Regulation of Plasma Potassium - RS

Question 1

What are some of the consequences of being hyperkalemic?

Answer 1

Resting membrane potential depolarizes due to decreased outward flux of K+, muscle hyperexcitability, cardiac conduction disturbances leading to arrhythmias, metabolic acidosis (K+ plays a role in proton exchange). When [K+] is greater than 5.0 mM

Question 2

What are some of the consequences of being hypokalemic?

Answer 2

Resting membrane hyperpolarizes due to increased outward flux of K+, muscle hypoexcitability, cardiac disturbances of the pacemaker, metabolic alkalosis. When [K+] is less than 3.5 mM

Question 3

How can hyperkalemia cause acidosis?

Answer 3

due to the effective exchange of intracellular H+ for extracellular K+ across cell membranes, which adds acid (H+) to the plasma.

Question 4

How can hypokalemia cause acidosis?

Answer 4

due to the effective exchange of intracellular K+ for

extracellular H+ across cell membranes, which decreases acid (H+) in the plasma.

Question 5

Describe the renal handling of K+:

Answer 5

It is filtered, reabsorbed and secreted. (Na is not secreted).

Question 6

What is the first line of defense against hyperkalemia?

Answer 6

Translocation and sequestration of K+ into cells, mediated by the Na/K- ATPase, is the first line of defense against a K+ load and rise in plasma [K+].

Question 7

Which hormones mediate hyperkalemia and how do they function?

Answer 7

Insulin, epinephrine, and aldosterone promote an increased cellular uptake of K+ and a shift of K+ from the extracellular fluid into cells. These hormones induce “de novo” synthesis of Na/K-ATPase and induce fusion of intracellular membrane vesicles, populated with Na/K-ATPase, with the plasma membrane

Question 8

What is a consequence of acidosis?

Answer 8

H+ for K+ exchange lead to an increase in plasma K+ (hyperkalemia) resulting from an effective shift of K+ from the intracellular to the extracellular fluid compartment. The resulting increase in intracellular H+ concentration inhibits the Na/K-ATPase as well as the Na/K/2Cl co-transporter

Question 9

What is a consequence of alkalosis?

Answer 9

H+ for K+ exchange leads to a decrease in plasma K+ (hypokalemia), resulting from an effective shift of K+ from the extracellular to the intracellular fluid compartment. The resulting decrease in intracellular H+ concentration “dis-inhibits” or stimulates the Na/K-ATPase as well as the Na/K/Cl co-transporter.

Question 10

Does regulation of K+ occur by changing the absorption in the digestive tract?

Answer 10

NO!

Question 11

How does the proximal tubule handle K+? What percent does it reabsorb?

Answer 11

The reabsorption of K+ in the proximal tubule is not regulated and does not increase when plasma K+ is reduced or decrease when plasma K+ is increased. The “renal handling” of K+ by the proximal tubule does NOT include secretion of K+. It reabsorbs 80%.

Question 12

How does the distal nephron handle K+?

Answer 12

The distal nephron (late distal tubule and cortical collecting duct) includes reabsorption as well as secretion, depending on the prevailing K+ balance. The “renal handling” of K+ by the distal nephron is regulated where “net” reabsorption occurs when plasma K+ is below normal levels and “net” secretion occurs when plasma K+ is above normal levels.

Question 13

What is the consequence of chronic deficiency of K+ intake?

Answer 13

the effect of a chronic dietary K+ deficiency on plasma K+
may only be corrected by an increase in K+ consumption. Hypokalemia will result because the kidney can not compensate for it.

Question 14

What percent of K+ is absorbed by the proximal tubule AND loop of henle? Is it constitutive?

Answer 14

90% and yes it is. 80% in the proximal tubule and 10% in the Loop of Henle. Doesn’t matter wtf else is going on out there.

Question 15

How is K+ reabsorbed in the proximal tubule?

Answer 15

Paracellularly by solvent drag in the early proximal tubule and by passive electro-diffusion in the late proximal tubule.

Question 16

How is K+ reabsorbed in the thick ascending limb?

Answer 16

By both transcellular (via Na/K/2Cl transporter) and paracellular (again by electro-diffusion) mechanisms.

Question 17

How is K+ reabsorbed in the distal nephron?

Answer 17

The reabsorption of K+ in the distal nephron is transcellular and occurs by active, concentrative accumulation of K+ across the luminal membrane mediated by a K/H ATPase, which actively transports K+ into the cell in exchange for H+ transported out of the cell. This drives HCO3- formation.

Question 18

Can K+ reabsorption cause alkalosis?

Answer 18

Yes, The increase in HCO3 absorption occurring simultaneously with increased K+ reabsorption may induce a secondary metabolic alkalosis. This is secondary metabolic alkalosis.

Question 19

How is Na and K reabsorption linked?

Answer 19

Sodium reabsorption in the distal nephron is functionally coupled to potassium secretion such that an increase or decrease in transcellular sodium reabsorption occurs simultaneously with an increase or decrease in transcellular potassium secretion.

Question 20

Can reabsorption of Na cause Hypokalemia?

Answer 20

Yes, the functional coupling of sodium reabsorption to potassium secretion in the distal nephron is important because an increased delivery of sodium to these terminal nephron segments will not only result in a compensatory increase in sodium reabsorption but also an increase in potassium secretion which increases potassium loss in the urine and possible hypokalemia.

Question 21

What affect does aldosterone have on K secretion?

Answer 21

It increases secretion of K+ (kind of because it increases reabsorption of Na)

Question 22

What does alkalosis do to distal nephron K+ secretion?

Answer 22

It increases it. A respiratory or metabolic alkalosis, where plasma pH is increased, will induce a “shift” of protons (H+) from cells to plasma and a “shift” of K+ from plasma to cells, effectively exchanging intracellular H+ for extracellular K+ . Intracellular K+ is increased and ultimately that drives secretion of K+ at a faster rate. It can lead to hypokalemic metabolic alkalosis

Question 23

What does acidosis do to distal nephron K+ secretion?

Answer 23

It decreases it. A respiratory or metabolic acidosis where plasma pH is decreased will induce a “shift” of protons (H+) into cells from plasma and a “shift” of K+ out of cells to plasma, effectively exchanging intracellular K+ for extracellular H+. It decreases intracellular K+ and thus the driving force of K+ secretion. It can lead to hyperkalemic metabolic acidosis.

Question 24

What can a negative K+ balance lead to?

Answer 24

A negative K+ balance where plasma K+ is reduced (hypokalemia) will induce a “shift” of K+ from cells to plasma and a “shift” of H+ from plasma to cells, effectively exchanging intracellular K+ for extracellular H+ . The resulting decrease in extracellular H+ increases plasma pH, possibly causing a metabolic alkalosis.

Question 25

What can a positive K+ balance lead to?

Answer 25

A positive K+ balance where plasma K+ is increased (hyperkalemia) will induce a “shift” of K+ into cells from the plasma and a “shift” of H+ from cells to the plasma, effectively exchanging intracellular H+ for extracellular K+ . The resulting increase in extracellular H+ decreases plasma pH, possibly causing a metabolic acidosis.