levels are very low, as occurs in central diabetes insipidus, fluid in the distal and collecting tubules, and the collecting ducts is further diluted by the reabsorption of sodium chloride and the failure to reabsorb water. This lead to a very dilute urine.

87. Long-term administration of furosemide (Lasix) would do what? A) Inhibit the Na+-Cl − co-transporter in the renal distal tubules B) Inhibit the Na+-Cl − -K+ co-transporter in the renal tubules C) Tend to reduce renal concentrating ability D) Tend to cause hyperkalemia E) A and C F) B and C G) B, C, and D

F) Furosemide (Lasix) is a "loop" diuretic that inhibits the Na+-Cl − -K+ co-transporter in the thick ascending loop of Henle, thus reducing urine-concentrating ability; increasing renal excretion of Na+, Cl − , and K+; and tending to cause hypokalemia.