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Urinary system > Regulation of potassium > Flashcards

Regulation of potassium Flashcards

1
Q

What is the normal range for potassium?

A
  • 3.5-5.5 mmol/L
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2
Q

What happens if extracellular K+ rises?

A
  • Resting membrane potential is decreased i.e. becomes less negative (depolarised)
  • Can lead to asystole
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3
Q

What happens if extracellular K+ falls?

A
  • Resting membrane potential is increased - i.e. becomes more negative (hyperpolarised)
  • Can result in ventricular fibrillation
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4
Q

What features are seen on an ECG if someone has hypokalaemia?

A
  • Slightly prolonged PR interval
  • Slightly peaked P wave
  • ST wave depression
  • Shallow T wave
  • Prominent U wave
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5
Q

What features are seen on an ECG if someone has hyperkalaemia?

A
  • Wide, flat P wave
  • Prolonged PR interval
  • Widened QRS
  • Decreased R wave amplitude
  • Depressed ST segment
  • Tall, tented T wave
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6
Q

How is potassium handled in the nephron?

A
  • K+ is brought into the cell by Na+/K+/2Cl- transporter
  • K+ secreted into lumen of nephron by ROMK - then excreted in urine
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7
Q

What are the clinical features of hyperkalaemia?

A
  • Can be asymptomatic so only picked up on ECG
  • Muscle weakness
  • Cardiac arrhythmias
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8
Q

What can hyperkalaemia result from?

A
  • Lack of excretion
  • Release from cells e.g. during rhabdomyolysis
  • Excess administration (too much K+ in fluid)
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9
Q

What is the emergency treatment for hyperkalaemia?

A
  • Calcium gluconate
  • Insulin
  • Calcium resonium
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10
Q

How does calcium gluconate treat hyperkalaemia?

A
  • Ca2+ stabilises the myocardium
  • Prevents arrhythmias
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11
Q

How does insulin treat hyperkalaemia?

A
  • Drives K+ into cells
  • Lowers plasma concentration
  • Given with glucose to avoid hypoglycaemia
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12
Q

How does calcium resonium treat hyperkalaemia?

A
  • Removes K+ by increasing excretion from the bowels
  • Only way to remove K+ without renal replacement therapy
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13
Q

How do we treat hyperkalaemia after the emergency treatment?

A
  • Low potassium diet
  • Stop offending medications
  • Furosemide enhances potassium loss in urine
  • Dialysis?
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14
Q

What causes hypokalaemia?

A
  • Reduced dietary intake
  • Increased entry into cells
  • Increased GI losses
  • Increased urine loss
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15
Q

What are the clinical effects of hypokalaemia?

A
  • Muscle weakness, cramps, tetany starting in lower extremities
  • Vasoconstriction and cardiac arrhythmias
  • Impaired ADH action causing thirst, polyuria, and no concentration of urine
  • Metabolic alkalosis due to increase in intracellular H+ concentration
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16
Q

How do we treat hypokalaemia?

A
  • Treat the cause - diuretics, diarrhoea, poor oral intake of potassium
  • Give potassium replacement
  • Oral: bananas, oranges, sando-K
  • IV - add KCl to IV bags
  • Potassium sparing diuretics - spironolactone, amiloride
17
Q

Where is most body potassium found?

A
  • Intracellularly
18
Q

How is K+ excreted from the body?

A
  • Kidneys excrete 80% of K+
  • Bowel excretes 20%
19
Q

How does the kidney respond to acidosis?

A
  • Alpha cells (of collecting duct)
  • Carbonic anhydrase convert H2O and CO2 from respiration into H2CO3
  • H2CO3 breaks down to H+ and HCO3-
  • H+ is exchanged for K+ by H+/K+ ATPase
  • K+ brought into cells and H+ excreted in urine
  • HCO3- goes into blood and buffers H+, making H2CO3
  • K+ also moves into blood
20
Q

How does the kidney respond to alkalosis?

A
  • Beta cells (of collecting duct)
  • H2O and CO2 from respiration are converted to HCO3- and H+ by carbonic anhydrase
  • HCO3- exchanged with Cl- (HCO3- excreted in urine)
  • K+ brought into beta cells and exchanged for H+
  • H+ moves into blood
21
Q

How can acidosis affect potassium levels in the blood?

A
  • Can cause hyperkalaemia
22
Q

How can alkalosis affect potassium levels in the blood?

A
  • Can cause hypokalaemia
23
Q

How can acidosis lead to hyperkalaemia?

A
  • H+ is taken up into cells in exchange for K+ ions which are released into the blood
24
Q

How can alkalosis lead to hypokalaemia?

A
  • H+ is released from cells in exchange for K+ ions which are taken up into cells

Urinary system (22 decks)

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