Potassium balance

Question 1

What is the normal serum potassium levels (ECF)?

Answer 1

3.5-5 mmol/L

Question 2

___ potassium is absorbed in the gut and ____ is excreted in urine

Answer 2

100%, >90%

Question 3

Importance of Potassium?

Answer 3

most abundant ion, major intracellular cation, and important for resting membrane potential of cells - the leak of potassium out of cells keeps cells negatively charged

Question 4

HYPOKALEMIA = When there is low K in ECF the RMP is more negative which means:

Answer 4

cell is hyperpolarized which means actual muscle contraction is harder to do, weakness and heart rhythm disturbances

Question 5

HYPERKALEMIA = when there is high K in ECF the RMP is less negative which means:

Answer 5

cell is depolarized which means repolarization is harded to do, muscle stiffness and weakness and abnormal ECG

Question 6

What is the relationship between insulin and potassium?

Answer 6

insulin promotes muscle cell potassium uptake, in order for ingested potassium not to cause cardiac arrest.

Question 7

What is the relationship between adrenaline and potassium?

Answer 7

exercise causes muscles to release potassium, which causes local arterioles to dilate, which increases muscle blood flow, adrenaline helps resdistribute potassium that was in the ECF

Question 8

What does a high potassium diet do?

Answer 8

lowers blood pressure, as potassium acts like a vasodilator

Question 9

Dietary potassium =

Answer 9

urinary potassium excretion (normally)

Question 10

Cortical collecting duct regulates K excretion by adjusting K secretion and the mediators is

Answer 10

aldosterone

Question 11

Increased serum K =

Answer 11

increased excretion

Question 12

decreased serum K =

Answer 12

decreased excretion

Question 13

What are the features of the Cortical Collecting Duct?

Answer 13

Basolateral Na-K-ATPase
Lumenal membrane Na channel (ENaC)
Relatively impermeable to chloride
Lumen hegative due to absorption of Na>Cl
Lumenal K channel (ROMK)
Lumen-negative charge (relative to peritubular cappillary) drives K secretion into lumen

Question 14

What is the action of aldosterone on the collecting duct?

Answer 14

Increases number and open probability of sodium channels
increase sodium reabsorption
increases lumen negativeity
increases k secretion

Question 15

What increases potassium secretion by the Cortical collecting duct?

Answer 15

aldosterone

increased sodium and water delivery to the collecting duct

Question 16

What decreases potassium secretion by the Cortical collecting duct?

Answer 16

low aldosterone

low delivery of sodium and water to collecting duct

Question 17

hyperkalmeia ______ aldosterone secretion

Answer 17

stimulates

Question 18

hypokalemia ______ aldosterone secretion

Answer 18

inhibits

Question 19

angiotensin II is increased with ___ ____ and ang 2 _______ aldosterone secretion.

Answer 19

low effective circulating volume, increased

Question 20

How can aldosterone regulate both sodium and potassium?

Answer 20

it is not completely understood. But is can regulate excretion of them seperately

Question 21

How is K Balance achieved with changes in effective circulating volume?

Answer 21

low ECFV -> increases renin, ang 2 and aldosterone -> reduced GFR and flow to CCD *increased alosterone and reduced flow to CCD counteract each other so normal K excretion and GFR

high ECFV -> inhibits renin, agn 2 and aldosterone -> increased GFR and flow ->inhibits proximal reabsorption -> *low aldosterone and increased CCD flow counteract each other

Question 22

Aldosterone and CCD flow when ____ will always ____ each other

Answer 22

opposite, counteract

Question 23

what is hyperaldosteroniam?

Answer 23

it is a rare cause of hypertension which happens in 40-50s where they have high blood pressure and low serum potassium, because they have excess potassium secretion and too much sodium reabsorption and low renin and angiotensin 2

Question 24

What is diuretic-induced hypokalemia?

Answer 24

when drugs block DCT Na-Cl transporter and increases its secretion, which reduces ECFV and then increased renin/angio 2 and aldosterone which increased CCD flow rate and high aldosterone, and K excretion is increased

Question 25

What is the mechanisms of hyperkalemia?

Answer 25

reduced aldosterone secretion (from adrenal disease, ang 2 inibitors, drugs) which decreased CCD flow, increase K reasorption
could also be an insulin deficieny or abnormality or muscle cell injury or death