kidney function SDL

Question 1

why might an animal that has dramatic polyuria end up with a low blood urea concentration

Answer 1

If filtrate flow rate is high through the nephron, there is not a lot of time to pick up the urea from the filtrate as it passes through the collecting ducts. Urea (as well as water) picked up in the collecting ducts is ADH dependent so e.g., primary diabetes insipidus cases will have no ADH mediated water or urea pick up and so there will be less retained in the body (and there will be poor medullary concentration).

Question 2

list endocrine conditions associated with polyuria and their associated mechanisms

Answer 2

Question 3

4. A blood test has been performed in an unwell dog and the creatinine result has come back high. How could you tell if that is because there is insufficient blood supply to the kidneys (hypovolaemia such as dehydration) or if it because the kidneys themselves are damaged?

Answer 3

We can do this by checking how concentrated the urine is by measuring its specific gravity (USG). If dehydrated with good renal function, USG will be high (e.g. >1.035) but if the kidneys themselves are damaged there will be an inappropriately dilute USG (1.008-1.012). If we have very dilute urine (<1.008) then the kidneys are still doing something (diluting the filtrate) so are not completely broken – this dilute urine suggests some form of diabetes insipidus

Question 4

5. How does hypoadrenocorticism result in a dangerously high blood potassium level?

Answer 4

Aldosterone’s role in the distal kidney (at the end of a line of mechanisms (RAAS) stimulated by poor renal perfusion) is to bring Na+ back into the body from the filtrate dragging water with it to restore blood volume. The Na+ is swapped for K+ to maintain electro-neutrality. If there is not aldosterone, that mechanism for getting rid of potassium is gone/limited and it can build up in the blood