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ENDOCRINOLOGY > 3) Neurohypophysial disorders > Flashcards

3) Neurohypophysial disorders Flashcards

1
Q

What is the neurohypophysis + what type of tissue is it made up of?

A

PPG

Neural tissue

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2
Q

What are the 2 PPG hormones?

A

Vasopressin

Oxytocin

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3
Q

How does the PPG appear on an MRI?

A

Bright spot

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4
Q

What does Vasopressin cause?

A

Water reabsorption

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5
Q

What does an anti-diuretic do?

A

Reduces urine production by increasing water reabsorption

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6
Q

How does vasopressin actually increase water reabsorption?

A

1) Vasopressin binds to V2 receptors on collecting duct
2) intracellular signalling cascade
3) aquaporins inserted into apical membrane

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7
Q

How is vasopressin release regulated?

A

Osmoreceptors in hypothalamus detect osmorality

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8
Q

Define osmolarity:

A

How many solutes there are (concentration)

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9
Q

How do osmoreceptors respond to increased plasma osmolality?

A

1) water leaves osmoreceptors
2) osmoreceptors shrink –> increases their firing rate
3) Vasopressin release increases

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10
Q

What is the normal response to a water deprivation test?

A

Increased plasma osmolality
Detected by osmoreceptors-increased VP secretion + thirst
Increased water reabsorption + reduced urination=plasma osmorality decreases

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11
Q

What 2 things can osmoreceptors cause?

A

Increased vasopressin secretion

Thirst

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12
Q

2 types of Diabetes insipidus:

A

Cranial-no vasopressin released

Neprogenic-vasopressin resistance

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13
Q

2 causes of diabetes insipidus:

A

Acquired-tumour/trauma/lithium

Congenital-mutation in V2R

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14
Q

5 symptoms of diabetes insipidus:

A 
Polyuria
Polydipsia
Hypo-osmolar
Dehydration
Sleep disturbance
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15
Q

So what do patients with diabetes insipidus do when plasma osmorality increases?

A

DRINK

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16
Q

What is psychogenic polydipsia?

A

Polyuria + polydipsia but no issue with the vasopressin system

17
Q

What is normal, diabetes insipidus and psychogenic polydipsia plasma osmolaltiy?

A

Diabetes insipidus=above normal (290)
Normal=280
Psychogenic polydipsia=below normal (270)-as you’re diluting yourself

18
Q

Compare the primary issue in diabetes insipidus and psychogenic polydipsia:

A

DI: urination causes thirst
PP: thirst causes urination

19
Q

Compare biochemical features of diabetes insipidus and psychogenic polydipsia:

A

DI:
Increased plasma osmolality-increased urea + hypernatremia
Hypo-osmolar urine

PP:
Decreased plasma osmolality-hyponatremia
Hypo-osmolar urine

20
Q

What 2 things are measured during a water deprivation test?

A

Urine volume

Urine + blood osmolality

21
Q

State the results of a water deprivation test for a normal person vs psychogenic polydipsia vs diabetes insipidus:

A

Normal=little concentrated urine produced
PP: normal result as issue is drinking which has now stopped
DI: no VP so can’t reabsorb water so still urinating

22
Q

How can you use a water deprivation test to identify whether the diabetes insipidus is cranial or nephrogenic?

A 
Give DDAVPA (vasopressin analogue)
Cranial-normal response
Nephrogenic-kidneys can't respond to VP so response doesn't change
23
Q

What must you remember to do during a water deprivation test?

A

Measure body weight every hour-if more than 3% lost=clinical dehydration

24
Q

Summarise the issue in SIADH vs DI vs PP:

A

SIADH=excess vasopressin
DI=lack of/resistance to vasopressin
PP=drinking alot

25
Q

Define SIADH (syndrome of inappropriate ADH):

A

Excess vasopressin

Vasopressin level is inappropriate for plasma osmolality

26
Q

5 causes of SIADH:

A

Tumour-PPG or ectopic

CNS/pulmonary disease/drugs/idiopathic

27
Q

Biochemical features of SIADH:

A

Hyponatremia

28
Q

Symptoms of SIADH:

A

Symptomless

When Na+ levels get v low=CNS affected

29
Q

Treatment of SIADH:

A

IMMEDIATELY REDUCE FLUID INTAKE
Surgery-remove tumour
V2 receptor antagonist-VAPTAINS

30
Q

How is diabetes insipidus treated?

A

Cranial-desmopressin (V2 R agonist)

  • nasally administered
  • must tell patients to decrease fluid intake

Nephrogenic=thiazide diuretics

ENDOCRINOLOGY (19 decks)

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