Potassium balance Flashcards
What is the normal serum potassium levels (ECF)?
3.5-5 mmol/L
___ potassium is absorbed in the gut and ____ is excreted in urine
100%, >90%
Importance of Potassium?
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
HYPOKALEMIA = When there is low K in ECF the RMP is more negative which means:
cell is hyperpolarized which means actual muscle contraction is harder to do, weakness and heart rhythm disturbances
HYPERKALEMIA = when there is high K in ECF the RMP is less negative which means:
cell is depolarized which means repolarization is harded to do, muscle stiffness and weakness and abnormal ECG
What is the relationship between insulin and potassium?
insulin promotes muscle cell potassium uptake, in order for ingested potassium not to cause cardiac arrest.
What is the relationship between adrenaline and potassium?
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
What does a high potassium diet do?
lowers blood pressure, as potassium acts like a vasodilator
Dietary potassium =
urinary potassium excretion (normally)
Cortical collecting duct regulates K excretion by adjusting K secretion and the mediators is
aldosterone
Increased serum K =
increased excretion
decreased serum K =
decreased excretion
What are the features of the Cortical Collecting Duct?
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
What is the action of aldosterone on the collecting duct?
Increases number and open probability of sodium channels
increase sodium reabsorption
increases lumen negativeity
increases k secretion
What increases potassium secretion by the Cortical collecting duct?
aldosterone
increased sodium and water delivery to the collecting duct
What decreases potassium secretion by the Cortical collecting duct?
low aldosterone
low delivery of sodium and water to collecting duct
hyperkalmeia ______ aldosterone secretion
stimulates
hypokalemia ______ aldosterone secretion
inhibits
angiotensin II is increased with ___ ____ and ang 2 _______ aldosterone secretion.
low effective circulating volume, increased
How can aldosterone regulate both sodium and potassium?
it is not completely understood. But is can regulate excretion of them seperately
How is K Balance achieved with changes in effective circulating volume?
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
Aldosterone and CCD flow when ____ will always ____ each other
opposite, counteract
what is hyperaldosteroniam?
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
What is diuretic-induced hypokalemia?
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
What is the mechanisms of hyperkalemia?
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
