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Urinary > 3. Potassium And Magnesium Homeostasis > Flashcards

3. Potassium And Magnesium Homeostasis Flashcards

1
Q

What happens if extracellular K+ rises to the resting membrane potential?

A

Resting membrane potential is decreased (depolarised)

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2
Q

What happens if extracellular K+ falls to the resting membrane potential?

A

Resting membrane potential is increased (hyperpolarised)

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3
Q

Where is K+ reabsorbed?

A

PCT reabsorbs 65% - passive, through tight junctions, via conc gradients/solvent drag
TAL reabsorbs 20% - transcellular, paracellular

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4
Q

What can cause hypokalemia?

A 
Excess insulin
Alkalosis 
Certain catecholamines 
Insufficient intake - anorexia, prolonged fasting 
Too much aldosterone - primary aldosteronism, compensated heart failure, cirrhosis
Diuretics
Vomiting
Diarrhoea
Sweat
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5
Q

What are the symptoms of hypokalemia?

A

Asymptotic until conc is below 2-2.5mmol/L
Decreased resting potential
Less sensitive to depolarising stimuli
Less action potentials generated and paralysis ensues

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6
Q

What are the clinical effects of hypokalaemia?

A

Muscle weakness, cramps, tetany
Impaired liver conversion of glucose to glycogen
Vasoconstriction and cardiac arrhythmias
Impaired ADH action causing thirst, polyuria and no conc of urine
Metabolic alkalosis due to increase in intracellular H+ conc

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7
Q

What is the treatment of hypokalaemia?

A

Treating underlying cause

Oral or IV K+ may be required

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8
Q

What can hyperkalaemia result from?

A 
Reduced renal excretion due to AKI or CKD, mineralocorticoid deficiency, K+ sparing diuretics or renal tubular defects
Increased plasma load
Insulin deficiency 
Transcellular shift of K+ out of cells
Pseudohyperkalaemia 
Certain catecholamines
Hypoaldosteronism
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9
Q

What are the clinical features of hyperkalaemia?

A

Can be asymptomatic

Muscle weakness, cardiac arrhythmias

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10
Q

What is the emergency treatment of hyperkalaemia?

A

Calcium gluconate
Insulin
Calcium resonium

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11
Q

How does calcium gluconate treat hyperkalaemia?

A

Ca2+ stabilises the myocardium, preventing arrhythmias

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12
Q

How does insulin treat hyperkalaemia?

A

Drives K+ into cells to lower plasma concentrations, given with glucose

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13
Q

How does calcium resonium treat hyperkalaemia?

A

Removes K+ by increasing excretion from the bowels

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14
Q

What are some other treatments for hyperkalaemia?

A

Salbutamol
Sodium bicarbonate
Renal replacement therapy

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15
Q

How does salbutamol treat hyperkalaemia?

A

Drives K+ into cells when given nebuliser or IV

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16
Q

How does sodium bicarbonate treat hyperkalaemia?

A

Correction of acidosis, would also drive K+ into cells

17
Q

What is the role of magnesium?

A

Controls mitochondrial oxidative metabolism and so regulates energy production
Is vital for protein synthesis
Regulates K+ and Ca2+ channels in cell membranes

18
Q

What is hypomagnesaemia caused by?

A 
Decreased intake
Diarrhoea
Absorption disorder including fat absorption defects
Renal wasting
Uncontrolled diabetes 
Excessive alcohol consumption
19
Q

What is hypomagnesaemia commonly associated with?

A

Hypokalaemia

Hypocalcaemia - Mg2+ needed to make PTH

20
Q

What are the signs and symptoms of hypomagnesaemia?

A

Uncontrolled stimulation of nerves and tetany

21
Q

What is the treatment for hypomagnesaemia?

A

Oral supplementation or IV/IM magnesium sulphate

Treat underlying cause

22
Q

What is hypermagnesaemia caused by?

A

Renal failure

Ingestion of Mg2+

23
Q

What are the signs and symptoms of hypermagnesaemia?

A

Reduced muscle contraction
High Mg2+ inhibits PTH release - hypocalcaemia
Very high levels Mg2+ alter the electrical potential across cardiac cell membrane, lead to cardiac arrhythmias

24
Q

What is the treatment for hypermagnesaemia?

A

Reduce intake
Calcium gluconate injection
Furosemide to increase excretion
Haemodialysis in severe cases

Urinary (30 decks)

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