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BRS YR2 > Disorders of Vasopressin > Flashcards

Disorders of Vasopressin Flashcards

1
Q

What neurones are present in the hypothalamus and the posterior pituitary gland?

A

Hypothalamic magnocellular neurons

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2
Q

What do hypothalamic magnocellular neurons contain?

A

AVP or oxytocin

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3
Q

Describe hypothalamic magnocellular neurons?

A

Long, originate in supraoptic and paraventricular neurons

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4
Q

What is the main physiological action of vasopression/ADH?

A

Stimulation of water reabsorption in the renal collecting duct (concentrating urine)

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5
Q

Where does vasopressin act?

A

the V2 receptor in the kidney

also the V1 receptor

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6
Q

What is the secondary action of vasopressin?

A
  • vasoconstriction via the V1 receptor
  • stimulates the release of ACTH from the anterior pituitary gland
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7
Q

How does vasopressin concentrate urine?

A
  • binds to the V2 receptor on the basolateral membrane
  • encourages the movement of water from the apical membrane to the basolateral membrane (into the blood) via aquaporin-2 and aquaporin-3
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8
Q

How does the posterior pituitary gland look in MRIs?

A

shows as a bright spot, not visualised in all healthy individuals

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9
Q

What is the stimuli for AVP release?

A
  • Response to dehydration
  • Increase in plasma osmolality sensed by osmoreceptors
  • Osmoreceptors are special sensory receptors in the hypothalamus
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10
Q

How do osmoreceptors regulate vasopressin?

A
  1. increase in extracellular Na+
  2. water moves out of osmoreceptor
  3. osmoreceptor shrinks
  4. increased osmoreceptor firing
  5. AVP release from the hypothalamic neurons
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11
Q

What is the physiological response to water deprivation?

A
  • increased plasma osmolarity
  • stimulation of osmoreceptors
  • thirst
  • release of AVP
  • increased water reabsorption from renal collecting ducts
  • reduced urine volume, increased urine osmolarity
  • reduction in plasma osmolarity
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12
Q

What are the symptoms of vasopressin insufficency?

A
  • polyuria
  • nocturia
  • thirst (often extreme)
  • polydipsia
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13
Q

What is the difference between diabetes mellitus and vasopressin insufficency?

A

In diabetes mellitus, the symptoms are caused by osmotic diuresis.
In vasopressin insufficency, the symptoms are caused due to a problem with AVP

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14
Q

What are the two different types of VI?

A
  • vasopressin deficiecny (cranial diabetes insipidus)
  • vasopressin resistance (nephrogenic diabetes insipidus)
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15
Q

Describe vasopressin deficiency

A

A problem with the hypothalamus and/or the posterior pituitary - unable to make AVP

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16
Q

Describe vasopressin resistance

A
  • Normal AVP production (normal hypothalamus and posterior pituitary)
  • Abnormal kidney collecting duct (unable to respond)
17
Q

What are the possible causes of vasopressin deficiency?

A

Acquired (more common)
* Traumatic brain injury
* Pituitary surgery
* Pituitary tumours
* Metastasis to the pituitary gland eg breast
* Granulomatous infiltration of pituitary stalk eg TB, sarcoidosis
* Autoimmune
Congenital

18
Q

What are the possible causes of vasopressin resistance?

A

Much less common than vasopressin deficiency
Congenital
- rare (e.g. mutation in gene encoding V2 receptor, aquaporin 2 type water channel)
Acquired
- Drugs (e.g. lithium)

19
Q

What is the presentation of vasopressin insufficency

A 
Urine
- very dilute (hypo-osmolar)
- large volumes
Plasma
- increased concentration (hyper-osmolar)
- increases sodium (hypernatraemia)
- NORMAL GLUCOSE
20
Q

Can vasopressin insuffieceny cause death?

A

Only if there is not a constant access to water, as it will lead to dehydration and death.

21
Q

What is psychogenic polydipsia?

A

Problem caused by overconsumption of water leading to large volumes of dilute urine

22
Q

How does psychogenic polydipsia present?

A 
same as diabetes insipidus
- nocturia
- polyuria
- polydipsia
(BUT no problem with AVP)
23
Q

What causes the symptoms of psychogenic polydipsia?

A
  • increased drinking (polydipsia)
  • plasma osmolarity falls
  • less AVP is secreted by the posterior pituitary
  • large volumes of dilute (hypotonic) urine
  • plasma osmolarity returns to normal
24
Q

How to distinguish between vasopressin insufficency and psychogenic polydipsia?

A

A water deprivation test

25
Q

What is involved in a water deprivation test?

A 
no access to any drink 
over time, measure:
- urine volumes
- urine concentration
- plasma concentration
weigh regularly, if lose more than 3% of body weight (significant dehydration) stop.
26
Q

How to differentiate between vasopressin insufficency and psychogenic polydipsia based on the results of the water deprivation test?

A

Psychogenic polydipsia:
* urine osmolarity increases are time progresses, but not to the same extent as normal
Diabetes Insipidus:
* no change in urine osmolarity over time (as problem with AVP)

27
Q

How to distinguish between vasopressin deficiecny and vasopressin resistance during a water deprivation test?

A
  • give ddAVP (similar to AVP)
    if AVP-D:
    will respond to ddAVP, urine will concentrate as collecting duct is fine
    if AVP-R:
    no response, and no change to urine concentration as collecting duct is resistant to AVP.
28
Q

What is the approximate plasma osmolarity with vasopressin insufficency?

A

> 290 mOsm/kg

29
Q

What is the approximate plasma osmolarity with psychogenic polydipsia?

A

<270 mOsm/kg

30
Q

What is the treatment of vasopressin deficiency?

A
  • replace AVP with desmopressin
  • selective for V2 receptor (V1 would be unhelpful)
  • available either in tablets or intranasal
31
Q

Hospital neglect and diabetes insipidus?

A
  • desmopressin nasal spray is often disregarded upon admission
  • fluid restriction which may sometimes be necessary is dangerous and can cause death in patients with VI
32
Q

What is the treatment for vasopressin resistance?

A

Difficult to treat successfully but luckily very rare

33
Q

What is the Syndrome of Inappropriate Anti-Diuretic Hormone (SIADH)?

A

The presence of too much AVP

34
Q

How does SIADH present?

A
  • reduced urine output
  • water retention
  • high urine osmolarity
  • low plasma osmolarity
  • dilutional hyponatraemia
35
Q

What are the causes of SIADH?

A 
CNS
- head injury
- stroke
- tumour
Pulmonary disease
- pneumonia
- bronchiectasis
Malignancy
- small cell lung cancer
Drug related
- Carbamazepine
- SSRIs
Idiopathic
36
Q

What is the management plan for SIADH?

A
  • fluid restriction
  • can use vasopressin antagonist (vaptan) that binds to V2 receptors in the kidney
    (£££)
37
Q

What was vasopressin insufficency formerly known as?

A

Diabetes insipidus

38
Q

What is desmopressin?

A

Modified, non-biodegradable version of vasopressin to counteract its short half life

BRS YR2 (67 decks)

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