The Loop of Henle

Question 1

What is the anatomical difference between cortical nephrons and juxtaglomerular nephrons?

Answer 1

Cortical nephrons have a shorter loop than juxtaglomerular nephrons

Question 2

Why must water and solute reabsorption be done separately?

Answer 2

Otherwise, only isotonic reabsorption can occur

Question 3

What percentages of ions and water does the Loop of Henle reabsorb?

Answer 3

20% of NaCl, water and calcium
10% of potassium
80% of magnesium

Question 4

At which section of the Loop of Henle is osmolarity increasing?

Answer 4

Descending limb

Question 5

At which section of the Loop of Henle is osmolarity decreasing?

Answer 5

Ascending limb

Question 6

Describe the transport that occurs in the thick ascending limb

Answer 6

Na, K, Ca and Mg all move paracellularly
A Na and K gradient is set up across the basolateral membrane via Na/K/ATPase
Sodium is reabsorbed via Na/H exchanger and Na/Cl cotransporter
Protons are secreted after being produced from carbonic anhydrase
Potassium is secreted and then reabsorbed
Chloride and potassium are transported out of the cell via Cl/K cotransporter

Question 7

Which limb does no water transport occur and why?

Answer 7

Thick ascending limb as there are no aquaporins

Question 8

Describe countercurrent multiplication

Answer 8

Salt is pumped into the interstitium from the thick ascending limb
This draws water out of the thin descending limb via osmosis
Causes concentration of the luminal fluid followed by dilution

Question 9

Describe countercurrent exchange in the vasa recta

Answer 9

Exchange occurs between the interstitium, tubules and vasculature
The continuous blood flow’s osmolarity does not equilibrate, but this restricts blood and nutrient supply

Question 10

What are the requirements for counter current multiplication?

Answer 10

High water permeability in the descending limb but low in the ascending limb
Low passive sodium permeability
Active salt pumping in the ascending limb

Question 11

Why can’t countercurrent multiplication occur in the ascending thin limb of juxtaglomerular nephrons?

Answer 11

High passive sodium permeability

Little active salt pumping

Question 12

Describe the process of urea recycling

Answer 12

Urea is freely filtered through the glomerulus
Water loss in PT increases urea concentration
Urea is partially secreted into the ascending limb from the medulla which increases urea concentration
ADH allows urea transport out of the collecting duct which decreases urea concentration
Collecting duct and medulla equilibrate so some medullary urea is secreted into ascending limb

Question 13

How does urea recycling aid salt rebasorption in the thin ascending limb?

Answer 13

Urea concentration in the medulla becomes higher than that of salt
Salt then passively diffuses out of the thin ascending limb