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Endocrinology > 3 - Hypothalamo-neurohypohysial system > Flashcards

3 - Hypothalamo-neurohypohysial system Flashcards

1
Q

What is the posterior pituitary gland also known as?

A

Neurohypophysis

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2
Q

What 2 hormones are secreated from the posterior pituitary gland?

A

Vasopressin

Oxytocin

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3
Q

What does vasopressin do?

A

Vasoconstriction

It stimulates water reabsorption in the renal collecting ducts.
It has an antidiuretic effect.
ADH is vasopressin

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4
Q

What are the 5 other effects of vasopressin?

A
  • Vasoconstriction
  • Corticotrophin release (together with CRH)
  • CNS effects (acts as a neurotransmitter)
  • Synthesis of blood clotting factors (VIII and Von Willbrandt factor)
  • Hepatic glycolgenolysis
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5
Q

What are the 2 types of vasopressin receptors?

A

V1 and V2

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6
Q

How do V1 receptors work?

A

USED FOR VASOCONSTRICTION

  • Linked via G proteins to phospholipase C
  • which acts on membrane phospholipids
  • to produce IP3 (and diacyl glycerol) which increase cytoplasmic [Ca2+] and other intracellular mediators
  • which produce cellular response.
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7
Q

How do V2 receptors work?

A

USED FOR WATER REABSORPTION

  • Linked via G proteins to adenyl cyclase
  • ATP —> cyclic AMP
  • Activates protein kinase A —> activates other intracellular mediators
  • which produce cellular response - aquaporins (AQP2)
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8
Q

What are the 2 types of hypothalamic nuclei that send messages to the posterior pituitary?

A

Paraventricular nuclei

Supra-optic nuclei

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9
Q

Draw a diagram showing the hypothalamo-neurohypophysial axis.

A

Draw picture

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10
Q

What are magnocellular neurones?

Which cell bodies do they come from?

A

Neurones that travel from the cell bodies of…
-Paraventricular nuclei
-AND supra-optic nuclei
Directly to the posterior pituitary.

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11
Q

What are parvocellular neurones?

Which cell bodies do they come from?

A

Neurones that come from…
Paraventricular nuclei
That go to the median eminence (or other parts of the brain).

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12
Q

Where are herring bodies found and what is their function?

A

Along supra-optic neurones.

Function is to store oxytocin and vasopressin on the way.

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13
Q

How do supra-optic neurones secrete hormones?

3 steps

A
  1. Hormones are stored in the hypothalamic supra-optic nuclei.
  2. They pass down the magnocellular neurone through the median eminence.
  3. Neurone terminates in neurohypophysis.
    They are EITHER vasopressinergic OR oxytocinergic.
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14
Q

How do messages from paraventricular nuclei travel?

How do they travel down the paraventricular neurones?

A
  1. The majority of neurones are magnocellular, these terminate in the neurohypophysis.
  2. Some neurones are parvocellular. These terminate in either the median eminence (VP only) or other parts of the brain.
  3. Paraventricular neurones are EITHER vasopressinergic OR oxytocinergic.
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15
Q

Describe the structures of vasopressin and oxytocin.

What is the difference

A 
BOTH:
NONAPEPTIDES (9 amino acids)
Ring structure of 6
3 attached to ring.
Disulphide bond between 2 adjacent cysteine's in the ring.

Differences:
Arginine Vasopressin (AVP) has Phe and Arg
Oxytocin has Ile and Leu
(All other amino acids are the same)

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16
Q

How is vasopressin synthesised?

A
  1. Pre-provasopressin is made in the nucleus. Its has a signal peptide
  2. Provasopressin moves all the way down the neurone with neurophysin attached (important stability properties in axon) and glycopeptide.
  3. Neurophysin and glycopeptide are cleaved at the end of the neurone. Vasopressin is produced.

NOTE ** exactly the same for oxytocin but neurophysin differs and there is no gylcopeptide.

17
Q

What are the 2 types of V1 receptors and what do they do?

A

V1a

  • Found in arteriole smooth muscle for vasoconstriction
  • Found in hepatocytes for glycogenolysis
  • Found in CNS neurones for behaviour

V1b
- Found in corticotrophs for ACTH production.

18
Q

What do V2 receptors do?

A
  • Collecting duct walls for water reabsorption

- Other effects elsewhere

19
Q

What is the main physiological action of vasopressin?

clue - What is an antidiuretic effect?

A

In the renal collecting duct.
Stimulates water reabsorption.
It therefore has an antidiuretic effect.

20
Q

Draw a flowchart of the physiological action of vasopressin (antidiuretic hormone) in the kidney.

A

Picture

21
Q

What are the physiological effects of oxytocin?

A

MAJOR- (therapeutic advantage)
Uterus
Mammary gland - myoepithelial cells

MINOR - (unwanted effects)
Cardiovascular system - constriction of umbilical arteries and veins
Kidneys

Additional
CNS - behavioural (tend and befriend)

22
Q

How does oxytocin lead to milk ejection?

What cells are involved?

A

Oxytocin

  • Breast during lactation
  • Myoepithelial cells
  • Contration
  • Milk ejection
23
Q

How does oxytocin lead to delivery of a baby?

What cells are involved?

A

Oxytocin

  • Uterus at parturition
  • Myometrial cells
  • Contraction, increased prostanoid production
  • Breakdown of collagen & dilation of cervix
  • Delivery of baby
24
Q

What surpasses and enhances the uterine actions of oxytocin?

A

Enhanced by oestrogen
Surpassed by progesterone

(marked late in pregnancy as more oxytocin receptors nearer the end)

25
Q

What are the major clinical uses of oxytocin?

A
  • Induction of labour
  • Prevent treatment of postpartum haemorrhage (vasoconstriction - surpasses bleeding)
  • Facilitation of milk let down
  • Autism (studies)
26
Q

When would plasma osmolality increase?

A

Dehydration

27
Q

How is vasopressin controlled?

In terms of water

A
  • Plasma osmolality increases
  • Recognised by osmoreceptors (fluid leaves them as blood passes by, cell body shrinks)
  • Vasopressin released
  • Increased water reabsorption in nephron
  • Decreased plasma osmolality
28
Q

How is vasopressin controlled?

In terms of constriction

A
  • Blood pressure falls
  • Baroreceptors recognise this (firing rate goes down), they have an inhibitory effect
  • REDUCED INHIBITION
  • Vasopressin released
  • Increased vasoconstriction
  • Increased blood pressure
29
Q

What is the neuroendocrine reflex arc for oxytocin?

A 
Stimulus: suckling
Receptors around nipple
Via neural afferent limb
To Hypothalamus
To Neurohypophysis
Via Endocrine efferent limb - Oxytocin
=Milk ejection
30
Q

What could happen if you lack oxytocin or vasopressin?

A

Oxytocin
Parturition and milk ejection replaced with other things

Vasopressin
Diabetes insipidus
(Too much vasopressin = syndrome of inappropriate ADH)

31
Q

What are the 2 types of diabetes insidious?

A

Cranial (central)
Lack of ADH production

Nephrogenic
Resistance in the kidneys to ADH

32
Q

Causes of cranial?

A

Autoimmunity
Head trauma
Tumour

33
Q

Causes of nephrogenic?

A

Drug induced

34
Q

Signs of diabetes insidious?

A

Polydipsia - thirst
Polyuria - need to wee
Dilute urine

Endocrinology (18 decks)

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