Regulation of urea and nitrogen

Question 1

Mammals excrete how many nitrogen atoms per molecule of urea?

Answer 1

2 nitrogen atoms

Question 2

Birds and reptiles excrete how many atoms of nitrogen per molecule of uric acid?

Answer 2

4 nitrogen atoms

Question 3

Urea is permeable across all cell compartment and is freely filtered across the?

Answer 3

glomerulus

Question 4

In what section of the collecting duct does urea exit via the concentration gradient?

Answer 4

The distal end.

Question 5

What happens to urea absorption when GFR is increased?

Answer 5

If filtrate is flowing quickly less time for urea to pass into the interstitium so it decreases. Urea reabsorption depends on flow rates.
Blood urea concentration will go up in dehydrated animals with low flow rates.

Question 6

In what situations will urea concentration increase?

Answer 6

When GFR decreased
— Reduced filtration
— Increased urea absorption (slow flow so less
opportunity to excrete.)
Increased nitrogen intake
— Post-prandial
— GI haemorrhage

Question 7

What are the limitations of using urea as a renal clearance marker in horses?

Answer 7

In horses there is colonic secretion of urea and metabolism by GI bacteria

Question 8

Why would reading Urea as a renal flow marker be pointless in birds?

Answer 8

They have very low urea blood levels.

Question 9

How do hibernating animals maintain their fluid balance?

Answer 9

Almost all ultrafiltrate is reabsorbed but about 100m I/day still filters through kidney goes to bladder, which uniquely in mammals is able to reabsorb this filtrate (urine) back to body.

Question 10

How do hibernating bears cope with urea?

Answer 10

Urease expressing gut bacteria hydolyse urea to free the N which is used to form new amino acids to maintain muscle mass this happens in all diurnal animals to some extent.