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PBL SEM 4 > renal physiology : maintaining electrolyte balance > Flashcards

renal physiology : maintaining electrolyte balance Flashcards

1
Q

cortical vs juxtamedullary nephrons structure

A
  • cortical — dip a little into outer part of the medulla
  • juxtamedullary — located much lower down in cortex - have long loops of henle that dip low into medulla. responsibel for concentrating
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2
Q

what is the name of the capillary network downstream of glomerulus which surrounds the loop of henle and collecting ducts?

A

vasa recta

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3
Q

what is the descending limb impermeable to?

A

NaCl

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4
Q

what is the ascending limb impermeable to?

A

water

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5
Q

____ moves out but ____ doesnt, so fluid becomes sequentially more concentrated towards bottom of loop

A
  • water
  • nacl
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6
Q

NaCl is transproted out in the ascending limb due to the gradient set up by what?

A

NaK ATPase

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7
Q

what is the maximum horizontal osmotic gradient established by the NaCl transporters (NKCC2) in the ascending limb of the loop of henle?

A

200 mOsm/kg

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8
Q

where is ADH (vasopressin) produced/stored?

A

produced in hypothalamus and stored in psoterior pituitary

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9
Q

what detect dehydration? what happens?

A

osmoreceptors in hypothalamus — ADH released — makes collecting duct more permeable to water — water reabsorbed — concentrated urine

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10
Q

what is the main signal for ADH release?

A

an increase in plasma osmolality

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11
Q

how does aldosterone indirectly cause water reabsorption?

A

needs ADH

  • aldosterone generates and inserts ENaC into apical membrane of late distal/collecting duct
  • aldosterone opens K+ channels allowing K+ put into tubular fluid
  • ADH released and binds to V2 receptors on collecting duct cells
  • V2 activation by ADH leads to insertion of H2O channels (esp AQP2) into apical membrane
  • when present, AQP2 allows H2o to enter down osmotic gradient created by Na+ entry through ENaC
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12
Q

AQP2 vs AQP3/4

A

AQP2 = apical membrane of late distal/collecting duct, ADH leads to its insertion

AQP3/4 = permanently inserted into basolateral (blood) membrane — basolateral side therefore always permeable to water

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13
Q

how does blood flow in vasa recta?

A

in opposite direction to tubular fluid

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14
Q

what does the length of the loop of Henle determine?

A

the max conc of urine

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15
Q

how does hyperglycaemia in diabetes lead to thirst?

A
  • glucose is osmotically active — encourages water to stay in tubular fluid
  • osmotic diuresis
  • dehydration detected in hypothalamus
  • angiotensin II release — stimulates thirst centres
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16
Q

following a head trauma, a patient develops central diabetes insipidus which is associated with a reduction in vasopressin secretion. the osmolality of a spot urine sample is expected to be what?

A

100 mOsm/kg

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17
Q

activation of V2 receptors in collecting duct by vasopressin leads to insertion of what?

A

AQP2 into apical membrane

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18
Q

where is msot of K+ found?

A

98% in cell, 2% in ECF

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19
Q

what moves K+ against its conc grad from ECF into cell?

A

NaK ATPase

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20
Q

what happens if there is a fall in ECF plasma K+ conc?

A

hypokalaemia —> hyperpolarisation —> paralysis —> death

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21
Q

what happens if there is an increase in ECF plasma K+ conc?

A

hyperkalaemia —> depolarisation —> paralysis —> death

22
Q

how is excess K+ excreted?

A

92% in urine, 8% via colon

23
Q

K+ in PCT, LoH, DCT/CD

A
  • PCT — 65% K+ reabsorbed
  • LoH — 25% K+ reabsorbed
  • DCT + CD — variable K+ reabsorption AND secretion into tubular fluid in excess
24
Q

how and why does the net charge of tubular fluid change?

A

starts more -ve and ends more +ve due to reabsorption of K+

25
Q

how is K+ reabsorbed in the PCT

A

by the passive movement of K+ paracellulary down an electrochemical gradient back into blood

  • K+ being repelled by +ve charge of tubular fluid
26
Q

what happens to K+ in the thick ascending limb?

A
  • taken back into cell through NKCC2 (SLC12A1)
  • leaves cell on basolateral side through K+ channel
27
Q

what channel allows K+ recycling in the thick ascending limb?

A

ROMK2 = renal outer medulla K+ channel — transports K+ out on apical side

28
Q

what is the majority cell type in the collecting duct?

A

principal cells

29
Q

what channel creates an osmotic gradient for water to be reabsorbed in the presence of ADH in principal cells?

A

ENaC

30
Q

in hyperkalaemic states, what take K+ out of the cell into tubular fluid?

A
  • KCl cotransporter
  • ROMK1 and 3 — K+ channels
31
Q

summarise the actions of aldosterone in the collecting duct

A
  • opens ENaC
  • opens ROMK — to allow loss of K+ from IC space to tubular fluid
  • reverse direction of basolateral K+ channel - K+ goes into cell to allow movement of K+ pout throguh ROMK1 and 3
32
Q

name the collecting duct cells that are less common than and interspersed with principle cells?

A

intercalated cells

33
Q

in hypokalaemic states, K+ goes into cell in exchange for what in intercalated cells?

A

H+

34
Q

what does insulin stimulate to help restore K+?

A

NaH exchanger — therefore more substrate for NaK ATPase

35
Q

how do high/low calcium levels affect the depolarisation threshold?

A

hypocalcaemia — lowers depolarisation threshold

hypercalcaemia — raises depolarisation threshold

36
Q

how do low/high magnesium levels affect heart rate?

A

hypomagnesaemia = raises HR

hypermagnesaemia = lowered HR

37
Q

what take up Ca and Mg from ECF?

A

osteoblasts

38
Q

what release Ca and Mg?

A

osteoclasts

39
Q

what is the principle store of Ca++ and Mg++?

A

bone

40
Q

how are Ca++ and Mg++ reabsorbed in the PCT/LoH and DCT?

A

PCT/LoH:
- 91% Ca++ reabsorbed - paracellular route
- 89% Mg++ reabsorbed - paracellular route

DCT:
- 3-7% Ca++ reabsorption
- 5-6% Mg++ reabsorption

41
Q

why and how is Ca++ transported in the distal tubule cells?

A

bound to a carrying molecule = calbindin-D28k — because Ca++ is an intracellular signalling messenger by itself

42
Q

via what does Ca++ enter the cell in the distal tubule?

A

TRPV5

43
Q

what is TRPV5 opened by?

A

parathyroid hormone, vitamin D, sex hormones

44
Q

Ca++ leaves the cell in the distal tubule on the basolateral side into the blood via what 1 of what 2 routes?

A
  1. NCX1 = Na/Ca exchanger
  2. PMCA1b = Ca++ ATPase pump
45
Q

what is the name of the endocrine regulator in tubular fluid that helps open TRPV5 on the apical membrane of the distal tubule for Ca++ entry into teh cell?

A

Klotho

involved in ageing?

46
Q

via what does Mg enter the cell in the distal tubule?

A

TRPM6

47
Q

what is Mg++ uptake driven by

A

electrical gradient

K+ leaves cell down conc grad into tubular lumen — more +ve in tubular fluid — drives Mg++ into the more -ve cell

48
Q

what binds on the basolateral membrnae of the distal tubule and stimulats Mg++ uptake through TRPM6 opening?

A

epidermal growth factor

49
Q

how does Mg++ leave the cell on the basolateral side?

A

unknown

some sort of exchange r

50
Q

the intracellular K+ conc is maintained at approx _______ by the actions of ________

A
  • 150 mmol/L
  • NaK ATPase pump
51
Q

insulin can be used to _____ extracellular fluid K+ conc through its actions on _______

A
  • lower
  • NaH exchangers

PBL SEM 4 (50 decks)

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