Urinary 4 - Control of K+

Question 1

Where is the majority of K+ found in the body?

Answer 1

Intracellular fluid of:

• Skeletal muscle cells
• Liver cells
• RBCs
• Bone cells

Question 2

What is the approximate intracellular fluid [K+]?

Answer 2

120-150 mM

Question 3

What is the approximate extracellular fluid [K+]?

Answer 3

3.5-5 mM

Question 4

Is the concentration of K+ higher in intracellular fluid or extracellular fluid?

Answer 4

Higher [K+] INTRAcellularly

Question 5

How the the difference of [K+] between the ICF and ECF maintained?

Answer 5

Na+/K+-ATPase

Question 6

What is the average intake of K+ during a meal?

Answer 6

30 mM

Question 7

What is the average time taken for excretion of K+ after a meal?

Answer 7

6-12hrs

Question 8

What are the main treatments used for hyperkalaemia?

Answer 8

• IV Insulin and Dextrose
• IV Calcium Gluconate
• Salbutamol

Question 9

Why is Insulin and Dextrose given to treat hyperkalaemia?

Answer 9

Insulin stimulates Na+/K+-ATPase (increasing absorption of K+ into cells)
Dextrose prevents hypoglycaemia occurring

Question 10

Hyperkalaemia stimulates the secretion of which 2 hormones? Why?

Answer 10

1) Insulin
2) Aldosterone
(Also catecholamines)
These increase Na+/K+-ATPase activity, driving K+ absorption into cells to decrease the ECF [K+]

Question 11

What percentage of K+ is reabsorbed in the PCT?

Answer 11

67%

Question 12

In what part of the tubule does the majority of K+ reabsorption occur?

Answer 12

PCT

Question 13

What percentage of K+ is reabsorbed in the TAL (Thick ascending limb of LoH)?

Answer 13

20%

Question 14

via what channel is K+ reabsorbed across the apical membrane of the TAL cells (Thick ascending limb of LoH)?

Answer 14

Na+/K+/2Cl- symporter (NKCC2)

Question 15

In what part of the tubule is K+ passively reabsorbed?

Answer 15

PCT

Question 16

In what part of the tubule is K+ actively reabsorbed?

Answer 16

• TAL (thick ascending limb of LoH)
• Distal tubule
• Collecting duct

Question 17

What type of cell actively reabsorbs K+ from the lumen of the late distal tubule and early collecting duct? What channel mediates this active reabsorbtion?

Answer 17

Alpha Intercalated cells

H+/K+-ATPase

Question 18

What cells of the tubule secrete K+? What channels are involved?

Answer 18

Principle cells (of late DT and early CD)
Na+/K+-ATPase on the basolateral membrane
ROMK on the apical membrane

Question 19

How would acidosis affect K+ secretion into the tubular lumen?

Answer 19

Inhibits Na+/K+-ATPase = inhibits K+ secretion

Question 20

How would an increase in Aldosterone affect K+ secretion into the tubular lumen?

Answer 20

Increase K+ secretion

Question 21

Name the main causes of HYPERkalaemia:

Answer 21

• Increased intake
• Cell lysis (tumour/trauma)
• Exercise
• Decreased renal excretion (AKI/CKI/drugs)
• Diabetic ketoacidosis
• Metabolic acidosis

Question 22

How does DKA and metabolic acidosis lead to hyperkalaemia?

Answer 22

Acidosis inhibits the Na+/K+-ATPase, inhibiting K+ renal secretion

Question 23

How does exercise cause an increase in serum K+? How does the body reverse this quickly?

Answer 23

• K+ released from muscle cells during exercise as Na+/K+-ATPase cannot keep up with the repeated repolarisation
• Exercise causes increase in catecholamines, which increase activity of Na+/K+-ATPase, driving the uptake of K+ back into the cells

Question 24

What are the common symptoms of hyperkalaemia?

Answer 24

• Heart abnormalities (arrhythmias, bradycardia)

- Fatigue and muscle weakness

Question 25

In an emergency situation, how would you remove excess K+ from a hyperkalaemic patient?

Answer 25

Dialysis

Question 26

Name some of the common causes of HYPOkalaemia:

Answer 26

• Excessive loss (diarrhoea, vomiting, diuretic drugs)
• Reduced intake (malnourished/eating disorders)
• Metabolic alkalosis

Question 27

What are the common symptoms of hypokalaemia?

Answer 27

• Irregular heatbeat / palpitations
• Constipation
• Muscle weakness/tingling