Renal regulation of potassium and other ions

Question 1

Why does Na-K-ATPase maintain such a high potassium concentration intracellularly (~98% of total body potassium)?

Answer 1

Extracellular potassium must be kept minimum due to the role of potassium in nerve and muscle excitability

Question 2

Extracellular potassium is a function of what two variables?

Answer 2

1. Total body potassium
2. Distribution of potassium between ECF and ICF

Question 3

What is the effect of insulin and/or β-agonists on ECF and ICF potassium? Do they drive potassium into or out of a cell?

Answer 3

Drive potassium into the cell

Question 4

What is the effect of hyperosmolarity, exercise, and/or cell lysis on ICF and ECF potassium concentrations? Do they drive potassium into or out of a cell?

Answer 4

Drive potassium out of a cell

Question 5

What effect does epinephrine have on α and β-adrenergic receptors? How does it affect the distribution of K+ across cell membranes?

Answer 5

Activates α-adrenergic receptors; increases K+ release from cells (especially in the liver)

Activates β2-adrenergic receptors; increases K+ uptake into the cell

Question 6

Why is β2 activation important for the prevention of hyperkalemia during exercise?

Answer 6

Exercise causes K+ to be released from cells and epinephrine activates β2 receptors to increase K+ reuptake by cells

Question 7

What effect does insulin have on plasma K+?

Answer 7

Stimulates K+ reuptake

(diabetics may have trouble moving K+ into cells after K+ rich meals)

Question 8

What effect does aldosterone have on plasma K+?

Answer 8

Promotes K+ uptake

Question 9

Excessive levels of aldosterone may cause ______.

Answer 9

hypokalemia

Question 10

When extracellular fluid is alkalotic, which directions do H+ and K+ move? What metabolic disorder is this associated with?

Answer 10

H+ moves out of cells

K+ moves into cells

Hypokalemia

Question 11

When extracellular fluid is acidotic, which directions do H+ and K+ move? What metabolic disorder is this associated with?

Answer 11

H+ moves into cells

K+ moves out of cells

Hyperkalemia

Question 12

Why is the movement of K+ necessary in regard to acid-base regulation?

Answer 12

Maintains net neutrality when H+ ions cross membranes; anions (Cl-, sulfate, and other INORGANIC acids) left behind must be neutralized

Question 13

How does an increase in plasma osmolarity affect K+ movement?

Answer 13

Enhances K+ release by cells

Question 14

How does a decrease in plasma osmolarity affect K+ movement?

Answer 14

Reduces K+ movement out of cells

Question 15

Does cell lysis cause hypokalemia or hyperkalemia?

Answer 15

Hyperkalemia; releases intracellular K+

Question 16

How much of the total amount of potassium filtered is excreted in urine?

Answer 16

5-15% of the filtered quantity

Question 17

The proximal tubule reabsorbs how much of the total filtered potassium? Mechanism?

Answer 17

65%

Transcellular (mechanism unknown)

Question 18

The thick ascending Loop of Henle reabsorbs how much of the total filtered potassium? Mechanism?

Answer 18

25%

Na-K-2Cl cotransporter (luminal)

K-Cl cotransporter (basolateral)

Question 19

The medullary collecting duct reabsorbs how much of the total filtered potassium? Mechanism?

Answer 19

5%

H+-K+-ATPase countertransporter of α-intercalated cells

Question 20

What part of the nephron regulates secretion of K+ under normal circumstances? What cells are responsible for this?

Answer 20

Cortical collecting duct

Principal cells

Question 21

What factors regulate K+ secretion? (5)

Answer 21

1. Plasma [K+]
2. Aldosterone
3. Flow of tubular fluid
4. Diuretics
5. Acid-base balance

Question 22

Describe the cascade of events that occur in regard to aldosterone when plasma K+ increases.

Answer 22

Adrenal cortex secretes more aldosterone

Stimulates K+ secretion by principal cells of cortical collecting duct

Increased K+ excretion

Question 23

Describe the cascade of events that occur in regard to the renin-angiotensin system when plasma volume is decreased (due to hemorrhage or diarrhea).

Answer 23

Increased renin secretion

Increased angiotensin II AND increased plasma K

Increased aldosterone secretion

Decreased Na excretion and increased K excretion

Question 24

What are the effects of diuretics (2)

Answer 24

Increased fluid delivery to cortical collecting duct

Increased K secretion

Question 25

Where along the nephron is Ca reabsorbed (2)? How are they reabsorbed?

Answer 25

Thick ascending LoH: paracellularly down its electrochemical gradient

Distal tubule: calcium channels

Question 26

What hormone is secreted in response to hypocalcemia? What does it do?

Answer 26

Parathyroid hormone: increases calcium reabsorption in the distal tubule

Question 27

Where along the nephron is free phosphate reabsorbed? How much is reabsorbed?

Answer 27

Proximal tubule

85% reabsorbed

15% excreted

Question 28

How does parathyroid hormone regulate reabsorption of phosphate in the proximal tubule?

Answer 28

Inhibition of Na+-phosphate cotransporter; decreases phosphate reabsorption

Question 29

Where along the nephron is Mg reabsorbed (3)? How much is reabsorbed in each limb?

Answer 29

Proximal tubule: 30%

Thick ascending LoH: 60%

Distal tubule: 5%

5% excreted

Question 30

How is Mg reabsorbed in the thick ascending LoH?

Answer 30

Paracellularly down its electrochemical gradient

Question 31

How are organic anions secreted? Where does this occur?

Answer 31

Active secretory transport in proximal tubule

(low specificity; single transporter for ALL anions)

Question 32

How are organic cations secreted? Where does this occur?

Answer 32

Basolateral membrane: diffusion driven by K+ entering the cell

Luminal membrane: OC+-H+ antiporter (nonspecific)

Collecting duct