EN3 Flashcards
Neurohypophysial disorder
Principle effect of VP
reduce production of urine
Describe how VP work to reduce the production of urine
reduction in plasma osmolality ==> osmoreceptor loses water ==> shrink so become irritable ==> fire ==> hypothalamus produces VP down the neurohypophysis ==> VP binds to V2 receptor on the collecting duct cells on basal membrane ==> triggers G protein phosphrylation ==> activate adenylyl cyclase ==> increase cAMP from ATP ==> Increase in PKA ==> synthesis of AQP2 ==> migration of aggraphores and insertions of AQP2 into the apical membrane ==> water can be reabsorbed
What’s the name of the osmoreceptor
organum vasculosum
two types of DI
Cranial/central: lack of circulating VP due to inability to produce VP from neurohypophysis
Nephrogenic: kidneys resistant to VP i.e still able to produce normally
common cause of cranial DI
Often damage to neurohypophysis:
- traumatic brain injury
- pituitary surgery
- pituitary tumours, craniopharyngioma
- metastasis to pituitary gland e.g from the breast
- graulomatous infiltration of median eminence e.g TB, sarcoidosis
*very rare it’s congenital
common cause of nephrogenic DI
congenital: mutation in gene encoding for V2, AQP2 (rare)
Acquired: drugs e.g lithium toxicity
Signs and symptoms of DI
polyuria hypo-osmolar urine polydipsia dehydration if fluid is not provided disruption to sleep
what is psychogenic polydipsia (PP)
nothing wrong with VP production or response
Common symptoms:
1. polydipsia ==> psychiatric problems
2. polyuria ==> due to excess intake of water
what is the difference between a DI patient and a PP patient
the DI patient will have a higher plasma osmolality than PP as DI can’t reabsorb water at all
Biochemical features of DI
hypernatraemia
raised urea
high plasma osmolality
dilute urine
Biochemical features of PP
mild hyponatraemia
low plasma osmolality
dilute urine
way to administer DDAVP
nasal
oral
injection
what does DDAVP do cranial DI
reduce in urine volume
increase in urine osmolality
what is SIADH
the plasma VP is inappropriately high for the existing plasma osmolality
what does SIADH do
too much VP ==> increase water reabsorption ==> increase EC volume ==> Hyponatraemia, concentrate urine ==> confusion CNS problem