hypothalamo-neurohypoysial system Flashcards
describe the hypothalamo-neurohypopysial system
hypothalamic neuron project to posterior pituitary
blood stream
describe the neurons in the hypothalamo-neurohypopysial system
cell bodies are in the supraoptic paraventricular nuclei
mainly magnocellular (large) neurons
terminate in neurohypophysis
some parvocellular (small) neurons from parvoventricular nuclei - terminate in median eminence or other parts of the brain - behaviour, either vasopressinergic or oxytocinergic
describe the surpraoptic neurons
leave hapothalamic supraoptic nuclei pass through median eminence terminate in neurohypophysis herring bodies along axon - sites of storage of vasopressin and oxytocin - vesicles pass down to end of neuron wither casopressinergic or oxytocinergic
describe the paraventricular neurons
originate in paraventricular nuclei
some parvocellular neurons pass to other ports of the brain, some terminate in median eminence - affect ant pit
majority of neurons magnocellular pass into post pit
compare vasopressin and oxytocin
only difference is 2 AA
quite a lot of functional overlap
what is the signal peptide responsible for in the neurohypophysial hormone synthesis, storage and release
direct pre-provasopressin to Golgi - cleaved and lost
describe the neurohypophysial hormone synthesis, storage and release
signal peptide to Golgi
in cell body of neuron - vesicles contain provasopressin and enzymes to cleave it
as vesicles move along axon enzyme works
neurophysin - guides to end of neuron
glycopeptide - function not known (only in vasopressin, not in oxytocin, also neurophysin differs slightly
vasopressin receptors involved in signalling
V1 - increased intracellular calcium
V2 - increased cAMP which activates PKA
vasopressin receptors location
V1a - arterial/arteriolar smooth muscle - vasoconstriction
V1b - corticotrophs - work with CRH ant pit
V2 - collecting duct for water reabsorption
physiological action of vasopressin
renel collecting duct
stimulate water reabsorption
antidiuretic effect
describe the antidiuretic effect of vasopressin
VP from blood bind to V2 - basolateral membrane
stimulate AC
elevate cAMP
activate PKA
synthesis of aquaporin 2
migration of aggraphores to apical membrane, bind to apical membrane (tubule lumen - heading to bladder) which is impermeable to water
AQP3 and 4 bind to apical membrane to move water into the plasma - less sensitive to vasopressin - don’t need to be that responsive
describe the physiological actions of oxytocin
stim contraction uterus
mammary gland
vasopressin like - cardiovascular system and kidney
additional physiological - CNS
action of oxytocin on uterus
uterus at parturition
myometrial cells (muscle)
contraction
delivery of baby
rhythmic contraction fundus – cervix
increased local prostanoid production
dilation of cervix
suppressed by progesterone and enhanced by oestrogen
most sensitive in late stages of pregnancy
action of oxytocin in breast
during lactation
act on myoepithelial cells - contraction
promote milk ejection
action of oxytocin tend and befriend
care for children, social support
behavioural response to stress
inhibit stress response
clinical uses of oxytocin
induction of labour - controlled iv infusion
prevention of post-partum haemorrhage - slow iv infusion, local poresser action in uterus suppresses bleeding
facilitation of milk let down - internasal spray
autism social responsiveness - experimental, internasal spray
describe the control of vasopressin
increased plasma osmolality (conc molecules in blood eg Na)
osmoreceptors recognise increase - shrink as water leaves cells
directly stimulate vasopressin secretion
physiological - narrow boundaries
decreased arterial Bp
reduce baroreceptor firing rate
vasopressin inhibited less
Bp has to be dropped significantly
control of oxytocin
receptors around nipple activate afferent nerve stimulate oxytocin production in post pit
secretion into blood efferent limb and to peripheral tissue
milk ejection - contraction of myoepithial cells
what happens with a lack of oxytocin
parturition and milk ejection effects induced/replaced by other means
what happens with a lack of vasopressin
diabetes insipidus - urine not sweet
central/cranial - head trauma/autoimmune - can’t produce VP
nephrogenic - kidney doesn’t respond
polydipsia, polyurea, urine very dilute
what happens with excess vasopressin
syndrome of inappropriate ADH
eg tumour
absorb too much water
describe the relationship between vasopressin and ACTH
both VP and corticotrophin releasing hormone needed to make ACTH
without VP CRH is less effective
other actions of oxytocin
cardiovascular - transient vasodilation and tachycardia, constriction of umbilical arteries and veins (pharmacological)
Renal - anti-diuresis and secondary hyponatraemia - vasopressin like (pharmacological)
CNS - social behaviour and social recognition (physiological)
where vasopressin and oxytocin produced
hypothalamus
is vasopressin a neurosecretory molecule
yes
