Lecture 3 - Hypothalamo-hypophysial axis: Neurohypophysis

Question 1

What are the key features of hypothalamo-neurohypophysial system (HNHS)?

Answer 1

Suprachiasmatic nucleus - makes vasopressin

Paraventricular nucleus - axons go to NH and to other parts of CNS

Supraoptic nucleus - above optic chiasm

Median eminence

Hypothalamus

Question 2

Where are the cell bodies present (of HNHS)?

Answer 2

In supraoptic and paraventricular nuclei

Question 3

Where do the magnocellular neurones terminate and what main feature do they have?

Answer 3

In neurohypophysis and have a long axon

Question 4

Where do parvoventricular neurones originate?

Answer 4

Paraventricular nuclei

Question 5

Where do parvoventricular neurones terminate?

Answer 5

In median eminence or other parts of brain

Question 6

What do supraoptic neurones synthesise?

Answer 6

EITHER vasopressin OR oxytocin - so they’re either VPergic or oxytocinergic

Question 7

Describe supraoptic nuclei’s way of reaching the neurohypophysis:

Answer 7

They leave hypothalamic supraoptic nuceli Pass through the median eminence Terminate in neurohypophysis Has Herring bodies along axon - store hormones and can release it into surrounding medium

Question 8

What are the types of paraventricular neurones?

Answer 8

Parvocellular Magnocellular

Question 9

Where do parvocellular neurones terminate?

Answer 9

Some to other parts of the brain Some are VP neurones and terminate in median eminence

Question 10

How is vasopressin synthesised?

Answer 10

Initially synthesised as prohormones: Pre-provasopressin > Pro-vasopressin > Vasopressin + Neurophysin + glycopeptide

Question 11

How is oxytocin synthesised?

Answer 11

Pre-prooxytocin > pro-oxytocin > oxytocin + Neurophysin

Question 12

Difference between oxytocin and vasopressin synthesis

Answer 12

The neurophysin differs by two amino acid: AVP has an arginine in 2nd position and Phe in square bit OT has a Leucine in 2nd position and Ile in square bit

Question 13

Give examples and definition of a nonapeptide

Answer 13

A nonapeptide is an oligopeptide containing 9 a.a. residues Examples: Oxytocin and VP

Question 14

Name the principal action of VP

Answer 14

Stimulates water reabsorption in the renal collecting ducts - results in ANTIDIURETIC effect Na+ reabsorption in other parts of kidneys

Question 15

Describe other actions of VP

Answer 15

VASOCONSTRICTION

Corticotrophin release

CNS effects

Acts as neurotransmitter (aspects of behaviour - finding a partner/looking after young)

Synthesis of blood clotting factors (VIII and von Willbrandt factor)

Hepatic glycogenolysis (caused by every stressor)

Question 16

List the different Vasopressin receptors

Answer 16

V1a V2 V1b (V3) - adenohypophysial corticotrophs (corticotrophin production)

Question 17

Describe the function of V1

Answer 17

Involved in vasoconstriction - Arterial smooth muscle Glycogenolysis - hepatocytes Behavioural and other effects - CNS neurones

Question 18

Describe the function of V2 - MOST IMPORTANT RECEPTOR

Answer 18

Water reabsorption - collecting duct cells Factor VIII and von Willbrandt factor synthesis

Question 19

Describe how V1 is activated

Answer 19

Linked via G proteins to phospholipase C PLC acts on PL to produce inositol triphosphate (IP3) (and DAG) IP3 increases cytoplasmic [Ca2+] and PKC Producing cellular response

Question 20

Describe how V2 is activated

Answer 20

Linked via G proteins to Adenyl Cyclase Actos on ATP to form cAMP cAMP activates PKA which activates other celular mediators Which produce cellular response (AQ2)

Question 21

Describe the process of AQ2 insertion into cell membrane

Answer 21

VP in the blood attaches to V2 receptors on cell membrane Activating G-protein, ATP > cAMP cAMP activates PKA which activates other intracellular mediators This synthesises AQ2 which migrate the aggraphores to the apical membrane AQ2 are inserted into apical membrane, allowing water to enter AQ3 and 4 are inserted into the basolateral membrane allowing water to enter into plasma

Question 22

How is VP controlled when there is increased plasma osmolality?

Answer 22

Osmoreceptors detect the dehydration - which have a stimulatory effect on hypothalamic nuclei, increasing VP production Increasing water reabsorption DECREASING plasma osmolality

Question 23

How is VP controlled when there is decreased arterial blood pressure?

Answer 23

Detected by baroreceptors/volume receptors

Reduces inhibition of VP, Stimulates hypothalamic nuclei to produce more VP

VP released in to blood Increases vasoconstriction INCREASES blood pressure (also can be influenced by higher centres - stress, so more VP secreted)

Question 24

List the actions of oxytocin:

Answer 24

Central effects - behavioural Affects breast during lactation > myoepithelial cells contract > causing milk ejection Affects uterus at parturition > myometrial cells > contraction > delivery of baby

Question 25

What is the neuroendocrine reflex arc for oxytocin?

Answer 25

Question 26

List the clinical conditions caused by VP

Answer 26

Diabetes insipidus

Syndrome of Inappropriate ADH

Question 27

Describe the 2 types of DI:

Answer 27

Central DI - no VP present

Nephrogenic DI - tissue insensitivity DI causes Polyurea and Polydipsia

Question 28

What are the causes of DI?

Answer 28

Central: problem in brain - trauma to head, tumour, autoimmune, inflammation Nephrogenic: problem in kidneys (psychogenic polydipsia - caused by psychological issues)