16. Renal Physiology Session 3

Question 1

What molecules are reabsorbed in the early proximal convoluted tubule?

Answer 1

NaHCO3, NaCl, glucose, amino acids.

K reabsorbed via paracellular pathway.

Question 2

How is NaHCO3 reabsorbed in the PCT?

Answer 2

Via Na+/H+ exchanger located in luminal membrane of epithelial cells.

Question 3

What enzyme catalyzes the formation of H2CO3 from CO2 and water and vice versa?

Answer 3

Carbonic anhydrase

It will make H2CO3 in the epithelial cells. It will make CO2 and water in the lumen/urine.

Question 4

What are the effects of carbonic anhydrase inhibitors?

Answer 4

Decreased H+ formation inside PCT cell
Decrease of Na+/H+ antiport
Increase Na+ and HCO3 in lumen
Increased diuresis
Increase urine pH
Decrease body pH

Question 5

What is reabsorbed in the thin descending limb of the loop of Henle?

Answer 5

Water

Question 6

What is reabsorbed in the thick ascending limb of the loop of Henle?

Answer 6

Na+, K+, 2Cl-, Mg2+, Ca2+

Impermeable to water

Question 7

How are Mg2+ and Ca2+ reabsorbed?

Answer 7

Increased K+ concentration in cells causes K+ to leak into lumen. This creates a positive potential that drives reabsorption of Mg2+ and Ca2+.

Question 8

What are the consequences of the inhibition of the luminal Na+/K+/2Cl- cotransporter by loop diuretics?

Answer 8

Decreased intracellular Na+, K+, 2Cl-.
Decreased back diffusion of K+, so less Mg2+ and Ca2+ reabsorbed
Decreased urine pH
Increased body pH

Question 9

How is NaCl reabsorbed in the DCT?

Answer 9

Na+/Cl- cotransporter (NCC)

Question 10

How is Ca2+ reabsorbed in the DCT?

Answer 10

Calcium channels

Regulated by parathyroid hormone (PTH)

Question 11

What are the effects of thiazide diuretics on the DCT?

Answer 11

Inhibits Na+/Cl- cotransporter (NCC)
Decreased urine pH
Increased body pH

Also enhances reabsorption of Ca2+ in both DCT and PCT.

Question 12

What is the most important site for K+ secretion?

Answer 12

Collecting tubule (CCT)

Question 13

How is Na+ reabsorbed in the collecting tubule?

Answer 13

Epithelial sodium channel (ENaC)

Question 14

What are the two mechanisms for K+ sparing diuretics? How does this effect pH?

Answer 14

Inhibition of aldosterone receptor, leading to decreased expression of ENaC

Inhibition of ENaC directly

Both increase urine pH, and decrease body pH (where K+ goes, H+ follows).

Question 15

Where does the secretion and reabsorption of organic acids and bases occur?

Answer 15

Proximal tubule, straight segments

Question 16

What effect does ADH have on urea permeability in inner medullary collecting ducts (IMCD)?

Answer 16

It increases its permeability and urea diffuses down the gradient into the interstitium. Shortly after, it encounters the loop of Henle and is diffused back in. The process repeats.

Question 17

What is ADH’s effect on NKCC2 cotransporter in the TAL?

Answer 17

Increases presence of NKCC2 channels. More Na+, C+, and 2Cl- are reabsorbed.

Question 18

Why is the entire medullary interstitium kept salty?

Answer 18

The descending limb of the LoH is only permeable to water. The hypertonic medulla is the major driving force of water reabsorption. It stays salty because of the pumps in the ascending limb of the LoH.

Question 19

How does one calculate free water clearance, C(H2O)?

Answer 19

V - Cosm

V: urine flow rate
Cosm: osmolar clearance

If negative, excess solutes are removed. If positive, more excess water is being removed.

Question 20

How does one calculate osmolar clearance (Cosm)?

Answer 20

(Uosm x V) / Posm

Question 21

How does one calculate obligatory urine volume (OUV)?

Answer 21

(minimum solute excretion per day) / (max urine concentrating ability)

Question 22

What is the key cotransporter located in the thick ascending limb of the loop of Henle?

Answer 22

Na+/K+/2Cl- cotransporter (NKCC2)

Question 23

What channels do aldosterone act on?

Answer 23

Increases expression of ENaC channels in the collecting tubule.

Also increases basolateral Na+/K+ ATPase.

Question 24

Where does ADH increase the expression of AQP2 channels?

Answer 24

Collecting tubule