C4

Question 1

Where is potassium found in the body?

Answer 1

• It is the most abundant cation in the ICF

- Present in all tissues

Question 2

How is potassium distributed between the 2 fluid compartments?

Answer 2

ICF concentration 30-40x greater than the ECF concentration

Question 3

How is the gradient between the ICF and ECF potassium maintained?

Answer 3

by the Na-K-ATPase pump

Question 4

How are potassium levels tested?

Answer 4

• Specimens: serum and urine

- Testing method: ion-selective electrode

Question 5

What is the function of potassium in the body?

Answer 5

• Normal cell function: maintains ICF volume and resting potential

Question 6

What causes and influx of potassium from the ECF to the ICF?

Answer 6

• catecholamines (adrenaline)
• insulin
• aldosterone
• alkalosis (increased pH)

Question 7

What causes an efflux of potassium from the ICF to the ECF?

Answer 7

acidosis (decreased pH)

Question 8

What are the sources of potassium intake?

Answer 8

diet and IV

Question 9

How does the Na-K-ATPase pump regulate potassium?

Answer 9

It keeps K+ in the ICF and Na+ in the ECF

Question 10

What is the effect of cell membrane integrity on potassium levels?

Answer 10

If the cell is damaged, K+ leaks out

Question 11

What the sources of potassium output?

Answer 11

• Renal: urine flow rate: ↑/↓ flow -> ↑/↓ K+ secretion
  pH: acidosis/alkalosis
  aldosterone:↑aldosterone = ↑K+ excretion
  ↓ aldosterone = ↓ K+ excretion
• Extra-renal: diarrhoea/vomitting = loss of K+

Question 12

What is the renal handling of potassium?

Answer 12

• Bowman’s capsule: large amount of K+ in glomerular filtrate, but reabsorbed
• Fine-tuning of K+ with aldosterone
• 98% reabsorbed and 2% excreted

Question 13

What are the mechanisms of reabsorption of potassium in the kidneys?

Answer 13

• proximal tubule and ascending loop of Henle: transcellular shift by pump and paracellular shift by diffusion
• distal tubule and collecting ducts: hormones (aldosterone)