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Renal potassium balance Flashcards

1
Q

What is the physiology of potassium metabolism?

A
  1. Potassium intake
    -Diet (70-150mmol/day)
  2. Absorption
    -GI tract
  3. Distribution
    -ICF (98%)
    -ECF (2%)
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2
Q

What is the normal plasma K+ range in the ECF?

A

Normal plasma K+ range: 3.5 to 5.5mmol/L

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3
Q

What is hypokalaemia?

A

low potassium, <3.5 mmol/L

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4
Q

What can cause hypokalaemia?

A
  • Drugs e.g. diuretics
  • GI loss
  • Mineralocorticoid excess
  • Genetic disease (Gitelmans and Bartters)
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5
Q

What is hyperkalaemia?

A

Hyperkalaemia (raised potassium, >5.5 mmol/L)

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6
Q

What can cause hyperkalaemia?

A
  • Drugs e.g. potassium sparing diuretics, ACEi or ARBs,
  • CKD/ESKD
  • Addison’s
  • Food ingestion
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7
Q

What are the 4 mechanisms of K+ balance?

A
  1. K+ intake through diet
  2. GI losses
    - GI tract secretes 5-10% of absorbed K+ daily
  3. Renal losses
    -90-95% is regulated by the kidney
  4. Transcellular K+ shift
    - Overall K+ stores remain the same but redistribute
    between the ICF and ECF
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8
Q

How much K+ is reabsorbed in PCT?

A

Reabsorbs 65-70% of filtered K+

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9
Q

What process is K+ reabsorption via in PCT?

A

K+ reabsorption is via diffusion and solvent drag

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10
Q

What percentage of K+ does the thick ascending loop of henle reabsorb?

A

Re-absorbs 10-25% of K

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11
Q

What is the active transporter affinity like when tubular K+ fluid are low in thick ascending loop of henle?

A

Transporter affinity for Na+, K+ high when tubular fluid K are low

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12
Q

How does K absorption occur in DCT and CD?

A

Occurs via a transcellular pathway and is mediated by alpha and beta
intercalated cells

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13
Q

What do intercalated cells do in DCT and CD?

A

Reabsorb K+

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14
Q

What are the 2 steps of reabsorption of potassium ?

A
  • The apical H+-K+-ATPase mediates the movement of H+ into
    the lumen, driving K+ into the intercalated cell
  • Then, the basolateral K+ channel allows the K+ inside the intercalated cell to
    leak out into the bloodstream.
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15
Q

What is the primary regulatory site of K+ excretion?

A

Principal Cell

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16
Q

What is the primary regulatory site of K+ excretion?

A

Principal cells

17
Q

How does K+ excretion work with principal cells?

A
  • Concentration Gradient across
    luminal membrane
  • Electrical gradient generated by
    reabsorption of Na+ via luminal Na+
    channels (ENaC)
  • K+ permeability of luminal
    membrane
    -number of open K+ channels
18
Q

How does aldosterone affect K+ secretion into tubular fluid?

A
  • Aldosterone- augments K+
    secretion in principal cells
  • Increase number of open Na+
    and K+ channels in luminal
    membrane
  • Enhance activity of Na+K+
    ATPase pump
19
Q

How does plasma K+ affect K+ secretion into tubular fluid?

A
  • Plasma K+
  • Increases number of open Na+
    and K+ channels in luminal
    membrane
    -Enhances activity of Na+K+ATPase
    pump
20
Q

How does distal flow rate(so flow of tubular fluid) affect K+ secretion into tubular fluid?

A
  • Distal flow rate- so flow of tubular fluid
  • Increase in distal flow rate washes secreted K+ away and replaces with
    relatively K+ free fluid which allows favorable gradient for secretion into
    tubular fluid
21
Q

How does distal sodium delivery affect K+ secretion into tubular fluid?

A
  • Distal sodium delivery
  • Entry of Na+ via ENaC makes lumen more electronegative
  • Transport of Na+ into peritubular capillary by ATPase which pumps more K+ into
    cell
  • More K+ secreted into electronegative lumen
22
Q

What do intercalating cells in collecting ducts do in terms of K+ and how?

A

K+ reabsorption
-Active re-absorption by H+ K+ ATPase enables urinary K+ excretion to decrease to <15mmol/d in severe K+ deficiency

23
Q

Potassium handling in the nephron

A

REFER TO SLIDES

24
Q

What is maintenance of intracellular K+ critical for?

A
  • nerve conduction
  • muscle contraction
  • Heart function
25
Q

What causes the resting membrane potential to arise?

A

The difference between potassium (K+) inside the cell and sodium (Na+) outside is what CAUSES the resting membrane potential (RMP)

26
Q

What needs to be established in order to create a RMP across a cells plasma membrane and how is this done?

A

To create the RMP across a cell’s plasma membrane, K+ and Na+ gradients are established by the sodium-potassium pump* —-Transport of 2 potassium ions inside and 3 sodium ions outside with each adenosine triphosphate (ATP) molecule
-When the cell depolarizes, permeability changes, K+ rushes out and Na+ rushes in to try to establish electroneutrality
-Then when the cell repolarizes, K+ is pumped back in and Na+ out, to re-establish the gradient.

27
Q

What are the direct electrophysiological effects in hypokalaemia?

A
  • hyperpolarization of the RMP (the RMP becomes more negative) due to the altered K+ gradient.
  • As a result, a greater than normal stimulus is required for depolarization of the membrane in order to initiate an action potential (the cells become less excitable).
28
Q

What does an increased action potential threshold and lack of K+ for cellular membrane depolarization lead to?

A

An increased action potential threshold and lack of K+ for cellular membrane repolarization led to decreases in skeletal and smooth muscle contraction.

29
Q

What is affected due to hypokalemia impacts direct effects on electrophysiology?

A

Skeletal and smooth muscle cells, as well as nerve cells, were affected. This leads to weakness (skeletal muscle effect), impaired nerve signaling, constipation (smooth muscle effect) and change in heartbeats (cardiac muscle effect)

30
Q

Management of hyperkalaemia depends on severity

A

LOOK AT SLIDE FOR MANAGEMENT

31
Q

What is the management of hyperkalaemia to protect the heart, the mechanism of action of drugs and what the drugs are called?

A

The drugs used are calcium gluconate and calcium chloride
-Drugs to stabilise the membrane potential

32
Q

What is the management of hyperkalaemia to shift potassium into cells, the mechanism of action of the drugs and what the drugs are called?

A

The drugs are called Insulin+dextrose, salbutamol and NaHCO3
-Drugs which move potassium into cells

33
Q

What is the management of hyperkalaemia to remove potassium from body, the mechanism of action of the drug and what the drugs are called?

A

Sodium Zirconium Cyclosilicate, Patiromer
-Drugs which increase potassium secretion in the gut
Frusemide, Bumetanide, Metolozone
Bendroflumethiazide
-Drugs which increase renal potassium loss
Dialysis

34
Q

What is the management of hyperkalaemia to prevent reoccurence?

A

-Stop drugs which cause high potassium
-Low potassium

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