Disorders of vasopressin

Question 1

From which nuclei do magnocellular neurons arise?

Answer 1

paraventricular and supraoptic nuclei in the hypothalamus

Question 2

Which nucleus releases vasopressin?

Answer 2

paraventricular nucleus

Question 3

What are the two functions of vasopressin?

Answer 3

1. vasoconstriction 2. stimulates water reabsorption in renal collecting duct

Question 4

Which receptor does vasopressin act on to stimulate water reabsorption in the collecting duct?

Answer 4

V2

Question 5

How does vasopressin work to concentrate the urine?

Answer 5

binds to V2 receptors in collecting duct and activates a G protein, resulting in an intracellular cascade, causing the transport of aquaporins to the apical membrane.

Question 6

What are the two stimuli for vasopressin release?

Answer 6

rise in plasma osmolarity, and a reduced pressure detected by atrial stretch receptors.

Question 7

what happens during haemorrhage, in terms of vasopressin?

Answer 7

Reduction in BP detected by atrial stretch receptors, resulting in less vasopressin inhibition, meaning more vasopressin is released and more water is absorbed into the plasma from the collecting duct.

Question 8

Where are the osmoreceptors located?

Answer 8

organum vasculosum and subfornical organ

Question 9

when sodium concentration increases, what happens to the osmoreceptors and subsequent release of vasopressin?

Answer 9

osmoreceptors shrink due to water leaving them due to osmosis. They increase their firing rate, increasing the release of vasopressin from the paraventricular nucleus, and subsequently the posterior pituitary. This causes more water to be reabsorbed from the collecting duct into the blood, reducing plasma osmolality.

Question 10

name 3 symptoms of diabetes insipidus?

Answer 10

polyuria, polydipsia, nocturia

Question 11

In a blood test, what would show in a DI patient?

Answer 11

hyperosmolar blood plasma, hypernatraemia, normal glucose

Question 12

when the posterior pituitary is not releasing vasopressin, what is this called?

Answer 12

cranial diabetes insipidus

Question 13

when the collecting ducts don’t respond to vasopressin, what is this called?

Answer 13

nephrogenic diabetes insipidus

Question 14

lithium is a cause of which type of DI?

Answer 14

nephrogenic

Question 15

traumatic brain injury, pituitary tumours, pituitary surgery, metastasis, autoimmunity and granulomatous infiltration of pituitary stalk eg. sarcoidosis are a cause of which type of DI?

Answer 15

cranial

Question 16

How do you distinguish between psychogenic polydipsia and diabetes insipidus?

Answer 16

water deprivation test

Question 17

compare and contrast the results of the water deprivation test between someone with DI and someone with psychogenic polydipsia

Answer 17

In psychogenic polydipsia, urine osmolality would increase in a similar way to a normal person, but slightly less because their body is used to drinking more. In DI, urine osmolality will not increase much, if it all

Question 18

Why is it important to weigh the patient regularly during the water deprivation test?

Answer 18

The test must be stopped if the patient loses >3% of their body weight which is a marker of severe dehydration

Question 19

How do you distinguish between cranial and nephrogenic diabetes insipidus?

Answer 19

Give ddAVP (desmopressin) which will cause urine osmolality to rise in a similar way to a normal person, in someone with cranial DI, but in nephrogenic DI, will not see any increase as the collecting duct is unable to respond.

Question 20

What is the normal range for plasma osmolality?

Answer 20

270-290 mOsm/kg H2O

Question 21

Decreased plasma osmolality is a sign of DI or psychogenic polydipsia?

Answer 21

psychogenic polydipsia

Question 22

what is the treatment for cranial DI?

Answer 22

ddAVP

Question 23

what is the treatment for nephrogenic DI?

Answer 23

thiazide diuretics

Question 24

what does SIADH stand for?

Answer 24

syndrome of inappropriate anti-diuretic hormone

Question 25

Too much arginine vasopressin release is known as?

Answer 25

SIADH

Question 26

low plasma osmolarity, reduced urine output and water retention are symptoms of?

Answer 26

SIADH

Question 27

head injury, stroke, tumour, pneumonia, bronchiestasis , lung cancer, carbemazepine, SSRIs are a cause of?

Answer 27

SIADH

Question 28

A patient has these symptoms: Wakes up in night to pass urine excessive thirst polyuria in the day excessive drinking water What tests would you do?

Answer 28

blood tests to check glucose + hbA1c and rule out diabetes mellitus if this comes back normal, do: serum sodium water deprivation test

Question 29

How would you distinguish between psychogenic polydipsia and diabetes insipidus?

Answer 29

water deprivation test

Question 30

How would you distinguish between cranial and nephrogenic diabetes insipidus?

Answer 30

ddAVP (synthetic arginine vasopressin), see an increase in urine osmolality in cranial, no response in nephrogenic

Question 31

If you diagnose cranial DI, what other tests/scans should you do?

Answer 31

MRI scan

Question 32

what’s the diagnosis?

Answer 32

cranial diabetes insipidus

Question 33

A patient has:

• high plasma osmolality
• low urine osmolality
• polydipsia
• nocturia
• polyuria
• normal blood glucose and hbA1c

what’s the most likely diagnoses?

Answer 33

diabetes insipidus - cranial or nephrogenic

Question 34

what does high plasma sodium indicate?

Answer 34

dehydration

Question 35

A patient has these results/symptoms:

• polydipsia
• polyuria
• nocturia
• low serum/plasma osmolality
• hyponatraemia
• low urine osmolality that increases in osmolality during the water deprivation test

What is the diagnosis?

Answer 35

psychogenic polydipsia