Regulation of Potassium and Hydrogen

Question 1

• What are the major intracellular and extracellular cations?

Answer 1

Intracellular – potassium, extracellular – sodium

Question 2

• What is the primary cause of the depolarisation of the cell membrane?

Answer 2

Increase in the permeability of the membrane to Na+

Question 3

• When is the intracellular concentration of Na+ greater than the intracellular concentration of K+?

Answer 3

Never

Question 4

• What effect does hyperkalaemia have on the cell membrane?

Answer 4

Initially makes the cell more excitable, but also slows repolarisation of the cell if resting potential is greater than threshold potential

Question 5

• Why do increased extracellular potassium levels result in depolarisation of the cell?

Answer 5

Open some voltage gated Na channels, these then inactivate and become refractory raising the charge closer to the AP threshold

Question 6

• What would you see on an ECG from a patient with hyperkalaemia?

Answer 6

Peaked T waves, loss of P wave amplitude and widening of the QRS complex

Question 7

• How is K+ mainly controlled?

Answer 7

By excretion, 90-95% is removed via the kidneys

Question 8

• Which hormones promote the uptake of K+ into liver and muscle cells?

Answer 8

Insulin, aldosterone & adrenaline

Question 9

• What happens to K+ in acidosis?

Answer 9

Moves from ICF to ECF

Question 10

• What is insulin an agonist for, relating to the uptake of K+ into cells?

Answer 10

Na: K ATPase

Question 11

• Where does the bulk reabsorption of K+ occur?

Answer 11

70% in PT, 10-20% in AL of loop of Henle

Question 12

• By what routes is K+ reabsorbed in the proximal tubule?

Answer 12

Solvent drag, K channel & K/Cl co-transporter

Question 13

• By what route does most K+ reabsorption occur in the TALH?

Answer 13

Transcellular route

Question 14

• What takes place in the distal tubule?

Answer 14

K+ secretion and Na+ reabsorption

Question 15

• Where are principal cells and what are they responsible for?

Answer 15

In the connecting tubule and collecting duct, responsible for K+ secretion

Question 16

• How do sodium, potassium and hydrogen influence renal potassium excretion?

Answer 16

High sodium and potassium (stimulates aldosterone) lead to increased K+ excretion, high hydrogen decreases excretion of potassium

Question 17

• What is the effect of aldosterone on [K+] in plasma?

Answer 17

Increases the excretion of K+, reducing levels in the plasma towards normal

Question 18

• What is the purpose of the increased tubular flow rate?

Answer 18

Helps to preserve normal K+ excretion during high Na+ intake (would expect a decrease)

Question 19

• What are some of the common causes of hyperkalaemia?

Answer 19

Pseudohyperkalaemia, increased intake, translocation (ICF  ECF), decreased excretion