Lecture 8: Regulation of Potassium Balance

Question 1

Where is most K+ located?

Answer 1

ICF

Question 2

How is ICF K+ controlled?

Answer 2

Na+/K+ pump

Question 3

Internal K balance

Answer 3

Distribution of K+ across cell membranes

Question 4

External K Balance

Answer 4

Renal mechanisms to manage variations in K+ intake

Question 5

What pump helps with internal K+ balance and with buffering when needed?

Answer 5

H+/K+ pump

Question 6

Alkalemia is accompanied by what condition

Answer 6

Hypokalemia

Question 7

What is the mechanism that causes Alkalemia

Answer 7

Hydrogen in blood decreases, so H+ leaves to enter ECF and K+ enters cells

Question 8

Acidemia is accompanied by what condition

Answer 8

Hyperkalemia

Question 9

What is the mechanism that causes acidemia?

Answer 9

Hydrogen in blood increases, so H+ enters and K+ leaves the cell exchange

Question 10

Do acid-base disturbances always cause a K+ shift across membranes?

Answer 10

No (particularly if disturbance is respiratory acidosis or respiratory alkalosis)

Question 11

Hyperkalemia leads to what kind of cells

Answer 11

Hyperexcitable

Question 12

Hypokalemia leads to what in cells

Answer 12

Hyperpolarization

Question 13

Why does hyperkalemia lead to hyperexcitable cells?

Answer 13

More potassium outside of cell and concentration of K more equal than between inside and outside. Decreased concentration gradient so less driving force for K+ to leave inside of cell –> RMP more positive/closer to threshold

Question 14

Why does Hypokalemia lead to hyperpolarization

Answer 14

K+ shifts into cells, so have more K inside than normal. Concentration gradient increases even more, so K leaves via channels because driving force is increase, so RMP even more negative and harder to reach threshold

Question 15

Insulin increases what pump activity

Answer 15

Na+/K+ ATPase activity

Question 16

Insulin increases uptake of what into cells

Answer 16

K+

Question 17

What condition does insulin prevent?

Answer 17

Hyperkalemia

Question 18

What happens if insulin is deficient (Type 1 diabetes)?

Answer 18

Decreases K intake after meals –> Hyperkalemia

Question 19

What are the 6 major factors that disturb internal K+ balance?

Answer 19

Catecholamines
Osmolarity
Cell lysis
Exercise
Insulin
Acid-base abnormalities

Question 20

Beta-2 adrenergic agonists increase activity of what

Answer 20

Na+/K+ ATP (increase potassium in cell, hypokalemia)

Question 21

Alpha-adrenergic agonist cause shift in K+ where

Answer 21

Out of cells - hyperkalemia

Question 22

Alkalemia

Answer 22

Less hydrogen in blood

Question 23

Acidemia

Answer 23

More hydrogen in blood

Question 24

How does hyperosmolarity impact internal K+ balance?

Answer 24

Water moves from ICF to ECF to increase concentration of K+ inside cells, drives diffusion of K into ECF

Question 25

How does cell lysis impact internal K+ balance?

Answer 25

Breakdown of cell membranes releases K+ from ICF

Question 26

How does exercise impact internal K+ balance?

Answer 26

Causes shift of K+ out of cells Can result in hyperkalemia in those with renal failure, or if taking beta2 adrenergic antagonist

Question 27

K+ balance = ? + ?

Answer 27

Daily urinary excretion of K+ + dietary K+ intake

Question 28

If excretion of K+ less than intake then what kind of K balance?

Answer 28

Positive K balance

Question 29

If excretion of K+ greater than intake, then what kind of K balance?

Answer 29

Negative K balance

Question 30

Filtration/filtered load is dependent on

Answer 30

Blood K concentration

Question 31

Reabsorption is dependent on

Answer 31

Need to conserve (increases if need to conserve increases)

Question 32

Secretion is dependent on

Answer 32

If need to excrete more, increased secretion

Question 33

What part handles 67% K+ filtered?

Answer 33

PCT

Question 34

Where is K+ reabsorption relatively constant?

Answer 34

PCT and TAL

Question 35

What part reabsorbs ~20% of K+ in filtered load?

Answer 35

TAL

Question 36

What transporter is used in the TAL for K

Answer 36

Na/K/2Cl transporter

Question 37

Distal tubule and collecting ducts are responsible for

Answer 37

Fine tuning of K+ excretion

Question 38

What part of the renal tubule is K+ excretion dependent upon diet

Answer 38

CD and DT

Question 39

If there is a low K+ diet, then what happens and what cells do it

Answer 39

Reabsorption by alpha-intercalated cells

Question 40

If there is normal to high K+ diet then what happens and what cells do it

Answer 40

Secretion by principal cells

Question 41

What pump controls K+ reabsorption by alpha intercalated cells on luminal membrane?

Answer 41

H+/K+ ATPase

Question 42

What pump controls K+ reabsorption by alpha intercalated cells on basolateral membrane?

Answer 42

K+ channel

Question 43

How do principal cells move K+ from blood to lumen of tubule (what transporter)

Answer 43

Na/K ATPase

Question 44

Magnitude of K+ secretion is determined by what

Answer 44

Size of electrochemical gradient for K across the luminal membrane (ie how much K is entering cells?)

Question 45

What factors influence magnitude of secretion of K?

Answer 45

Dietary K Presence of aldosterone Acid-base disturbances Alkalosis Acidosis

Question 46

What does dietary K+ do to influence magnitude of secretion of K+? (High and low)

Answer 46

High: Causes K+ to enter principal cells, increases ICF K+ concentration, driving force for K+ secretion Low: K+ decreases K+ in principal cells

Question 47

How does presence aldosterone affect K+ secretion?

Answer 47

K+ will be secreted more by principal cells (because aldosterone increases Na+ reabsorption)

Question 48

Increase potassium in cells is driving force for

Answer 48

Secretion

Question 49

How does alkalosis impact secretion of K+

Answer 49

Less H+ in ECF, H+ leaves cells, K+ enters cells, driving force for secretion

Question 50

How does acidosis impact secretion of K+

Answer 50

Usually decreases K+ secretion (hyperkalemia) More H+ in ECF, so H+ enters cells K+ leaves, decreases K+ in cells, so less secreted