K+ balance Flashcards
avg dietary intake for K+ per day
100 mmol /day
avg net uptake of K+ per day
90 mmol /day (bc 10% is lost to feces)
where is most K+ stored
ICF (98% of K+)
avg amount of K+ filtered into kidneys per day
810 mmol /day
avg amount of K+ reabsorbed from kidneys per day
770 mmol /day
avg amount of K+ secreted by kidneys per day
50 mmol /day
avg amount of K+ excreted in urine per day
90 mmol /day
ECF K+ homeostasis is critical for _____, especially _____
cell function, especially excitable cells
disruption of ECF [K+] would affect _____ & _____
membrane potential across cell membranes
acid/base balance
how is K+ balanced with acute K+ INCREASE
K+ shifts out of ECF, into ICF (buffered into cells until kidneys have time to catch up)
how is K+ balanced chronically
changes in K+ reabsorption / secretion in the kidney
what can stimulate K+ moving from ECF -> to ICF
-insulin
-beta2-adrenergic receptor activators/agonists (norepi, epi)
-alkalosis
what can stimulate K+ moving from ICF -> to ECF
-acidosis
-hyperosmolarity
-exercise
-cell lysis
filtered load of K+ equation
filtered load = GFR x (P k+)
(P k+): [K+ in ECF]
what does it specifically mean if we have net reabsorption of K+ in the kidney
excrete < 800 mmol K+ /day
what does it specifically mean if we have net secretion of K+ in the kidney
excreting > 800 mmol K+ /day
where does most K+ reabsorption occur in the kidney, how much of filtered K+ load is reabsorbed here
proximal tubule (PCT)
65-80% of filtered K+ load is reabsorbed in PCT
mechanism of reabsorption of K+ in the PCT
passive
paracellular (around cells)
how much filtered K+ load is reabsorbed in TALH
10-25%
mechanism of K+ reabsorption in the TALH
transcellular (via NKCC)
apical K+ channel (ROMK) also secretes K+ -> that can be used at NKCC to bring in other ions needed with it
what happens at principal cells w HIGH K+ diet
K+ secretion (20-150%) via ROMK
what happens at alpha-intercalated cells w HIGH K+ diet
K+ reabsorption (5%) via apical H+/K+ ATPase
what controls K+ secretion in principal cells
aldosterone (a hormone)
anything that promotes Na+ reabsorption thru ENaC, promotes _____
K+ secretion thru ROMK
anything that inhibits Na+ reabsorption thru ENaC, inhibits _____
K+ secretion thru ROMK
factors that act on basolateral membrane of principal cells to stimulate K+ secretion
increased K+ intake
increased [K+ in ECF]
aldosterone
increased ECF pH (extracellular alkalosis)
factors that act on basolateral membrane of principal cells to inhibit K+ secretion
epinephrine
decreased ECF pH (extracellular acidosis)
factors that act on apical (luminal) membrane of principal cells to stimulate K+ secretion
increasing flow rate
increased [Na+ in tubular fluid]
decreased [Cl- in tubular fluid]
negative voltage (on luminal side of apical membrane)
factors that act on apical (luminal) membrane of principal cells to inhibit K+ secretion
increased [K+ in tubular fluid]
Ba2+ (barium- blocks ROMK)
amiloride (blocks ENaC)
anything that increases tubular flow rate and/or [Na+] past distal nephron & collecting ducts -> will increase _____
K+ excretion
ex. diuretics
in distal nephron, rate of net K+ secretion is dependent on _____
flow rate
_____ is the most potent stimulator of aldosterone secretion
hyperkalemia
hyperkalemia stimulating aldosterone secretion mechanism
elevated [K+] = depol of membrane
->
depol opens the voltage-gated Ca2+ channels
->
increases [cytoplasmic Ca2+] -> which is signal for aldosterone secretion
hyperkalemia stimulating K+ secretion 2 mechanisms
stimulates Na+ reabsorption thru ENaC
->
increases K+ secretion across apical membrane
increases activity of basolateral Na+/K+ ATPase
->
increases [cytoplasmic K+]
K+ wasting diuretics
-examples
-mechanism
-location
-may lead to
ex. loop diuretics, thiazides
increases K+ excretion (by increasing flow rate & [Na+] of TF)
-works upstream of principal cells
-hypokalemia
K+ sparing diuretics
-examples
-mechanism
-may lead to
ex. ENaC blockers, MR blockers
inhibits K+ secretion (by inhibiting Na+/K+ coupled secretion via ROMK)
-hyperkalemia
