Regulation of Potassium

Question 1

What is the normal potassium range?

Answer 1

3.5 - 5.5 mmol/L

Question 2

Relationship between extracellular {K+] and resting membrane potential

Answer 2

• If extracellular [K+] rises, RMP decreases > depolarised
• if extracellular [K+] falls, RMP increases > hyperpolarised

Question 3

Hypokalemia signs on ECG

Answer 3

prolonged PR interval
ST depression
Shallow T wave
Prominent U wave

Question 4

Hyperkalemia signs on ECG

Answer 4

Wide P wave
Prolonged PR interval
Decreased R wave amplitude
Widened QRS
Depressed ST
Tall, peaked T wave

Question 5

Where is most potassium reabsorbed in the nephron?

Answer 5

PCT

Question 6

What happens to potassium in the collecting duct?

Answer 6

Secreted

Question 7

What cells in the collecting duct control acid base balance + K+ regulation?

Answer 7

Intercalated cells
a - acidosis
B - alkalosis

Question 8

Causes of hyperkalaemia

Answer 8

Lack of excretion:
- potassium sparing diuretics
- kidney injury
- acidosis
- Addison’s disease

Release from cells:
- cell death e.g. crush injury, rhabdomyolysis

Excess administration:
- K+ supplements
- high dietary intake

Question 9

Short term treatment of hyperkalaemia

Answer 9

• calcium gluconate: Ca2+ stabilises myocardium > prevents arrhythmias
• insulin: drives K+ into cells to lower plasma conc. | given with glucose to avoid hypoglycaemia
• calcium resonium: increases K+ excretion from bowels

Question 10

What is the only way to increase K+ excretion without renal replacement therapy?

Answer 10

Calcium resonium
Excreted in bowels

Question 11

Long term treatment of hyperkalaemia

Answer 11

• Low potassium diet
• Stop offending meds
• furosemide > enhances K+ loss in urine | give IV fluids to prevent dehydration
• Dialysis

Question 12

Causes of hypokalaemia

Answer 12

Reduced dietary intake
Increased entry into cells e.g. alkalosis
Increased GI losses e.g. vomiting, diarrhoea
Increases urine loss e.g. increased aldosterone, potassium wasting diuretics

Question 13

Clinical effects of hypokalaemia

Answer 13

• Muscle weakness, cramps, tetany (spasms)
• vasoconstriction + cardiac arrhythmias
• impaired ADH action > thirst, polyuria, not concentrated urine
• metabolic alkalosis due to increased intracellular [H+]

Question 14

Treatment of hypokalaemia

Answer 14

Treat the cause
Potassium replacement

Question 15

What can you use for potassium replacement?

Answer 15

• oral: bananas, oranges, avocados
• IV: add KCl to IV bags
• potassium sparing diuretics e.g. spironolactone, amiloride

Question 16

Which intercalated cells treat acidosis?
How do they do this?

Answer 16

Alpha intercalated cell
- H2O + CO2 > H+ + HCO3-
- H+ into lumen via H+ ATPase and HK ATPase
- HCO3- reabsorbed into into blood in exchange for Cl-

Question 17

Which intercalated cells treat alkalosis?
How do they do this?

Answer 17

Beta intercalated cells
- H2O + CO2 > H+ + HCO3-
- HCO3- exchanged with Cl- into the lumen
- H+ into blood via H+ ATPase and HK ATPase

Question 18

What is the effect of regulation of acidosis on K+ levels?

Answer 18

• K+ is reabsorbed into blood as a result of H+ K+ ATPase
• in all cells in the body H+ is taken up in exchnage for K+
• can result in Hyperkalaemia

Question 19

What is the effect of regulation of alkalosis on K+ levels?

Answer 19

• K+ is lost from the cell + blood as it enters the nephron lumen
• in all cells in the body K+ is taken up in exchange for H+
• can result in hypokalaemia

Question 20

Why is calcium gluconate used in short term treatment of hyperkalaemia?

Answer 20

• Ca2+ stabilises myocardium
• This prevents arrhythmias

Question 21

Why is insulin used in the short term treatment of hyperkalaemia?

Answer 21

• drives K+ into cells to lower plasma conc
• given with glucose to avoid hypoglycaemia

Question 22

Insulin can be used as a short term treatment for hyperkalaemia, what needs to be given with it?

Answer 22

Glucose
To avoid hypoglycaemia

Question 23

Why is calcium resonium used in the short term treatment of hypokalaemia?

Answer 23

Increases K+ excretion from bowels

Question 24

Two examples of potassium sparing diuretics

Answer 24

spironolactone
amiloride