Regulation of K+ Balance

Question 1

What effect does epinephrine have on Serum [K+]?

Answer 1

Depends on whether it is activating alpha or beta adrenergic receptors

Alpha receptors - INCREASE serum [K+] by impairing cell uptake of K+ via Na-K-ATPase

Beta Receptors - DECREASE serum [K+] by enhancing cell uptake of K+ via Na-K-ATPase

Question 2

What effect does insulin have on serum [K+]?

Answer 2

Insulin DECREASES serum [K+] by enhancing cell uptake of K+ via Na-K-ATPase

Question 3

What effect does Aldosterone have on serum [K+]?

Answer 3

Aldosterone DECREASES serum [K+] by promoting K+ secretion into the Nephron tubule lumen

Also promotes K+ secretion into intestinal lumen and saliva

Question 4

What effect does acidosis have on serum [K+]?

Answer 4

Acidosis means high serum [H+]

Principal cells have a K+/H+ Exchanger that moves H+ into the cell and moves K+ out of the cell, thus increasing Serum [K+] and reducing the driving force for K+ secretion

Additionally, acidosis inhibits Na-K-ATPase, which promotes an increase in ECF [K+]

Question 5

What effect does alkalosis have on serum [K+]?

Answer 5

Alkalosis means serum [H+] is low

This causes movement of H+ into the serum while promoting K+ movement into the cells, increasing the driving force for K+ secretion.

“k is lo”

Question 6

What effect does cell damage have on serum [K+]

Answer 6

Cell damage results in the emptying of cell contents into ECF, including the larger concentration of K+

Thus serum K+ increases

Question 7

What effect does hyperosmolality have on cellular [K+}?

Answer 7

Hypersomolality (high salt concentration in ECF) causes movement of water from cell into interstitium (cell shrinks)

As cell shrinks, K+ concentration increases, and cell efflux of K+ increases

Question 8

What effect does strenuous exercise have on K+ levels?

Answer 8

Strenuous exercise increases activation of alpha-adrenergic receptors (epinephrine). Therefore, inhibits Na-K-ATPase activity, resulting in cellular K+ efflux

Question 9

How does K+ reabsorption occur in the Proximal Tubule?

Answer 9

Initially, in the early PCT, lots of Na+ is reabsorbed

This leaves a negative potential in the lumen that drives Cl- to be reabsorbed paracellularly

As Cl- leaves the lumen, the potential in the lumen becomes positive, resulting in Na+ and K+ being reabsorbed paracellularly

Question 10

Explain how K+ recycling works and why it is important

Answer 10

K+ is secreted into the Cortical Collecting Duct

K+ is reabsorbed in the Medullary collecting duct where it it increases K+ concentration in the medullary interstitium.

K+ is secreted into the Late Proximal tubule and the Descending Thin Limb of the Loop of Henle

The Increase in medullary interstitium [K+] causes inactivation of the NKCC2 channels in the ascending Limb of the Loop of Henle.

Inactivation of NKCC2 causes accumulation of Na+ in the distal tubule

Accumulation of Na+ in Distal Tubule promotes Na+ reabsorption and K+ secretion

This is important for K+ excretion after dietary K+ loading

Question 11

What do Principal Cells Reabsorb?

Answer 11

H2O and Na+

Question 12

What do Principal Cells Secrete?

Answer 12

K+

Question 13

What do Beta-Intercalated Cells Reabsorb?

Answer 13

H+ and Cl-

Question 14

What do Beta Intercalated Cells Secrete?

Answer 14

K+ and HCO3-

Question 15

What do Alpha Intercalated Cells Reabsorb?

Answer 15

K+ and HCO3-

Question 16

What do Alpha Intercalated Cells Secrete?

Answer 16

H+ and Cl-

Question 17

What channel(s) are found on the apical membrane of Principal Cells and what do they do?

Answer 17

ENaC (Epithelial Na+ Channel; allows Na+ movement into cell)

BK (Big K+ channel; allows K+ movement out into tubule lumen)

ROMK (Renal Outer Medullary K+ Channel; allows K+ movement out into the tubule lumen)

Aquaporin

Question 18

What channel(s) are found on the Basolateral Membrane of the Principal Cells and what do they do?

Answer 18

Na-K-ATPase (move 3 Na+ out; move 2 K+ in; uses ATP)

Question 19

What channel(s) are found on the apical membrane of of Beta-Interalated Cells and what do they do?

Answer 19

HCO3-/Cl Exchanger (Moves HCO3- out into tubule lumen; moves Cl- into the cell)

K+ Channel (allows K+ to move out into the tubule lumen)

Question 20

What channel(s) are found on the basolateral membrane of the Beta-Intercalated cell and what do they do?

Answer 20

Na-K-ATPase (move 3 Na+ out; move 2 K+ in; use ATP)

H-K-ATPase (move H+ out into interstitium; move K+ into cell; use ATP)

H-ATPase (move H+ into the interstitium; use ATP)

Cl- Channel (move Cl- out into the intersititum

Question 21

What channel(s) are found on the apical membrane of Alpha-Intercalated cells and what do they do?

Answer 21

H-ATPase (move H+ out into the tubule lumen; use ATP)

H-K-ATPase (move H+ out into the tubule lumen; move K+ into the cell)

Cl- Channel (move chlorine into the tubule lumen)

Question 22

What channel(s) are found on the basolateral membrane of Alpha-Intercalated cells and what do they do?

Answer 22

HCO3-/Cl Exchanger (Move HCO3- out into the interstitium; move Cl- into the cell)

K+ Channel (Move K+ out into the interstitium)

Question 23

What are the most important factors that stimulate K+ secretion?

Answer 23

Aldosterone
Increased ECF [K+]
Increased Tubular flow rate

Question 24

What are the most important factors that stimulate K+ reabsorption?

Answer 24

K+ deficiency; Low dietary K+; hypokalemia

K+ loss through severe diarrhea

Question 25

What five events would occur in response to a Buildup of extracellular [K+]?

Answer 25

- Activation of Na-K-ATPase on basolateral membrane - Reduced back leakage of K+ from the ICF to renal interstiitum - Aldosterone Secretion - Increased Distal Tubular flow rate - Synthesis and insertion of K+ channels on apical membrane

Question 26

How does flow rate affect K+ secretion?

Answer 26

Flow rate inreases K+ secretion

Question 27

What causes flow rate to increase?

Answer 27

High K+ or High Na+ intake

Question 28

Explain the counterbalancing that occurs with K+ excretion after High Na+ intake

Answer 28

High sodium intake causes a decrease in aldosterone secretion, which inhibits K+ secretion At the same time, Na+ intake causes an increase in GFR and Distal Tubule Flow rate, which increases K+ secretion.

Question 29

What is Acute Alkalosis and what is its effect on K+?

Answer 29

Acute process that decreases H+ion concentration in the ECF ``` Promotes Na-K-ATPase activity Increases Intracellular [K+] Increases passive diffusion of K+ into the tubule lumen Increases K+ channels Increases K+ secretion End result: Hypokalemia (k is lo) ```

Question 30

What is Acute Acidosis and what is its effect on K+?

Answer 30

Acute process that increases H+ ion concentration in the ECF ``` Inhibits Na-K-ATPase activity Decreases intracellular [K+] Decreases passive diffusion of K+ into the tubule lumen Decreases K+ channels Decreases K+ secretion End result: Hyperkalemia ```

Question 31

How is acute acidosis different from chronic acidosis?

Answer 31

Acute Acidosis inhibits K+ secretion whereas Chronic Acidosis ultimately promotes K+ secretion The reason this happens is because if acidosis initially blocks secretion of K+, this means that K+ accumulates causing Hyperkalemia. Hyperkalemia triggers release of Aldosterone, which promotes K+ secretion.

Question 32

What opposing factors in acidosis stabilize K+ seretion?

Answer 32

Acidosis blocks Na-K-ATPase activity, reducing intracellular [K+] (which inhibits Distal Secretion of K+) Acidosis blocks Proximal reabsorption, which increases distal tubular flow (which promotes K+ secretion)

Question 33

What opposing factors in volume expansion stabilize K+ secretion?

Answer 33

Volume expansion means Blood Pressure is increased, which decreases RAAS activation, and therefore decreased Aldosterone release (Decreases K+ secretion) Volume expansion causes a decrease in proximal reabsorption which increases distal tubular flow (which promotes K+ secretion)

Question 34

What opposing factors in High water intake (water diuresis) stabilize K+ secretion?

Answer 34

Water diuresis causes a decrease in ADH release from posterior pituitary gland. Decreased ADH results in a decrease in Blood Pressure, which will inhibit RAAS and Aldosterone activation (which decreases K+ secretion). Water diuresis causes a decrease in ADH release, which reduces reabsorption of water (which increases distal flow; which promotes K+ secretion)

Question 35

What opposite factors in Volume contraction stabilize K+ secretion?

Answer 35

Volume contraction stimulate Renin secretion, which activates Angiotensin II, which stimulates Aldosterone secretion (which promotes K+ secretion) Volume Contraction means GFR will be decreased, which results in a decrease in Distal Tubular Flow (which decreases K+ secretion)

Question 36

What effect do glucocorticoids have on K+ secretion?

Answer 36

Increase K+ secretion (via binding of mineralcorticoid receptor, increasing GFR, and fluid flow rate

Question 37

``` How do the following factors affect K+ secretion: ADH Luminal Flow Rate Acidosis Akalosis Glucocorticoids Anion Delivery ```

Answer 37

``` ADH - Increases K+ secretion Luminal Flow Rate - Increases K+ secretion Acidosis - Decreases K+ secretion Alkalosis - Increases K+ secretion Glucocorticoids - Increases K+ secretion Anion Delivery - Increases K+ secretion ```

Question 38

Which segment of the nephron is responsible for the greatest K+ reabsorption?

Answer 38

The proximal tubule Control K+ excretion is highly regulated by K+ secretion in the late distal tubule and collecting duct, but very little K+ reabsorption occurs there. Some K+ reabsorption occurs in the loop of Henle