Flashcards in PSL301: Water 6 Deck (75)
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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
