Hypothalamo-Neurohypophysial System COPY

Question 1

What is a hypothalamic nucleus?

Answer 1

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

Question 2

State the two main hypothalamic nuclei.

Answer 2

Supraoptic (above optic chiasm) Paraventricular (next to 3rd ventricle)

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: Terminate in median eminence or the neurones pass to other parts of the brain. Originate in hypothalamus ( supraoptic or paraventricular nuceli)

Magnocellular: Neurones pass through median eminence and terminate in neurophysis

Question 6

Describe supraoptic neurones.

Answer 6

ALL MAGNOCELLULAR 1. Leave hypothalammic nuclei 2. Pass through median eminence 3. Terminate in neurohypophysis

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(An oligopeptide formed from nine amino acids)
• 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

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

Answer 14

1. AVP binds to V2 on collecting duct cells 2. Activates adenylate cyclase —> increase in cAMP —> activate PKA. 3. Activated PKA increases synthesis of AQUAPORIN 2 AQP2 —> assembled into aggraphores —> aggraphores migrate to apical membrane 4. Aggraporins fuse with membrane so water can move into cell and out of cell down concentration gradient via AQP3 + AQP4

Question 15

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

Answer 15

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

Question 16

What are the two main actions of oxytocin?

Answer 16

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 17

Explain these two actions of oxytocin.

Answer 17

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 18

What is a stimulus for oxytocin release when breastfeeding?

Answer 18

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 19

What’s difference between central and nephrogenic diabetes insipidus?

Answer 19

central diabetes insipidus - NO VASOPRESSIN produced nephrogenic - collecting duct cells develop resistance to vasopressin

Question 20

What is the suprachiasmatic nucleus ?

Answer 20

some vasopressingergic neurones originate here ( where the biological shock resides )

Question 21

How does V1 receptor work?

Answer 21

• Linked to PLC (phospholipase) via Gq protein linked
• PLC acts on membrane membrane phospholipids to produce IP3 + DAG
• This increase cytoplasmic Ca+2

Question 22

How does V2 receptors work?

Answer 22

• Linked to adenyl cyclase via Gs proteins - Increase cAMP which activates PKA - Activates other intracellular mediators which hen produces aquaporins AQP2.

Question 23

How is vasopresssin synthesised?

Answer 23

1. Preprovasopressin cleaved so signal peptide(moves PPV into GA) is removed. 2. Provasopressin is broken down by enzymes in GA: Vasopressin , Neurophysin and Glycopeptide.

Question 24

How is oxytocin synthesised ?

Answer 24

same as vasopressin sequence except nuerophysin differs and Glycopeptide is absent

Question 25

What’s the role of `neurophysin?

Answer 25

Prevents early break down of vasopressin Guides it to the end of the neurone

Question 26

What’s the physiological role of vasopressin on its different receptors?

Answer 26

V1a: vasoconstriction of arterial /arteriolar smooth muscle, glycogenolysis in hepatocytes and behavioural effects. V1b: Corticotrophs ACTH production( works with CRH) V2: Collecting duct cells ( water reabsorption)

Question 27

What’s the difference between central and nephrogenic diabetes insipidus?

Answer 27

Central _ compete lack of vasopressin Nephrogenic - insensitvity to vasopressin , vasopressin still stimulates some response

Question 28

What are the 3 main symptoms of diabetes insipidus?

Answer 28

hypo-osomolar: very dilute urine Polyuria: large volumes of urine Polydipsia: increased thirst

Question 29

What’s the structural difference between oxytocin and vasopressin?

Answer 29

Differ by 2 amino acids

Question 30

What are Herring Bodies?

Answer 30

storage units along paraventricular neurones where vasopressin and oxytocin and are stored.

Question 31

Describe Paraventriculalr neurones

Answer 31

PARVOCELLULAR AND MAGNOCELLULAR Originate in paraventricular nuclei Parvocellular: pass to other parts of the brain + some teminate in median eminence Magnocelluar: majority, terminate in neurohypophysis

Question 32

What is SIADH

Answer 32

-too much ADH produced - decreases plasma osmolality - increases urine concentration

Question 33

Give 3 differences between vasopressin and oxytocin

Answer 33

• structure similar , 2 amino acids are different (position 3 and 8, isoleucine and leucine in oxytocin are replaced by phenylanine and arginine in vasopressin, respectively) - both hormones are nonapeptides - both initially prohormones and cleaved from hormone, neurophysin ( and glycopeptide in VP)