Nephron Physiology - 2: Loop of Henle

Question 1

What is the concentration of glucose/amino acids/proteins as filtrate enters the thin descending loop of henle?

Answer 1

None - have been reabsorbed in the PCT.

Question 2

What is the concentration of Na+ as filtrate enters the thin descending loop of henle?

Answer 2

Isotonic w/ plasma pretty much. (water followed it into the PCT at the same rate).

Question 3

What is the concentration of K+ as filtrate enters the thin descending loop of henle?

Answer 3

High. K+ could move back and forth pretty easily in the PCT.

Question 4

What is the concentration of Cl- as filtrate enters the thin descending loop of henle?

Answer 4

Greater than plasma. Doesn’t get reabsorbed dramatically in the PCT.

Question 5

What is the thin descending loop of Henle permeable to?

Answer 5

Water.

Question 6

Can sodium and Cl- be absorbed in the thin descending loop of Henle?

Answer 6

No.

Question 7

What is the main event in the thin descending loop of Henle?

Answer 7

Water is reabsorbed via medullary hypertonicity. Urine is more and more dramatically concentrated the deeper you go.

Question 8

What happens to the permeability of the nephron as thin descending loop becomes thin ascending loop?

Answer 8

Thin ascending loop is NOT permeable to water, and IS permeable to Na+ and Cl-.
As filtrate travels up the thin ascending loop, Na+ and CL- exit the tubule filtrate.

Question 9

What is the most important transporter in the thick ascending loop?

Answer 9

NKCC2 transporter on the lumenal side of the tubule.

Question 10

What does the NKCC2 transporter do? What drives this transport?

Answer 10

1. Reabsorbs Na+, K+ and 2 Cl into the epithelial cell

2. Driven by Na+ gradient created by basolateral Na+/K+ATPases.

Question 11

What happens to the Cl absorbed by the NKCC2?

Answer 11

It diffuses down electrochemical gradient through Cl channel in basolateral membrane out of the cell

Question 12

What happens to the K+ absorbed by the NKCC2?

Answer 12

K+ backleaks out through ROMK channel back into the lumen. Allows NKCC2 transporter to keep moving (needs all the pieces to work).

Question 13

What happens to Mg2+ and Ca2+ in the thick ascending loop?

Answer 13

K+ cycling back into the lumen so much makes it positively charged. Mg2+ and Ca2+ are absorbed paracellularly.

Question 14

Is the thick ascending loop permeable to water? What is the effect of this on urine concentration?

Answer 14

Thick ascending loop is not permeable to water.
Solutes leave, water stays.
Urine becomes less concentrated.

Question 15

What % of Na is absorbed in the thick ascending loop?

Answer 15

10-20%.

Question 16

What do loop diuretics such as furosemide do?

Answer 16

Block the action of NKCC2 transporter.

Na, Cl, and H20 keep moving on down the nephron, overwhelm distal transport mechanisms.

Question 17

What happens to ammonium (NH4+) in the thick ascending loop of henle?

Answer 17

It can take K+’s place on the NKCC2 and come back into the cell, but it can’t get back out into the lumen through ROMK.