Renal regulation of urea and nitrogen

Question 1

What part of the collecting duct is permeable to urea?

Answer 1

The first section of the CD is impermeable to urea, so the urea stays in the tubule
Further down the CD, ADH makes the tubule permeable to urea so it urea exits the tubule down the concentration gradient

Question 2

Why does urea exit in the lower half of the CD?

Answer 2

This is because In the presence of ADH urea adds to the concentration gradient and more water can be reabsorbed from the CD

Question 3

If urea is being reabsorbed how can we get rid of it?

Answer 3

Urea recycling:
Urea is transported into the interstitium at the collecting duct
Urea enters the vasa recta at the distal end of the hairpin loop
Vasa recta passes near descending limb of nearby nephrons
Urea transporters return the urea to the lumen for excretion

Question 4

If GFR is decreased there will be an ……………….. in urea absorbtion due to…

Answer 4

Increase

Slow flow

Question 5

What are the three types of decreased excretion?

Answer 5

Pre-renal: Poor renal perfusion eg. Dehydration, hypovolaemia, decreased Cardiac output
Renal: Too few functional nephrons
Post-renal: Urinary tract obstruction/rupture

Question 6

Is urea a good marker for renal function?

Answer 6

Never use in isolation

Use with creatinine and urine specific gravity

Question 7

What is special about horses urea excretion?

Answer 7

They can secrete some urea into the colon for bacterial metabolism