Endo 3 - Neurohypophysial Disorders Flashcards
Name the two main nuclei which neurones of the neurohypophysis have their cell bodies?
- Paraventricular
- Supraoptic
What two hormones are produced by the neurohypophysis?
- Oxytocin
- Vasopressin
What does oxytocin stimulate?
- Constriction of myometrium at parturition
- milk ejection
Is a lack of Oxytocin that important?
No
What is the principal action of vasopressin?
acts of V2 receptors in the renal cortical and medullary collecting ducts
stimulates the synthesis and assembly of aquaporin 2
this then increases water reasborption and so has an antidiuretic effect
Is vasopressin a diuretic or antidiuretic?
Antidiuretic - increases water REabsorption
What are the other actions of vasopressin?
- vasoconstriction
- corticotrophin release
- vWf factor and Factor 8 release
Lack of vasopressin leads to?
Diabetes Insipidus
What are the two forms of diabetes insipidus?
- Cranial (Central)
- Nephrogenic (Peripheral)
What is the difference between cranial and nephrogenic diabetes insipidus?
cranial = lack of circulating vasopressin nephrogenic = kidneys resistant to vasopressin
What are the causes of cranial diabetes insipidus?
- injury to neurohypophysis system
- surgery
- tumours
What are the causes of nephrogenic diabetes insipidus?
- drugs e.g. DMCT or lithium
- familial
What are the signs and symptoms of diabetes insipidus?
- polyuria
- polydipsia
- nocturia
- hypo-osmolar urine
- dehydration if thirst not met
Explain the cycle in diabetes insipidus in terms of polyuria and polydipsia?
- lack of vasopressin
- increased urine excretion of hypotonic urine
- plasma osmolarity increases
- reduction in ECFV
- polydipsia
- expansion of ECFV
- so increased urine
What is the normal range for plasma osmolarity?
270-290mOsm
State another cause of polydipsia which is not diabetes?
psychogenic polydipsia
What is psychogenic polydipsia?
central disturbance that increases the drive to drink
Describe the cycle in psychogenic polydipsia?
- increased drinking due to central disturbance e.g. doctor telling them to drink loads of water
- expansion of ECFV
- reduced plasma osmolarity
- less vasopressin secreted via posterior pituitary
- large volumes of hypotonic urine excreted
- reduction of ECFV
- thirst triggered
What test is used to diagnose and differentiate between Diabetes insipidus and psychogenic polydipsia?
Fluid Deprivation test
Explain how a fluid deprivation test works?
- normal person will be able to concentrate urine as vasopressin working, so less and less urine produced
- pyschogenic - will be able to concentrate urine as vasopressin working so less and less urine produced
- cranial and nephrogenic will NOT be able to concentrate urine as vasopressin not working - will produce excessive amounts of hypo-osmolar urine
What test is used to differentiate between cranial and nephrogenic diabetes insipidus?
Desmopressin Administration
How does the desmopressin administration test differentiate between the two forms of diabetes?
- cranial = will be able to concentrate urine as desmopressin will work on the V2 receptors on kidneys to allow for aquaporin 2 to be made
- nephrogenic - receptors resistant so will not be able to concentrate urine
What is the treatment of cranial diabetes insipidus?
- vasopresin or argipressin
- v1 stimulation causes vasoconstriction so give desmopressin
What is the treatment of Nephrogenic DI?
thiazides which inhibit Na+/Cl- transport so reabsorption of water
What is SIADH?
Syndrome of Inappropriate ADH - where the plasma vasopressin concentration is inappropriate for the existing plasma osmolality
What hormone is in excess in SIADH?
Vasopressin
What are the signs of SIADH?
decreased urine volume
increase urine osmolality
What does increased vasopressin do?
increases water reabsorption
What would SIADH do to plasma osmolality?
decreases plasma osmolarity
What would SIADH do to Sodium levels?
reduced sodium concentration so Hyponatraemia
What is the main consequence of SIADH?
Hyponatraemia
When Na+ levels fall below 120mMol you get?
- generalised weakness
- poor mental function
- nausea
When Na+ levels fall below 110mM you get?
confusion, coma or deth
What are the causes of SIADH?
- Tumours
- neurohypophysial malfunction
- endocrine disease
- drugs
How is SIADH treated?
- fluid restriction
- and then treat the cause e.g surgery
What is the name given to exogenous vasopressin?
Argipressin
Where are V1 receptors found?
- vascular smooth muscle
- anterior pituitary
- liver
- platelets
Where are V2 receptors found?
Kidneys and endothelial cells
Name the pharmacological actions of argipressin?
- natriuresis
- pressor action
- contraction of vascular smooth muscle
- increased ACTH secretion
Name a v2 selective vasopressin agonist?
Desmopressin
State some clinical uses of desmopressin?
treatment of diabetes insipidus
Name a v1 vasopressin agonist and its use?
Terlipressin - oesophageal varices
What are vaptans?
used to treat hyponatraemia in SIADH
