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Burt's Renal Final > Renal Transport Mechanisms > Flashcards

Renal Transport Mechanisms Flashcards

1
Q

What is primarily resorbed in the PCT

A

Water, Na, K, Cl, HCO3, Ca, Pi

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2
Q

What should be completely resorbed in the PCT

A

Glucose and AA

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3
Q

What is TF:P?

A

The ultrafiltrate concentration ratios for various solutes as a function of proximal tube length

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4
Q

TF:P ratios greater than 1 are? Less than 1?

A

Secreted; reabsorbed

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5
Q

What fraction of filtered water is reabsorbed by the proximal tubule

A

2/3

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6
Q

Why doesn’t the Na TF:P ratio change

A

Na is being reabsorbed at the same rate as water

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7
Q

Why do we see Urea and Cl increase in TF:P diagrams

A

They are being reasborbed as quickly as water is

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8
Q

Is PAH being reabsorbed?

A

No, it is secreted into the tubule

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9
Q

What are the Na symporters in the early proximal tubule

A
  • glucose
  • amino acids
  • Pi
  • HCO3
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10
Q

What are the antiporters for Na in the early proximal tubule

A
  • H

- organic solutes

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11
Q

What drives reabsorption

A

Na-K ATPase

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12
Q

What causes water to cross from the tubule to the capillary

A

There is an osmolality gradient that pulls water into the capillaries

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13
Q

What causes Cl to be reabsorbed

A
  1. Water flow concentrates Cl
  2. Causes increase in tubular [Cl]
  3. Generates negative transepithelial potential difference
  4. Drives transepithetlial paracellular reabsorption of Na and Cl
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14
Q

What is the driving force for paracellular reabsorption

A

Concentration gradient between lumen and interstitium

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15
Q

What does paracellular Cl reabsorption depend on

A

Passive process but depends on Na and water reabsorption

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16
Q

How is the late proximal tubule kept neutral when moving charged substances

A

They exchange things that are charged similarly

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17
Q

What does Na exchange with in the lumen to come into cells

A

Na comes in; H goes out

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18
Q

What is Cl exchanged for in the late proximal tubule

A

Cl in; base out

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19
Q

What bases are used in the late proximal tubule to move Cl

A

Formate, oxalate, bicarbonate

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20
Q

What in the late proximal tubule moves Na into the interstitium from cells

A

NaK ATPase pump

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21
Q

What moves Cl in the late proximal tubule from the cells to the interstitium

A

Cl crosses basolateral membrane via Cl channels

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22
Q

What pushes water from the interstitium into capillaries

A

π_c since proteins never left the capillaries and P_i pushes it back in

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23
Q

What moves glucose from the lumen to the cell

A

SGLT

Sodium glucose transporter (brings gluc and Na in)

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24
Q

What is glucose into the cell dependent on

A

NaK ATPase b/c SGLT relies on there being a decent gradient set up

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25
Q

If the _______________ exceeds the saturation (of GLUT) then you will get _________________

A

Filtered load; glucosuria

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26
Q

Does the filtered load affect the transporter’s saturation

A

No

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27
Q

Where is secretion most active in the nephron

A

Proximal tubule

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28
Q

What all is secreted in the proximal tubule

A
  • organic anions
  • organic cations
  • PAH
  • creatinine
  • weak acids and bases
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29
Q

On the basolateral membrane organic anions are exchanged for what

A

OA go in; α-ketoglutarate goes out

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30
Q

What moves organic anions from the capillaries to the cell

A

OAT1-3

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31
Q

What moves α-ketoglutarate into the cells from the capillaries

A

NaDC3

Na goes in; α-ketoglutarate goes out

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32
Q

What moves organic anions into the tubules

A
  • MRP2/4
  • BCRP (ATP dependent)
  • OAT4 (in exchange for α-ketoglutarate)
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33
Q

What moves organic cations from the caps to the cells

A

OCT2

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34
Q

What moves organic cations out of the cells and into the tubules

A
  • MDR1 (ATP dependent)

- MATE (H+ in and OC out)

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35
Q

PAH is moved into the urine where

A

Mostly secreted in tubules but some is filtered

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36
Q

What is the issue with PAH secretion

A

It can be saturated giving inaccurate measurements of RPF

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37
Q

What is creatinine

A

Organic cation

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38
Q

How is creatinine secreted into the tubules

A

Organic cation and anion transporters

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39
Q

Increased luminal pH causes what to be preferential reabsorbed? Secreted?

A

Reabs of bases

Excretion of acids

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40
Q

What would you do to increase secretion of aspirin

A

Increase luminal pH so acids (salicylic acid) is excreted

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41
Q

Low luminal pH causes what to be reabsorbed preferentially? Excreted?

A

Favors reabsorption of acids

Favors excretion of bases

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42
Q

What causes increased intracellular K

A
  • insulin
  • aldosterone
  • β-adrenergic stim
  • alkalosis
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43
Q

What causes decreased intracellular K

A
  • diabetes mellitus
  • aldosterone deficiency (addisons)
  • β-adrenergic blockade
  • acidosis
  • cell-lysis
  • strenuous exercise
  • increased extracellular fluid osmolality
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44
Q

What does low K do to skeletal muscle

A

Hyperpolarizes it, makes it more difficult to fire

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45
Q

What does high K cause in skeletal muscle

A

Hypopolarizes it; causes it to be easier to fire

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46
Q

What happens in cardiomyocytes with high K

A
  • High T waves
  • eventually v-fib
  • “too much repolarization” which is why we see high T
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47
Q

What happens in cardiomyoctes with low K

A
  • low T wave
  • high U wave
  • “too little repolarization” which is why we see the low T wave
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48
Q

Where is K secreted or reabsorbed

A

Late DT (distal tubule) and cortical CD (collecting duct)

49
Q

What types of cells secrete K

A

Prinicipal cells and β-intercalated cells

50
Q

What stimulates secretion of K

A
  1. Increased ECF [K]
  2. Aldosterone
  3. Increased tubular flow rate
51
Q

What drives K secretion in principal cells

A

Na

52
Q

What drives K secretion in β intercalated cells

A

H and HCO3

53
Q

What moves K out of the principal cells

A

BK and ROMK

54
Q

What is reabsorbed by principal cells

A

Na and H2O

55
Q

What is secreted by principal cells

A

K

56
Q

What is reabsorbed by α intercalated cells

A

K and HCO3

57
Q

What is secreted by α intercalated cells

A

H

58
Q

What is reabsorbed by β intercalated cells

A

H and Cl

59
Q

What is secreted by β intercalated cells

A

K and HCO3

60
Q

What is normal serum K

A

4.2 mEq/L

61
Q

Increased tubular flow rate causes increased secretion of what

A

K

62
Q

What does increased aldosterone do for K secretion

A

Increased aldosterone increases K secretion

63
Q

What causes hypokalemia with acute alkalosis

A

Increased activity of NaK ATPase —> increased [K]i —> passive diffusion of K into lumen —> increased K channels —> increased K secretion

This causes hypokalemia

64
Q

What does acute alkalosis do for K

A

Causes hypokalemia

65
Q

What does acute acidosis do for K

A

Causes hyperkalemia

66
Q

How does acute acidosis cause hyperkalemia

A

Decreased activity of NaK ATPase —> decreased [K]i —> decreased passive diffusion of K into lumen —> decreased K channels —> decreased K secretion —> hyperkalemia

67
Q

How does chronic acidosis differ from acute

A

Chronic acidosis stimulates K+ secretion

68
Q

How does chronic acidosis stimulate K secretion

A

Chronic acidosis decreases reabs of water and solutes which inhibits the NaK ATPase

Increase tubular flow to DT and CD which increase K secretion

RAAS is stimulated which causes K secretion

69
Q

During acidosis what favors K secretion? What opposes it?

A

Increased distal flow; decreased [K]i

70
Q

What part of volume expansino favors K secretion? Opposes it?

A

Increased distal flow; decreased aldosterone

71
Q

What part of high water intake favors K secretion? What opposes it?

A

Increased aldosterone; decreased distal flow

72
Q

What competes for binding sites on plasma albumin

A

H and Ca

73
Q

What does hypoalbuminemia cause

A

Increased plasma Ca

74
Q

What does hyperalbuminemia cause

A

Decreased plasma Ca

75
Q

What does hyperalbuminemia cause

A

Decreases plasma Ca

76
Q

In acidosis there is more/less free calcium in circulation

A

More

77
Q

In alkalosis there is more/less calcium in circulation

A

Less

It is bound to plasma proteins

78
Q

What does alkalosis predispose you to

A

Hypocalcemic tetany

79
Q

What can induce symptoms that look like hypocalcemia

A

Acute alkalosis

80
Q

Why can’t 100% of plasma calcium be filtered

A

The remainder is bound to proteins in the plasma

81
Q

A decrease in calcium causes what to change

A
  • increased intestinal Ca absorption through vitamin D
  • increased PTH which increases renal Ca reabsorption
  • increased Ca release from the bones
82
Q

Where is the majority of calcium reabsorbed

A

Proximal tubule

83
Q

What drives calcium reabsorption at the proximal tubule

A

Passive transport following water and Na

84
Q

How is calcium absorbed in the thick ascending limb

A

Paracellularly due to lumen positive voltage pushing Ca away

85
Q

What is the major site of regulation for Ca reabsorption

A

Distal tubule

86
Q

How is Ca reabsorbed in the distal tubule

A

Active transport through TRPV5 which is regulated by Vit D3

87
Q

What increases Ca reabsorption at the proximal tubule

A

Volume contraction

88
Q

What is Ca reabsorption at the thick ascending loop related to

A

Na

As Ca abs goes up so does Na and vice versa

89
Q

What stimulates Ca reabsorption at the thick ascending loop

A

ADH

90
Q

Loop diuretics inhibit Na reabsorption in TAL. What effect does this have on Ca

A

Reduces magnitude of lumen transepithelial voltage thuse reduces Ca uptake and increases excretion

91
Q

Loop diuretics can be used to treat what Ca issue

A

Hyercalcemia

92
Q

How does Ca in the distal tubule cells get from the cell to the interstitium?

A

NCE

Sodium calcium exchanger

93
Q

What is the diuretic that inhibits Na reabsorption in the DT? How does this affect Ca

A

Thiazide diuretics

Stimulates reabsorption of Ca which reduces excretion and can be used to treat Ca containing stones

94
Q

What stimulates reabsorption of Ca in the distal tubule

A
  • PTH
  • Vit D
  • Calcitriol
  • Thiazide diuretics
95
Q

Acidemia increases Ca excretion in the distal tubule by what means

A

Inhibits TRPV5

Alkalemia stimulates TRPV5

96
Q

Where is most Pi reabsorbed

A

Proximal tubule

97
Q

What does FGF 23 do?

A

Fibroblast growth factor 23 is released by bone to increase phosphate excretion

98
Q

What causes FGF23 to be released

A

Secreted by bones in response to PTH, calcitriol, and hyperphosphatemia

99
Q

What transporter reabsorbs Pi from the lumen

A

NaPi-IIa/c

They both pull sodium across with it

100
Q

What causes Pi to cross the basolateral membrane

A

An unknown transporter

101
Q

PTH inhibits what transporters

A

NaPi and NaH antiporter in apical membrane of proximal tubule

102
Q

Vitamin D3 does what to Pi

A

Increases serum Pi by increasing intestinal absorption

103
Q

What does insulin do to Pi

A

Lowers serum levels by shifting Pi into cells

104
Q

Chronic acidosis and alkalosis do what to Pi

A

CAc- increases Pi excretion

CAl - decreases Pi excretion

105
Q

Where is the majority of Mg reabsorbed

A

thick ascending loop

106
Q

What 2 ions in the TAL depend on the lumen-positive voltage

A

Mg Ca

107
Q

How is Mg reabsorbed in the proximal tubule

A

Paracellular and follows Na and water

108
Q

What does TAL reuptake of Mg depend on

A

Uptake of NaK via NKCC2

109
Q

What is the site of fine tuning for Mg

A

DCT

110
Q

What is the primary driver of Mg in the DCT

A

Electrical potential since [Mg]i ~ [Mg]e

111
Q

How does Mg cross the border in the DCT

A

TRPM6

112
Q

How does Mg get to the interstitium

A

Unknown mechanism

113
Q

What is the main regulator for Mg reabsorption for us

A

Mg depletion since most Americans don’t meet dietary requirements

114
Q

What increases Mg reabsorption

A
  • Mg depletion
  • Ca depletion
  • Elevated PTH
  • Decreased ECV
  • Alkalosis
115
Q

What is the main factor leading to decreased Mg reabsorption

A

Diuretics

116
Q

When is TF:P less than 1? Greater?

A

Reabsorbed more quickly than water; reabsorbed more slowly than water

117
Q

What channel do prostaglandins act on? What is the end effect of this

A

K channels in the TAL

Increased intracellular Cl, which hinders NKCC channels, and thus reduces NaCl reasborption

118
Q

What does FGF23 do

A

Increase Pi excretion

Burt's Renal Final (7 decks)

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