Renal and Acid-Base Physiology - BRS & Guyton and Hall

Question 1

Secretion of K+ by distal tubule will be decreased by:

a. metabolic alkalosis
b. a high-K+ diet
c. hyperaldosteronism
d. spironolactone administration
e. thiazide diuretic administration

Answer 1

a-c: increases K+ secretion in distal cells

d. spironolactone = aldosterone antagonist: reduces K+ secretion
e. thiazide diuretics increase flow through distal tubule and dilute luminal [K+] so that driving force for K+ secretion is increased

Question 2

Which of the following causes a decrease in renal Ca2+ clearance?

a. hypoparathyroidism
b. treatment with chlorothiazide
c. treatment with furosemide
d. ECF volume expansion
e. hypermagnesemia

Answer 2

b. thiazide diuretics = calcium sparing in distal tubule

furosemide inhibits sodium reabsorption in TAL and ECF volume expansion inhibits sodium reabsorption in proximal tubule –> at these sites, calcium reabsorption is linked to sodium reabsorption and calcium clearance would be increased

b/c Mg2+ competes with Ca2+ for reabsorption in TAL, hypermagnesemia will cause increased calcium clearance

Question 3

A woman has a plasma osmolarity of 300 mOsm/L and a urine osmolarity of 1200 mOsm/L. The correct diagnosis is:

a. SIADH
b. water deprivation
c. central/neurogenic DI
d. nephrogenic DI
e. drinking large volumes of distilled water

Answer 3

b. water deprivation

plasma osm is on high side (ref: 285-295) so ADH is being secreted –> ADH acts on collecting ducts to increase water reabsorption and produce hyper osmotic urine

SIADH would also make hyper osmotic urine but plasma osm would be lower than normal b/c of excessive water retention

DI would produce hypoosmotic/dilute urine

Question 4

A woman runs a marathon in 90 degrees F and replaces all volume lost in sweat by drinking distilled water. After the marathon, she will have:

a. decreased total body water
b. decreased hematocrit
c. decreased ICF vol
d. decreased plasma osm
e. increased intracellular osm

Answer 4

hypervolemic hyponatremia (net loss of sodium without loss of H2O)

d. decreased plasma osm

shift of water from extracellular to intracellular will dec. intracellular osm and increase hematocrit (volume in RBCs)

total body water remains unchanged

Question 5

Which of the following is a cause of metabolic alkalosis?

a. diarrhea
b. chronic renal failure
c. ethylene glycol ingestion
d. treatment with acetazolamide
e. hyperaldosteronism
f. salicylate poisoning

Answer 5

hyperaldosteronism

increased aldosterone levels cause increased H+ secretion by distal tubule and increased reabsorption of “new” HCO3

• diarrhea causes loss of HCO3- from GI –> hyperchloremic meta acid w/ normal AG
• acetazolamide causes loss of HCO3- in urine –> hyperchloremic meta acid w/ normal AG

c and f –> meta acid with increased AG

Question 6

A 53-year-old man with multiple myeloma is hospitalized after 2 days of polyuria (large volume of dilute urine), polydipsia, and increasing confusion. Laboratory tests show an elevated serum calcium of 15 mg/dL and treatment is initiated to decrease it. The patient’s serum osmolarity is 310 mOsm/L.

What is the most likely reason for polyuria in this man?

a. increased circulating levels of ADH
b. increased circulating levels of aldosterone
c. inhibition of the action of ADH on renal tubule
d. stimulation of action of ADH on renal tubule
e. psychogenic water drinking

Answer 6

c. inhibition of ADH action on renal tubule

w/ severe hypercalcemia, calcium accumulates in the inner medulla and papilla of kidney and inhibits adenylate cyclase, blocking the effect of ADH on water permeability

b/c ADH is ineffective, urine cannot be concentrated and patient excretes large volumes of dilute urine

polydipsia is a result of increased serum osm.

Question 7

A 40-year-old woman has arterial pH of 7.25. PCO2 = 30 mmHg and serum [K+] = 2.8 mEq/L.

BP = 100/80 when supine and 80/50 when standing. What is the cause of her abnormal blood values?

a. vomiting
b. diarrhea
c. treatment with loop diuretic
d. treatment with thiazide diuretic

Answer 7

b. diarrhea
metabolic acidosis, hypokalemia, and orthostatic hypotension; diarrhea is associated with loss of HCO3- and K+ from GI tract

diuretics could cause vol. contraction and hypokalemia but cause meta alk rather than meta acid.

vomiting causes meta alk and hypokalemia

Question 8

A 37-year-old woman suffers a severe head injury. She becomes polydipsia and polyuric. Her urine osmolarity is 75 most/L, and her serum osmolarity is 305 mOsm/L. Treatment with 1-deamino-8-D-argnine vasopressin (dDAVP) causes an increase in her urine osmalrity to 450 mOsm/L. Which diagnosis is correct?

a. primary polydipsia
b. central DI
c. nephrogenic DI
d. water deprivation
e. SIADH

Answer 8

history of head injury w/ production of dilute urine + elevated serum ism. suggests = central DI

response of the kidney to exogenous ADH eliminates nephrogenic DI

Question 9

Which diuretic inhibits sodium reabsorption and K+ secretion in the distal tubule by acting as an aldosterone antagonist

a. acetazolamide
b. chlorothiazide
c. furosemide
d. spironolactone

Answer 9

d. spironolactone

Question 10

Which diuretic causes increased urinary excretion of sodium and potassium and decreased urinary excretion of calcium?

a. acetazolamide
b. chlorothiazide
c. furosemide
d. spironolactone

Answer 10

b. chlorothiazide (enhance calcium reabsorption so that urinary excretion of Na+ is increased will urinary excretion of calcium is decreased)

potassium excretion is increased b/c flow rate is increased at site of distal tubular K+ secretion

Question 11

A 28-year-old man who is receiving lithium treatment for bipolar disorder becomes polyuric. His urine osmolarity is 90 mOsm/L; it remains at that level when he is given a nasal spray of dDAVP. Which diagnosis is correct?

a. primary polydipsia
b. central DI
c. nephrogenic DI
d. water deprivation
e. SIADH

Answer 11

c. nephrogenic DI

b/c the defect is in the target tissue for ADH, exogenous ADH administered by nasal spray will not correct it

Question 12

A 32-year-old woman who is thirsty has a urine osmolarity of 950 mOsm/L and a serum osmolarity of 297 mOsm/L. Which diagnosis is correct?

a. primary polydipsia
b. central DI
c. nephrogenic DI
d. water deprivation
e. SIADH

Answer 12

d. water deprivation

serum osm. is slightly higher than normal b/c insensible water loss is not being replaced by drinking water

increased serum osm. stimulates (via osmoreceptors in anterior hypothalamus) release of ADH from posterior pituitary –> ADH then circulates to the kidney and stimulates water reabsorption from the collecting ducts to concentrate urine

Question 13

A decrease in which of the following would be expected to occur in response to a direct increase in renal arterial pressure?

a. water excretion
b. sodium excretion
c. ECF vol.
d. GFR
e. inrushing of blood into the ventricles in the early to middle part of diastole

Answer 13

c. ECF vol.

Increase in renal arterial pressure –> pressure natriuresis and diuresis

Question 14

A decrease in which of the following would be expected to occur in response to an increase in sodium intake?

a. AII
b. NO
c. Sodium excretion
d. ANP

Answer 14

a. AII

Question 15

Which of the following would be expected to occur in response to constriction of the renal artery?

a. inc. in sodium excretion
b. dec. in arterial pressure
c. dec. in renin release
d. inc. in AII

Answer 15

d. inc. in AII

sodium excretion decreases but only transiently b/c as arterial pressure increases, sodium excretion returns to normal levels via a pressure natriuresis mech

Question 16

Which of the following normally causes either renal sodium or water retention during compensated heart failure?

a. dec. AII formation
b. dec. aldosterone formation
c. SNS vasodilation of afferent arterioles
d. Inc. GFR
e. Inc. ADH formation

Answer 16

e. Inc. ADH formation

In compensated heart failure, SNS output inc. One of the results is a sympathetic vasoconstriction of afferent arterioles of kidney… this dec. GFR resulting in inc. sodium and water retention

Increased release of AII also occurs which causes direct renal sodium retention and also stimulates aldosterone secretion which will cause further increase in sodium retention in kidney.

The excess sodium in the body will inc. osmolality and this increases the release of ADH which causes renal water retention.

Question 17

Which of the following occurs during heart failure and causes an increase in renal sodium excretion?

a. increased aldosterone release
b. increased ANP release
c. decreased GFR
d. increased AII release
e. decreased MAP

Answer 17

b. increased ANP release

during heart failure, blood vol. increases, resulting in increased cardiac stretch. ANP increases causing a release of ANF resulting in an increase in renal sodium excretion

Question 18

Which of the following tends to decrease potassium secretion by the CCT?

a. Increased plasma K+ concentration
b. Diuretic that dec. proximal tubule sodium reabsorption
c. Diuretic that inhibits action of aldosterone (e.g., spironolactone)
d. Acute alkalosis
e. High sodium intake

Answer 18

c. aldosterone antagonist

Question 19

Which of the following changes tends to increase peritubular capillary fluid reabsorption?

a. increased blood pressure
b. decreased filtration fraction
c. increased efferent arteriolar resistance
d. decreased AII
e. increased RBF

Answer 19

c. increased efferent arteriolar resistance

reduces peritubular capillary hydrostatic pressure and therefore increases the net force favoring fluid reabsorption

increased RBF raises peritubular capillary hydrostatic pressure and decrease fluid reabsorption

Question 20

Which of the following changes tends to increase GFR?

a. inc. afferent arteriolar resistance
b. dec. efferent arteriolar resistance
c. inc. glomerular capillary filtration coefficient
d. inc. bowman’s capsule hydrostatic pressure
e. dec. glomerular capillary hydrostatic pressure

Answer 20

c. inc. glomerular capillary filtration coefficient

Question 21

A patient complains of headaches, and an examination reveals that her BP is 175/112 mm Hg. Lab tests: plasma renin activity = 11.5 ng AI (normal = 1), plasma Na = 144 mmol/L, and plasma K+ = 3.4 mmol/L.

MRI suggested that she has a renin-secreting tumor.

Describe her:

• Renal blood flow
• Filtration fraction
• Glomerular capillary hydrostatic pressure
• Peritubular capillary hydrostatic pressure

Answer 21

Renin-secreting tumor –> AII –> vasoconstriction of efferent arteriole

• Renal blood flow: dec.
• Filtration fraction: inc.
• Glomerular capillary hydrostatic pressure: inc.
• Peritubular capillary hydrostatic pressure: dec.

Question 22

A female patient has unexplained severe hypernatremia (plasma sodium = 167 mmil?L) and complains of 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). Lab tests reveal: plasma renin activity = 3 ng (normal 1), plasma ADH = 30 (normal 3), and plasma aldosterone = 20 (normal 6). Which of the following is the most likely reason for her hypernatremia?

a. simple dehydration due to decreased water uptake
b. nephrogenic DI
c. central DI
d. SIADH
e. primary aldosteronism
f. renin-secreting tumor

Answer 22

b. nephrogenic DI

hypernatremia can be caused by excessive sodium retention or water loss.

patient excreting large volumes of dilute urine suggested excessive urinary water excretion

not central DI b/c ADH is high level

simple dehydration unlikely b/c patient is peeing a lot

Question 23

Administration of a thiazide diuretic would be expected to cause which of the following effects as its primary mechanism of action?

a. Inhibition of NaCl co-transport in the early distal tubules
b. Inhibition of NaCl co-transport in the proximal tubules
c. Inhibition of Na-2Cl-K co-transport in the loop of Henle
d. Inhibition of Na-2Cl-K co-transport in the collecting tubules
e. Inhibition of the renal tubular actions of aldosterone
f. Blockade of sodium channels in the collecting tubules

Answer 23

a. Inhibition of NaCl co-transport in the early distal tubules

Question 24

Which of the following would you expect to find in a dehydrated person deprived of water for 24 hours?

a. dec. PRA
b. dec. plasma ADH
c. inc. plasma ANP
d. inc. water permeability of the collecting duct
e. inc. water permeability in the ascending loop of Henle

Answer 24

d. inc. water permeability of the collecting duct

Dehydration inc. plasma sodium concentration which stimulates ADH secretion. Increased ADH increases water permeability in the collecting ducts.

Question 25

Describe

• Filtration, Reabsorption, Secretion Status
• Relative concentrations of the following in the renal artery vs. renal vein
• (C) and GFR
• Most proteins
• Inulin
• Urea
• Glucose
• Creatinine

Answer 25

Most proteins

• Not filtered
• [x]ra = [x]rv
• C = zero (healthy kidneys do not clear proteins)

Inulin

• Filtered, neither reabsorbed nor secreted
• [In]ra > [In] rv
• C = GFR

Urea

• Filtered, partially reabsorbed
• [Urea]ra > [Urea]rv
• C [Cr]rv
• C = GFR

Question 26

An elderly patient complains of muscle weakness and lethargy. A urine specimen reveals a sodium concentration of 600 mmol/L and an osmolarity of 1200 mOsm/L. Additional lab tests provide the following information:

plasma Na+ = 167 mmol/L
PRA = 4 (normal = 1)
plasma ADH = 60 (normal = 3)
plasma aldosterone = 15 (normal = 6)

Which of the following is the most likely reason for this patient’s hypernatremia?

a. Dehydration caused by decreased fluid intake
b. SIADH
c. Nephrogenic DI
d. Primary aldosteronism
e. Renin-secreting tumor

Answer 26

a. Dehydration caused by decreased fluid intake

Plasma Na concentration is markedly increased but urine Na concentration is relatively normal. Urine osmolarity is almost maximally increased.

Increases in paslam renin, ADH, and aldosterone –> consistent with dehydration.

SIADH would result in decrease in plasma sodium concentration, as well as suppression of renin and aldosterone secretion.

Nephrogenic DI (kidney’s 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 Na concentration and a marked reduction in the secretion of renin.

Renin-secreting tumor would be associated with increases in plasma aldosterone concentration and PRA but only a modest change in plasma Na concentration.