Renal Physiology 6 - Checked and Complete Flashcards
What is a typical range for serum potassium?
~3.6 - 5.2 mEq/L
How can muscles regulate serum potassium?
They can uptake potassium if the concentration becomes to high
What hormones help sweep up serum potassium into muscle?
Epinephrine and Insulin
How does insulin/epinephrine work molecularly in regard to potassium?
Stimulate Na/K ATP pump activity
How does acidity/alkalinity affect serum potassium?
Acidosis (i.e. high plasma H+ concentration) promotes net K+ movement out of cells.
**Alkalosis does the opposite - potassium into cells. **
Where is the majority of potassium reabsorbed in the nephron?
80% in the PCT
List percentages of Potassium absorbed in the Nephron and where
80% PCT
10% Thick ascending limb
6-20% Collecting Duct
How is K+ reabsorbed in the PCT?
Passive paracellular diffusion through tight junctions
How is K+ reabsorbed in the thick ascending loop of Henle?
via the Na-K-2Cl symporter in apical membrane
How do the DCT and collecting duct contribute to K+ reabsorption during periods of low dietary K+?
They do very little (can remain inert and by so doing potassium is reabsorbed very well)
2% reabsorbed at DCT
6% reabsorbed at collecting duct
How does the DCT and collecting duct contribute to potassium control when potassium is normal/high in the diet?
**The DCT can secrete up to 150% of filtered potassium load. **
The collecting duct always absorbs, but cannot capture that much potassium
Which area of the nephron is MOST responsible for K+ secretion?
Cortical collecting duct
This is more than DCT
Medullary collecting duct only absorbs
Which cells mediate secretion of potassium? Which regulate secretion?
The principle cells mediate K+ secretion.
The intercalated cells mediate K+ reabsorption.
Describe K+ secretion mechanism in principle cell
Sodium/Potassium pump actively brings potassium into the cell
Potassium accrues inside cell, leaves out of apical membrane via potassium channel
How can Potassium secretion be regulated?
Apical potassium channels can be open or closed via aldosterone
Opening or closing apical sodium channels such that sodium cannot find its way inside the cell to be used by the sodium/potassium pump
Low or high plasma levels of potassium to be placed into the interstitium and build a gradient to be transported
Tubular potassium levels and flow rates - Low flow rate = potassium accumulates more than usual in nephron = less is secreted and usual amount absorbed
Describe how Potassium and Aldosterone regulate each other
Rise in serum potassium changes the surface membrane potential of adrenal cells to modulate aldosterone release
Aldosterone opens apical potassium channels and stimulates the basolateral sodium/potassium pump so more potassium is secreted
How does increased serum potassium increase potassium secretion independent of aldosterone?
Potassium builds up in serum = builds up in interstitium = more substrate for sodium/potassium pump and stronger gradient = more secreted
How does tubular flow affect potassium secretion?
Increased tubular flow = more potassium secretion
What is an unwanted side effect of a diuretic?
Increases Potassium secretion into urine
What is a ‘potassium-sparing’ diuretic?
A diuretic that acts on the collecting duct principle cells so tubular flow is not super fast before that, leading to excess potassium secretion
Why would a potassium-sparing diuretic not be chosen?
Not as effective as other kinds of diuretics
Describe hyper and hypo calcemia
Hypocalcemia = increased excitability of nerves and muscles which may lead to muscle spasms and/or hypocalcemic tetany
Hypercalcemia = reduced excitability leading to lethargy and even cardiac arrhythmias
What are the effects of PTH?
1) promoting active vitamin D formation
2) moving Ca2+ from bone to blood
**3) promoting renal Ca2+ reabsorption **
What is the body’s store for calcium? What is the body’s store for potassium?
Bone
Muscle
