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TAS Nephrology > Tubular Disorders ✅ > Flashcards

Tubular Disorders ✅ Flashcards

1
Q

How much plasma does the adult kidney filter per day on average?

A

150L of plasma

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2
Q

How much sodium does the adult kidney filter per day on average?

A

22.5mmol

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3
Q

What % of filtered sodium is reabsorbed by the tubules?

A

99%

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4
Q

What do disorders in sodium handling affect?

A

BP

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5
Q

What effect does sodium-losing disorders have on BP?

A

Hypotension

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6
Q

What effect to sodium-retaining disorders have on BP?

A

Hypertension

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7
Q

What transporter is important in sodium homeostasis?

A

Na/K-ATPase

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8
Q

What cells is Na-K-ATPase present in?

A

All cells

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9
Q

What is the importance of Na/K-ATPase?

A

It is the driving force which generates a favourable eletrochemical gradient for Na entry into the cell

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10
Q

What does the sodium gradient allow?

A

Co-transport of other substances, such as glucose, amino acids, phosphate

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11
Q

What happens to fractional excretion of sodium in renal salt-wasting disorders?

A

It is almost always normal

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12
Q

Why is fractional excretion of sodium normal in almost all renal salt-wasting disorders?

A

Because sodium is the main determinant of intravascular volume, so in salt-wasting disorders there is activation of RAAS

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13
Q

What are the functions of the proximal tubule?

A
  • Glucose transport
  • Phosphate transport
  • Amino acid transport
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14
Q

What renal tubular disorders affect the proximal tubule?

A
  • Renal glycosuria
  • Hypophosphataemic rickets
  • Isolated, generalised aminoaciduria
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15
Q

What is generalised dysfunction of the proximal tubule called?

A

Fanconi syndrome

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16
Q

What is the function of the ascending limb of Henle?

A

Sodium, potassium, and chloride transport

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17
Q

What renal tubular disorder affects the ascending limb of Henle?

A

Bartter syndrome

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18
Q

What are the functions of the distal tubule?

A
  • Proton (H+) secretion

- Sodium chloride transport

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19
Q

What renal tubular disorders affect the distal tubule?

A

Distal renal tubular acidosis

Gitelman syndrome

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20
Q

What are the functions of the collecting duct?

A
  • Water transport

- Sodium and potassium transport

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21
Q

What renal tubular disorders affect the collecting duct?

A
  • Nephrogenic diabetes insipdius
  • Pseudohypoaldosteronism
  • Liddle syndrome
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22
Q

What is Fanconi syndrome?

A

A generalised proximal tubular disorder

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23
Q

What happens to glomerular function in Fanconi syndrome?

A

It is at least initially well preserved

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24
Q

What can the causes of Fanconi syndrome be divided into?

A
  • Congenital
  • Acquired
  • Renal
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25
Q

What are the cardinal clinical features of Fanconi syndrome?

A
  • Growth faltering
  • Polyuria
  • Rickets
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26
Q

What is found biochemically in Fanconi syndrome?

A
  • Normal plasma anion gap
  • Metabolic acidosis
  • Hypophosphataemia
  • Hypokalaemia
  • Generalised aminoaciduria
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27
Q

What is involved in supportive management of Fanconi syndrome?

A
  • Salt, water, and nutritional supplementation

- Bicarbonate, electrolyte, and phosphate replacement

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28
Q

What are the congenital causes of Fanconi syndrome?

A
  • Familial idiopathic form
  • Cystinosis
  • Tyrosinaemia
  • Galactosaemia
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29
Q

What are the acquired causes of Fanconi syndrome?

A
  • Medications
  • Poisoning
  • Renal transplantation
  • Renal diseases
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30
Q

What medications can cause Fanconi syndrome?

A
  • Aminoglycosides
  • Sodium valproate
  • 6-mercaptopurine
  • Ifosfamide
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31
Q

What poisons can cause Fanconi syndrome?

A
  • Toluene

- Paraquat

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32
Q

What renal diseases can cause Fanconi syndrome? -

A
  • ATN
  • Tubulointerstitial nephritis
  • Focal and segmental glomeruloscerlosis
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33
Q

What phase of ATN might Fanconi syndrome occur in?

A

The recovery phase

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34
Q

What is the most common cause of Fanconi syndrome in Europe and North America?

A

Nephropathic cystinosis

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35
Q

What is nephropathic cystinosis?

A

A disorder of lysosomal cystine transport

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36
Q

What is the inheritance pattern of nephropathic cystinosis?

A

Autosomal recessive

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37
Q

What is the pathological process in nephropathic cystinosis?

A

Excessive intracellular accumulation of free cystine in many organs, including the kidney, eyes, and thyroids

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38
Q

How is nephropathic cystinosis managed?

A

Mercaptamine

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39
Q

How does mercaptamine treat nephropathic cystinosis?

A

It prevents accumulation of lysosomal cystine

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40
Q

What structure is involved in Bartter syndrome?

A

The thick ascending loop of Henle

41
Q

What structure is involved in Gitelman syndrome?

A

The distal convulted tubule

42
Q

What biochemical abnormalities are produced by Bartter and Gitelman syndromes?

A
  • Hypokalaemia
  • Hypochloraemia
  • Metabolic alkalosis
  • Salt wasting
43
Q

What is the main problem in Bartter/Gitelman syndromes?

A

Tubular loss of sodium and chloride, and secondarily excess loss of potassium in the distal tubule associated with hyperreninaemia and hyperaldosteronism

44
Q

What is sodium reabsorption linked to in the distal tubule?

A

Chloride reabsorption

45
Q

What channel is disrupted in Bartter syndrome?

A

The sodium-potassium chloride channel (NKCC2)

46
Q

Where is the NKCC2 channel located?

A

In the loop of Henle

47
Q

What drug is the NKCC2 channel sensitive to?

A

Furosemide

48
Q

What channel is disrupted in Gitelman syndrome?

A

The sodium-chloride channel (NCCT)

49
Q

Where is the NCCT located?

A

In the early DCT

50
Q

What drug is the NCCT channel sensitive to?

A

Thiazide

51
Q

What are salt wasting disorders from the distal nephron always associated with?

A

Urinary chloride loss

52
Q

Why are salt wasting disorders from the distal nephron always associated with urinary chloride loss in excess of urinary sodium loss?

A
  • All chloride reabsorption is linked with sodium, with twice as much chloride as sodium reabsorbed via NKCC2 (so if these receptors are disrupted, it has a bigger impact on chloride reabsorption)
  • Sodium reabsorption but not chloride reabsorption can occur partly via the paracellular route
  • There is no capacity for chloride reabsorption more distally within the nephron
53
Q

What biochemical abnormalities are specific to Bartter syndrome?

A

Hypercalciuria

54
Q

Why does Bartter syndrome cause hypercalciuria?

A

Because calcium reabsorption is a linked paracellular process

55
Q

Does hypomagnesaemia occur in Bartter syndrome?

A

No

56
Q

Why does hypomagnesaemia not occur in Bartter syndrome?

A

Because of compensatory reabsorption in the early DCT

57
Q

What biochemical abnormalities are specific to Gitelman syndrome?

A
  • Hypocalciuria

- Hypomagnesaemia

58
Q

Why do you get hypocalcuria and hypomagnesaemia in Gitelman syndrome?

A

Because of a compensatory mechanisms in the early DCT which down-regulates cells expressing NCCT and an apical magnesium channel in favour of cells which reabsorb sodium and calcium

59
Q

When does Gitelman syndrome present?

A

Typically in older children or adults

60
Q

How does Gitelman syndrome present?

A
  • Muscle weakness and cramps

- Short stature

61
Q

What might Gitelman syndrome be diagnosed following the investigation of?

A
  • Constipation
  • Growth problems
  • Enuresis
62
Q

When does Bartter syndrome present?

A

Early childhood

63
Q

How does Bartter syndrome present?

A
  • Growth faltering
  • Dehydration
  • Hypotonia
  • Lethargy
64
Q

What is often present in the history in Bartter syndrome?

A

Maternal polyhydraminos

65
Q

Is Gitelman or Bartter syndrome more severe?

A

Bartter

66
Q

How does the kidney achieve acid-base balance?

A
  • Bicarbonate reabsorption

- Acid secretion

67
Q

Where does most bicarbonate reabsorption occur in the kidneys?

A

Proximal tubules

68
Q

What % of filtered bicarbonate is reabsorbed in the proximal tubules?

A

Up to 90%

69
Q

Which part of the nephron is principally responsible for acid secretion?

A

The distal collecting tubules

70
Q

What is the minimal achievable urine pH?

A

4.5 to 5

71
Q

What allows the excretion of the daily acid load within the limits of the minimal achievable urine pH?

A

Buffers in the tubular lumen bind free hydrogen ions

72
Q

What are the main urinary buffers of hydrogen ions?

A
  • Ammonia

- Phosphate

73
Q

How is ammonia formed?

A

Amino acid metabolism

74
Q

How does ammonia enter the tubular lumen?

A

It freely diffuses across tubular membranes

75
Q

What is formed when ammonia combines with free hydrogen ions in the tubular lumen?

A

Ammonium (NH4+)

76
Q

Can ammonium be reabsorbed?

A

No, it is trapped within the tubular lumen

77
Q

What are the ways in which renal tubular acidosis can occur?

A
  • Bicarbonate wasting in the proximal tubule
  • Impairment in formation of ammonia
  • Failure to adequately secrete hydrogen ions
78
Q

What was RTA caused by bicarbonate wasting in the proximal tubule historically known as?

A

Type 2 RTA

79
Q

What does RTA due to bicarbonate wasting in the proximal tubule almost always occur as part of?

A

Fanconi syndrome

80
Q

What is RTA caused by an impairment in the formation of ammonia known as?

A

Type 4 RTA

81
Q

What does type 4 RTA lead to?

A

Renal failure

82
Q

What is the acidosis in type 4 RTA associated with?

A

Hyperkalaemia

83
Q

What is RTA caused by a failure to adequately secrete hydrogen ions associated with?

A

Hypokalaemia

84
Q

Are most cases of childhood distal RTA genetic or acquired?

A

Genetic

85
Q

What might autosomal recessive forms of childhood distal RTA be associated with?

A

Sensorineural deafness

86
Q

What gene is involved in autosomal recessive childhood distal RTA associated with sensorineural deafness?

A

ATP6V1B1

87
Q

What gene is involved in autosomal recessive childhood distal RTA not associated with sensorineural deafness?

A

ATP6V0A4

88
Q

What do mutated genes causing autosomal recessive childhood distal RTA code for?

A

Subunits of the H-ATPase apical hydrogen ion transporter

89
Q

What gene is involved in autosomal dominant childhood distal RTA?

A

SLC4A1

90
Q

What does the gene involved in autosomal dominant childhood distal RTA code for?

A

The chloride-bicarbonate exchanger on the basolateral membrane

91
Q

How does the urine pH in distal RTA compare to proximal RTA?

A

In distal RTA it is always >5.5, whereas in proximal RTA it varies

92
Q

What does the urine pH vary according to in proximal RTA?

A

Plasma bicarbonate

93
Q

What should initial correction of acidosis take into account in distal RTA?

A

Potassium and calcium

94
Q

Why do potassium and calcium need to be taken into account in the initial correction of acidosis in distal RTA?

A

Because they will both decrease in response to alkali treatment

95
Q

What does maintenance treatment consist of in distal RTA?

A

Sodium bicarbonate or citrate (sodium and/or potassium)

96
Q

How does the doses of base required in distal RTA compare to that in proximal RTA?

A

They are generally less than for proximal RTA

97
Q

What is required long-term in distal RTA?

A

Lifelong follow up

98
Q

Why is lifelong follow up required in distal RTA?

A

They are at risk of nephrolithiasis and long-term deterioration in renal function from the nephrocalcinosis

TAS Nephrology (16 decks)

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