Renal Regulation Of Potassium, Calcium And Phosphate

Question 1

Where is most K+ in the body?

Answer 1

Inside cells

Question 2

What 3 hormones will affect K+ distribution?

Answer 2

Epinephrine

Insulin

Aldosterone

Question 3

How can epinephrine affect K+ distribution?

Answer 3

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)

Question 4

What effect on K+ levels will β2 blockers have?

Answer 4

Hyperkalemia

Question 5

What effect will insulin have on K+ levels?

Answer 5

Increases K+ uptake into cells

Stimulates Na+, K+ ATPase

Question 6

What effect will aldosterone have on K+ levels?

Answer 6

Increase K+ excretion

Stimulates Na+,K+ ATPase

Question 7

Acidosis is often accompanied by ____________

Answer 7

HYPERkalemia

SUPER IMPORTANT!!!!**

Question 8

Alkalosis is often accompanied by ______________

Answer 8

HYPOkalemia

**VERY IMPORTANT***

Question 9

Why would acidosis often cause hyperkalemia?

Answer 9

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

Question 10

Why would alkalosis be accompanied by hypokalemia?

Answer 10

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

Question 11

When H2O shifts from the ICF to the ECF, what will it bring with it?

Answer 11

K+

Question 12

If your K+ input is too high, where in the kidney will the tweaking of K+ levels happen?

Answer 12

Distal tubule and collecting duct

In the PT and LOH, K+ is absorbed in FIXED ratios, no matter what****

Question 13

Do we usually eat too much or too little K+?

Answer 13

Too much

Question 14

What happens to K+ secretion when Na+ load to distal nephron increases?

Answer 14

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)

Question 15

Aldosterone is stimulated by (high/low) plasma K+

Answer 15

High

Question 16

Why would high consumption of K+ stimulate aldosterone?

Answer 16

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

Question 17

If you have a low K+ diet, where in the nephron will K+ be reabsorbed?

Answer 17

87% of it will be reabsorbed in the PT and LOH

The remaining K+ will be absorbed in the distal nephron

Question 18

Which cells reabsorb K+?

Answer 18

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

Question 19

Where is calcium stored?

Answer 19

99% bone

1% intracellular fluid

0.1% in the extracellular fluid

Question 20

Of the plasma calcium, how much of it is free ions that are biologically active?

Answer 20

50% of it

40% is bound to plasma proteins

10% is complexed with anions like CaPO4

Question 21

Can the calcium that is bound to plasma proteins be filtered?

Answer 21

NO

Question 22

What percentage of calcium in the blood can be filtered into the nephron?

Answer 22

60%

Question 23

How do you calculate the filtered load of calcium?

Answer 23

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

Question 24

Does a lot of the filtered calcium end up in the urine?

Answer 24

No, 99% of it is reabsorbed

1% appears in the urine

Question 25

Where in the nephron is calcium reabsorbed?

Answer 25

Proximal tubule 67%

Thick ascending limb 25%** blocked by Lasix

Distal tubule 5-10%** where fine tuning happens

Collecting duct <5%

Excreted 1%

Question 26

Is calcium reabsorption in the proximal tubule active or passive?

Answer 26

Passive. It is coupled to Na+

Question 27

When _____ uptake is high, so is Calcium uptake

Answer 27

Na+

Question 28

Is calcium reabsorbed through the paracellular route, or transcellular route?

Answer 28

Paracellular.

Question 29

What drives calcium reabsorption in the thick ascending limb of LOH?

Answer 29

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)

Question 30

Loop diuretics will cause more or less calcium to be reabsorbed?

Answer 30

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)

Question 31

A side effect of Lasix is (hypo/hyper) calcemia

Answer 31

Hypocalcemia

Question 32

In the Distal Tubule, how is calcium reabsorbed?

Answer 32

Apical membrane: Ca+ channels

Basolateral membrane: Na+ Ca+ exchange pump AND Ca+ ATPase

Question 33

Parathyroid hormone (inhibits/stimulates) Calcium uptake in the distal tubule

Answer 33

Stimulates

Question 34

Thiazide diuretics (increase/decrease) calcium reabsorption

Answer 34

Increase! (OPPOSITE OF LOOP)

Question 35

Why do thiazides increase calcium reabsorption?

Answer 35

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

Question 36

What role does phosphate have in the urine?

Answer 36

It is an important buffer anion

Question 37

Will Parathyroid hormone increase or decrease phosphate reabsorption?

Answer 37

Decrease (Proximal tubule)

It increases Calcium reabsorption in the distal tubule, and they do opposite things

Question 38

Does all of the phosphate that gets filtered get reabsorbed?

Answer 38

No, 15% of it is excreted

Question 39

Why does parathyroid hormone cause you to excrete more phosphate?

Answer 39

Because calcium+phosphate= bone

You don’t want those two reuniting and forming bone in your blood