hypothalamo-neurohypoysial system

Question 1

describe the hypothalamo-neurohypopysial system

Answer 1

hypothalamic neuron project to posterior pituitary

blood stream

Question 2

describe the neurons in the hypothalamo-neurohypopysial system

Answer 2

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

Question 3

describe the surpraoptic neurons

Answer 3

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

Question 4

describe the paraventricular neurons

Answer 4

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

Question 5

compare vasopressin and oxytocin

Answer 5

only difference is 2 AA

quite a lot of functional overlap

Question 6

what is the signal peptide responsible for in the neurohypophysial hormone synthesis, storage and release

Answer 6

direct pre-provasopressin to Golgi - cleaved and lost

Question 7

describe the neurohypophysial hormone synthesis, storage and release

Answer 7

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

Question 8

vasopressin receptors involved in signalling

Answer 8

V1 - increased intracellular calcium

V2 - increased cAMP which activates PKA

Question 9

vasopressin receptors location

Answer 9

V1a - arterial/arteriolar smooth muscle - vasoconstriction
V1b - corticotrophs - work with CRH ant pit
V2 - collecting duct for water reabsorption

Question 10

physiological action of vasopressin

Answer 10

renel collecting duct
stimulate water reabsorption
antidiuretic effect

Question 11

describe the antidiuretic effect of vasopressin

Answer 11

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

Question 12

describe the physiological actions of oxytocin

Answer 12

stim contraction uterus
mammary gland
vasopressin like - cardiovascular system and kidney
additional physiological - CNS

Question 13

action of oxytocin on uterus

Answer 13

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

Question 14

action of oxytocin in breast

Answer 14

during lactation
act on myoepithelial cells - contraction
promote milk ejection

Question 15

action of oxytocin tend and befriend

Answer 15

care for children, social support
behavioural response to stress
inhibit stress response

Question 16

clinical uses of oxytocin

Answer 16

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

Question 17

describe the control of vasopressin

Answer 17

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

Question 18

control of oxytocin

Answer 18

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

Question 19

what happens with a lack of oxytocin

Answer 19

parturition and milk ejection effects induced/replaced by other means

Question 20

what happens with a lack of vasopressin

Answer 20

diabetes insipidus - urine not sweet
central/cranial - head trauma/autoimmune - can’t produce VP
nephrogenic - kidney doesn’t respond
polydipsia, polyurea, urine very dilute

Question 21

what happens with excess vasopressin

Answer 21

syndrome of inappropriate ADH
eg tumour
absorb too much water

Question 22

describe the relationship between vasopressin and ACTH

Answer 22

both VP and corticotrophin releasing hormone needed to make ACTH
without VP CRH is less effective

Question 23

other actions of oxytocin

Answer 23

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)

Question 24

where vasopressin and oxytocin produced

Answer 24

hypothalamus

Question 25

is vasopressin a neurosecretory molecule

Answer 25

yes