disorders of vasopressin Flashcards
what are the two posterior pituitary hormones
avp and oxytocin
what is the name given to the neurones which connect hypothalamus with posterior pituitary
hypothalamic magnocellular neurones
how do we describe positioning of the hypothalamic nuclei?
supraoptic and paraventricular
what is oxytocin responsible for
milk ejection
what is avp/adh responsible for?
stimulates water reabsorption of water in urine
acts on v2 receptor in kidney
also vasoconstrictor via v1 receptor
amd stimulates acth from anterior pituitary
how does vasopressin concentrate urine?
avp binds to v2 receptor on collecting duct causes signalling cascade
results in aquaporins 2 on tubular membrane
reabsorption of water
what are the stimuli for vasopressin release?
- osmotic - rise in plasma osmolality(conc) by osmoreceptors
- non osmotic - decrease in atrial pressure sensed by atrial stretch receptors
what groups of cells detect plasma osmolality
organum vasculosum and
subfornical organ
- sit around 3rd ventricle
how do organum vasculosum and subfornical organ work?
no bbb - so neurons can respond to changes in systemic circulation
highly vascularised
neurons project into supraoptic nucleus
how do osmoreceptors regulate vasopressin
via osmosis water moves out osmoreceptor to area of high plasma osmolality
osmoreceptor shrinks
increased osmo receptor firing
avp rlease from hypothalmic neurons
how does non osmotic stimulation of vasopressin release work
atrial stretch receptors in right atrium detect pressure
usually inhibit vp release via vagal afferents
if low pressure - less inhibition of vp - more vp release
why do we need more vp following haemorrhage/reduction in circulating volume
vp release results in increased water reabsorption in kidneys via v2 - to increase circulating vol
vasoconstriction via v1 receptors
what happens when slightly dehydrated
plasma osmolality increases stimulation of osmoreceptors thirst increase avp release less urine vol - high urine osmolality causes red in plasma osmolality
what are some symptoms of diabetes insipidus
polyuria
nocturia
thirst - often extreme
polydipsia
what is cranial DI
cranial/central
-problem with hypothalamus/pituitary
vasopressin insufficiency
what is nephrogenic DI
kidney is unable to respond to vasopressin
- vasopressin resistance
what are some causes of cranial di
traumatic brain injury pituitary surgery pituitary tumours metastasis granulatomous infiltration of pituitary stalk - tb, sarcodosis autoimmune congenital -rare
causes of nephrogenic di
much less common
congenital - mutation in v2 receptor. aq2
acquired - e.g lithium drug
what is the presentation of DI
very dilute large vol of urine increased plasma osmolality becoming dehydrated hypernatreamia normal glucose
if you dont let patients drink water what can happen
dehydration and death
what is psychogenic polydipsia
no problem with vasopressin
patients drinks all the time therefore passes large vol of dilute urine
in psychogenic polydipsia is avp low or high
low because plasma osmolaltiy is low
how to distinguish between DI and psychogenic polydipsia
water deprivation test over time measure urine vol, urine osmolality and plasma osmolality weigh regularly stop test if >3 % body weight loss
how can we distinguish between cranial and nephrogenic DI
give ddAVP (v2 receptor agonists) which acts like vasopressin in cranial - will see response - increase in urine osmolality nephrogenic - no change
