6 Urine Concentration and dilution

Question 1

Usually, how does osmolality change along the nephron?

Answer 1

not much over PCT
increases to base of loop of Henle
by end of loop, decreased
variable water reabsorption over remaining tubule

Question 2

How does flow rate change over the nephron?

Answer 2

decreases along the whole lot tbh

Question 3

How does ADH increase water reaborption?

Answer 3

binds to V2 receptor
increases synthesis of new AQP2 via PKA
causes insertion of AQP channels pre-formed in vesicles

also increases urea absorption by increasing UT-A1 by the same mechanisms

Question 4

What happens to the nephron when there is no ADH?

Answer 4

we don’t have water reabsorption, so the urine is dilute, increasing flow rate and decreasing osmolality

Question 5

What happens to the nephron when there is maximum ADH?

Answer 5

More water reabsorption, concentrated urine
higher osmolality
lower flow rate

Question 6

What happens in selective protein starvation?

Answer 6

less nitrogen is excreted in the form of urine

it is therefore harder to concentrate urine

Question 7

What happens to reabsorbed urea?

Answer 7

it accumulates in the medulla, forming an area of high osmolality

this is observed in the deeper areas of the loop of henle

Question 8

Why might cells struggle to survive in the renal medulla? How do they survive?

Answer 8

because the osmolality is so high due to the amount of urine

they accumulate lots of organic osmolytes within them to hold the water there, preventing them from dehydrating

Question 9

What osmolytes are within medullary cells?

Answer 9

sorbitol
inositol
betain
glycerophosphorylcholine

Question 10

What are the 2 types of diabetes insipidus?

Answer 10

Central diabetes insipidus

nephrogenic diabetes insipidus

Question 11

What is the pathogenesis behind central diabetes insipidus?

Answer 11

often due to head injnury (subarachnoid haemorrhage)

less ADH is released

Question 12

How is central diabetes Insipidus treated?

Answer 12

ADH analogue (desmopressin)
paradoxical use of thiazide diuretics

Question 13

what are the different causes of nephrogenic DI?

Answer 13

lithium toxicity (bipolar meds)
hypercalcaemia
genetic, mutations in V2 of AQP2 (very rare)

Question 14

How is nephrogenic DI treated?

Answer 14

thiazide diuretic

low salt diet

Question 15

Why would you not used desmopressin to treat Nephrogenic DI?

Answer 15

it is insensitive to it

Question 16

What is SIADH?

Answer 16

syndromes in Inappropriate ADH (high ADH, concentrated urine)

Question 17

What might cause SIADH?

Answer 17

head injury

Question 18

What are the effects of SIADH?

Answer 18

become hyonatraemic, as water is retained, so it dilutes the sodium

Question 19

How might you treat SIADH

Answer 19

fluid restriction
give urea (although this sin't really done in the uk anymore as you would have to give so much)
Aquaretic drugs

Question 20

What do aquaretic drugs do?

Answer 20

cause water loss without salt loss
V2 receptor antagonists
Vaptans
act on the late portion of the distal tubule and the collecting duct