Renal Regulation Of Potassium, Calcium And Phosphate Flashcards
Where is most K+ in the body?
Inside cells
What 3 hormones will affect K+ distribution?
Epinephrine
Insulin
Aldosterone
How can epinephrine affect K+ distribution?
If it binds to:
α1 receptors- shifts K+ out of cells and may cause hyperkalemia
β2 receptors- K+ uptake into cells and may cause hypokalemia
(β2 is more sensitive to epinephrine than α1 though)
What effect on K+ levels will β2 blockers have?
Hyperkalemia
What effect will insulin have on K+ levels?
Increases K+ uptake into cells
Stimulates Na+, K+ ATPase
What effect will aldosterone have on K+ levels?
Increase K+ excretion
Stimulates Na+,K+ ATPase
Acidosis is often accompanied by ____________
HYPERkalemia
SUPER IMPORTANT!!!!**
Alkalosis is often accompanied by ______________
HYPOkalemia
**VERY IMPORTANT***
Why would acidosis often cause hyperkalemia?
If there’s a ton of H+ in your ECF, the cells will try to help you by absorbing it, but they will release K+ to maintain charge balance
Why would alkalosis be accompanied by hypokalemia?
Because if there’s not enough H+ in your ECF, your cells will try to help you by releasing H+, but they will also suck up K+ to maintain the charge balance
When H2O shifts from the ICF to the ECF, what will it bring with it?
K+
If your K+ input is too high, where in the kidney will the tweaking of K+ levels happen?
Distal tubule and collecting duct
In the PT and LOH, K+ is absorbed in FIXED ratios, no matter what****
Do we usually eat too much or too little K+?
Too much
What happens to K+ secretion when Na+ load to distal nephron increases?
K+ secretion will increase (more K+ lost in urine)
(The principal cell will uptake Na+ and then the Na+,K+ ATPase on the basal membrane will pump Na+ into the blood and K+ back into the urine)
Aldosterone is stimulated by (high/low) plasma K+
High
Why would high consumption of K+ stimulate aldosterone?
Because aldosterone will stimulate the basolateral membrane Na+,K+ ATPase, as well as the apical K+ channel and more K+ will be secreted into the urine
If you have a low K+ diet, where in the nephron will K+ be reabsorbed?
87% of it will be reabsorbed in the PT and LOH
The remaining K+ will be absorbed in the distal nephron
Which cells reabsorb K+?
α-intercalated cells of the distal nephron
(Using the K+/H+ exchanger in the apical membrane. H+ will be secreted into the urine)
K+ will then diffuse across the basolateral membrane
Where is calcium stored?
99% bone
1% intracellular fluid
0.1% in the extracellular fluid
Of the plasma calcium, how much of it is free ions that are biologically active?
50% of it
40% is bound to plasma proteins
10% is complexed with anions like CaPO4
Can the calcium that is bound to plasma proteins be filtered?
NO
What percentage of calcium in the blood can be filtered into the nephron?
60%
How do you calculate the filtered load of calcium?
FL=(GFR)(Pca)(0.6)
You have to multiply it by .6 since only 60% of calcium can be filtered!!
40% of it is bound to plasma proteins
Does a lot of the filtered calcium end up in the urine?
No, 99% of it is reabsorbed
1% appears in the urine
Where in the nephron is calcium reabsorbed?
Proximal tubule 67%
Thick ascending limb 25%** blocked by Lasix
Distal tubule 5-10%** where fine tuning happens
Collecting duct <5%
Excreted 1%
Is calcium reabsorption in the proximal tubule active or passive?
Passive. It is coupled to Na+
When _____ uptake is high, so is Calcium uptake
Na+
Is calcium reabsorbed through the paracellular route, or transcellular route?
Paracellular.
What drives calcium reabsorption in the thick ascending limb of LOH?
Some of the K+ that NKCC2 transported into the cell leaks back out into the urine, causing it to become slightly positive.
This causes Ca+ to leave the lumen via the paracellular pathway (sneaking between 2 cells)
Loop diuretics will cause more or less calcium to be reabsorbed?
Less calcium will be absorbed
(Loop diuretic will inhibit the NKCC2 so the K+ that originally leaked out and turned the lumen positive will have never been absorbed in the first place)
A side effect of Lasix is (hypo/hyper) calcemia
Hypocalcemia
In the Distal Tubule, how is calcium reabsorbed?
Apical membrane: Ca+ channels
Basolateral membrane: Na+ Ca+ exchange pump AND Ca+ ATPase
Parathyroid hormone (inhibits/stimulates) Calcium uptake in the distal tubule
Stimulates
Thiazide diuretics (increase/decrease) calcium reabsorption
Increase! (OPPOSITE OF LOOP)
Why do thiazides increase calcium reabsorption?
Thiazides block the NaCl pump on the apical membrane.
Na+ REALLY wants to get into the cell, so it will come in from the basolateral membrane via the Na-Ca exchanger.
This draws calcium out of the cell, and thus also increases Calcium uptake from the lumen
What role does phosphate have in the urine?
It is an important buffer anion
Will Parathyroid hormone increase or decrease phosphate reabsorption?
Decrease (Proximal tubule)
It increases Calcium reabsorption in the distal tubule, and they do opposite things
Does all of the phosphate that gets filtered get reabsorbed?
No, 15% of it is excreted
Why does parathyroid hormone cause you to excrete more phosphate?
Because calcium+phosphate= bone
You don’t want those two reuniting and forming bone in your blood
