Neurohypophysial Disorders Flashcards
(54 cards)
Supraoptic nucleus?
- Magnocellular Neurones
- Terminate in neurohypophysis
- Release neurosecretions into neurohypophysis
- Herring Bodies - sites of storage of the NS/hormone
2 hormones of the neurohypophysis?
Vasopressin (ADH)
Oxytocin
Principal effect of vasopressin?
Anti-diuretic
i.e. increases water reabsorption from renal cortical & collecting duct via V2 receptors
Diuresis?
Increase in urine production
SO
anti-diuretic - decreases urine production
Vasopressin action?
- VP binds to V2 receptors (Gs receptors)
- AQP2 created which more to apical membrane in aggraphores
- AQP2 insert into apical membrane = water reabsorption
What regulates vasopressin release?
Osmoreceptors in the Organum Vasculosum
How do these osmoreceptors work?
Project axons into the hypothalamic PVN and SON
When do osmoreceptors fire the most?
Increased blood plasma osmolality
Send more signals as they shrink to release VP
2 types of diabetes insipidus?
Cranial (central)
Nephrogenic
Definition of the 2 types of diabetes insipidus?
Cranial - ABSENCE/LACK of circulating VP
Nephrogenic - End-organ (kidneys) RESISTANCE to VP
2 subtypes of cranial DI - which is more rare?
Acquired (more common)
Congenital (rare)
Aetiology of acquired cranial DI?
Damage to Neurohypophysial system x Traumatic brain injury x Pituitary surgery x Pituitary tumours, craniopharyngioma x Metastasis to the pituitary gland x Granulomatous infiltration of median eminence e.g. TB (pituitary stalk issue!)
2 subtypes of nephrogenic DI - which is more rare?
Cogenital (rare)
Acquired
Aetiology of nephrogenic diabetes?
Cogenital - mutation in V2 receptor/AQP2
Acquired - drugs e.g. lithium (used in depression medication)
Signs/symptoms of DI?
x Polyuria
x Hypo-osmolar urine (very dilute)
x Polydipsia (increased thirst & drinking)
x Dehydration - if fluid intake not maintained could lead to death
x Possible sleep disruption & fatigue
What keeps patients with DI from dying?
Access to water - keeps them just about hydrated
If remove access to water = dehydration & death
What is psychogenic polydipsia?
Polydipsia & Polyuria as excess fluid intake
BUT
unlike DI, ability to secrete VP is preserved
When can you get psychogenic polydipsia?
x Psychiatric patients - anti-cholinergic effects of mediaition (‘dry-mouth)
x Can also be seen in patients told to ‘drink plenty’ by healthcare progessionals
Difference in plasma osmolality between DI and PP patients? Why?
DI - HIGH plasma osmolality
PP - LOW plasma osmolality
Even though both drink LOTS of water, difference lies in VP
How can you diagnose if a patient has DI or PP?
Water deprivation test
cannula inserted to take regular readings
What can be seen in the water deprivation test when the patient is deprived of fluid?
Normal - urine osmolality increases
PP - urine osmolality increases
DI - urine osmolality does NOT increase (as cannot reabsorb water!)
*pay attention its URINE osmolality NOT plasma!
What is a limitation of the water deprivation test and how can it be overcome?
Cannot differentiate between central & nephrogenic DI if just deprive fluid
Need to administer DDAVP
DDAVP?
Synthetic AVP - analogue of VP
Why does a PP patient have a slightly lower urine osmolality than a normal patient?
The polydipsia has ‘washed away’ the [graidnet] in the medulla slightly
