The hypothalamo-neurohypophysial axis

Question 1

Name 2 hormones released from the neurohypophysis

Answer 1

Oxytocin

Vasopressin

Question 2

Where do the neurones innervating the pituitary gland originate?

Answer 2

Supraoptic and paraventricular nuclei in hypothalamus

Question 3

Magnocellular neurones

Answer 3

Long

Majority of neurones from hypothalamus to pituitary

Question 4

Parvocellular neurones

Answer 4

Short
Originate from paraventricular nuclei
Terminate in median eminence/ other areas

Question 5

Supraoptic neurones have Herring bodies along their axon

Answer 5

To store vasopressin/ oxytocin vesicles

Question 6

Describe supraoptic neurone transmission

Answer 6

Leave hypothalamic supraoptic nuclei
Pass through median eminence
Terminate in neurohypophysis

Question 7

What are the 2 types of supraoptic neurones?

Answer 7

Vasopressinergic

Oxytocinergic

Question 8

Where do paraventricular neurones originate?

Answer 8

paraventricular nuclei

Question 9

Some paraventricular neurones are parvocellular

Answer 9

Pass to other parts of brain

If VP, terminate in median eminence

Question 10

Majority of paraventricular neurones are

Answer 10

Mangocellular

Terminate in neurohypophysis

Question 11

2 types of paraventricular neurones

Answer 11

Vasopressinergic

Oxytocinergic

Question 12

Vasopressin and CRH are both secreted from paraventricular neurones.
Are they secreted at the same anatomical location?

Answer 12

Yes

Vasopressin neurones terminate in median eminence where CRH is also released

Question 13

How many amino acids in oxytocin and vasopressin?

Answer 13

9

= Nonapeptides

Question 14

How different are vasopressin and oxytocin?

Answer 14

Only 2 different AAs
Very similar
Similar effects

Question 15

Neurohypophysial Hormone Synthesis

Answer 15

Initially synthesized as prohormones

Cleaved to form hormones & their neurophysin proteins (released together)

Question 16

How many Vasopressin signalling pathways are there?

Answer 16

2

Question 17

What does activation of V1 receptors lead to?

Answer 17

Increased intracellular calcium

Question 18

What does activation of V2 receptors lead to?

Answer 18

Increased cAMP

Question 19

V1 receptor mechanism

Answer 19

Linked via G proteins to phospholipase C which acts on membrane phospholipids to produce IP3
Increase cytoplasmic calcium and other intracellular mediators

Question 20

V2 receptor mechanism

Answer 20

Linked via G proteins to adenyl cyclase
Which acts on ATP to form cyclic AMP
Which activates protein kinase A
Which activates intracellular mediators
Which produce cellular response (aquaporins)

Question 21

Where are V1a receptors located?

Answer 21

Arterial/ arteriolar smooth muscle
Hepatocytes
CNS Neurones

Question 22

What do V1a receptors allow in arterial smooth muscle?

Answer 22

Vasoconstriction

Question 23

What do V1a receptors allow in hepatocytes?

Answer 23

Glycogenolysis

Question 24

What do V1a receptors allow in CNS neurones?

Answer 24

Behavioural/ other effects

Question 25

Where are V1b receptors located and what do they allow?

Answer 25

Corticotrophs | Increase ACTH production

Question 26

Where are V2 receptors located and what do they allow?

Answer 26

Collecting duct cells | Water reabsorption

Question 27

What factors do V2 receptors on endothelial cells relate to?

Answer 27

Factor VIII and von Willbrandt factor

Question 28

What is vasopressin also known as?

Answer 28

Antidiuretic hormone (ADH)

Question 29

Where is vasopressins principle physiological action

Answer 29

Renal collecting ducts | Stimulates water reabsorption

Question 30

What are the cellular responses caused by vasopressin?

Answer 30

``` Synthesis of AQP 2 molecules Move aggraphores towards apical membrane AQP 2 inserted into apical membrane Apical membrane impermeable to water until AQP 2 inserted Allows water reabsorption ```

Question 31

Aquaporin 2 abbreviation

Answer 31

APQ 2

Question 32

Aggraphores

Answer 32

Vesicles housing APQ 2

Question 33

Major physiological action of oxytocin

Answer 33

``` Uterus Mammary gland (myoepithelial cells) ```

Question 34

Minor physiological action of oxytocin

Answer 34

Unwanted, on: Cardiovascular system Kidney

Question 35

Additional physiological action of oxytocin

Answer 35

CNS

Question 36

What does oxytocin cause in the uterus?

Answer 36

Rhythmic contraction towards cervix Increased local prostanoid production Dilation of cervix

Question 37

How are uterine actions of oxytocin regulated?

Answer 37

Suppressed by progesterone | Enhanced by oestrogen

Question 38

Uterus sensitivity to oxytocin increases throughout pregnancy

Answer 38

Causes powerful contraction | Promotes delivery

Question 39

What does oxytocin cause in the mammary gland

Answer 39

Contraction of myoepithelial cells | Milk ejection

Question 40

How does oxytocin effect the cardiovascular system?

Answer 40

Pharmacologically Transient vasodilation Tachycardia Constriction of umbilical arteries and veins

Question 41

How does oxytocin effect the renal system?

Answer 41

Pharmacologically Anti-diuresis Secondary hyponatraemia (low sodium- vasopressin like)

Question 42

How does oxytocin effect the CNS?

Answer 42

Physiologically Maternal behaviour Social recognition "Tend and befriend"

Question 43

What are the major clinical uses of oxytocin?

Answer 43

Induction of labour at term (IV infusion) Prevention treatment of post-partum haemorrhage (IV) = local pressor action in uterus suppresses bleeding Facilitation of milk let-down Autism: social responsiveness

Question 44

How does vasopressin regulate increased plasma osmolarity?

Answer 44

Recognised by osmoreceptors in hypothalamus Water wants to leave cell to enter blood as sodium levels in blood rising Cells shrink Stimulates neurones that cause vasopressin secretion Vasopressin causes water reabsorption in kidney Stimulates other neurones to stimulate thirst

Question 45

How does vasopressin regulate decreased blood pressure?

Answer 45

Change detected by baroreceptors Baroreceptor neurone inhibits Vasopressin neurone Low BP= Low baroreceptor firing rate= Less inhibition of vasopressin Increased secretion of vasopressin Vasopressin acts as vasoconstrictor Increases BP

Question 46

How is baroreceptor firing rate linked to blood pressure?

Answer 46

High BP = High firing rate

Question 47

When is regulation of BP by vasopressin seen?

Answer 47

Extreme situations, as doesn't have major effect on BP: Haemorrhage Dehydration

Question 48

Neuroendocrine reflex arc controlling release of oxytocin

Answer 48

Suckling activates afferent nerves Stimulates Oxytocin producing neurone in hypothalamus Activates endocrine limb causing release of oxytocin Efferent secretion of oxytocin into blood

Question 49

Lack of oxytocin

Answer 49

Parturition and milk ejection effects induced/ replaced by other means

Question 50

Lack of vasopressin

Answer 50

Diabetes insipidus

Question 51

Excess vasopressin

Answer 51

Syndrome of inappropriate ADH

Question 52

Diabetes insipidus taste of urine

Answer 52

Not sweet, insipid

Question 53

2 forms of diabetes insipidus

Answer 53

Central (Cranial) | Nephrogenic

Question 54

What is central diabetes insipidus caused by?

Answer 54

Absence/ lack of circulating vasopressin

Question 55

What is nephrogenic diabetes insipidus caused by?

Answer 55

End-organ (kidneys) resistance to vasopressin

Question 56

Which form of diabetes insipidus is more prevalent and more serious?

Answer 56

Central (cranial)

Question 57

Symptoms of diabetes insipidus

Answer 57

Polydipsia Polyuria Urine very dilute (hypo-osmolar)