disorders of vasopressin

Question 1

what are the two posterior pituitary hormones

Answer 1

avp and oxytocin

Question 2

what is the name given to the neurones which connect hypothalamus with posterior pituitary

Answer 2

hypothalamic magnocellular neurones

Question 3

how do we describe positioning of the hypothalamic nuclei?

Answer 3

supraoptic and paraventricular

Question 4

what is oxytocin responsible for

Answer 4

milk ejection

Question 5

what is avp/adh responsible for?

Answer 5

stimulates water reabsorption of water in urine
acts on v2 receptor in kidney
also vasoconstrictor via v1 receptor
amd stimulates acth from anterior pituitary

Question 6

how does vasopressin concentrate urine?

Answer 6

avp binds to v2 receptor on collecting duct causes signalling cascade
results in aquaporins 2 on tubular membrane
reabsorption of water

Question 7

what are the stimuli for vasopressin release?

Answer 7

1. osmotic - rise in plasma osmolality(conc) by osmoreceptors
2. non osmotic - decrease in atrial pressure sensed by atrial stretch receptors

Question 8

what groups of cells detect plasma osmolality

Answer 8

organum vasculosum and
subfornical organ
- sit around 3rd ventricle

Question 9

how do organum vasculosum and subfornical organ work?

Answer 9

no bbb - so neurons can respond to changes in systemic circulation
highly vascularised
neurons project into supraoptic nucleus

Question 10

how do osmoreceptors regulate vasopressin

Answer 10

via osmosis water moves out osmoreceptor to area of high plasma osmolality
osmoreceptor shrinks
increased osmo receptor firing
avp rlease from hypothalmic neurons

Question 11

how does non osmotic stimulation of vasopressin release work

Answer 11

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

Question 12

why do we need more vp following haemorrhage/reduction in circulating volume

Answer 12

vp release results in increased water reabsorption in kidneys via v2 - to increase circulating vol
vasoconstriction via v1 receptors

Question 13

what happens when slightly dehydrated

Answer 13

plasma osmolality increases 
stimulation of osmoreceptors
thirst
increase avp release
less urine vol - high urine osmolality
causes red in plasma osmolality

Question 14

what are some symptoms of diabetes insipidus

Answer 14

polyuria
nocturia
thirst - often extreme
polydipsia

Question 15

what is cranial DI

Answer 15

cranial/central
-problem with hypothalamus/pituitary
vasopressin insufficiency

Question 16

what is nephrogenic DI

Answer 16

kidney is unable to respond to vasopressin

- vasopressin resistance

Question 17

what are some causes of cranial di

Answer 17

traumatic brain injury
pituitary surgery
pituitary tumours
metastasis
granulatomous infiltration of pituitary stalk - tb, sarcodosis
autoimmune
congenital  -rare

Question 18

causes of nephrogenic di

Answer 18

much less common
congenital - mutation in v2 receptor. aq2
acquired - e.g lithium drug

Question 19

what is the presentation of DI

Answer 19

very dilute large vol of urine
increased plasma osmolality
becoming dehydrated
hypernatreamia
normal glucose

Question 20

if you dont let patients drink water what can happen

Answer 20

dehydration and death

Question 21

what is psychogenic polydipsia

Answer 21

no problem with vasopressin

patients drinks all the time therefore passes large vol of dilute urine

Question 22

in psychogenic polydipsia is avp low or high

Answer 22

low because plasma osmolaltiy is low

Question 23

how to distinguish between DI and psychogenic polydipsia

Answer 23

water deprivation test
over time measure urine vol, 
urine osmolality and plasma osmolality 
weigh regularly 
stop test if >3 % body weight loss

Question 24

how can we distinguish between cranial and nephrogenic DI

Answer 24

give ddAVP (v2 receptor agonists) which acts like vasopressin 
in cranial - will see response - increase in urine osmolality
nephrogenic - no change

Question 25

normal range of plasma osmolality

Answer 25

280
higher - DI
lower - PP

Question 26

treatment of cranial DI

Answer 26

desmopressin

tablet/nasal spray

Question 27

treatment of nephrogenic DI

Answer 27

thiazide diueretics

- unclear mechanism

Question 28

what is syndrome of inapprop adh

Answer 28

too much vasopressin
reduced urine output
low plasma osmolality
hyponatraemia

Question 29

causes of siadh

Answer 29

cns - head injury/ trauma
pulmonary disease
malignancy
drug related e.g carbamazepine, SSRIs
idiopathic

Question 30

management of siadh

Answer 30

fluid restriction
vaptan - vasopressin antagonist - acts on v2 receptors in kidney
Very expensive