Regulation of Potassium Balance

Question 1

How does renal failure affect plasma K+?

Answer 1

It increases

Question 2

What is the typical value of plasma potassium?

Answer 2

~4.2 +/- 0.3 mEq/L

Question 3

What percentage of K+ is in the ECF? ICF?

Answer 3

2% in the ECF; 98% in the ICF

Question 4

What is hyperkalemia? Hypokalemia?

Answer 4

Hyperkalemia is when the ECF [K+] is > 5 mEq/L; Hypokalemia when ECF [K+] when ECF

Question 5

What is kaliuresis?

Answer 5

Enhanced K+ excretion

Question 6

How common is hypokalemia in the hospitalized patient population?

Answer 6

20% of pop. will have or have experience hypokalemia

Question 7

What are the possible side effects of doubling normal plasma [K+]?

Answer 7

Cardiac arrhythmias and cardiac arrest

Question 8

What can result from severe drop in plasma [K+]?

Answer 8

Paralysis, cardiac arrhythmias, and death

Question 9

What is the primary organ responsible for K+ balance?

Answer 9

Kidneys

Question 10

True or False: Na+/K+ ATPase is found in every cell?

Answer 10

True

Question 11

What are the major primary active potassium transport proteins?

Answer 11

Na+/K+-ATPase, Ca++-ATPase, H+-ATPase, H+/K+-ATPase

Question 12

What is the mechanism of the Na+/K+-ATPase?

Answer 12

Pumps 3 Na+ into the ECF and pumps 2 K+ into the cell by hydrolyzing ATP to ADP

Question 13

What is the daily intake of potassium relative to the daily output?

Answer 13

Equal

Question 14

Approximately what percentage of K+ in the diet is absorbed?

Answer 14

90%

Question 15

What hormones stimulate the uptake of potassium into the ICF? How do they do this?

Answer 15

Insulin, Epinephrine, and aldosterone– all by increasing the activity of Na+/K-ATPase and aldosterone also increases the number of the pumps

Question 16

How does acidemia affect K+ distribution?

Answer 16

High levels of H+ and inhibit Na+/K+ ATPase, which has a net effect of decreasing the K+ uptake into the cells and increasing ECF [K+]

Question 17

How does alkalemia affect K+ distribution?

Answer 17

There is reduced H+ entry into the cells and so there is increased K+ entry into the cells, decreasing plasma [K+]

Question 18

K+ handling by the nephron is dependent on what?

Answer 18

Dietary K+ intake

Question 19

In the case of normal- high K+ intake where is K+reabsorbed and where is it secreted?

Answer 19

Reabsorbed by the proximal tubule and TAL, and secreted by DT and CCD

Question 20

With low dietary K+ intake, where is K+ reabsorbed and secreted?

Answer 20

Reabsorbed in the PT, TAL, DT, and CCD– no secretion

Question 21

What is the total possible range of filtered K+ load that can be excreted through the urine?

Answer 21

1-80%

Question 22

Is the filtered load of K+ greater or less than that of Na+? Why?

Answer 22

Less bc there is a small plasma [K+]

Question 23

Between what plasma [K+] values is there a linear relationship between plasma [K+] and K+ secretion by DT and CCD? What does this mean?

Answer 23

~4-5 mEq/L; There is very tight control of plasma [K+] right around the normal value

Question 24

How is potassium transported in the TAL?

Answer 24

It is reabsorbed through the apical membrane via NKCC2, secreted through ROMK channels, pumped into cell through BL membrane via Na+/K+ ATPase, diffuses out of BL down concentration gradient; reabsorbed paracellularly

Question 25

What is a ROMK? What is its action?

Answer 25

Renal Outer-Medullary K+ Channel- an inward rectifying potassium channel that secretes K+ into tubular lumen

Question 26

What is the importance of the TAL both reabsorbing and secreting K+?

Answer 26

In order for NKCC2 to function, all of the substrates (Na+, K+, Cl-) must be present in the tubular lumen, and so secreting K+ ensures there is enough to fuel the NKCC2

Question 27

Where are alpha-intercalated cells found?

Answer 27

In the cortical collecting tubule

Question 28

How is K+ transported in the alpha intercalated cells? When does this transport occur?

Answer 28

Apical uptake via H+/K+-ATPase and exit via basolateral K+ channel; occurs with low dietary intake of K+

Question 29

How is K+ secreted from the principal cell?

Answer 29

K+ is taken up through BL membrane via Na+/K+-ATPase and then passively moves out into the tubular lumen through ROML

Question 30

Where is K+ reabsorbed paracellularly in the nephron?

Answer 30

In the PT and TAL

Question 31

K+ excretion depends on what three rates?

Answer 31

Filtration, reabsorption, and secretion

Question 32

What are the major physiological regulators of K+ excretion?

Answer 32

Plasma [K+] and aldosterone

Question 33

How is K+ excretion controlled?

Answer 33

By varying the rate of K+ secretion by principal cells of the late DCT- CD through alterations in the electrochemical gradient

Question 34

What is K+ secretion regulated by?

Answer 34

Plasma [K+], aldosterone, ADH

Question 35

What are some causes of hypokalemia?

Answer 35

Certain diuretics, chronic or severe vomiting/ diarrhea, hyperaldosteronism, poor K+ intake

Question 36

What are the two mechanisms of aldosterone release?

Answer 36

1) high plasma [K+] directly stimulates aldosterone release; 2) decrease in plasma volume will stimulate renal baroreceptors in juxtaglomerular cells, increasing their secretion of renin which promotes formation of angiotensin II, which stimulates aldosterone release

Question 37

What is the overall effect of aldosterone on the cortical collecting duct?

Answer 37

Increases Na+ reabsorption and increases K+ secretion

Question 38

How does aldosterone increase K+ secretion?

Answer 38

Increasing ENaC activity makes the lumen more negative, driving K+ secretion due to electrochemical forces; Increases # and activity of ROMK channels; Increases Na+/K+-ATPase

Question 39

How does hyperkalemia, stimulate K+ secreted by the DT and CD?

Answer 39

Increased Na+/K+ ATPase activity increases the intracellular [K+] and the electrochemical driving force that facilitates K+ secretion; increased apical permeability to K+, stimulation of aldosterone; increased tubular flow

Question 40

What are K+-Sparing Diuretics?

Answer 40

Drugs (amiloride) that inhibit Na+ (and H2O) reabsorption, decrease lumen negativity and decreases the electrochemical driving force for K+ secretion