Potassium Balance

Question 1

What proportion of potassium is intracellular?

Answer 1

95%

Question 2

What is the internal [K+]?

Answer 2

150 mmol/L

Question 3

What is the external [K+]?

Answer 3

4.5 mmol/L

Question 4

What is internal potassium balance under the influence of?

Answer 4

Insulin, adrenaline, pH and aldosterone

Question 5

How do we get potassium into our bodies?

Answer 5

Diet

Question 6

How do we remove potassium from our diet?

Answer 6

Urine, stools, sweat

Question 7

What is the external potassium balance influenced by?

Answer 7

Intake and output

Question 8

What are the two types of potassium regulation?

Answer 8

Acute and chronic

Question 9

What does acute potassium regulation deal with?

Answer 9

Distribution of potassium between intra and extracellular fluid compartments (internal balance)

Question 10

How is chronic potassium regulation achieved?

Answer 10

By the kidney adjusting potassium excretion and reabsorption (external balance)

Question 11

What are the functions of potassium in the body?

Answer 11

Determines intracellular fluid osmolality, resting membrane potential and affects vascular resistance

Question 12

What does the sodium potassium ATPase do in terms of ion concentrations?

Answer 12

High intracellular [K+] and low intracellular [Na+]

Question 13

What is the threshold for hyperkalaemia?

Answer 13

Plasma [K+]> 5.5mm

Question 14

What is the threshold for hypokalaemia?

Answer 14

Plasma [K+]<3.5mm

Question 15

What is the definition of a resting membrane potential?

Answer 15

Membrane potential formed by creation of ionic gradients (combination of electrical and chemical gradients)

Question 16

What changes to an ECG do you see in hypokalaemia?

Answer 16

Decreased T wave amplitude, long Q-U interval and prolonged P wave

Question 17

What changes to an ECG do you see in hyperkalaemia?

Answer 17

Increased QRS complex, increased T wave amplitude and eventual loss of P-wave

Question 18

What happens to the resting potential at low [K+]o?

Answer 18

Hyperpolarisation- less excitable as further from threshold point

Question 19

What happens to the resting potential at high [K+]o?

Answer 19

Depolarisation (closer to threshold) - more excitable

Question 20

What is hypokalaemia caused by?

Answer 20

• extensive diuretic use
• hyperaldosteronism
• prolonged vomiting
• profuse diarrhoea

Question 21

How does prolonged vomiting -> hypokalaemia?

Answer 21

Sodium loss -> inc aldosterone secretion -> potassium excretion in kidneys

Question 22

What does hypokalaemia result in?

Answer 22

Decreased resting membrane potential and a decreased release of adrenaline, aldosterone and insulin

Question 23

When is acute hyperkalaemia normal?

Answer 23

Prolonged exercise

Question 24

What can cause hyperkalaemia?

Answer 24

• insufficient renal excretion
• increased release from damaged body cells
• long term use of potassium sparing diuretics
• Addison’s disease

Question 25

What types of damaged cells release potassium?

Answer 25

Chemo, long lasting hunger, prolonged exercise or severe burns

Question 26

What happens if plasma [K+] >7mm?

Answer 26

Life threatening as leads to systolic cardiac arrest

Question 27

What mechanisms are used to drive potassium back into cells?

Answer 27

Insulin/ glucose infusion and aldosterone and adrenaline stimulate the sodium potassium pump

Question 28

How can CVD treatments lead to hyperkalaemia?

Answer 28

Beta blockers and ACE inhibitors increase serum potassium levels

Loop diuretics result in net potassium loss

Question 29

How does potassium concentration change in the proximal convoluted tubule?

Answer 29

Potassium ions are reabsorbed passively between cells

Question 30

How is potassium reabsorbed in the loop of henle?

Answer 30

SGLT2 transporters transport sodium, chloride and potassium

Question 31

What determines potassium secretion in the distal convoluted tubule?

Answer 31

Increased potassium intake, changes in blood pH

Question 32

How does increased plasma [K+] increase potassium secretion?

Answer 32

• Slows exit from basolateral membrane
• Increased activity of sodium potassium ATPase
• stimulates aldosterone secretion

Question 33

What is the major regulator of potassium balance in the body?

Answer 33

Aldosterone

Question 34

How does aldosterone affect potassium concentration?

Answer 34

Increased plasma aldosterone -> cortical collecting ducts increasing potassium excretion

Question 35

What does aldosterone act to do?

Answer 35

Increase Na+/K+ ATPase pump
Increase ENaC channels
Redistribute ENaC from intracellular localisation to membrane
Increased permeability of luminal membrane

Question 36

What happens to potassium conc in alkalosis?

Answer 36

Sodium potassium ATPase Increased so cellular K+ conc is increased -> more K+ secretion and more sodium is taken into epithelial cells

Question 37

What happens to potassium conc in acidosis?

Answer 37

Inhibition of sodium potassium ATPase so less potassium in and so less it secreted

Question 38

What is an increased flow rate in the nephron caused by?

Answer 38

Increased GFR, inhibition of reabsorption or potassium wasting diuretics

Question 39

What happens to potassium concentration when ADH increases?

Answer 39

Increased potassium channel activity so increased secretion and therefore decreased cellular potassium concentration

Question 40

Where is potassium reabsorbed in severe hypokalaemia?

Answer 40

Alpha intercalated cells or the late distal convoluted tubule is active

Question 41

What effect does increased aldosterone have on potassium concentration?

Answer 41

Increased potassium secretion

Question 42

What effect does increased sodium reabsorption have on potassium concentration?

Answer 42

Decreased flow rate in the tubules so less potassium secretion so increased potassium concentration