04c: K regulation

Question 1

T/F: K is the most abundant cation in body.

Answer 1

True

Question 2

Most, (X)%, of K is located in which body compartment? At which concentration?

Answer 2

X = 98
ICF;
150 mEq/L

Question 3

Most K is found in which organ/structure?

Answer 3

Muscle

Question 4

(X)% of K is in the ECF at (Y) concentration. Plasma K concentration is a (good/poor) indicator of total body K.

Answer 4

X = 2
Y = 3.5-5 mEq/L
Poor

Question 5

T/F: In response to acute K load, kidney excretion plays key role in maintaining plasma K normal.

Answer 5

False - too slow of a process (hours)

Question 6

In response to acute K load, (X) process plays key role in preventing life-threatening hyperkalemia. This process is controlled by (Y).

Answer 6

X = uptake of ingested K by cells

Y = hormones

Question 7

After meal, most of K is taken up into cells via (X) (channel/transporter). List factors that activate (X) and star the most important one.

Answer 7

X = NaK pump

1. Rise of plasma K
2. Epi
3. Insulin*

Question 8

Subject treated with propranolol (beta adrenergic receptor blocker) will have (reduction/elevation) in plasma K after K load.

Answer 8

Elevation

Question 9

Why is there a shift of K (into/out of) cells in acidosis?

Answer 9

Out of;

Increased H is buffered within cells, so as it moves in, K moves out

Question 10

List two mechanisms proposed for loss of K from cells in acidosis.

Answer 10

1. Release of protein-bound cellular K

2. Inhibition of NaK pump (due to low pH)

Question 11

During exercise, there’s increased K movement (into/out of) cells. In which scenario can this be life-threatening?

Answer 11

Out;

Patient on beta-adr. receptor blocker

Question 12

Increase in osmolality of ECF leads to K movement (into/out of) cells. Why? Give an example.

Answer 12

Out of
(i.e. hyperglycemia);

Cell shrinkage increases intracellular K conc and increases chem gradient for K efflux

Question 13

To remain in K balance, individual must excrete about (X) K daily in urine. This excretion is regulated by which two factors?

Answer 13

X = 90 mEq

1. Plasma K
2. Aldosterone

Question 14

T/F: K is freely filtered at glomerulus.

Answer 14

True

Question 15

K is filtered at glomerulus at a rate of (X) per day. Most of K is reabsorbed at which tubular locations?

Answer 15

X = 600-900 mEq

PT (80%) and TAL (10%)

Question 16

At PT, K reabsorption is primarily (passive/active) transport that’s secondary to (X).

Answer 16

Passive diffusion;

X = increased tubular K conc due to water reabsorption

Question 17

T/F: Transcellular pathway is not involved in K reabsorption.

Answer 17

True

Question 18

T/F: K reabsorption at PT is downhill.

Answer 18

False - although electrical potential favors K movement into cell, chemical gradient driving K out is much greater

Question 19

Reabsorption of K at TAL involves mainly (X) transporter/channel at luminal membrane and (Y) transporter/channel at basolateral membrane.

Answer 19

X = NaKCl co-transporter
Y = KCl transporter and K channels

Question 20

T/F: PT, TAL, and distal tubules are capable of either reabsorption or secretion of K.

Answer 20

False - only distal tubules have dual capabilities

Question 21

Changes in excretion rate of K is handled primarily by (PT/TAL/distal) segments.

Answer 21

Distal

Question 22

List the cell types that influence K transport in distal nephron. Star the more numerous one, also responsible for (X) ion reabsorption.

Answer 22

X = Na

1. Principal* (K secretion)
2. Intercalated alpha-type (K reabsorption)

Question 23

K reabsorption occurs mainly in (cortical/medullary) collecting duct/tubules. And secretion?

Answer 23

Reab: cortical;
Secretion: medullary

Question 24

List the apical/basolateral transporters and channels involved in K secretion.

Answer 24

NaK pump (basolateral) followed by apical K channels secreting K into tubular lumen

Question 25

T/F: There are K channels on both apical and basolateral membranes in collecting duct/tubules.

Answer 25

True

Question 26

T/F: K preferentially diffuses across the basolateral membrane.

Answer 26

False - apical (K cahnenels have overall larger conductance on apical membrane)

Question 27

At the cell level, list the three factors controlling K secretion from tubules.

Answer 27

1. NaK pump activity
2. Electrochemical gradient
3. Apical membrane permeability to K

Question 28

A K-H (transporter/pump) is present in (X) tubular cells and (cotransports/exchanges) H and K (into/out of) lumen.

Answer 28

Pump (ATPase);
X = alpha-intercalated
Exchanges; H into lumen, K into cell

Question 29

In (high/low) ADH state, the medullary collecting duct is also able to passively reabsorb K.

Answer 29

High (high reabs of water favors K diffusion into tubular cell)

Question 30

During K depletion (low K intake), you’d expect (reabsorption/secretion) of K to prevail in distal segments, thus (raising/lowering) K excretion values to about (X)% of filtered load.

Answer 30

Reabsorption;
Lowering;
X = 1%

Question 31

With normal K intake, K excretion amounts to (X)% of filtration load per day.

Answer 31

X = 10-15

Question 32

Hyperkalemia favors K (reabsorption/secretion) in distal segments by directly affecting (X) and (Y).

Answer 32

Secretion;
X = NaK pump (increases activity)
Y = K permeability (increased) of luminal membrane

Question 33

T/F: Aldosterone secretion is stimulated by AII as well as low plasma K conc.

Answer 33

False - HIGH plasma K

Question 34

The MAIN cellular effect of aldosterone is (X) in (Y) cells/segments of nephron.

Answer 34

X = Increase synthesis of transport proteins (NaK pumps, Na and K channels)
Y = distal segments, principal cells

Question 35

In general, aldosterone effect is to enhance (X) (reabsorption/secretion).

Answer 35

X = Na reabsorption and K secretion

Question 36

A rise in the flow of tubular fluid would be expected to result from (diuresis/antidiuresis) and (expansion/contraction) of ECF.

Answer 36

Diuresis; expansion

Question 37

You’d expect (increased/decreased) secretion of K from distal nephron during diuresis.

Answer 37

Increased (high tubular flow)

Question 38

Severe vomiting/diarrhea results in (increase/decrease) of K secretion from distal tubule.

Answer 38

Decrease (low tubular flow)

Question 39

High tubular flow rate (increases/decreases) K secretion mechanically through which proposed steps?

Answer 39

Increase;

1. Deforms mechano-sensitive cilia of principal cell
2. Prompts intracell release of Ca
3. Opening of Ca-sensitive K channels

Question 40

High tubular flow rate generally affects K secretion by which 3 mechanisms?

Answer 40

1. Cilia
2. Dilution of tubular K (chemical gradient favors secretion)
3. Increased Na delivery/reabsorption

Question 41

Diuretics (increase/decrease) K secretion by (increasing/decreasing) (X).

Answer 41

Increase;
Increasing;
X = tubular flow rate

Question 42

Presence of ADH favors both K secretion via (X) and reabsorption by (Y).

Answer 42

X = enhancing Na reabsorption by principal cells
Y = decreasing tubular flow (by increasing distal reabsorption of water)

Question 43

Presence of AII favors both K secretion via (X) and reabsorption by (Y).

Answer 43

X = increasing aldosterone levels
Y = decreasing tubular flow (by increasing proximal reabsorption of water)

Question 44

Acidosis will (increase/decrease) K secretion.

Answer 44

Decrease

Question 45

As transepithelial potential decreases (becomes more positive), K secretion (increases/decreases) in distal segments.

Answer 45

Decreases