Hypothalamo-Neurohypophysial System Flashcards Preview

LCRS - Endocrinology - Laz > Hypothalamo-Neurohypophysial System > Flashcards

Flashcards in Hypothalamo-Neurohypophysial System Deck (21)
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1
Q

What is a hypothalamic nucleus?

A

A collection of cell bodies that send their axons to a particular place.

2
Q

State the two main hypothalamic nuclei.

A

Supraoptic

Paraventricular

3
Q

What is the other hypothalamic nucleus where the biological clock resides?

A

Suprachiasmatic

4
Q

What two molecules are produced by the neurohypophysis?

A

Vasopressin

Oxytocin

5
Q

What are the two types of neurone and how do they differ?

A
Parvocellular:
Average sized
Terminate in the median eminence and other parts of the brain 
ONLY from paraventricular nucleus
Magnocellular:
LARGE
Terminate in neurohypophysis
Nuclei in both paraventricular AND supraoptic nuclei
6
Q

Describe supraoptic neurones.

A

They are ALL MAGNOCELLULAR and terminate in the neurohypophysis
They are either oxytocinergic or vasopressinergic. The neurosecretions are hormones because they release directly into the circulation.

7
Q

What is a key feature of magnocellular neurones?

A

Herring Bodies - areas where neurosecretions can be stored on their way down to the neurohypophysis

8
Q

Describe the synthesis of Vasopressin. What other molecules are produced when the prohormone is cleaved?

A
Vasopressin is synthesised from Pre-provasopressin
Cleaved to produce:
Arginine vasopressin
Glycopeptide
Neurophysin
9
Q

Describe the synthesis of Oxytocin.

A
Synthesised from pre-prooxytocin
Cleaved to produce:
Oxytocin
Neurophysin (different to that produced from pre-provasopressin)
Does NOT produced glycopeptide
10
Q

State the main differences between Arginine Vasopressin and Oxytocin.

A

AVP has PHENYLALANINE instead of ISOLEUCINE

AVP has ARGININE instead of LEUCINE

11
Q

State some similarities between Arginine Vasopressin and Oxytocin.

A

They are both nonapeptides
They are both synthesised from prohormones
Prohormones are cleaved to produce neurophysin

12
Q

What is the main effect of vasopressin?

A

Increased water reabsorption in the kidney collecting ducts

13
Q

What are some other effects of vasopressin?

A

Vasoconstriction
Synthesis of blood clotting factors
Corticotrophin release
Hepatic glycogenolysis

14
Q

What are the different types of vasopressin receptor and which cells express these receptors?

A
V1a
MOST IMPORTANT
Vasculature
Brain
V1b
Involved in control of corticotrophin release
Adenohypophysial cells (corticotrophs)
V2
Involved in  antidiuretic effect
Kidney collecting duct cells
15
Q

Describe how V1 and V2 receptors work.

A
V1 = Gq protein linked receptor (PLC; PIP2 ---> IP3 + DAG; increase in [Ca2+])
V2 = Gs protein linked receptor (adenylate cyclase; increase cAMP; PKA)
16
Q

Explain how vasopressin acts on cells in the kidney collecting duct.

A

AVP binds to V2 on collecting duct cells
Activates adenylate cyclase —> increase in cAMP —-> activate PKA
—> increased synthesis of AQUAPORIN 2
AQP2 —> assembled into aggraphores —> aggraphores migrate to apical membrane —> water moves in —> water moves out of cell down concentration gradient via AQP3 + AQP4

17
Q

What are the two main functions of vasopressin and how is vasopressin release stimulated?

A
Water Reabsorption 
Vasoconstriction
Stimuli:
Increase in plasma osmolality
Fall in blood pressure
18
Q

What are the two main actions of oxytocin?

A

Oxytocin is a CONTRACTOR molecule. Main actions:
Contraction of the myometrial cells during CHILDBIRTH
MILK EJECTION - contraction of myoepithelial cells in the breast during lactation

19
Q

Explain these two actions of oxytocin.

A

Oxytocin is release in massive amounts during delivery
It acts on the myometrial cells to cause contraction
Prolactin stimulates milk PRODUCTION but NOT milk ejection
Oxytocin stimulates the contractile myoepithelial cells around the ducts and alveoli to cause MILK EJECTION

20
Q

What is a stimulus for oxytocin release when breastfeeding?

A

Stimulation of tactile receptors around the nipple passes message via a neuroendocrine reflex arc to the neurohypophysis and stimulates oxytocinergic neurons, resulting in oxytocin release.
NOTE: this is a different neuroendocrine arc to the one that stimulates release of prolactin from the adenohypophysis

21
Q

State two conditions associated with vasopressin.

A

SIADH - too much ADH produced, decreases plasma osmolality, increases urine concentration
Diabetes Insipidus - characterised by polydypsia and polyuria, in central diabetes insipidus - NO VASOPRESSIN produced