8. Renal Transport Mechanisms – NaCl and Water Absorption along the Nephron

Question 1

What percentage of water and sodium is reabsorbed in the proximal convoluted tubule?

Answer 1

65 to 70%

Question 2

What is the primary player in resorption?

Answer 2

Na/K ATPase

Question 3

What is the advantage of taking a paracellular route?

Answer 3

The paracellular route does not require energy.

Question 4

Where is the Na/K ATPase pump physically located?

Answer 4

In the basolateral membrane

Question 5

What form of cellular transport is utilized in the reclamation of bicarbonate?

Answer 5

Trans-cellular

Question 6

What 2 actions are completed by carbonic anhydrase in the reclamation of bicarbonate?

Answer 6

1. The initial conversion of bicarbonate and hydrogen into carbonic acid
2. The conversion of carbonic acid back into bicarbonate and hydrogen within the cell

Question 7

What form of cellular transport is utilized in chloride reabsorption?

How does this occur?

Answer 7

Paracellular movement

More water than chloride is the absorbed in the 1st half of the proximal tubule, so the concentration of chloride increases. This creates a gradient for passive movement of chloride paracellularly.

Question 8

Do we see more water transport in the thin descending limb of the loop of Henle, or the thick ascending limb of the loop of Henle?

Answer 8

Water flows freely out of the thin descending limb of the loop of Henle through both aquaporin proteins and loose junctions.

The thick ascending limb is impermeable to water, it has both tight junctions and a lack of aquaporin.

Question 9

Where do we find aquaporin I proteins in the nephron?

Answer 9

In the proximal tubule, as well as in the thin descending limb of the loop of Henle.

Question 10

Where do we find aquaporin II proteins?

Answer 10

In the collecting duct and late distal tubule.

Question 11

What type of water movement is allowed in the collecting duct and late distal tubule?

Answer 11

Transcellular water movement only:
there are tight junctions, but they are also aquaporin II channels.

Question 12

What is the main glucose transporter (the glucose transporter that is responsible for the majority of glucose)?

Answer 12

SGLT2

Question 13

What transporter did we talk about as a common target for diabetic drugs?

Answer 13

SGLT2

Question 14

Approximately how much water is absorbed by the descending loop of Henle?

Answer 14

15% of water filtered is through the descending loop of Henle

Question 15

How is the descending loop of Henle able to concentrate solutes in the tubular fluid?

Answer 15

By re-absorbing water, but being impermeable to sodium chloride.

Question 16

How does the ascending loop of Henle modify the concentration of the tubular fluid?

Answer 16

It decreases the concentration by being impermeable to water, but allowing the reabsorption of solutes.

Question 17

How much sodium is absorbed by the ascending loop of Henle?

Answer 17

Approximately 25% of the filtered sodium

Question 18

Where do we find the Na-K-2Cl cotransporter?

Answer 18

On the thick ascending loop of Henle

Question 19

Where do we see the Na/Cl co-transporter?

Why do we care about it?

Answer 19

In the distal tubule

Because it is inhibited by thiazide diuretics

Question 20

How does furosemide function?

Answer 20

It inhibits sodium chloride reabsorption by competing for the chloride binding site on the Na-K-2Cl transporter.

Question 21

What type of cell does aldosterone target, and what is it doing?

Answer 21

It targets the principal cells of the collecting duct, in order to increase luminal Na-K transporters. This increases sodium reabsorption and decreases potassium reabsorption.

Question 22

How do thiazide diuretics function?

Answer 22

They inhibit reabsorption of sodium and chloride in the distal convoluted tubule by inhibiting the sodium chloride symporter.

They also reduce urinary excretion of calcium (increase reabsorption of calcium).

Question 23

How does spironolactone function?

Answer 23

It is essentially the opposite of aldosterone, and inhibits sodium potassium exchange in the other direction.

Potassium is spared and sodium is lost (along with water)