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Endocrinology BM > Hypothalamo-neurohypophysis System 3 > Flashcards

Hypothalamo-neurohypophysis System 3 Flashcards

1
Q

What is vasopressin?

A

Anti-diuretic Hormone

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2
Q

What is the posterior hypophysis made of?

A

It is made of nerve axons and some other cell types

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3
Q

Describe the nerves used to communicate

A

The cell bodies are located in hypothalamus and the axons pass through the pituitary stalk into the neurohypophysis. Neural secretion occurs here and not in the median eminence

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4
Q

Describe the types of neurone cell body

A

Paraventricular nucleus - located closer to the 3rd ventricle

Suproptic nucleus - locted above the optic chiasma

Mainly magnocellular neurones (large) terminate in the neurohypophysis. However, some parvocellular (normal sized)ones do as well or in the median eminence for other parts of the brain. These are sourced from paraventricular nuclei

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5
Q

What is the final nucleus type?

A

Suprachiasmatic nucleus - some vasopressinergic neurones originate here

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6
Q

Explain what a herring body is?

A

Areas in a supraoptic neurone where neurosecretions can be stored on the way down to the neurohypophysis

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7
Q

Describe supraoptic neurones

A
  • leave hypothalmic suproptic nuclei
  • pass through the median eminence
  • have herring bodies
  • either oxytocinergic or vasopressinergic
  • magnocellular
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8
Q

Describe paraventricular neurones

A
  • originate in paraventricular nuclei
  • some parvocellular neurones pass to the median eminence of other parts of the brain
  • the magnocellular neurones pass down to the neurohypophysis and these are either vasopressinergic/oxytocinergic
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9
Q

Describe vasopressin synthesis

A

Pre-prohormone —-> Prohormone —-> hormone

  • Prohormone breaks down into Vasopressin (AVP), Neurophysin (large protein specific to vasopressin) and a glycopeptide (may be a prolactin releasing factor)
  • pre-provasopressin has a signal peptide that directs the protein to where it needs to go. Then, provasopressin travels down neurone axon where the break occurs.
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10
Q

Differences between Arginine Vasopressin (AVP) and Oxytocin

A
  • AVP has phenylalanine instead of isoleucine
  • AVP has Arginine instead of Leucine
  • AVP prohormone forms AVP, neurophysin and glycopeptide
  • Oxytocin prohormone forms oxytocin and neurophysin
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11
Q

Similarities between Arginine Vasopressin (AVP) and Oxytocin

A
  • both are nonapeptides
  • both synthesised as prohormones
  • prohormones both form target hormone and neurophysin
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12
Q

Vasopressin Actions

A

Primarily, stimulating H20 reabsorption in the collecing duct (antidiuretic)

  • vasoconstriction
  • cortiocotrophin release
  • CNS effects
  • acts as neurotransmitter
  • factor 8 synthesis
  • hepatic glycogenolysis
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13
Q

Vasopressin Receptor Types

A
  • V1a
  • V2
  • V1b (V3)
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14
Q

V1a Locations

A
  • arterial/arteriolar smooth muscle
  • Hepatocytes
  • CNS Neurones
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15
Q

V2 Locations

A
  • collecting duct cells

- associated with clotting factors (factor VIII and von willenbrandt factor)

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16
Q

V1b (V3) locations

A

Adenohypophysial cortiocotrophs

17
Q

V1 Mechanism

A
  • Gq protein linked receptor
  • Gq linked to Phospholipase C
  • Activation causes PLC to convert PIP3 to IP3 and DAG. This increases cytoplasmic Ca2+ and activates other like Protein Kinase C (PKC)
18
Q

V2 Mechanism

A
  • Gs protein linked receptor
  • Linked via a G protein to adenylate cyclase
    This converts ATP to cAMP. cAMP activates Protein Kinase A (PKA) which activates other mediators to cause cellular responses e.g. aquaporin recruitment
19
Q

Vasopressin Function in Principal Cells

A
  • Vasopressin binds to V2 receptors (on basolateral membrane), causing adenylate cyclase to convert ATP to cAMP. This activates PKA
  • PKA causes synthesis of Aquaporin 2 molecules. This type is vasopressin dependant
  • Aquaporins accumulate in aggraphores and , under influence of vasopressin, migrate to the apical membrane (facing inside of the collecting duct
  • Once inserted into membrane, water travels into cell and then from cell into the blood streat through AQP3 and AQP4
  • there needs to be an osmotic gradient to transport the water from the collecting duct, through the cell and into the bloodstream
20
Q

Vasopressin Control Stimuli

A

+ve =
Increased plasma osmolality
Decreased Arterial blood pressure (via baroreceptors)
Influences from higher areas e.g. stress

21
Q

Oxytocin Molecule type and target areas

A
  • Oxytocin is a contractor molecules

Main targets are uterus during childbirth and breast during lactation

22
Q

Describe Uterine Oxytocin Actions

A

Released in huge quantities during childbirth and it acts on the uterine smooth muscle to cause rhythmical contractions from the fundus to the cervix

  • It is suppressed by progesterone and enhanced by oestrogen so that sensitivity to oxytocin increases towards the end of pregnancy
23
Q

Describe Breast Oxytocin Actions

A
  • prolactin causes milk production but no contraction
  • the cells and ducts that cause milk synthesis are surrounded by contractil myoepithelilal cells that have myoepithelial receptors.
  • Baby suckling via tactile recepots causes oxytocin release that causes milk ejection
24
Q

Unwanted effects of Oxytocin

A
  • can cause vasoconstriction in cardiovascular system

- can cause more reabsorption in kidneys

25
Q

Clinical Uses of Oxytocin

A
  • Induction of labour at term (IV)
  • Prevention treatment of post-partum haemorrhage
  • Facilitation of milk let-down
  • Autism and increased social responsiveness
26
Q

What is too much ADH/Vasopressin release?

A

Syndrome of Inappropriate ADH (SIADH)

  • descreases plasma osmolality
  • urine is very concentrated
27
Q

Describe Diabetes Insipidus

A

Symptoms:

  • looks like diabetes but no sugar in the urine
  • polydipsia (drinking lots of water)
  • polyuria (producing lots of urine)
  • very dilute urine (hypo-osmolar)
28
Q

Diabetes Insipidus Types

A

Central:
- Does not produce Vasopressin. Caused by head trauma, tumours or autoimmune destruction of vasopressin producing neurones

Nephrogenic:
- Resistance to vasopressin in the kidneys. This is harder to treat but less severe. Some drugs reduce sensitivity in the kidneys

Endocrinology BM (12 decks)

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