Regulation Of Potassium and Magnesium

Question 1

What happens to resting membrane potential if Extracellular K+ rises?

What

Answer 1

RMP is decreased (Depolarised )

Question 2

What happens to resting membrane potential if Extracellular K+ falls?

Answer 2

RMP is increased (Hyperpolarized)

Question 3

How much K+ is reabsorbed in PCT?

Via what methods?

Answer 3

65%

• Passive, paracellular movement, down conc. gradient
• Solvent drag with H2O

Question 4

How much K+ is reabsorbed in TAL?

Via what 2 pathways?

Answer 4

20%

• Transcellular
• Paracellular

Question 5

Describe K+ transport in DCT and CD

Answer 5

Early DCT:
- K+ leakage and reabsorption equal (Unless K+ deficient)

Late DCT and CD:

• Secretion by principal cells, Reabsorption by intercalated cells
• Normal/ high K+ diet-> 15 to 120% secretion
• 10 to 12% reabsorbed if body is trying preserve K+

Question 6

List 9 causes of Hypokalaemia

Answer 6

• Excess insulin (K+ taken into cell along with glucose)
• Alkalosis (To lower blood pH, K+ moved into cell while H+ moved out)
• Some Catecholamines (B2 agonists, Alpha antagonists)
• Insufficient intake
• Excess aldosterone
• Diuretics
• Diarrhoea
• Sweat
• Vomit (H lost, so alkalosis mechanism triggers)

Question 7

Below what concentration is hypokaelemia asymptomatic?

How are nerves affected?

Answer 7

• Asymptomatic until K+< 2-2.5 mmol/L
• Decreased RMP-< Nerves hyperpolarized
• Less sensitive to depolarization
• Thus less APs generated and paralysis follows

Question 8

Describe 5 signs and symptoms of Hypokalaemia

Answer 8

• Muscle weakness, cramps, tetany
• Impaired conversion of glucose to glycogen
• vasoconstriction and cardiac arrhythmias
• impaired ADH action-> Polydipsia, polyuria
• Metabolic alkalosis due to increased Intracellular H+

Question 9

How is Hypokalaemia treated?

Answer 9

• Treat underlying cause

- Oral/ IV Potassium may be needed

Question 10

List 8 causes of Hyperkalaemia

Answer 10

• Reduced excretion
• Insulin deficiency (type 1, not enough insulin to remove K+ and glucose from blood)
• Diet
• IV infusion
• Cell breakdown
• K+ moved out of cells due to metabolic acidosis (H+ moved into cell)
• some Catecholamines (B2 antagonists, Alba agonists)
• Hypoaldosteronism

Question 11

Describe the symptoms of hyperkalaemia

Answer 11

• Can be asymptomatic until quite high

- Muscle weakness, cardiac arrhythmias

Question 12

How do we treat Hyperkalaemia in an emergency situation?

What is an emergency situation?

Answer 12

• > 6.5 mM/ ECG changes needs emergency treatment
• Calcium Gluconate (Ca stabilises myocardium, prevents arrhythmia)
• Insulin (Give alongside glucose)
• Calcium Resonium (increases K+ excretion from bowels)

Question 13

Describe 3 non-emergency treatments for Hyperkalaemia

Answer 13

• Salbutamol: Drives K+ into cells, NOT with patients with Ischaemic Heart Disease/ Arrythmias
• Na Bicarbonate: Corrects acidosis, drives K+ into cells, NOT with patients at risk of fluid overload
• Renal replacement therapy: Dialysis/ haemofiltration, ONLY used as last resort

Question 14

Mg2+ is an intracellular cation.

What are 3 of its functions

Answer 14

• Controls mitochondrial oxidative metabolism, thus regulating energy production
• Needed for protein synthesis
• Regulates K+ and Ca2+ channels in cell membranes

Question 15

State the range of plasma Mg2+

How much is protein bound?

Answer 15

• 2.12 to 2.65mM

- 20% is protein bound

Question 16

Mg2+ reabsorption is generally passive.

How much reabsorption occurs in;

• PCT
• LoH
• DCT

How much is excreted?

Answer 16

PCT: 30%

LoH: 60%

DCT: 5%

5% excreted

Question 17

Maximum absorption of Mg2+ is EQUAL to maximum filtration.

What if Mg2+ in blood is high?

Answer 17

• High plasma Mg2+-> High filtration

- Therefore, increase in excreted Mg2+, as maximum reabsorption cannot increase

Question 18

What hormone regulates Mg2+ reabsorption in LoH?

Answer 18

PTH

Question 19

List 6 causes of Hypomagnesaemia

Answer 19

• Decreased intake
• Diarrhoea
• Absorption disorder
• Renal wasting
• Uncontrolled diabetes Mellitus (Large urine flow-> Less time for Mg absorption)
• Excess alcohol consumption (Increases renal excretion and tendency of alcoholics to have poor diets)

Question 20

What are 2 things commonly associated with Hypomagnesaemia?

What is the significance of this in terms of symptoms?

Answer 20

• Hypokalaemia (many conditions cause both)
• Hypocalcaemia (Mg needed to make PTH)
• Symptoms are similar to those of above 2 conditions (Tetany, uncontrolled nerve stimulation)

Question 21

How do you treat Hypomagnesaemia?

Answer 21

• Treat underlying cause

- Oral/ IV/ IM Magnesium Suplhate

Question 22

List 2 causes of Hypermagnesaemia

Answer 22

Renal failure;
- Unable to excrete Mg2+

Ingestion;

• Incorrectly prepared IV infusion
• Medication containing Mg2+

Question 23

List 3 symptoms/signs of Hypermagnesaemia

Answer 23

• Reduced muscle contraction
• Inhibits PTH release-> Hypocalcaemia symptoms (muscle weakness, diminished reflexes, respiratory failure)
• Altered electric potential across cardiac cell membranes-> Cardiac arrhythmias

Question 24

How do we treat Hypermagnesaemia?

Give 4 ways

Answer 24

• Reduce intake
• Calcium gluconate (Ca and Mg compete)
• Furosemide to increase excretion
• Haemodialysis if severe