Disorders of vasopressin Flashcards
From which nuclei do magnocellular neurons arise?
paraventricular and supraoptic nuclei in the hypothalamus
Which nucleus releases vasopressin?
paraventricular nucleus
What are the two functions of vasopressin?
- vasoconstriction 2. stimulates water reabsorption in renal collecting duct
Which receptor does vasopressin act on to stimulate water reabsorption in the collecting duct?
V2
How does vasopressin work to concentrate the urine?
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.
What are the two stimuli for vasopressin release?
rise in plasma osmolarity, and a reduced pressure detected by atrial stretch receptors.
what happens during haemorrhage, in terms of vasopressin?
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.
Where are the osmoreceptors located?
organum vasculosum and subfornical organ
when sodium concentration increases, what happens to the osmoreceptors and subsequent release of vasopressin?
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.
name 3 symptoms of diabetes insipidus?
polyuria, polydipsia, nocturia
In a blood test, what would show in a DI patient?
hyperosmolar blood plasma, hypernatraemia, normal glucose
when the posterior pituitary is not releasing vasopressin, what is this called?
cranial diabetes insipidus
when the collecting ducts don’t respond to vasopressin, what is this called?
nephrogenic diabetes insipidus
lithium is a cause of which type of DI?
nephrogenic
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?
cranial
How do you distinguish between psychogenic polydipsia and diabetes insipidus?
water deprivation test
compare and contrast the results of the water deprivation test between someone with DI and someone with psychogenic polydipsia
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
Why is it important to weigh the patient regularly during the water deprivation test?
The test must be stopped if the patient loses >3% of their body weight which is a marker of severe dehydration
How do you distinguish between cranial and nephrogenic diabetes insipidus?
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.
What is the normal range for plasma osmolality?
270-290 mOsm/kg H2O
Decreased plasma osmolality is a sign of DI or psychogenic polydipsia?
psychogenic polydipsia
what is the treatment for cranial DI?
ddAVP
what is the treatment for nephrogenic DI?
thiazide diuretics
what does SIADH stand for?
syndrome of inappropriate anti-diuretic hormone
Too much arginine vasopressin release is known as?
SIADH
low plasma osmolarity, reduced urine output and water retention are symptoms of?
SIADH
head injury, stroke, tumour, pneumonia, bronchiestasis , lung cancer, carbemazepine, SSRIs are a cause of?
SIADH
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?
blood tests to check glucose + hbA1c and rule out diabetes mellitus if this comes back normal, do: serum sodium water deprivation test
How would you distinguish between psychogenic polydipsia and diabetes insipidus?
water deprivation test
How would you distinguish between cranial and nephrogenic diabetes insipidus?
ddAVP (synthetic arginine vasopressin), see an increase in urine osmolality in cranial, no response in nephrogenic
If you diagnose cranial DI, what other tests/scans should you do?
MRI scan
what’s the diagnosis?
cranial diabetes insipidus
A patient has:
- high plasma osmolality
- low urine osmolality
- polydipsia
- nocturia
- polyuria
- normal blood glucose and hbA1c
what’s the most likely diagnoses?
diabetes insipidus - cranial or nephrogenic
what does high plasma sodium indicate?
dehydration
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?
psychogenic polydipsia
