ADH

Question 1

Where is ADH synthesised?

Answer 1

synthesized in the supraoptic nuclei of the hypothalamus

Question 2

How is ADH release controlled and regulated?

Answer 2

Osmoreceptorsin the hypothalamus regulate ADH release by detecting and responding to changes in plasma osmotic pressure:

If osmolarity increases, i.e. following a fall in plasma volume, *
* stimulates osmoreceptor cells to contract.
* This sends afferent signals from the hypothalamus to the posterior pituitary to increase the release of ADH.
*
- If osmolarity is decreased, i.e. following an increase in total body volume,
* osmoreceptors will expand.
* This sends afferent signals to the posterior pituitary to decrease the release of ADH.

Question 3

What is the effect of ADH on blood vessels?

Answer 3

Vasoconstriction - increases total peripheral resistance

Question 4

What is the effect of ADH on the kidneys?

Answer 4

1. ADH binds to V2 receptors in the collecting tubule
2. Increased transcription and insertion of water channels (Aquaporin-2) into theapical membraneof collecting tubule
3. Aquaporins allow water to move down their osmotic gradient and out of the nephron,
4. increasing the amount of water re-absorbed from the filtrate back into the bloodstream.
5. Resulting in, less volume of more concentrated urine

Question 5

What is the definition of Diabetes insipidus?

Answer 5

the passage of vast volumes of dilute urine.

In some cases, as much as 20 litres of urine can be produced in 24 hours, leading to rapid dehydration and potentially death.

Question 6

What is the definition of Neurogenic diabetes insipidus?

Answer 6

occurs due to decreased circulating levels of ADH due to impaired production/release within the central nervous system

Question 7

What are the causes of neurogenic diabetes insipidus?

Answer 7

1. Mutations in vasopressin gene
2. Malignancy: pituitary adenomas, craniopharyngiomas/metastases
3. Trauma
4. Infection: Meningitis
5. Vascular: Sheehan’s Syndrome
6. Sarcoidosis (formation of granulomas in the pituitary gland)
7. Haemochromatosis (deposition of iron in the hypothalamus and pituitary gland)

Question 8

What is the management of Neurogenic Diabetes Insipidus?

Answer 8

replacement therapy with vasopressin analogues , such asdesmopressin.

Question 9

What is the definition of nephrogenic diabetes insipidus?

Answer 9

occurs when ADH cannot bind to their receptors in the kidney.

Question 10

What are the causes of nephrogenic diabetes insipidus?

Answer 10

1. Mutations in ADH receptor gene or aquaporin-2 gene
2. Metabolic: hypercalcaemia, hyperglycaemia, hypokalaemia
3. Drugs
4. Chronic renal disease
5. Amyloidosis

Question 11

What is the pathophysiology of SIADH?

Answer 11

Continual ADH production occurs independent of serum osmolality

Question 12

What are the lab values seen in SIADH?

Answer 12

1. abnormally low serum sodium levels
2. highly osmolar urine
3. high urinary sodium levels.

Question 13

What are the causes of SIADH?

Answer 13

1. brain injury
2. malignancy
3. drugs
4. infection
5. hypothyroidism.

Question 14

What is the treatment of SIADH?

Answer 14

identifying the underlying cause and fluid restriction.