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Renal Week 2 > Clinical Disorders of the Distal Nephron > Flashcards

Clinical Disorders of the Distal Nephron Flashcards

1
Q

Where is Na+ reabsorbed?

A
  • 65-70% in the PT
  • 25% in the thick ascending limb
  • 5% in the distal tubule
  • 1-2% in the CD
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2
Q

What is Bartter syndrome?

A

a hypochloremic, hypokalemic metabolic alkalosis (figure out why) caused by by mutations of genes encoding proteins that transport ions across renal cells in the thick ascending limb of the nephron (can be a mutation in the NAKCl pump, NAK ATPase, or in Ca sensing)

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3
Q

What is the MOI of Bartter syndrome?

A

AR

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4
Q

What is Bartter syndrome associated with?

A
  • secondary hyperaldosteronism (via hyperplasia of the juxtaglomerular apparatus) from volume depletion
  • elevated PGE2 to help perfuse the glomeruli
  • Failure to thrive
  • Hypercalciuria /nephrocalcinosis (in some)
  • enormous salt cravings
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5
Q

How is Bartter syndrome treated?

A

-K+ supplements, and Mg supplements if needed

low K+ can cause renal cysts and failure

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6
Q

What things are associated with neonatal Bartter syndrome?

A
  • polyhydramnios due to fetal polyuria (can cause the baby to need to be born premature)
  • salt wasting at birth
  • nephrocalcinosis /hypercalciuria
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7
Q

How would neonatal bartter syndrome present?

A
  • massive polyhydramnios due to fetal polyuria
  • Amniotic fluid has elevated levels of PGE2
  • Massive salt wasting at birth
  • Nephrocalcinosis /hypercalciuria
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8
Q

How is neonatal bartter syndrome treated?

A

Sometimes treated with cyclooxygenase inhibitors

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9
Q

What are some potential Bartter causing mutations?

A

Bumetanide-sensitive Na+-K+-Cl-cotransporter (NKCC2)

Apical ATP-sensitive K+ channel (ROMK)

BL Cl- channel A subunit (CLCNKA)
BL Cl- channel B subunit (CLCNKB)

Barttin (necessary for insertion of Cl- channel A and B subunits in BL membrane in kidney and inner ear-associated in deafness)

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10
Q

What is Gitelman Syndrome?

A

AR syndrome of hypochloremic metabolic alkalosis and hypokalemia, but patients present later and usually have normal growth because it affects a less important transporter

milder

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11
Q

What causes Gitelman Syndrome?

A

Mutation in the thiazide-sensitive Na+-Cl-cotransporter of the distal convoluted tubule only

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12
Q

Symptoms of Gitelman Syndrome?

A

Hypomagnesemia, hypokalemia is common

Hypocalciuria (rather than hypercalciuria)- thus, thiazides can be used for kidney stones

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13
Q

What is Liddle syndrome?

A

Results from a gain-of function in the β or γ subunit of the Enac channel (aldosterone-sensitive channel; “stuck open”)

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14
Q

What does Liddle syndrome result in/cause?

A

AD MOI cause of hypertension with low renin and low aldosterone, hypokalemia, and metabolic alkalosis

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15
Q

How is Liddle syndrome treated?

A

salt restriction and diuretics

NOTE: Mirror image of pseudohypoaldosteronism type I

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16
Q

What are some causes of hypokalemia?

A
  • Diuretics

- Hyperaldosteronism (primary or 2ndary)

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17
Q

What are some causes of hyperkalemia?

A
  • Hypoaldosteronism

- Pseudohypoaldosteronism

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18
Q

What is a TTKG?

A

The transtubular potassium gradient (TTKG) is utilized to held determine whether the renal response to hyperkalemia or hypokalemia is appropriate.

During hyperkalemia, the TTKG should be greater than 7; lower values suggest hypoaldosteronism.

During hypokalemia, the TTKG should be less than 3; greater values suggest renal potassium wasting.

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19
Q

What are the requirements of a TTKG?

A

Assumes that the only thing that happens between the cortical collecting duct, where K+ is secreted, and the final urine is that water is reabsorbed

Requires measured urine and plasma osmolality

Urine osmolality must be greater than plasma osmolality

Urine sodium must be > 25 mmol/L

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20
Q

Eqn for a TTKG?

A

([K]urine/[K]plasma)/(U/Posm)

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21
Q

What are some requirements of a TTKG?

A
  • urine Na must be below 20mEq/L

- Uosm must be less than 300mOsm/kg

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22
Q

What things can cause primary hyperaldosteronism?

A

adrenal tumors or genetic disorders such as GRA or AME

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23
Q

What things can cause secondary hyperaldosteronism?

A
  • Dehydration (pyloric stenosis- increased with with erthyromycin)
  • Sodium-wasting disorders (Bartter-Gitelman)

will see a little hypokalemia

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24
Q

What is GRA?

A

Glucococorticoid-remediable hyperaldosteronism that results from recombination of the homologous genes for 11-β-hydroxysteroid dehydrogenase (11βHSD) (involved in cortisol synthesis pathway) and aldosterone synthase resulting in a hybrid that hyper-activates aldosterone in times of stress (when cortisol would normally be made)

25
Q

What does recombination of the homologous genes for 11-β-hydroxysteroid dehydrogenase (11βHSD) and aldosterone synthase cause?

A

Produces a hybrid molecule that makes aldosterone in response to stress causing low renin hypertension and hypokalemia

26
Q

How is GRA treated?

A

physiologic doses of glucocorticoids

27
Q

What is AME?

A

Apparent Mineralocorticoid Excess that results from mutations in the kidney isozyme of 11βHSD (involved in cortisol synthesis pathway) causing increased levels of cortisol in the kidney which cross-react and activate the mineralocorticoid receptor (like extra aldosterone) causing low renin HTN and hypokalemia

treated the same as GRA

28
Q

One of the main causes of hyperkalemia is hypoaldosteronism. What things can cause hypoaldosteronism?

A
  • Congenital adrenal hypoplasia
  • Congenital adrenal hyperplasia (block in cortisol synthesis in adrenal gland promotes formation of androgen)
  • Autoimmune mediated
29
Q

The other major cause of hyperkalemia is pseudohypoaldosteronism (PHA). What can cause this?

A
  • PHA Type I (single gene)
  • PHA Type II (single gene)
  • Tubular injury (obstructive uropathy)
30
Q

How does PHA Type I present?

A
  • Hyperkalemia
  • Hyponatremia
  • Prone to severe volume depletion, hypotension

“Mirror image” of Liddle syndrome

look like no aldosterone is present

31
Q

What are the causes of PHA type I?

A

Mutations in mineralocorticoid receptor
-Associated with “childhood” PHA (This is AD) OR

Loss-of-function mutation in the ENaC (“stuck shut”)

  • Associated with defects in Na+ transport in other organs
  • This is AR
32
Q

How is PHA type I treated?

A

Treated with sodium supplements, high fluid intake, and K+-binding resin (sodium polystyrene sulfonate, Kayexalate®)

33
Q

How does PHA Type II (aka Gordon syndrome) present?

A
  • Hyperkalemia, hyperchloremic metabolic acidosis
  • Hypertension
  • Low renin and aldosterone levels or “chloride shunt” syndrome
34
Q

PHA Type II is a mirror image of what disease?

A

Gitelman syndrome

35
Q

What causes PHA Type II?

A

mutations in WNK1 and WNK4, serine-threonine kinases that regulate NCCT, the thiazide-sensitive Na+-Cl- cotransporter

36
Q

How is PHA type II treated?

A

Treated with thiazide diuretics

37
Q

What is the eqn for the plasma anion gap?

A

Na+ – (Cl- + HCO3)

38
Q

What is a normal plasma anion gap?

A

Normal is 8-20 at Le Bonheur; in adults normal range is 10-12

When you are confronted with a patient with acidosis, always check the anion gap: Is it normal or elevated?

39
Q

What are potential causes of elevated anion gap acidosis?

A
  • Ketoacidosis
  • Lactic acidosis
  • Inborn errors of metabolism (methylmalonic acidemia, propionic acidemia, etc.)
  • Poisons: Methanol, ethylene glycol, salicylates, etc.)

MUDPILES

40
Q

What are the causes of normal anion gap acidosis (aka Hyperchloremic Metabolic Acidosis)?

A
  • GI losses of bicarbonate (i.e., diarrhea)
  • Exogenous chloride (arginine HCl challenge, volume expansion with NaCl)
  • Renal tubular acidosis
41
Q

T or F. RTA is a normal anion gap acidosis

A

T. If normal, check the UAG

UAG= (Na+K)-Cl

42
Q

Type II (proximal) RTA is almost always associated with what?

A

Fanconi syndrome

43
Q

How does Type I RTA present?

A

very rare and presents with hypokalemia, hypercalciuria, nephrolithiasis, and failure to thrive

44
Q

What is Type IV RTA (most common)?

A 
Type IV (hyperkalemic) RTA is a syndrome of aldosterone deficiency or unresponsiveness
RTA almost never presents with diarrhea because they present with low K+ which is constipating
45
Q

How can you test for RTA?

A
  • Fractional excretion of bicarbonate
  • Urine pH
  • Urine anion gap
  • U-B PCO2
46
Q

What is the eqn for Fractional Excretion of Bicarbonate?

How does it vary with different RTAs?

A

FEHCO3 = UHCO3- x (PCr/PHCO3-) x UCr

> 10-15% in proximal RTA (which is a threshold problem) (type II)

less than 5% in classical distal RTA (type I)

less than 5-10% in hyperkalemic RTA (type IV)

47
Q

Why is Bartter syndrome associated with hypo magnesia?

A

Potassium from the NAKCl pump in the thick ATL is able to diffuse back into the tubule lumen through apical potassium channels, returning a net positive charge to the lumen and establishing a positive voltage between the lumen and interstitial space.

This charge gradient is obligatory for the paracellular reabsorption of both calcium and magnesium ions.

48
Q

How is neonatal Bartter Syndrome treated?

A

cyclo-oxygenase inhibitors limit the amount of fluid output, thus limiting the amount of fluid needed for the babies

49
Q

What diuretic could cause Pna to gradually increase after prolonged use?

A

Furosemide. Thiazides will lower it.

50
Q

What other disease could thiazides be useful in?

A

DI nephrogenic

51
Q

Why is urine pH not that helpful?

A

If you let urine sit, the Co2 evaporates and pH increases

52
Q

What is the equation for UAG?

A

(UNa+ UK+) - UCl-

these are the principal urianryc ions

53
Q

When is a UAG helpful?

A

for metabolic acidosis with normal anion gap

54
Q

Interpretation of UAG results.

A

If negative, normal distal acidification is occurring (e.g. diarrhea)

If negative, tubular acidosis occurring (e.g. proximal, type I and hyperkalemic RTA)

55
Q

What is U-B Co2?

A

Giben a biarcarbonate load of acetazolamide, causing bicarbonaturia. HCO3+ combines with H+ in the proximal tubule to form H2O and Co2 (using CA). Co2 is then excreted in urine

56
Q

What is a normal U-B Co2?

A

greater than 10-15 mmHg

57
Q

When is U-B Co2 low?

A

normal in proximal RTA (type II) but low in types I and IV

58
Q

Which RTA has high plasma K+?

A

Type IV (I and II are both low)

Renal Week 2 (13 decks)

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