L8: Renal Regulation of K, Ca, and Phosphate

Question 1

Where does the majority of K reside?

Answer 1

Inside cells (98%)

Question 2

What are the 3 hormones that closely regulate K levels?

Answer 2

Epi
Insulin
Aldosterone

Question 3

How does epi regulate K levels?

Answer 3

Alpha 1 activation: shift of K out of cells may result in hyperkalemia
B2 activation: stimulates K uptake into cells and may cause hypokalemia (B2 antagonists block this and can cause hyperkalemia)

Question 4

How does insulin regulate K levels?

Answer 4

Insulin released post meal
Causes K uptake into cells
Stimulates Na/K ATPase

Question 5

How does aldosterone regulate K levels?

Answer 5

Increases K uptake into tubule cells and increases K excretion
Stimulates Na/K ATPase
(promotes hypokalemia)

Question 6

What 3 conditions cause movement of K outside of the cell?

Answer 6

Hyperosmolarity
Exercise
ACIDosis

Question 7

What 3 conditions cause movement of K into the cell?

Answer 7

Insulin
B agonists
ALKALosis

Question 8

Is hyperkalemia an acidotic or alkalotic process?

Answer 8

Acidotic (HYPOkalemia causes K to move from ICF to ECF; messes with charge balance; H+ ions rush in)

Question 9

What is required for K balance to occur?

Answer 9

Input = output

Question 10

What 2 parts of the nephron do NOT change in the face of increased or decrease total body K?

Answer 10

Proximal tubule

LOH

Question 11

Where does physiological regulation of K occur?

Answer 11

Distal tubule

Collecting duct

Question 12

The magnitude of K secretion depends on the size of ____.

Answer 12

the electrochemical gradient for K across luminal membrane.

Question 13

Name 5 factors that cause K secretion.

Answer 13

1. Increased dietary intake
2. When aldosterone is present
3. During alkaloses (ICF K increases due to efflux of H out of cell)
4. High urine flow rates (luminal K kept low)
5. K secretion increases when Na load to distal nephron increases

Question 14

Name 2 diuretics that cause an increase in Na reabsorption to the distal nephron, and therefore an increased loss of potassium.

Answer 14

Loop diuretics
Thiazides
*****Na/K ATPase stimulated on basolateral side

Question 15

What 2 diuretics are potassium sparing?

Answer 15

Amiloride

Spironolactone

Question 16

A high potassium diet stimulates/inhibits aldosterone.

Answer 16

Stimulates (need to get rid of K)

Question 17

Describe the process of aldosterone increasing secretion of K.

Answer 17

Na/K ATPase on basolateral side stimulated
Room for Na to move in from lumen; Apical K channel upregulated (both through uniporters)
Lumen potential -50mV; electrochemical gradient strongly favors K secretion! (negative charge)

Question 18

A low potassium diet stimulates/inhibits aldosterone.

Answer 18

Inhibits (decreases K excretion)

Question 19

In a low K situation, where is most of the K reabsorbed?

Answer 19

PT and LOH (distal nephron gets the rest)

Question 20

What cells allow for K reabsorption? Describe the process.

Answer 20

Alpha intercalated cells
K reabsorption in exchange for H secretion
K then diffuses across basolateral membrane

Question 21

What are the 3 forms plasma Ca exists in (include %)

Answer 21

50% ionized = biologically active
10% complexed to anions
40% bound to plasma proteins

40% bound, 60% filtered and reabsorbed

Question 22

Equation for fitlered load of Ca

Answer 22

FL = (GFR)(PCa)(0.6)

0.6 because 60% is filtered and reabsorbed

Question 23

Where does Ca reabsorption NOT occur?

Answer 23

Everywhere but descending limb of LOH

Question 24

What diuretic inhibits reabsorption of Ca? Where does this occur?

Answer 24

Furosemide in the ascending limb of LOH

Question 25

What is a hormone and diuretic that stimulates reabsorption of Ca? Where does this occur?

Answer 25

PTH, Thiazide diuretics
Distal tubule
**This is usually where we tweak reabsorption

Question 26

Describe Ca reabsorption in the proximal tubule.

Answer 26

Passive
Ca coupled to Na - brought in or out together (factors that affect Na reabsorption affect Ca reabsorption)
Reabsorbed through PARACELLULAR route

Question 27

Describe Ca reabsorption in the thick ascending limb of LOH.

Answer 27

Lumen + potential = drives Ca reabsorption (NKCC2 brings K in, K diffuses out into lumen which creates + charge)
Ca enters through PARACELLULAR route

Question 28

_____ diuretics are used to treat hypercalcemia.

Answer 28

Loop (inhibits Ca reabsorption in the thick ascending limb of LOH, so Ca is lost through urine)

Question 29

How does Ca cross the apical membrane in the distal tubule?

Answer 29

Ca2+ channels (just diffuses through its own channel)

Question 30

How does Ca cross the basolateral membrane?

Answer 30

Active transport via Ca-ATPase

Na-Ca exchange (Na into cell, Ca out to blood)

Question 31

What hormone stimulates Ca reuptake in the distal tubule?

Answer 31

PTH (mediated by cAMP)

Question 32

What role do thiazide diuretics have in Ca reabsorption?

Answer 32

INCREASE Ca reabsorption (opposite of loop diuretics)
Thiazide inhibits NCC (Na Cl) channel on apical membrane
This increases inward movement of Na on basolateral side via the Na/Ca exchanger (so Na being brought in extra emphasizes output of Ca on basolateral side)

Question 33

_____ phosphate is an important buffer in acid-balance

Answer 33

Urinary

Question 34

Where is phosphate primarily reabsorbed? How much is excreted?

Answer 34

Primarily filtered at glomerulus, reabsorbed at proximal tubule
15% excreted in urine- IMPORTANT BUFFER ANION

Question 35

If there is low ionized Ca2+, what happens to PTH? How does this effect on PTH effect PO4 and Ca2 absorption?

Answer 35

Low Ca = Increased PTH
Increased PTH = PO4 reabsorption DECREASED in PT = increased PO4 excretion
Increased PTH = Ca reabsorption INCREASED in DT = Increased plasma ionized Ca