Potassium Homeostasis Extrarenal Flashcards
In what body compartment can you measure K concentration?
ECF
when you have a potassium disturbance what three characteristics of the body system does Dr. Moe want us to know about?
steady state - is it in 0 flux?
balance - has there been a net +ve or -ve change since the start?
deficiency - relative to physio. norms is it up or down?
how does our diet now compare to our primordial diet?
more Na, less K
what are the body’s three mechanisms to handle a K load?
cellular uptake
renal excretion
colonic excretion
what are the physio norms for potassium? (ECF, ICF)
3.5-5 ECF
100-150 ICF
how much K can a body secrete in 4-6 hours (undefined load)
50%; 40% goes to ICF, 10% goes to ECF; meaning that if you ingest 14 mEq, you’ll only spike 1.4 mEq, which is acceptable
what’s the Nernst equation?
V (mV) = 61.5 * log(Cout/Cin)
what the difference between a total body hypokalemia (or hyperkalemia) and a cell shift only potassium disturbance?
in a total body disturbance, both the numerator and denominator of the Nernst equation (Cout/Cin) would be affected, meaning that the cell’s potential would not be so dramatically altered;
OTOH, in cell shift only disturbances, only the Cout would change, resulting in a dramatic change in the resting potential of the cell
are the kidneys required for K homeostasis?
they help, but no, in rats with nephrectomies infusions of KCl were handled (and better in rats that were conditioned to a high KCl diet)
how does aldosterone affect K homeostasis?
through the GI tract
K shift into cells is controlled by which three factors?
insulin, catecholamines and pH
what’s the threshold in delta-K for the release of insulin?
1 mEq in plasma
does exogenous insulin rescue hyperkalemic status?
yes
will a pancreatectomized animal survive a potassium spike?
no, cardiac arrest will ensue
does insulin have a constant state role in regulating K levels?
yes, it reduces potassium
what is the problem with poorly controlled diabetes mellitus and potassium?
the long term lack of insulin means that potassium has likely leaked out of cells (due to a drop in Na/K ATPase function) and not been replaced, therefore causing a total body hypokalemic state. Infusion of insulin may cause a severe hypokalemia
how does hyperkalemia activate insulin release?
the extra K on the outside of the beta cell causes depolarization that leads to insulin release (fundamentally the same mechanism as glucose mediated release)
what type of drug acts in the same manner as hyperkalemia on beta cells?
sulfonylureas
what happens to K when you exercise (during and after?)
K is released into the plasma when you exercise; this effect is mitigated by epi and B2 receptors
after exercise, K is taken back in, and this is inhibited by norepi and A receptors
what effect does K have on the muscle?
vasodilation to aid in nutrient delivery
what effect do inorganic acids have on K homeostasis
they can cause a shift of K from ICF to ECF
do organic acids have an effect on K?
probably not
why are metabolic pH disturbances more problematic than respiratory ones?
the proton generation location is key; anytime protons move in from ECF (like in metabolic disturbances) there are corresponding shifts of protons out of the ICF
how do we know that the gut is a homeostatic player in K handling?
the concentration of K in the gut changes with its concentration in the plasma
