Regulation of Potassium Flashcards
What is the normal potassium range?
3.5 - 5.5 mmol/L
Relationship between extracellular {K+] and resting membrane potential
- If extracellular [K+] rises, RMP decreases > depolarised
- if extracellular [K+] falls, RMP increases > hyperpolarised
Hypokalemia signs on ECG
prolonged PR interval
ST depression
Shallow T wave
Prominent U wave
Hyperkalemia signs on ECG
Wide P wave
Prolonged PR interval
Decreased R wave amplitude
Widened QRS
Depressed ST
Tall, peaked T wave
Where is most potassium reabsorbed in the nephron?
PCT
What happens to potassium in the collecting duct?
Secreted
What cells in the collecting duct control acid base balance + K+ regulation?
Intercalated cells
a - acidosis
B - alkalosis
Causes of hyperkalaemia
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
Short term treatment of hyperkalaemia
- 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
What is the only way to increase K+ excretion without renal replacement therapy?
Calcium resonium
Excreted in bowels
Long term treatment of hyperkalaemia
- Low potassium diet
- Stop offending meds
- furosemide > enhances K+ loss in urine | give IV fluids to prevent dehydration
- Dialysis
Causes of hypokalaemia
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
Clinical effects of hypokalaemia
- Muscle weakness, cramps, tetany (spasms)
- vasoconstriction + cardiac arrhythmias
- impaired ADH action > thirst, polyuria, not concentrated urine
- metabolic alkalosis due to increased intracellular [H+]
Treatment of hypokalaemia
Treat the cause
Potassium replacement
What can you use for potassium replacement?
- oral: bananas, oranges, avocados
- IV: add KCl to IV bags
- potassium sparing diuretics e.g. spironolactone, amiloride
Which intercalated cells treat acidosis?
How do they do this?
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-
Which intercalated cells treat alkalosis?
How do they do this?
Beta intercalated cells
- H2O + CO2 > H+ + HCO3-
- HCO3- exchanged with Cl- into the lumen
- H+ into blood via H+ ATPase and HK ATPase
What is the effect of regulation of acidosis on K+ levels?
- 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
What is the effect of regulation of alkalosis on K+ levels?
- 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
Why is calcium gluconate used in short term treatment of hyperkalaemia?
- Ca2+ stabilises myocardium
- This prevents arrhythmias
Why is insulin used in the short term treatment of hyperkalaemia?
- drives K+ into cells to lower plasma conc
- given with glucose to avoid hypoglycaemia
Insulin can be used as a short term treatment for hyperkalaemia, what needs to be given with it?
Glucose
To avoid hypoglycaemia
Why is calcium resonium used in the short term treatment of hypokalaemia?
Increases K+ excretion from bowels
Two examples of potassium sparing diuretics
spironolactone
amiloride
