Control Of Potassium

Question 0

Explain how potassium handling occurs in the various segments of the nephron

Answer 0

Renal secretion - principal cells of DCT, cortical collecting duct
Maintained by Na+/K+ATPase

Question 1

Explain why the internal balance of potassium is so important

Answer 1

98% body K+ intracellular (120-150mmol/L)

2% body K+ extracellular (3.5-5mmol/L)

Question 2

Describe potassium balance and the regulation of ECF and ICF potassium concentrations

Answer 2

120-150mmol/L intracellular
3.5-5mmol/L extracellular
Maintained by Na+/K+ATPase

Question 3

Demonstrate an understanding of hormonal control of potassium (e.g. adrenaline, insulin, aldosterone)

Answer 3

Affects intestinal absorption --> ECF 
Increased adrenaline (catecholamines) = hypokalaemia
Low insulin = diabetic ketoacidosis = hyperkalaemia 
Aldosterone affects potassium uptake (increased)

Question 4

Describe the pathophysiological factors that alter plasma potassium concentration (e.g. acid base balance, cell lysis, exercise, plasma osmolarity, drug related changes)

Answer 4

Acid base balance
Cell lysis e.g. trauma, chemotherapy = hyperkalaemia
Exercise - net release of K+ during recovery phase of ATP = hyperkalaemia
Plasma osmolarity
Drug related changes - drugs that block aldosterone action e.g. spironolactone, K+ sparing diuretics e.g. Amiloride, ACE inhibitors

Question 5

Describe common causes and treatment of hyperkalaemia

Answer 5

Causes:
Increased uptake - increased IV K+
Inadequate renal excretion - acute/chronic kidney injury
Decreased aldosterone - Addison’s disease, spironolactone, Amiloride, ACEi
Diabetic ketoacidosis - no insulin
Metabolic acidosis
Cell lysis - chemo, trauma, intravascular haemolysis
Exercise - net release of K+ during recovery phase of AP
Treatment:
IV calcium gluconate (stabilises membrane)
IV glucose + insulin
Dialysis
Nebulised B agonist

Question 6

Describe common causes and treatment of hypokalaemia

Answer 6

Causes:
Excessive loss - vomiting, diarrhoea, diuretics
Increased aldosterone - Cushing’s, Conn’s syndrome
Metabolic alkalosis - shift of K+ into ICF
Diabetes - increased insulin
Increased catecholamines (via B2 receptors) - adrenaline, dopamine
Treatment:
IV/oral K+
Drugs that block aldosterone action on principal cells
K+ soaring diuretic

Question 7

Describe the clinical features of hyperkalaemia

Answer 7

Muscle paralysis
Acidosis
Vasodilation 
Paralytic ileus
Heart arrhythmias (depolarises cardiac tissue --> Na channels remain in inactive form --> less excitable)

Question 8

Describe the clinical features of hypokalaemia

Answer 8

Unresponsive to ADH –> nephrogenic diabetes insipidus
Muscle weakness
Vasoconstriction
Paralytic ileus
Heart arrhythmias (hyperpolarises cardiac cells –> Na channels in active form –> more excitable)