Regulation of K balance

Question 1

Counterion of K

Answer 1

phosphate or sulfate, not chloride. Phosphate and sulfate are poorly resorbed in distal tubule and collecting duct. Some organic ions can be turned into HCO3-, and HCO3- in collecting duct facilitates potassium excretion.

Question 2

[K plasma]

Answer 2

3.5-5.0 meq/L

Question 3

Functions of intracellular K

Answer 3

Maintenance of cell volume (direct relationship)
Necessary for RNA/protein synthesis (deficiency = stunted growth)
Regulates acid/base balance (loss = acidosis, gain = alkalosis)
Maintains membrane potential
Cofactor for some enzymes 
Vascular function (low K = vasoconstriction, and opposite)

Question 4

Insulin

Answer 4

Brings glucose into cells,
Increases Na uptake bc it needs phosphate from Na/phosphate symporter
Pulls K out of blood
Can cause hyperkalemia right after starvation

Question 5

Epinephrine via B2-receptors

Answer 5

B-receptors increase Na-K ATPase activity, pulling more K into the cell and possible producing hypokalemia, limits K going out

Question 6

Norepinephrine via alpha-receptor

Answer 6

Causes K to shift out of cells, minimizes hypokalemia after exercise, limits K coming in

Question 7

Hypertonicity

Answer 7

Causes K to exit cell

Question 8

Exercise

Answer 8

Shifts K out of cells, where it functions as vasodilator

Someone treated with B-adrenergic antagonists can experience hyperkalemia after exercise

Question 9

External K intake

Answer 9

Low K diet reduces transcription of Na/K ATPase (less K going into cells)
High K diet increases transcription of Na/K ATPase
All intake of K is excreted by kidney

Question 10

Regulation of K absorption

Answer 10

85% is resorbed in proximal tubule. This is also primary site of regulation.

Question 11

Effects of Acid/Base balance on K

Answer 11

Mineral acids cause K to shift out of cells

Organic acids have minimal effect

Question 12

Effect of intracellular K on action potential

Answer 12

hypokalemia makes threshold potential more negative

hyperkalemia makes threshold potential less negative

Question 13

Effect of Ca+2 on excitability

Answer 13

Hypercalcemia raises threshold potential

Question 14

K secretion in nephron

Answer 14

K is secreted predominantly in proximal collecting duct but also in distal tubule

Question 15

Ion transport In TALH

Answer 15

K is taken up by Na/Cl/K transport on lumen side and ejected into lumen again via K channel. K also comes into the cell by Na/K ATPase on basolateral membrane

Question 16

Ion transport in collecting duct

Answer 16

Principal cells take in Na and secrete K via different channels, but Na/K ATPase on basolateral side connects the two events. Increasing Na resorption/K secretion also increase paracellular diffusion of Cl

Question 17

Effect of flow rate on K secretion in collecting duct

Answer 17

High flow means more K secretion

Higher sodium delivery = more K secretion

Question 18

Effect of ADH on K secretion

Answer 18

With no ADH, CD is impermeable to water and has high flow, maintaining high K secretion
ADH slows passage of water but also stimulates K secretion so there is no net change

Question 19

Acid-Base effects on K secretion

Answer 19

Acidosis in CD causes principal cells to decrease K secretion.
Alkalosis in causes principal cells to increase K secretion

Question 20

alpha-intercalated cell

Answer 20

Cell in CD that secretes H+ in exchange for K resorption

If Principal cell secretes more K, alpha-intercalated cell will pick up the extra K and secrete H

Question 21

Aldosterone

Answer 21

Hyperkalemia directly cause Aldosterone secretion, which increases K secretion
If aldosterone release is prompted by Na deficiency, Na resorption in nephron segments proximal to CD, leaving K secretion unchanged