POTASSIUM BALANCE

Question 1

Normal range of potassium

Answer 1

3,900 mg/day

Question 2

Where is K+ mostly in the body?

Answer 2

INTRACELLULAR

Question 3

roles of potassium

Answer 3

cofactor for enzymes (Na/K ATPase, pyruvate kinase), regulation of muscle blood flow, nerve and muscle excitability

Question 4

Consequences of [K] out

Answer 4

paralysis and arrythmias, cardiac and muscle disturbances

Question 5

Hypokalemia

Answer 5

low amounts of K+ in the cell
- hyperpolarizes RMP, making cell LESS excitable in neurons, cardiac and skeletal muscle

Question 6

Hyperkalemia

Answer 6

high amounts of K+ in the cell
- depolarizes RMP, making cell MORE excitable in neurons, cardiac and skeletal muscle

Question 7

Extra-renal regulators of K+ homeostasis

Answer 7

plasma [K+], insulin and epinephrine

Question 8

Regulation of [K+] in plasma

Answer 8

an increase in [K+] in plasma stimulates K+ uptake by the Na+/K+ ATPase

Question 9

Regulation of [K+] by insulin

Answer 9

insulin released after eating promotes K+ reuptake by Na+/K+ ATPase
- hyperglycemia often occurs with hyperkalemia
- insulin deficiency leads to hyperkalemia

Question 10

Exercise contributions to [K+]

Answer 10

exercise causes K+ release d/t recurring AP firing where 3Na+ enter cell and 2K+ exits cell

Question 11

Regulation of [K+] by Epinephrine

Answer 11

epinephrine receptors of sympathetic nervous system also promote the reuptake of K+ via NA+/K+ ATPase pump

Question 12

Treatment for hyperkalemia

Answer 12

insulin (w/ dextrose) and beta agonists
- both activate Na+/K+ ATPase pump

Question 13

Which is faster to act? renal or extra-renal homeostatic mechanisms?

Answer 13

extra-renal
- i.e epinephrine and insulin mediated K+ regulation temporarily and hormonally translocate K+ into tissue cells
- also role of aldosterone

Question 14

Effect of [K+] hyperosmolarity

Answer 14

cell shrinkage as water will move out to dilute the ECF, increasing intracellular [K+] and causing hyperkalemia

Question 15

Effect of K+ hypoosmolarity

Answer 15

cell swelling, as water will move into the cell to dilute the ICF, decreasing the intracellular [K+] and causing hypokalemia

Question 16

Rhabdomyolosis

Answer 16

the breakdown of skeletal muscle cells, releasing K+ into the ECF which increases its concentration, leading to hyperkalemia

Question 17

Acidosis

Answer 17

favors hyperkalemia development (increased H+) that reduces K+ secretion by inhibiting luminal and basolateral transporters (pH affects optimal activity)
- cells will compensate by moving protons out of the cell to bring K+ back into cell, lowering the [K+] in the ECF and returning homeostasis
- criticality of acid-base balance
- a NHE is not used

Question 18

Alkalosis

Answer 18

excess K+ secretion, favoring hypokalemic states

Question 19

How is K+ moved through the kidneys?

Answer 19

K+ is BOTH reabsorbed and secreted by the

Question 20

Where is K+ reabsorbed?

Answer 20

mostly at PT, secondary to water/salt reabsorption
- also at thick ascending limb via NKCC2 transporter

Question 21

Where is K+ secreted OR reabsorbed?

Answer 21

at late DT and CD
- done

Question 22

alpha intercalated cells

Answer 22

cells in the DT that secrete H+ in exchange for K+ (active transport) for increased K+ reabsorption
- K+ reabsorption, acid secretion and bicarb reabsorption
- driver of K+ homeostasis in low K+ diet to increase K+ reabsorption

Question 23

principal cells

Answer 23

ciliated epithelial cells in the late DT AND CD responsible for Na+ reabsorption and K+ secretion
- has ENaC and Na+/K+ ATPase
- regulates K+ secretion, Na+ and water reabsorption
- driver of K+ homeostasis in high K+ diet to secrete excess K+

Question 24

In a normal diet what typically predominates? reabsorption or secretion of K+?

Answer 24

Secretion!
- higher intracellular [K+], so cell already has what it needs and K+ leaving the kidney is typically what occurs in a normal healthy kidney

Question 25

Effect of Aldosterone of K+ secretion

Answer 25

hormone released by adrenal cortex that stimulates Na+/K+ pump activity and luminal Na+ (ENaC) and K+ permeability (ROMK, BK)

Question 26

Effect of high plasma [K+]

Answer 26

induces aldosterone secretion to stimulate Na/K pump and increased K+ permeability

Question 27

K+ transporters in principal cell

Answer 27

ROMK (renal outer medullary K+) and BK (big capacity K+) transporters

Question 28

K-sparing diuretics

Answer 28

medications that help the body get rid of excess fluid while conserving potassium levels - tend to work by inhibiting sodium reabsorption or blocking the action of certain hormones that regulate electrolyte levels

Question 29

Amiloride

Answer 29

K+ sparing diuretic that acts on the principle cell's ENaC transporter to block Na+ reabsorption while leaving K+ unchanged - used to avoid K+ wasting

Question 30

Effect of flow on K+ secretion

Answer 30

Increased flow --> increased K+ secretion - why diuretics often lead to hypokalemia (K+ wasting) - diuretics act before DT and CD at PT so by the time filtrate reaches DT, flow has increased

Question 31

Aldosterone Paradox

Answer 31

high RAAS activity should ultimately lead to increased K+ secretion so how does one not become hypokalemic in this scenario? How does the body independently regulate each electrolyte? - ANSWER: AT2 constricts afferent and efferent arterioles to decrease distal flow which minimizes K+ excretion