K+ balance

Question 1

avg dietary intake for K+ per day

Answer 1

100 mmol /day

Question 2

avg net uptake of K+ per day

Answer 2

90 mmol /day (bc 10% is lost to feces)

Question 3

where is most K+ stored

Answer 3

ICF (98% of K+)

Question 4

avg amount of K+ filtered into kidneys per day

Answer 4

810 mmol /day

Question 5

avg amount of K+ reabsorbed from kidneys per day

Answer 5

770 mmol /day

Question 6

avg amount of K+ secreted by kidneys per day

Answer 6

50 mmol /day

Question 7

avg amount of K+ excreted in urine per day

Answer 7

90 mmol /day

Question 8

ECF K+ homeostasis is critical for _____, especially _____

Answer 8

cell function, especially excitable cells

Question 9

disruption of ECF [K+] would affect _____ & _____

Answer 9

membrane potential across cell membranes

acid/base balance

Question 10

how is K+ balanced with acute K+ INCREASE

Answer 10

K+ shifts out of ECF, into ICF (buffered into cells until kidneys have time to catch up)

Question 11

how is K+ balanced chronically

Answer 11

changes in K+ reabsorption / secretion in the kidney

Question 12

what can stimulate K+ moving from ECF -> to ICF

Answer 12

-insulin
-beta2-adrenergic receptor activators/agonists (norepi, epi)
-alkalosis

Question 13

what can stimulate K+ moving from ICF -> to ECF

Answer 13

-acidosis
-hyperosmolarity
-exercise
-cell lysis

Question 14

filtered load of K+ equation

Answer 14

filtered load = GFR x (P k+)

(P k+): [K+ in ECF]

Question 15

what does it specifically mean if we have net reabsorption of K+ in the kidney

Answer 15

excrete < 800 mmol K+ /day

Question 16

what does it specifically mean if we have net secretion of K+ in the kidney

Answer 16

excreting > 800 mmol K+ /day

Question 18

where does most K+ reabsorption occur in the kidney, how much of filtered K+ load is reabsorbed here

Answer 18

proximal tubule (PCT)

65-80% of filtered K+ load is reabsorbed in PCT

Question 19

mechanism of reabsorption of K+ in the PCT

Answer 19

passive
paracellular (around cells)

Question 20

how much filtered K+ load is reabsorbed in TALH

Answer 20

10-25%

Question 21

mechanism of K+ reabsorption in the TALH

Answer 21

transcellular (via NKCC)

apical K+ channel (ROMK) also secretes K+ -> that can be used at NKCC to bring in other ions needed with it

Question 22

what happens at principal cells w HIGH K+ diet

Answer 22

K+ secretion (20-150%) via ROMK

Question 23

what happens at alpha-intercalated cells w HIGH K+ diet

Answer 23

K+ reabsorption (5%) via apical H+/K+ ATPase

Question 24

what controls K+ secretion in principal cells

Answer 24

aldosterone (a hormone)

Question 25

anything that promotes Na+ reabsorption thru ENaC, promotes _____

Answer 25

K+ secretion thru ROMK

Question 26

anything that inhibits Na+ reabsorption thru ENaC, inhibits _____

Answer 26

K+ secretion thru ROMK

Question 27

factors that act on basolateral membrane of principal cells to stimulate K+ secretion

Answer 27

increased K+ intake increased [K+ in ECF] aldosterone increased ECF pH (extracellular alkalosis)

Question 28

factors that act on basolateral membrane of principal cells to inhibit K+ secretion

Answer 28

epinephrine decreased ECF pH (extracellular acidosis)

Question 29

factors that act on apical (luminal) membrane of principal cells to stimulate K+ secretion

Answer 29

increasing flow rate increased [Na+ in tubular fluid] decreased [Cl- in tubular fluid] negative voltage (on luminal side of apical membrane)

Question 30

factors that act on apical (luminal) membrane of principal cells to inhibit K+ secretion

Answer 30

increased [K+ in tubular fluid] Ba2+ (barium- blocks ROMK) amiloride (blocks ENaC)

Question 31

anything that increases tubular flow rate and/or [Na+] past distal nephron & collecting ducts -> will increase _____

Answer 31

K+ excretion ex. diuretics

Question 32

in distal nephron, rate of net K+ secretion is dependent on _____

Answer 32

flow rate

Question 33

_____ is the most potent stimulator of aldosterone secretion

Answer 33

hyperkalemia

Question 34

hyperkalemia stimulating aldosterone secretion mechanism

Answer 34

elevated [K+] = depol of membrane -> depol opens the voltage-gated Ca2+ channels -> increases [cytoplasmic Ca2+] -> which is signal for aldosterone secretion

Question 35

hyperkalemia stimulating K+ secretion 2 mechanisms

Answer 35

stimulates Na+ reabsorption thru ENaC -> increases K+ secretion across apical membrane increases activity of basolateral Na+/K+ ATPase -> increases [cytoplasmic K+]

Question 36

K+ wasting diuretics -examples -mechanism -location -may lead to

Answer 36

ex. loop diuretics, thiazides increases K+ excretion (by increasing flow rate & [Na+] of TF) -works upstream of principal cells -hypokalemia

Question 37

K+ sparing diuretics -examples -mechanism -may lead to

Answer 37

ex. ENaC blockers, MR blockers inhibits K+ secretion (by inhibiting Na+/K+ coupled secretion via ROMK) -hyperkalemia