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Endocrinology > The hypothalamo-neurohypophysial axis > Flashcards

The hypothalamo-neurohypophysial axis Flashcards

1
Q

Name 2 hormones released from the neurohypophysis

A

Oxytocin

Vasopressin

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2
Q

Where do the neurones innervating the pituitary gland originate?

A

Supraoptic and paraventricular nuclei in hypothalamus

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3
Q

Magnocellular neurones

A

Long

Majority of neurones from hypothalamus to pituitary

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4
Q

Parvocellular neurones

A

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

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5
Q

Supraoptic neurones have Herring bodies along their axon

A

To store vasopressin/ oxytocin vesicles

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6
Q

Describe supraoptic neurone transmission

A

Leave hypothalamic supraoptic nuclei
Pass through median eminence
Terminate in neurohypophysis

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7
Q

What are the 2 types of supraoptic neurones?

A

Vasopressinergic

Oxytocinergic

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8
Q

Where do paraventricular neurones originate?

A

paraventricular nuclei

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9
Q

Some paraventricular neurones are parvocellular

A

Pass to other parts of brain

If VP, terminate in median eminence

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10
Q

Majority of paraventricular neurones are

A

Mangocellular

Terminate in neurohypophysis

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11
Q

2 types of paraventricular neurones

A

Vasopressinergic

Oxytocinergic

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12
Q

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

A

Yes

Vasopressin neurones terminate in median eminence where CRH is also released

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13
Q

How many amino acids in oxytocin and vasopressin?

A

9

= Nonapeptides

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14
Q

How different are vasopressin and oxytocin?

A

Only 2 different AAs
Very similar
Similar effects

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15
Q

Neurohypophysial Hormone Synthesis

A

Initially synthesized as prohormones

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

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16
Q

How many Vasopressin signalling pathways are there?

A

2

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17
Q

What does activation of V1 receptors lead to?

A

Increased intracellular calcium

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18
Q

What does activation of V2 receptors lead to?

A

Increased cAMP

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19
Q

V1 receptor mechanism

A

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

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20
Q

V2 receptor mechanism

A 
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)
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21
Q

Where are V1a receptors located?

A

Arterial/ arteriolar smooth muscle
Hepatocytes
CNS Neurones

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22
Q

What do V1a receptors allow in arterial smooth muscle?

A

Vasoconstriction

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23
Q

What do V1a receptors allow in hepatocytes?

A

Glycogenolysis

24
Q

What do V1a receptors allow in CNS neurones?

A

Behavioural/ other effects

25
Q

Where are V1b receptors located and what do they allow?

A

Corticotrophs

Increase ACTH production

26
Q

Where are V2 receptors located and what do they allow?

A

Collecting duct cells

Water reabsorption

27
Q

What factors do V2 receptors on endothelial cells relate to?

A

Factor VIII and von Willbrandt factor

28
Q

What is vasopressin also known as?

A

Antidiuretic hormone (ADH)

29
Q

Where is vasopressins principle physiological action

A

Renal collecting ducts

Stimulates water reabsorption

30
Q

What are the cellular responses caused by vasopressin?

A 
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
31
Q

Aquaporin 2 abbreviation

A

APQ 2

32
Q

Aggraphores

A

Vesicles housing APQ 2

33
Q

Major physiological action of oxytocin

A 
Uterus
Mammary gland (myoepithelial cells)
34
Q

Minor physiological action of oxytocin

A

Unwanted, on:
Cardiovascular system
Kidney

35
Q

Additional physiological action of oxytocin

A

CNS

36
Q

What does oxytocin cause in the uterus?

A

Rhythmic contraction towards cervix
Increased local prostanoid production
Dilation of cervix

37
Q

How are uterine actions of oxytocin regulated?

A

Suppressed by progesterone

Enhanced by oestrogen

38
Q

Uterus sensitivity to oxytocin increases throughout pregnancy

A

Causes powerful contraction

Promotes delivery

39
Q

What does oxytocin cause in the mammary gland

A

Contraction of myoepithelial cells

Milk ejection

40
Q

How does oxytocin effect the cardiovascular system?

A

Pharmacologically
Transient vasodilation
Tachycardia
Constriction of umbilical arteries and veins

41
Q

How does oxytocin effect the renal system?

A

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

42
Q

How does oxytocin effect the CNS?

A

Physiologically
Maternal behaviour
Social recognition
“Tend and befriend”

43
Q

What are the major clinical uses of oxytocin?

A

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

44
Q

How does vasopressin regulate increased plasma osmolarity?

A

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

45
Q

How does vasopressin regulate decreased blood pressure?

A

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

46
Q

How is baroreceptor firing rate linked to blood pressure?

A

High BP = High firing rate

47
Q

When is regulation of BP by vasopressin seen?

A

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

48
Q

Neuroendocrine reflex arc controlling release of oxytocin

A

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

49
Q

Lack of oxytocin

A

Parturition and milk ejection effects induced/ replaced by other means

50
Q

Lack of vasopressin

A

Diabetes insipidus

51
Q

Excess vasopressin

A

Syndrome of inappropriate ADH

52
Q

Diabetes insipidus taste of urine

A

Not sweet, insipid

53
Q

2 forms of diabetes insipidus

A

Central (Cranial)

Nephrogenic

54
Q

What is central diabetes insipidus caused by?

A

Absence/ lack of circulating vasopressin

55
Q

What is nephrogenic diabetes insipidus caused by?

A

End-organ (kidneys) resistance to vasopressin

56
Q

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

A

Central (cranial)

57
Q

Symptoms of diabetes insipidus

A

Polydipsia
Polyuria
Urine very dilute (hypo-osmolar)

Endocrinology (12 decks)

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