PSL301: Water 6 Flashcards Preview

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Flashcards in PSL301: Water 6 Deck (75):
1

sources of dietary potassium

fruits, veggies

2

where is potassium absorbed

100% absorbed from gut

3

K is excreted by...

>90% kidneys (urine)
very small amount in stool

4

Why is K important? (6)

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

5

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

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

6

Rate that K+ leaks out of cell depends on...

concentration

7

Nernst equation

[K]ecf / [K]icf = ratio of K outside vs. inside the cell
- determines cell's transmembrane potential

8

normal serum K+

3.5 - 5 mmol/L

9

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

too little;
hyperpolarized (less positive than normal)

10

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

too much;
depolarized (more positive than normal)

11

Hypokalemia: more K+ lost from ECF // ICF

ECF

12

Hypokalemia: Nernst equation change

decrease, since more K is lost from ECF

13

Symptoms of hypokalemia

- muscle weakness
- irregular heart rhythm

14

why do hypokalemic people experience weakness?

Hard to contract muscles due to hyperpolarized state of cells

15

Hyperkalemia: Nernst equation change

Increase, since ECF is more impacted than ICF

16

Symptoms of hyperkalemia

- muscle stiffness & weakness
- abnormal ECG
- life0threatening cardiac arrhythmias

17

Why do hyperkalemics experience muscle stiffness?

cells are depolarized, so muscles are constantly tense

18

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

hyperkalemia;
bigger effect on cardiac rhythm

19

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

Dialysis;
high levels of K means kidneys have probably failed

20

distribution of K in ECF vs. ICF

ECF: 2%
ICF: 98%

21

Serum K =

ECF K

22

effect of insulin in K

K uptake by cells

23

Insulin deficiency has what impact on K?

cause K to leak out of cells

24

effect of adrenaline binding to B2-catecholamine receptor on K

K uptake by cells

25

Effect of B-blockers on K

cause K to leak out of cells

26

adrenaline binding to _____ receptor causes K uptake?

B2-catecholamine

27

K will leave cells due to ___ stress, such as...
This has detrimental effects on the patient because...

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

28

What prevents hyperkalemia every time we eat?

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

29

Effect of exercise on K

cause K to leak out of cells
- dilation of arterioles
- increase muscle blood flow

30

What prevents hyperkalemia every time we exercise?

adrenaline redistributes excess K in ECF to resting tissue

31

Effect of K on blood pressure

high K = lower BP

32

Why is K good at lowering BP?

it is a local & systemic vasodilator

33

increased serum K tells kidneys to ___ excretion

increase

34

90% of filtered K is reabsorbed in...

proximal tubule & loop of Henle

35

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

Cortical collecting duct;
K secretion;
aldosterone

36

Cells on the cortical collecting duct is called...

principle cell

37

How does the principle cells secrete K?

- 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

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

Na/K-ATPase

39

What is the lumenal Na channel on the CCD called?

ENaC

40

K transporter on lumenal CCD

ROMK

41

ROMK

renal outer medullary potassium channel

42

Aldosterone acts on which part of the nephron?

CCD

43

Why does aldosterone promote K secretion?

- 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

Where are aldosterone receptors on CCD?

intracellular - affects gene transcription

45

Effect of aldosterone on CCD

increase number & open probability of Na channels

46

What is needed to make CCD lumen negative?

Reabsorption of Na+

47

What increases K secretion by the CCD?

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

48

What decreases K secretion by the CCD?

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

49

Which diuretic prevents K secretion? How does it work?

Spironolactone
- aldosterone receptor antagonist

Amiloride
- ENaC inhibitor

50

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

Spironolactone;
Amiloride;
Na excretion

51

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

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

52

Effect of hyperkalemia on aldosterone secretion

increases

53

Effect of hypokalemia on aldosterone secretion

decreases

54

aldosterone is secreted by the...

adrenal cortex (zona glomerulosa)

55

Effect of low effective circulating volume on K

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

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

1. More Na+ in lumen need to be reabsorbed
2. cause K+ to be secreted as counter-ion

57

Can aldosterone regulate Na and K independently?

Yes, but poorly understood mechansim

58

Effect of B2-angonists on K

uptake into cells

59

Irregular K loss from lower GI tract

- diarrhea
- laxatives

60

K loss in urine requires...

- high flow AND
- high aldosterone

61

Diuretics that are K sparing

- Spironolactone
- Amiloride

62

Diuretics that promote K loss

- Furosemide
- Thiazide

63

Genetic problem that cause K loss

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

64

Primary hyperaldosteronism = problem at...

adrenal cortex
- usually adrenal tumour

65

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

Too much aldosterone
- Na reabsorption (high BP)
- K secretion

66

Primary hyperaldosteronism has what effect on K?

hypokalemia

67

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

very rare

68

Symptoms:
- hypokalemia
- low renin, low ANG II
- high aldosterone

Problem?

Primary hyperaldosteronism: excess aldosterone secretion by adrenal tumour

69

Mechanism of thiazide action

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

Low kidney secretion of K means there is both...

1. low GFR / flow to CCD
2. low aldosterone

71

Low GFR usually means...

acute or chronic kidney failure

72

Explainations for low aldosterone

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

73

Treatment for genetic causes of K+ loss

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

74

Hyperkalemia is usually due to...

drugs that reduce aldosterone secretion & action

75

which drugs reduce aldosterone secretion & action?

- ACE inhibitors
- ANG II receptor blockers
- aldosterone receptor blockers