Renal Potassium

Question 0

What are the 5 factors that influence K+ secretion by Principal cells?

Answer 0

1) distal nephron flow rate
2) luminal Na+ concentration
3) alkalosis
4) aldosterone
5) high K+ diet

Question 1

What is the major stimulus for potassium secretion?

Answer 1

Distal nephron flow rate

Question 2

How does distal flow rate cause K+ secretion?

Answer 2

Washes K+ away, more K+ out

Increase Na+, electrically drive K+ out

Question 3

How does luminal Na+ cause K+ secretion?

Answer 3

Na+ creates electrical gradient for K+ to leave

Question 4

How does alkalosis increase K+ secretion?

Answer 4

Increases Na/K pump on basolateral, so K+ come into cell so can be excreted

Question 5

How does aldosterone increase K+ secretion?

Answer 5

Increase Na/K
Increase basolateral SA
Stimulate ENaC (Na in, drives K out)
Increase K conductance across apical

Question 6

How does high K diet increase K secretion?

Answer 6

Increase basolateral membrane SA
Increase aldosterone secretion
(Inhibit Na/H in prox tubule so greater loss of Na, so more Na past the principal cells)

Question 7

Aldosterone secretion stimulated by

Answer 7

ATII

High K

Question 8

What 2 things increase basolateral membrane SA?

Answer 8

Aldosterone

High K

Question 9

Kinetics of ingested potassium

Answer 9

K rapidly absorbed in GI and increase plasma K
Absorbed K rapidly absorbed into cells
K excreted by kidneys over hours (cell to blood to kidneys)

Question 10

What diuretics are potassium wasting and potassium sparing?

Answer 10

Potassium wasting: all upstream of principal cells

• lasix
• thiazide
• carbonic anhydrase inhibitors (diamox)

Potassium sparing:
- amiloride (acts on principal cells)

Question 11

Aldosterone paradox (general phenomenon)

Answer 11

Hypovolemic, aldosterone is high to increase sodium retention, but we don’t have excessive potassium loss

Question 12

Mechanism of aldosterone paradox in hypovolemia

Answer 12

Hypovolemia:
Both ATII and aldosterone elevated
Aldosterone incr NaCl reabs by principal cells
ATII inhibits apical K channel (prevents incr K loss)
ATII stimulates NaCl reabs by cells in early distal by incr NaCl cotransporter

Question 13

Mechanism of aldosterone paradox in hyperkalemia

Answer 13

Aldosterone stimulated in absence of elevated ATII

Aldosterone stimulates principal cells which increase both NaCl reabsorption and K secretion