Potassium Disorders

Question 1

What is the physiology of normal potassium regulation?

Answer 1

freely filtered by glomerulus but reabsorbed by proximal tubule and loop of Henle so little reaches distal
what reaches distal is secreted by CCD and excreted - amt excreted determined by rate of secretion

Question 2

What are the major physiologic determinants of renal potassium excretion?

Answer 2

mineralocorticoids
distal delivery of Na and water
nonreabsorbable anions

Question 3

How does the potassium cross the CCD?

Answer 3

transcellular (major) or paracellular
pumped in by NaK pump on BL membrane - diffuses out down conc gradient using K channel on luminal
paracellular driven by lumen negative voltage from Na being pumped in

Question 4

What are factors that influence the internal distribution of potassium?

Answer 4

insulin

b2 stimulation

Question 5

What are the cellular determinants of potassium secretion?

Answer 5

cell K concentration
luminal K concentration
Potential difference across luminal membrane
permeability of luminal membrane for K

Question 6

How do mineralocorticoids determine K excretion?

Answer 6

Aldo released with hyperkalemia - increases Na absorption through luminal channel and increases K secretion through NaK pump (increases in cell)
H+ secretion in intercalated duct also increased
also increase K permeability of luminal membrane

Question 7

How does distal delivery of Na affect K excretion?

Answer 7

more distal delivery means more uptake into cell - increases lumen negative potential
also causes NaK pump to go faster
luminal K concentration also lowered by more volume

Question 8

How do nonreabsorbable anions affect K excretion?

Answer 8

not absorbed proximally - increase distal delivery of Na and volume - increases K secretion
also increase lumen negative voltage because they can’t enter cell with Na like Cl can

Question 9

What are examples of non reabsorbable anions?

Answer 9

sulfate
phosphate
carbenicillin
sometimes bicarb

Question 10

When are abnormalities in renal K secretion seen?

Answer 10

when mineralocorticoids and distal Na delivery shift in same direction - primary mineralocorticoid excess, primary increase in distal Na delivery, primary decreases in either

Question 11

What physiologic factors increase cell K uptake?

Answer 11

plasma K
insulin - prevents post meal hyperkalemia
B adrenergic catecholamines - prevents post exercise hyperkalemia

Question 12

What findings are present in Conn’s syndrome?

Answer 12

low renin, high aldo
HTN
hypokalemic alkalosis

Question 13

How can Conn’s syndrome be differentiated from bilateral adrenal hyperplasia?

Answer 13

conn’s HTN corrects with tumor removal

HTN in bilateral won’t respond even to bilateral adrenalectomy

Question 14

How does 11betaHSD2 act in hypokalemia development?

Answer 14

usually converts cortisol to cortisone 
def allows cortisol to activate receptor

Question 15

What is Liddle syndrome?

Answer 15

low renin and aldo
no response to inhibitor of aldo secretion or spironolactone
triamterene/transplant normalizes BP and K

Question 16

What is Bartter’s syndrome?

Answer 16

genetic condition with primary defect in loop of Henle salt reabsorption
hypokalemic with high R and A

Question 17

What is Gitelman’s syndrome?

Answer 17

defect in DCT reabsorption of NaCl

Hypokalemic with high R and A

Question 18

What happens to K secretion in CKD?

Answer 18

decreased distal Na delivery and nephron dropout

but remaining nephrons develop increased ability to secrete K

Question 19

What two defenses against hyperkalemia do patients with CKD have?

Answer 19

Redistribute K faster into cells with K load

Increase rate of K excretion in stool

Question 20

What are the neuromuscular manifestations of hypo and hyperkalemia?

Answer 20

hypo - weakness leading to flaccid paralysis, rhabdo

hyper - paresthesias leading to paralysis

Question 21

What are cardiac manifestations of hypo and hyperkalemia?

Answer 21

hypo - arrhythmia, ST depression, T wave flattening, U wave

hyper - cardiac arrest

Question 22

How does hypokalemia affect the kidney?

Answer 22

concentrating defect

can cause hypernatremia by inducing nephrogenic DI

Question 23

What are the EKG changes in hyperkalemia?

Answer 23

peaked t wave first, then widening QRS, then sine wave

Question 24

What are the general rules of treatment for potassium disorders?

Answer 24

all patients should have serum K corrected, but those with EKG changes treated emergently
if hypokalemia AND acidosis - treat hypokalemia first, isolated treatment for acidosis can worsen hypokalemia