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PSL301 > PSL301: Water 6 > Flashcards

PSL301: Water 6 Flashcards

Potassium balance

1
Q

sources of dietary potassium

A

fruits, veggies

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2
Q

where is potassium absorbed

A

100% absorbed from gut

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3
Q

K is excreted by…

A

> 90% kidneys (urine)

very small amount in stool

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4
Q

Why is K important? (6)

A
  1. most abundant ion in body fluids
  2. major intracellular cation
  3. determines resting membrane potential of cells (muscle & cardiac function)
  4. determine cell’s transmembrane potential
  5. keep inside cell negative
  6. affects peripheral vascular resistance
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5
Q

What keeps the cell negatively charged (relating to K)?

A

K leak out of cells through K channels, which keeps inside the cells negative

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6
Q

Rate that K+ leaks out of cell depends on…

A

concentration

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7
Q

Nernst equation

A

[K]ecf / [K]icf = ratio of K outside vs. inside the cell

- determines cell’s transmembrane potential

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8
Q

normal serum K+

A

3.5 - 5 mmol/L

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9
Q

K depletion means there is ___ serum K, and the RMP is ___.

A

too little;

hyperpolarized (less positive than normal)

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10
Q

K excess means there is ___ ECF K, and the RMP is ___.

A

too much;

depolarized (more positive than normal)

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11
Q

Hypokalemia: more K+ lost from ECF // ICF

A

ECF

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12
Q

Hypokalemia: Nernst equation change

A

decrease, since more K is lost from ECF

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13
Q

Symptoms of hypokalemia

A
  • muscle weakness

- irregular heart rhythm

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14
Q

why do hypokalemic people experience weakness?

A

Hard to contract muscles due to hyperpolarized state of cells

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15
Q

Hyperkalemia: Nernst equation change

A

Increase, since ECF is more impacted than ICF

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16
Q

Symptoms of hyperkalemia

A
  • muscle stiffness & weakness
  • abnormal ECG
  • life0threatening cardiac arrhythmias
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17
Q

Why do hyperkalemics experience muscle stiffness?

A

cells are depolarized, so muscles are constantly tense

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18
Q

which is more life-threatening: hypokalemia or hyperkalemia? why?

A

hyperkalemia;

bigger effect on cardiac rhythm

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19
Q

what kidney treatment do people with hyperkalemia have to go through?

A

Dialysis;

high levels of K means kidneys have probably failed

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20
Q

distribution of K in ECF vs. ICF

A

ECF: 2%
ICF: 98%

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21
Q

Serum K =

A

ECF K

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22
Q

effect of insulin in K

A

K uptake by cells

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23
Q

Insulin deficiency has what impact on K?

A

cause K to leak out of cells

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24
Q

effect of adrenaline binding to B2-catecholamine receptor on K

A

K uptake by cells

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25
Q

Effect of B-blockers on K

A

cause K to leak out of cells

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26
Q

adrenaline binding to _____ receptor causes K uptake?

A

B2-catecholamine

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27
Q

K will leave cells due to ___ stress, such as…

This has detrimental effects on the patient because…

A

mechanical;
cell death, injury;
hyperkalemia, maybe can’t get treatment if crush injury or trapped somewhere

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28
Q

What prevents hyperkalemia every time we eat?

A
  • eating stimulates insulin secretion

- insulin promotes muscle cell uptake of K & promotion of secretion in urine

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29
Q

Effect of exercise on K

A

cause K to leak out of cells

  • dilation of arterioles
  • increase muscle blood flow
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30
Q

What prevents hyperkalemia every time we exercise?

A

adrenaline redistributes excess K in ECF to resting tissue

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31
Q

Effect of K on blood pressure

A

high K = lower BP

32
Q

Why is K good at lowering BP?

A

it is a local & systemic vasodilator

33
Q

increased serum K tells kidneys to ___ excretion

A

increase

34
Q

90% of filtered K is reabsorbed in…

A

proximal tubule & loop of Henle

35
Q

____ regulates K excretion by adjusting K _____. This is done using _____.

A

Cortical collecting duct;
K secretion;
aldosterone

36
Q

Cells on the cortical collecting duct is called…

A

principle cell

37
Q

How does the principle cells secrete K?

A
  • Cl- is prevented from entering the cell: neg lumen
  • Favours K+ going into lumen (electrochemical gradient)
  • K is excreted through renal outer medullary potassium channel (ROMK) on lumenal side
38
Q

What K transporter is present on the basolateral side of CCD?

A

Na/K-ATPase

39
Q

What is the lumenal Na channel on the CCD called?

A

ENaC

40
Q

K transporter on lumenal CCD

A

ROMK

41
Q

ROMK

A

renal outer medullary potassium channel

42
Q

Aldosterone acts on which part of the nephron?

A

CCD

43
Q

Why does aldosterone promote K secretion?

A
  • More Na channels on apical (lumen) side
  • More Na/K-ATPase on basolateral side
  • Loss of Na makes lumen neg
  • Neg charge drives K+ excretion
  • Na/K-ATPase also exchanges Na+ for K+
44
Q

Where are aldosterone receptors on CCD?

A

intracellular - affects gene transcription

45
Q

Effect of aldosterone on CCD

A

increase number & open probability of Na channels

46
Q

What is needed to make CCD lumen negative?

A

Reabsorption of Na+

47
Q

What increases K secretion by the CCD?

A
  • aldosterone

- Na and water delivery to the CCD = increased flow to CCD

48
Q

What decreases K secretion by the CCD?

A
  • low aldosterone

- low delivery of Na & water to CCD = decreased flow to CCD

49
Q

Which diuretic prevents K secretion? How does it work?

A

Spironolactone
- aldosterone receptor antagonist

Amiloride
- ENaC inhibitor

50
Q

___ and ___ reduce the effect of aldosterone on the kidney, and therefore reducing K excretion. However, they have a small effect on ____.

A

Spironolactone;
Amiloride;
Na excretion

51
Q

Why does spironolactone & amiloride have a small effect on Na excretion?

A

Collecting duct is only responsible for 1% of Na reabsorption, and 90% of K+ secretion

52
Q

Effect of hyperkalemia on aldosterone secretion

A

increases

53
Q

Effect of hypokalemia on aldosterone secretion

A

decreases

54
Q

aldosterone is secreted by the…

A

adrenal cortex (zona glomerulosa)

55
Q

Effect of low effective circulating volume on K

A
  1. cause renin secretion -> ANG II secretion -> aldosterone secretion
  2. aldosterone causes K secretion
  3. BUT low volume reduces GFR -> reduce flow to CCD
  4. reduced flow to CCD cause increased K secretion

= normal K excretion due to the opposing forces

56
Q

Why does increased flow of Na and water to CCD cause K secretion?

A
  1. More Na+ in lumen need to be reabsorbed

2. cause K+ to be secreted as counter-ion

57
Q

Can aldosterone regulate Na and K independently?

A

Yes, but poorly understood mechansim

58
Q

Effect of B2-angonists on K

A

uptake into cells

59
Q

Irregular K loss from lower GI tract

A
  • diarrhea

- laxatives

60
Q

K loss in urine requires…

A
  • high flow AND

- high aldosterone

61
Q

Diuretics that are K sparing

A
  • Spironolactone

- Amiloride

62
Q

Diuretics that promote K loss

A
  • Furosemide

- Thiazide

63
Q

Genetic problem that cause K loss

A
  • mutation in gene coding for NaCl transporter
  • transporters located @ loop of Henle & DCT
  • patient behave like constantly exposed to furosemide/thiazide
64
Q

Primary hyperaldosteronism = problem at…

A

adrenal cortex

- usually adrenal tumour

65
Q

Typically, people in their 40’s-50’s with high BP have low serum K. Why?

A

Too much aldosterone

  • Na reabsorption (high BP)
  • K secretion
66
Q

Primary hyperaldosteronism has what effect on K?

A

hypokalemia

67
Q

adrenal tumours are a common // rare cause of hypertension?

A

very rare

68
Q

Symptoms:

  • hypokalemia
  • low renin, low ANG II
  • high aldosterone

Problem?

A

Primary hyperaldosteronism: excess aldosterone secretion by adrenal tumour

69
Q

Mechanism of thiazide action

A
  1. block DCT Na/Cl cotransporter
  2. Na+ lost
  3. Decreased blood volume & pressure
  4. Stimulate RAAS
  5. High CCD flow rate (effect of diuretic) & high aldosterone (RAAS) = increased K+ secretion
70
Q

Low kidney secretion of K means there is both…

A
  1. low GFR / flow to CCD

2. low aldosterone

71
Q

Low GFR usually means…

A

acute or chronic kidney failure

72
Q

Explainations for low aldosterone

A
  1. adrenal disease
  2. ANG II inhibitors: ACE inhibitor, ANG II receptor blockers
  3. Spironolactone / amiloride
73
Q

Treatment for genetic causes of K+ loss

A
  • high K diet
  • K supplements
  • high doses of amiloride: block ENaC and prevents K+ from going in lumen (no more electro-gradient)
74
Q

Hyperkalemia is usually due to…

A

drugs that reduce aldosterone secretion & action

75
Q

which drugs reduce aldosterone secretion & action?

A
  • ACE inhibitors
  • ANG II receptor blockers
  • aldosterone receptor blockers

PSL301 (29 decks)

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