Hypothalamo-Neurohypophysial System

Question 1

What is a hypothalamic nucleus?

Answer 1

A collection of cell bodies that send their axons to a partic

Question 2

State the two main hypothalamic nuclei.

Answer 2

Supraoptic Paraventricular

Question 3

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

Answer 3

Suprachiasmatic

Question 4

What two molecules are produced by the neurohypophysis?

Answer 4

Vasopressin Oxytocin

Question 5

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

Answer 5

Parvocellular: oAverage sizedoTerminate in the median eminence and other parts of the brain oONLY from paraventricular nucleusMagnocellular: oLARGEoTerminate in neurohypophysisoNuclei in both paraventricular AND supraoptic nuclei

Question 6

Describe supraoptic neurones.

Answer 6

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.

Question 7

What is a key feature of magnocellular neurones?

Answer 7

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

Question 8

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

Answer 8

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

Question 9

Describe the synthesis of Oxytocin.

Answer 9

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

Question 10

State the main differences between Arginine Vasopressin and Oxytocin.

Answer 10

AVP has PHENYLALANINE instead of ISOLEUCINE AVP has ARGININE instead of LEUCINE

Question 11

State some similarities between Arginine Vasopressin and Oxytocin.

Answer 11

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

Question 12

What is the main effect of vasopressin?

Answer 12

Increased water reabsorption in the kidney collecting ducts

Question 13

What are some other effects of vasopressin?

Answer 13

Vasoconstriction Synthesis of blood clotting factors Corticotrophin release Hepatic glycogenolysis

Question 14

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

Answer 14

V1a
MOST IMPORTANT
VasculatureoBrainV1boInvolved in control of corticotrophin release
Adenohypophysial cells (corticotrophs)
V2
Involved in  antidiuretic effect
Kidney collecting duct cells

Question 15

Describe how V1 and V2 receptors work.

Answer 15

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

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

What are the two main actions of oxytocin?

Answer 18

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

Question 19

Explain these two actions of oxytocin.

Answer 19

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

Question 20

What is a stimulus for oxytocin release when breastfeeding?

Answer 20

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

Question 21

State two conditions associated with vasopressin.

Answer 21

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