7 Potassium Homeostasis

Question 1

What is the major cation in the intracellular space?

Answer 1

K

Question 2

What is responsible for maintaining the blanche between intracellular and extracellular space?

Answer 2

Na-K- ATPase

Question 3

What is the most important hormone regulating the distribution of K between IC and EC space?

Answer 3

Insulin

Question 4

What organ is primarily responsible for maintaining K homeostasis?

Answer 4

kidney

Question 5

Where does most of excreted K come from?

Answer 5

Distal tubular K secretion

Question 6

T-f–K is one of the most abundant cations in the body?

Answer 6

True

Question 7

Does ECF K stay quite constant despite large fluctuations in dietary intake?

Answer 7

Yes

Question 8

What are the two ways potassium balance is regulated?

Answer 8

1. Distribution between ECF and ICF–[insulin]

2. Renal K excretion [Distal nephron]

Question 9

What does the total body K =?

Answer 9

50 meq/kg (3500meq)

Question 10

What is the percentage distribution of K ICF and ECF?

Answer 10

98% at 150 meq/L

2% at 4 meq/L

Question 11

What is the normal [K] concentration in ECF?

Answer 11

3.5-5meq/L [Above or below is hyperkalemia or hypokalemia respectively]

Question 12

What plays the major role of internal potassium balance?

Answer 12

trancellular shifts—critical role of Na-K ATPase

Question 13

What plays the major role in external potassium balance?

Answer 13

kidney—excreting what excess has been ingested

Question 14

How much of daily potassium intake is excreted by way of feces?

Answer 14

10% —10 mmole/day estimate

Question 15

Is potassium secreted or filtered more by the kidneys?

Answer 15

filtered by a lot! [810 mmole/day vs. 50 mmole/day not all of the 810 is reabsorbed and thus amount excreted in urine is about 90]

Question 16

What does epinephrine on alpha receptors lead to in terms of potassium regulation?

Answer 16

release K from ICF to ECF

Question 17

What does epinephrine on Beta2 receptors do in regards to potassium regulation?

Answer 17

stimulates K uptake by cells

Question 18

What does aldosterone do in regards to K regulation?

Answer 18

• **promotes uptake of K by cells

* **also effects total body K by increasing renal K excretion!

Question 19

Do respiratory disturbances have an effect on K homeostasis?

Answer 19

little or no effect

Question 20

What potassium effect occurs in response to inorganic acidosis? organic acidosis?

Answer 20

inorganic= stimulate K egress from cells into ECF causing a rise in plasma K
Organic=little to no effect on [K] ion ECF

Question 21

What effect does alkalosis have on K concentrations within the body?

Answer 21

stimulates K influx into cells causing a fall in plasma K+

Question 22

What happens to K when a cell lyses?

Answer 22

Released into ECF

Question 23

What happens to K in the body during exercise?

Answer 23

Release of intracellular K to ECF by myocytes in response to vigorous exercise

Question 24

What are the 2 principles of solvent drag?

Answer 24

• Water moves out of cell to area of higher osmolarity.

- K moves with water via solvent drag

Question 25

In regards to hyperosmolarity, what happens to K during cellular water loss?

Answer 25

Very increased intracellular [k] AND increased extracellular K (really! It's weird!)

Question 26

Where is most of filtered K reabsorbed?

Answer 26

proximal convoluted tubule and TAL

Question 27

Is the absorption of K in the PCT active or passive?

Answer 27

Passive- dictated by Na and water reabsorption [not tightly regulated]

Question 28

Is K handling tightly regulated in the proximal or distal tubule?

Answer 28

Distal [only 10% reaches distal tubules, they determine final concentration in urine]

Question 29

What do distal tubule intercalated cells do? principal cells?

Answer 29

``` intercalated= absorb K principal= secrete K ```

Question 30

What is the 2 step process for K reabsorption in the distal tubule intercalated cell?

Answer 30

1. active uptake of K via pump on apical surface | 2. K movement through K channel on basolateral surface

Question 31

What is the 2 step process for K secretion via the principal cell?

Answer 31

1. uptake of K by Na-K ATPase on basolateral side | 2. Diffusion of K from cell into tubular fluid

Question 32

What is the key feature of regulation within the intercalated cell?

Answer 32

responsibility also for H secretion

Question 33

What are the key features of regulation within the principal cell? 3 of them

Answer 33

1. K electrochemical gradient across the membrane 2. K permeability across the apical membrane 3. Lumen negative potential difference across apical membrane

Question 34

what are the peritubular factors of K secretion regulation by DCT?

Answer 34

plasma K concentration and aldosterone

Question 35

What are the luminal factors of K secretion regulation by DCT?

Answer 35

Distal tubular flow rate and Na delivery | distal tubular anion composition

Question 36

What does hyperkalemia cause in regards to K secretion in the distal nephron?

Answer 36

stimulation of Na-K ATPase---> raises intracellular K---> stronger driving force for K to leave across apical membrane

Question 37

Does hyperkalemia stimulate aldosterone secretion?

Answer 37

yes, it is decreased by hypokalemia

Question 38

what 2 effects does aldosterone have on K secretion?

Answer 38

1. increase amount of NA-K ATPases in principal cells | 2. Stimulates Na channels---> depolarization---> driving force K to cross apical membrane is stronger

Question 39

Increase in tubular flow rate does what to K secretion?

Answer 39

stimulates secretion [maintains electrochemical gradient favoring K secretion]

Question 40

T-F---Physiologically increased tubular flow rate is often associated with increased distal tubular Na delivery? Why?

Answer 40

True- [ increased distal Na delivery leads to increased tubular Na reabsorption resulting in a lumen-negative potential difference, which will enhance K secretion]

Question 41

What is the normal potential difference of -15 to -50 mV in K secreting cells generated by?

Answer 41

- transport of Na across the apical membrane | - Finite lag time of Cl reabsorption

Question 42

Are other anions more or less well absorbed in the collecting duct than Cl?

Answer 42

less---[Na is reabsorbed but the more poorly reabsorb able anions add to the lumen negative potential difference which enhances gradient for K secretion]

Question 43

K into cells is promoted by?

Answer 43

- Insulin - Beta2 adrenergic R's - Aldosterone (ALSO helps excrete K+, think of it as 2 ways to get K+ out of blood) - Alkalemia - Hyperosmolarity (even more stays in than leaves)

Question 44

K out of cells is promoted by?

Answer 44

- Alpha2 adrenergic R's - Acidosis (unless organic) - Cell lysis - Exercise - Hyperosmolarity