Disorders of Vasopressin

Question 1

What kind of neurones provide for the anterior and posterior pituitary?

Answer 1

Anterior- Parvocellular
Posterior-Magnocellular

Question 2

What does the posterior pituitary release?

Answer 2

Vasopressin (AVP)
Oxytocin

Question 3

What does vasopressin do?

Answer 3

Stimulates aquaporin 2 channels in renal collecting duct = water reabsorption into kidneys
Stimulates ACTH for renin-angtiotensin system
Vasoconstricts via V1

Question 4

What does the posterior pituitary look like on an MRI?

Answer 4

A bight white spot

Question 5

How is AVP stimulated for release and inhbition?
What is the action mechanism of these two molecule?

Answer 5

Osmoreceptors in hypothalamus are stimulated by the increase in plasma osmolality
Osmoreceptors lose h20 to plasma due to increase in osmolality = osmoreceptors shrink increasing osmoreceptor firing = AVP release
Also atrial stretch receptors detect pressure in atrium which stimulates vagus nerve to inhibit

Question 6

How does Diabetes Insipidus present?

Answer 6

Polydipsia
Nocturia
Polyuria
Hypernatraemia
NORMAL GLUCOSE

Question 7

What are the causes of Diabetes Insipidus?

Answer 7

Trauma
Tumor
Pituitary surgery
Metastasis to pituitary
Autoimmune
congenital- mutation to V2 receptor
Drugs

Question 8

How can we distinguish between psychogenic polydipsia and DI?

Answer 8

Water deprivation test
if weight drops over 3% then stop test
Urine osmolality will not increase in patients with DI but it will in patients with psychogenic polydipsia

Question 9

How do we distinguish between Cranial DI and Nephrogenic DI?

Answer 9

During water deprivation test administer desmopressin
In Cranial, urine osmolality will rise whereas in nephrogenic it will stay the same as in nephrogenic DI body cannot respond to AVP whereas cranial can’t produce it

Question 10

What is the treatment for DI?

Answer 10

Cranial- desmopressin
Nephrogenic- harder to treat

Question 11

What is SIADH?
How does it present?
How it can be treated?
What can cause this?

Answer 11

Syndrome of inappropriate diuretic hormone
Reduced urine output, Water retention,Hyponatraemia
Can use Vaptan to treat
Pituitary injury

Question 12

What 3 blood tests can you do if you suspect DI?

Answer 12

HbA1c to rule out mellitus
Sodium concentration for hypernatraemia
Plasma osmolality