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ENDOCRINOLOGY phase 1b > 1b Disorders of Vasopressin > Flashcards

1b Disorders of Vasopressin Flashcards

1
Q

What is the physiological action of vasopressin?

A

Stimulation of water reabsorption into the renal collecting duct = concentrates the urine

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2
Q

Which receptor does AVP work through?

A

V2 receptor in the kidney

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3
Q

How does AVP work as a vasoconstrictor?

A

Via the V1 receptor

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4
Q

Describe how AVP concentrates the urine?

A
  • AVP binds to V2 receptor on basolateral membrane
  • This triggers intracellular cascade resulting in the movement of aquaporin-2 molecules onto the apical membrane
  • this allows the movement of water from the urine into the blood, therefore concentrating it
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5
Q

What is the bright spot on an MRI of the pituitary?

A

Posterior Pituitary

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6
Q

What are the two stimuli for vasopressin release?

A

Osmotic and Non-osmotic

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7
Q

Describe how the osmotic stimuli for vasopressin release works?

A

rise in plasma osmolality detected by osmoreceptors as they shrink when H2O released caused by high extracellular sodium.

there is increased osmoreceptor firing causing AVP release from hypothalamic neurons

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8
Q

Describe how the non-osmotic stimuli for vasopressin works?

A

decrease in atrial pressure sensed by atrial stretch receptors

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9
Q

Where do the neurones of the organosum vasculosum and subfornical organ project to?

A

the supraoptic nuclei

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10
Q

Describe how osmoreceptors regulate vasopressin?

A
  1. Increase in extracellular sodium
  2. Therefore movement of water out the osmoreceptor by diffusion
  3. Osmoreceptor shrinks
  4. This increases osmoreceptor firing
  5. More osmoreceptor firing leads to more AVP release from the hypothalamic neurones
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11
Q

How doe AVP trigger an increase in blood volume following haemorrhage?

A

Increased water absorption in the kidney via V2 receptor, therefore increasing blood volume and hence pressure as well

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12
Q

Which receptors does AVP initiate vasoconstriction through?

A

V1 receptors

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13
Q

What is the physiological response to water deprivation?

A
  1. Increased plasma concentration
  2. This stimulates the osmoreceptors to fire, leading to AVP release
  3. This stimulates water reabsorption from the renal collecting ducts
  4. Urine volume decreases, and the concentration of the urine increases as more water is kept
  5. This reduces the plasma concentration
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14
Q

What is the most common cause of polyuria, nocturia and polydipsia?

A

diabetes mellitus

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15
Q

What are the common symptoms in AVP deficiency and reisstance?

A

Polyuria
Polydipsia
Nocturia
Thirst

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16
Q

What is the difference between AVP deficiency and resistance?

A

Deficiency is due to a problem with the hypthalamus and posterior pituitary whereas resistance is a problem with kidney not being able to respond

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17
Q

What is the typical presentation of diabetes insipidus

A

Polyuria, nocturia, thirst and polydipsia

18
Q

What happens to the urine of a patient with diabetes insipidus?

A

Very dilute urine (hypoosmolar) and large volumes

19
Q

What happens to the plasma of a patient with AVP deficiency/resistance?

A

plasma concentration increases and becomes hyper
osmolar, as the patient becomes dehydrated as they are continually urinating large volumes of dilute urine

20
Q

what happens to the sodium concentration in the plasma of a patient with diabetes insipidus?

A

increases

21
Q

Why do patients with AVP deficiency/resistance have polydipsia?

A

The AVP problem results in impaired concentration of urine in the renal collecting duct

Therefore large volumes of dilute urine are produced

Increases in plasma osmolarity and sodium

Stimulation of osmoreceptors, leading to polydipsia

22
Q

How can AVP deficiency/resistance lead to death?

A

When the patient has polydipsia but no access to water -this
leads to dehydration and death

23
Q

What are causes of AVP defieciency?

A

Traumatic brain injury
Pituitary surgery or tumour
Metastasis to pituitary gland
Granulomatous infiltration of pituitary stalk
AUTOIMMUNE
Congenital is rare

24
Q

What are the causes of AVP resistance?

A

Less common than deficiency
CONGENITAL- rare e.g. mutation in gene encoding V2 receptor

ACQUIRED
drugs e.g. lithium

25
Q

What are the presentations with AVP deficiency/resistance?

A

Dilute large urine volume
Hyperosmolar plasma
Hypernatraemia
Normal glucose

26
Q

What is psychogenic polydipsia?

A

When the patient drinks too much water, and so passes large volumes of water - no problem with AVP

27
Q

How do symptoms arise from psychogenic polydipsia?

A

Increased drinking leads to a fall in plasma osmolarity and less AVP being secreted by the posterior pituitary so more urine is secreted

28
Q

How do you distinguish between AVP deficiency/resistance and psychogenic polydipsia?

A

Water deprivation test - No access to anything to drink - measuring urine volumes, urine and plasma conc

29
Q

What is the normal response to hours doing the water deprivation test?

A

The urine osmolarity increases as AVP helps to concentrate the urine

30
Q

During the water retention test, what is the difference between psychogenic polydipsia and AVP deficiency/resistance?

A

Urine osmolarity of the patient with psychogenic polydipsia will increase, however patient with AVP deficiency/resistance will not have any change (as they have no ADH and therefore cannot concentrate the urine)

31
Q

Why is it important to measure the weight of the patient regularly?

A

Stop the test if they lose more than 3% of their total body weight

32
Q

How to distinguish between AVP deficiency and resistance?

A

give desmopressin or ddAVP

33
Q

What is the effect in AVP deficiency/resistance giving them ddAVP?

A

AVP deficiency - the urine osmolarity will increase as the synthetic AVP works like AVP

AVP resistance - no increase in urine osmolarity with ddAVP as kidneys cannot respond

34
Q

What are the different presentations of desmopressin?

A

tablet or intranasal

35
Q

What are treatments for AVP deficiency/resistance?

A

for deficiency desmopressin but no treatment for resistance

36
Q

What is SIADH
?

A

Syndrome of Inappropriate Anti-Diuretic Hormone

37
Q

What are the symptoms of SAIDH?

A

reduced urine output
increased water retention
High urine osmolality
Low plasma osmolality

38
Q

How is SIADH managed?

A

Restrict fluids
Use a vasopressin antagonist (Vaptan) which binds to the V2 receptors in the kidney so AVP doesnt work

39
Q

What happens to sodium levels in SIADH?

A

low sodium = hypoatrenaemia

40
Q

Causes of SIADH?

A

CNS
Head injury, stroke, tumour

Pulmonary disease
Pneumonia, bronchiectasis

Malignancy
Lung cancer (small cell)

Drug-related
Carbamazepine, Serotonin Reuptake Inhibitors (SSSRIs)

Idiopathic

ENDOCRINOLOGY phase 1b (12 decks)

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