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HOS Unit 4 > 7 Potassium Homeostasis > Flashcards

7 Potassium Homeostasis Flashcards

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1
Q

What is the major cation in the intracellular space?

A

K

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2
Q

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

A

Na-K- ATPase

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3
Q

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

A

Insulin

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4
Q

What organ is primarily responsible for maintaining K homeostasis?

A

kidney

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5
Q

Where does most of excreted K come from?

A

Distal tubular K secretion

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6
Q

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

A

True

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7
Q

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

A

Yes

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8
Q

What are the two ways potassium balance is regulated?

A
  1. Distribution between ECF and ICF–[insulin]

2. Renal K excretion [Distal nephron]

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9
Q

What does the total body K =?

A

50 meq/kg (3500meq)

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10
Q

What is the percentage distribution of K ICF and ECF?

A

98% at 150 meq/L

2% at 4 meq/L

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11
Q

What is the normal [K] concentration in ECF?

A

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

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12
Q

What plays the major role of internal potassium balance?

A

trancellular shifts—critical role of Na-K ATPase

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13
Q

What plays the major role in external potassium balance?

A

kidney—excreting what excess has been ingested

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14
Q

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

A

10% —10 mmole/day estimate

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15
Q

Is potassium secreted or filtered more by the kidneys?

A

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]

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16
Q

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

A

release K from ICF to ECF

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17
Q

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

A

stimulates K uptake by cells

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18
Q

What does aldosterone do in regards to K regulation?

A
  • **promotes uptake of K by cells

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

19
Q

Do respiratory disturbances have an effect on K homeostasis?

A

little or no effect

20
Q

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

A

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

21
Q

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

A

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

22
Q

What happens to K when a cell lyses?

A

Released into ECF

23
Q

What happens to K in the body during exercise?

A

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

24
Q

What are the 2 principles of solvent drag?

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

- K moves with water via solvent drag

25
Q

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

A

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

26
Q

Where is most of filtered K reabsorbed?

A

proximal convoluted tubule and TAL

27
Q

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

A

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

28
Q

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

A

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

29
Q

What do distal tubule intercalated cells do? principal cells?

A 
intercalated= absorb K
principal= secrete K
30
Q

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

A
  1. active uptake of K via pump on apical surface

2. K movement through K channel on basolateral surface

31
Q

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

A
  1. uptake of K by Na-K ATPase on basolateral side

2. Diffusion of K from cell into tubular fluid

32
Q

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

A

responsibility also for H secretion

33
Q

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

A
  1. K electrochemical gradient across the membrane
  2. K permeability across the apical membrane
  3. Lumen negative potential difference across apical membrane
34
Q

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

A

plasma K concentration and aldosterone

35
Q

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

A

Distal tubular flow rate and Na delivery

distal tubular anion composition

36
Q

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

A

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

37
Q

Does hyperkalemia stimulate aldosterone secretion?

A

yes, it is decreased by hypokalemia

38
Q

what 2 effects does aldosterone have on K secretion?

A
  1. increase amount of NA-K ATPases in principal cells

2. Stimulates Na channels—> depolarization—> driving force K to cross apical membrane is stronger

39
Q

Increase in tubular flow rate does what to K secretion?

A

stimulates secretion [maintains electrochemical gradient favoring K secretion]

40
Q

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

A

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

41
Q

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

A
  • transport of Na across the apical membrane

- Finite lag time of Cl reabsorption

42
Q

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

A

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

43
Q

K into cells is promoted by?

A
  • 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)
44
Q

K out of cells is promoted by?

A
  • Alpha2 adrenergic R’s
  • Acidosis (unless organic)
  • Cell lysis
  • Exercise
  • Hyperosmolarity

HOS Unit 4 (18 decks)

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