EN3 Flashcards

Neurohypophysial disorder

1
Q

Principle effect of VP

A

reduce production of urine

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2
Q

Describe how VP work to reduce the production of urine

A

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

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3
Q

What’s the name of the osmoreceptor

A

organum vasculosum

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4
Q

two types of DI

A

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

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5
Q

common cause of cranial DI

A

Often damage to neurohypophysis:

  1. traumatic brain injury
  2. pituitary surgery
  3. pituitary tumours, craniopharyngioma
  4. metastasis to pituitary gland e.g from the breast
  5. graulomatous infiltration of median eminence e.g TB, sarcoidosis

*very rare it’s congenital

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6
Q

common cause of nephrogenic DI

A

congenital: mutation in gene encoding for V2, AQP2 (rare)
Acquired: drugs e.g lithium toxicity

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7
Q

Signs and symptoms of DI

A
polyuria
hypo-osmolar urine
polydipsia 
dehydration if fluid is not provided 
disruption to sleep
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8
Q

what is psychogenic polydipsia (PP)

A

nothing wrong with VP production or response
Common symptoms:
1. polydipsia ==> psychiatric problems
2. polyuria ==> due to excess intake of water

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9
Q

what is the difference between a DI patient and a PP patient

A

the DI patient will have a higher plasma osmolality than PP as DI can’t reabsorb water at all

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10
Q

Biochemical features of DI

A

hypernatraemia
raised urea
high plasma osmolality
dilute urine

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11
Q

Biochemical features of PP

A

mild hyponatraemia
low plasma osmolality
dilute urine

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12
Q

way to administer DDAVP

A

nasal
oral
injection

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13
Q

what does DDAVP do cranial DI

A

reduce in urine volume

increase in urine osmolality

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14
Q

what is SIADH

A

the plasma VP is inappropriately high for the existing plasma osmolality

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15
Q

what does SIADH do

A

too much VP ==> increase water reabsorption ==> increase EC volume ==> Hyponatraemia, concentrate urine ==> confusion CNS problem

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16
Q

Causes of SIADH

A
CNS e.g stroke
Pulmonary disease e.g pneumonia
Malignancy: lung
Drug: SSRI
idiopathic
17
Q

Treatment of SIADH

A
Surgery to remove the tumour
Fluid restriction (immediate)
Drug that stops VP action (long term) ==> VAPTANS which inhibit V2