11_HST110 Potassium Regulation 2017

Question 1

What percentage of K+ is intracellular? How is this maintained?

Answer 1

98%

Na+-K+-ATPase

Question 2

What are the two major physiologic function of K+?

Answer 2

Cell metabolism (e.g. protein, glycogen synthesis)

Resting membrane potential across cell membranes

Question 3

Ratio of the ICF and ECF [K+] is the major determinant of the (X)

Answer 3

X = resting membrane potential

Question 4

Hypo- and hyperkalemia can alter conduction in skeletal and cardiac muscle
Potentially fatal (X) and (Y)

Answer 4

X = muscle paralysis
Y = cardiac arrhythmias

Question 5

Low K+ (X) the resting membrane potential. High K+ does the opposite

Answer 5

(X) Decreases

This makes achieving the normal threshhold voltage more difficult

Question 6

How is normal plasma [K+] maintained? 2 mechanisms?

Answer 6

Distribution of K+ between ICF and ECF

Renal excretion of K+

Question 7

(X) is the key mediator for distribution of K+ between ICF/ECF

Answer 7

X = Na+-K+-ATPase

Question 8

What are 3 physiological factors influence the distribution of K+ between ICF/ECF

Answer 8

Plasma [K+]
Catecholamines
Insulin

Question 9

Catecholamines (Epinephrine): Can affect K+ distribution:
α-receptors = block cellular entry of (X)
β2-receptors = promote cellular entry of (X)

Uptake of K+ is mediated by activation of (Y)
Most occurs in skeletal muscle and liver

Answer 9

X = K+
Y = Na+-K+-ATPase

Question 10

Insulin
Promotes entry of K+ into skeletal muscle and liver

Increases (X) activity

Plays a physiologic role in regulating plasma [K+] following ingestion of food

Can be used to treat (Y)

Answer 10

X =  Na+-K+-ATPase
Y = hyperkalemia

Question 11

What other factors affect plasma[K+]?

Answer 11

Exercise
Acid-base balance
Plasma osmolality
Cell lysis

These factors SHIFT K+ between the ICF and ECF compartments

Question 12

Exercise: Plasma [K+] rises with muscular exercise

Local increase in plasma [K+] has (X) effect and increases (Y)

Answer 12

X = vasodilatory
Y = blood flow

Question 13

Acid-Base Balance and [K+]

Metabolic acidosis increases plasma [K+]
Inhibits (X)

Metabolic alkalosis decreases plasma [K+]
Activates (X)

MAINTAIN ELECTRONEUTRALITY

Respiratory acidosis and alkalosis do not cause large changes in plasma [K+]

Answer 13

X = Na+-K+-ATPase

Question 14

Describe the steps in the interaction between Plasma Osmolality and [K+]

Answer 14

Water shifts out of the cell, causing cell to shrink

1. Intracellular [K+] rises, drives K+ out of cells
2. Solvent drag
   * [K+] increases 0.4-0.8 mEq/L per 10 mOsm/kg

Question 15

Cell lysis releases cellular components, including K+

Name 3 conditions that can result in cell lysis

Answer 15

Severe trauma
Tumor lysis syndrome
Rhabdomyolysis

Question 16

Renal K+ Excretion:
Kidneys maintain K+ balance by matching excretion with intake. Excrete (X) of ingested dietary K+

Some K+ is lost in sweat and feces, but amount is relatively constant and unregulated

Renal K+ excretion is regulated and primarily determined by K+ secretion in the (Y) and (Z)

Answer 16

X = 90-95%
Y = distal tubule
Z = collecting duct

Question 17

Mechanisms of K+ Transport

(X) generates high intracellular [K+], provides driving force for (Y) K+ secretion

Principal cells secrete K+ via:

• (Z) channel
• (A) channel (flow sensitive)
• (B) symporter (KCC1)

α-intercalated cells:

• (A) channel
• Reabsorb K+ via (C)

Answer 17

X = Na+-K+-ATPase
Y = apical
Z = ROMK
A = BK
B = K+-Cl-
C = H+-K+-ATPase

Question 18

What are the 3 determinants of K+ secretion?

Answer 18

Electrochemical gradient across apical membrane

Permeability of apical membrane (ie, number of K+ channels)

Na+-K+-ATPase activity

Question 19

What 3 factors influence K+ excretion?

Answer 19

Plasma [K+]
Aldosterone
Tubular flow rate

Question 20

Regulation: Plasma [K+].

Plasma [K+] directly affects K+ secretion by (X) increasing the electrochemical gradient across apical membrane, (X) permeability of apical membrane, and (X) Na+-K+-ATPase activity

Answer 20

X = increasing

Question 21

Regulation: Aldosterone.

Aldosterone directly affects K+ secretion by (X) increasing the electrochemical gradient across apical membrane, (X) permeability of apical membrane, and (X) Na+-K+-ATPase activity

Answer 21

X = increasing

Question 22

Regulation: Tubular Flow Rate.

Increased tubular flow rate (X) K+ secretion
* e.g. Diuretics, volume expansion

Decreased tubular flow rate (Y) K+ secretion
*Volume depletion

Flow is sensed by primary cilia in (Z) cells, activates BK channels

Answer 22

X = increases
Y = decreases
Z = principal