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Y2 - Urinary > Lecture 8 - Regualtion Of Potassium > Flashcards

Lecture 8 - Regualtion Of Potassium Flashcards

1
Q

Briefly describe an action potential:

A

Cell sits at RMP
If stimulus reaches threshold Voltage gated sodium ion channels open allowing Na+ into cell (depolarisation)
Repolarisation where voltage gated sodium ion channels close and voltage gated K+ channels open, hyperpolarisation occurs
Na/K+ATPase reastablilshes the RMP

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2
Q

What happens to resting membrane potential (RMP) with high extracellular potassium?

A

RMP is decreased (depolarised/more positive) Meaning less of a stimulus is needed to reach threshold

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3
Q

What happens to resting membrane potential (RMP) with low extracellular potassium?

A

RMP is increased (hyperpolarised)

Meaning less of a stimulus is needed to reach threshold

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4
Q

What happens to an ECG with Hypokalemia?

A

Prolonged PR
ST depression
U wave

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5
Q

What happens to an ECG with hyperkalemia?

A

Wide flat P wave
Wide QRS
ST depression
Tall T wave

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6
Q

Look at the last slide, what pathology does 1 show and 2 show?

A

1 = hypokalaemia
2 = hyperkalemia

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7
Q

What affect does an increase in extracellular K+ levels (hyperkalaemia) have on the level of stimulus needed for an action potential?

A

It makes the RMP more depolarised making the cell “hyper excitable” this is because its much closer to threshold potential so needs a smaller stimulus to initiate an action potential

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8
Q

What is the total body composition of water in males?

A

60% fluid
40% solid mass

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9
Q

What is the distribution of total body water in an adult?

A

2/3 intracellular water
1/3 extracellular water

Of this 1/3 extracellular water:
-25% plasma
-75% interstitial water

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10
Q

Where is the majority of K+ located in the body?

A

Inside cells

Small amount in plasma

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11
Q

Why in a crush injury (rhabdomyolysis) does a patient present with hyperkalemia?

A

Crush injury leads to cell death/bursting leading to the intracellular stores of K+ being released into the plasma (hyperkalaemia)

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12
Q

Where is the majority of K+ reabsorbed from the filtrate in the nephron?

Where else is K+ reabsorbed?

A

Most (67%) in PCT
Ascending limb via NKCC

DCT

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13
Q

Via what mechanism is K+ reabsorbed by in the PCT?

A

Solvent drag via paracellular transport

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14
Q

What is the mechanism by which K+ is reabsorbed in the ascending limb of LOH?

A

NKCC

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15
Q

Where is potassium secreted in the nephron?

What transporter does this?

A

Collecting duct

ROMK

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16
Q

How are pH and K+ levels in the blood related?

A

If blood is Acidotic K+ levels are high in plasma

If blood is Alkalotic K+ levels in plasma are low

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17
Q

What are the 2 different cells that act to reabsorb K+ in the collecting duct?

A

Alpha intercalated cells
Beta intercalated cells

18
Q

In general when in Acidosis why are K+ levels in blood high (hyperkalaemia)?

A

Cells in body take up H+ from blood to help make blood less acidic, but in order to do this need to exchange the H+ with a K+
So K+ leaves cell into blood making blood hyperkalemic and H+ leaves blood into cell making it less acidic

19
Q

In general when in Alkalosis why are K+ levels in blood low (hypokalaemia)?

A

Cells in body put H+ into the blood to help make blood more acidic, but in order to do this need to exchange the H+ with a K+
So K+ enters the cell from the blood making blood hypokalemic and H+ enters into blood from cell making it more acidic

20
Q

Via what transporter are H+ and K+ exchanged from cells?

A

H+/K+ATPase

21
Q

What cell acts in the Acidosis in the collecting duct?

A

Alpha intercalated cells (A for acidosis)

22
Q

What is the overall function of the alpha intercalated cell in the collecting duct when its acidotic in the blood?

A

To secrete more H+ into CD lumen

Reabsorb more K+ and HCO3-

23
Q

What is the overall function of the beta intercalated cell in the collecting duct when its alkalotic in the blood?

A

Reabsorb as much H+ as possible

Secrete K+ and HCO3-

So blood becomes more acidic/less alkalotic

24
Q

Describe the processes taking place in the alpha intercalated cell in acidosis:

Think of the overall goal of the cell (secrete H+ and reabsorb as much HCO3- and K+)
Look at Neil the nephron

A

H2O + CO2 makes carbonic acid
Carbonic acid broken down into H+ and HCO3- (carbonic anhydrase)

Apical membrane: (in contact with lumen)
H+ pumped into lumen by H+ ATPase and via H+/K+ATPase (so K+ moves into a-intercalated cell)

Basolateral membrane (in contact with interstitium):
K+ leaks into blood
HCO3- transported into blood but is antiported with Cl- (Cl- goes into cell)
Cl- then leaks back into blood across a channel

25
Q

Describe the processes taking place in the beta intercalated cell in alkalosis:

Think of the overall goal of the cell

Look at Neil the nephron

A

Overall goal of B-intercalated cell is to reabsorb as much H+ as possible and secrete/excrete as much HCO3- and K+

So water and CO2 made into carbonic acid, broken down into HCO3- and H+ (carbonic anhydrase)

Apical membrane:
K+ leaks out into lumen via K+ channel
HCO3- moved into lumen but is antiported with Cl- (Cl- moved from lumen into cell)

Basolateral membrane:
Cl- leaks into blood across Cl- channel
H+ ATPase pumps protons into blood
H+/K+ ATPase works to pump H+ into blood and K+ into cell

26
Q

How can Hyperkalaemia present?

A

Muscle weakness
Cardiac arrhythmias

27
Q

What 3 things can cause hyperkalaemia?

A

Lack of excretion
Release from cells
Excess administration

28
Q

What conditions can cause hyperkalaemia from lack of excretion?

A

Addisons disease (lack of aldosterone)
Kidney injury (AKI/CKD)
Acidosis
Diuretics (K+ sparing diuretics)

29
Q

What can cause hyperkalaemia from release from cells?

A

Crush injures

30
Q

What are the 3 emergency treatments for hyperkalaemia?

A

Calcium Gluconate
Insulin
Calcium resonium

31
Q

How is calcium gluconate used to treat hyperkalaemia in an emergency?

A

Doesn’t actually treat the Hyperkalaemia

The Ca2+ stabilises the myocardium preventing arrhythmias

32
Q

How does insulin treat Hyperkalaemia in an emergency?

A

It drives K+ into cells

K+ follows glucose

So insulin drives the removal of glucose form the blood into cells so indirectly drives cellular absorption of K+

33
Q

When giving insulin to treat Hyperkalaemia what should you also give?

A

Glucose

To prevent hypoglycaemia

34
Q

How does Calcium resonium treat Hyperkalaemia in an emergency?

A

Increases loss of K+ via the bowels

This is the only way to actually remove K+ from the body without renal replacement therapy

35
Q

What long term treatments do you do for hyperkalaemia?

A

Low K+ diet
Stop offending medications (potassium sparring diuretics)
Furosemide to enhance potassium loss in urine (need to worry about dehydration)

36
Q

What can cause hypokalaemia?

A

Reduced dietary intake
Increased entry into cells (alkalotic)
Increased GI losses (vomiting + diarrhoea)
Increased urine loss

37
Q

What are the clinical signs of hypokalaemia?

A

Muscle weakness, cramps and tetany
Vasoconstriction and cardiac arrhythmias
Impaired ADH action causing thirst, polyuria and dilute urine
Metabolic alkalosis

38
Q

Why does Hypokalaemia cause metabolic alkalosis?

A

H+ moved from blood into the cells leading to increased Intracellular H+ conc

39
Q

How do you treat hypokalaemia?

A

Treat the cause of it (diuretics, diarrhoea, poor oral intake of K+)

Give potassium replacement:
Oral - Sando-K, bananas and oranges

IV- add KCl to IV bags

Potassium sparing diuretics - Spironolactone, amiloride

40
Q

What are some potassium sparing diuretics?

A

Spironolactone
Amiloride

41
Q

Why cant you infuse a high amount of K+ into the body?

A

Causes cell death

Y2 - Urinary (24 decks)

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