Endo 3 - Neurohypophysial Disorders Flashcards
On an MRI, how does the PPG look?
Bright spot
What are the 2 nuclei in relation to the PPG?
Supraoptic nuclei and paraventricular nuclei
What 2 hormones does the PPG secrete?
Oxytocin and ADH/Vasopressin
What does ADH do?
Increases water reabsorption from renal cortical and medullary collecting ducts, via V2 receptors
Where are osmoreceptors located?
What do the osmoreceptors project onto?
Located in organum vasculosum
Project onto hypothalamic supraoptic and paraventricular nuclei
How is VP release brought about by osmoreceptors?
- Increased extracellular Na conc
- Causes osmoreceptor to lose water and osmoreceptor shrinks
- Causes increased osmoreceptor firing
- VP release from PVN and SON neurones
How does increased water reabsorption from Renal CD impact urine osmolality (and volume) and serum osmolality?
Urine Volume = decreases
Urine osmolality = increases
Serum osmolality = decreases
What is diabetes insidious caused by?
Insufficient ADH or ADH unable to work
What are the 2 types of Diabetes insipidus and explain their characteristics
- Cranial / central (absence/lack of circulating VP)
2. Nephrogenic (kidneys resistant to VP)
Which is the more common form of diabetes insidious, cranial or nephrogenic?
Cranial is more common
Name 5 causes of acquired cranial diabetes insipidus
- Traumatic brain injury
- Pituitary surgery
- Pituitary tumours, craniopharyngima
- Metastasis to pituitary gland (e.g. breast)
- Infiltrative disease of median eminence (e.g. TB / sarcoidosis)
What is more common, acquired cranial diabetes insipidus or congenital cranial diabetes insipidus
Acquired cranial diabetes insipidus
What drug is given to treat bipolar disorder?
Lithium
What are congenital causes of nephrogenic diabetes insipidus?
Mutation in gene encoding V2 receptor / AQP2 water channel
RARE
What are acquired cause of nephrogenic diabetes insipidus?
Lithium
What are the signs and symptoms of diabetes insipidus?
- Polyuria
- Hypo-osmolar urine
- Polydipsia
- Dehydration if fluid intake not maintained - can cause death
- Disruption to sleep
Give an example of medications that can cause a dry mouth
Anti-cholinergic medications
What is the difference between psychogenic polydipsia and DI?
Psychogenic polydipsia does not involve a problem in secreting VP.
IE psychogenic polydipsia they drink and urinate a lot and have a higher urine osmolality than DI
What is the normal hydrated plasma osmolality range?
270 - 290 most/kg H2O
Above the reference range for plasma osmolality indicates?
Diabetes insipidus
Below the reference range for plasma osmolality indicates?
Psychogenic polydipsia
Why do patients with psychogenic polydipsia have a reasonable, but slightly lower urine osmolality when fluid deprived compared to normal?
Because they are drinking so much, the concentration gradient in the medulla is decreased
4 biochemical features of Diabetes insipidus? (sodium, urea, plasma osmolality, urine osmolality)
- Hypernatraemia
- Increased urea
- Increased plasma osmolality
- Low urine osmolality (hypo-osmolar urine / dilute)
Describe biochemical features of psychogenic polydipsia (sodium, plasma osmolality, urine osmolality)
- Mild hyponatraemia (excess water intake)
- Low plasma osmolality
- Low urine osmolality
