Regulation of Body Sodium

Question 1

• How do disorders of water balance manifest?

Answer 1

Changes in plasma osmolarity and therefore changes in plasma Na

Question 2

• How do kidneys handle salt load?

Answer 2

By hormones (RAAS) and altering GFR (tubular-glomerular feedback)

Question 3

• What factors affect salt excretion?

Answer 3

ECF volume, blood pressure & cardiac output

Question 4

• Where is sodium reabsorbed in the renal tubules?

Answer 4

67% in PT, 25% in ascending loop of Henle, 8% in DT

Question 5

• What is bulk Na+ resorption in the PT linked with?

Answer 5

H+ and K+ secretion

Question 6

• How is any remaining sodium reabsorbed in the DT and the CDs?

Answer 6

DT – Na+/Cl- symporter (NCC)

CD – ENaCs

Question 7

• What can inhibit sodium reabsorption?

Answer 7

Furosemide inhibits Na+K+2Cl- in the thick ascending limb
Thiazides inhibit NCC in the distal tubule
Amiloride inhibits ENaCs in the collecting ducts

Question 8

• What actions does the SNS initiate in order to conserve Na?

Answer 8

Reduces GFR, stimulates renin secretion

Question 9

• What does aldosterone stimulate?

Answer 9

Na+ uptake in the collecting duct by activating ENaCs

Question 10

• Why is the total Na+ regulated and not the plasma concentration?

Answer 10

Since water follows sodium and therefore volume is altered, but concentration isn’t

Question 11

• What does an increase in plasma K+ stimulate?

Answer 11

Aldosterone release from the adrenal gland, induces apical K+ channel insertion into principal cells

Question 12

• Give an example of when there is no aldosterone secretion?

Answer 12

Addison’s disease (hypoadrenocorticism)

Question 13

• What would inhibit renin secretion?

Answer 13

High Na+ load/ECF volume/blood pressure

Question 14

• How do the DTs and CDs fine tune Na+ resorption?

Answer 14

Inserts addition ENaCs and Na+/K+/ATPase proteins

Question 15

• What does ANP (sodium losing peptides) cause?

Answer 15

Renal vasodilation, increased GFR, decreased renin, decreased aldosterone, decreased ADH secretion

Question 16

• What does aldosterone have little impact on?

Answer 16

The concentration of Na+ in the ECF