Hypothalamo-neurohypophysial Axis

Question 1

What are the two main origins of hypothalmic nuclei that project into posterior pituitary?

Answer 1

Paraventricular nuclei

Supra-optic nuclei

Question 2

What is the posterior pituitary made up of?

Answer 2

Mainly nerve axons that originate in the hypothlamua

Question 3

What two molecules is the posterior pituitary mainly associated with?

Answer 3

Oxytocin

Vasopressin

Question 4

What are the two types of Hypothalamic nuclei?

Answer 4

Magnocellular:

• Large
• All terminate in Posterior pituitary

Parvocellular:

• Average sized
• Terminate in median eminence or other parts of the brain

Question 5

What are the areas on magnocellular neurones where neurosecretions can be stored on the way down to the neurohypophysis?

Answer 5

Herring bodies

Question 6

What is the difference between Supra-optic and Paraventricular neurones?

Answer 6

Supra-optic are exclusively magnocellular

Paraventricular have magnocellular and parvocellular components

Question 7

Where can a paraventricular neurone terminate?

Answer 7

Neurohypophysis, Median eminence, or other parts of the brain

Question 8

Describe the overall stages of oxytocin and vasopressin synthesis:

Answer 8

Preprohormone
Prohormone
Hormone + other products

Question 9

What can provasopressin be broken down into?

Answer 9

Arginine Vasopressin (AVP)
Neurophysin (specific to provasopressin)
Glycopeptide

Question 10

What can prooxytocin be broken down into?

Answer 10

Oxytocin
Neurophysin
NO GLYCOPEPTIDE

Question 11

What are the differences between oxytocin and vasopressin?

Answer 11

They differ by only 2 amino acids

Question 12

How long are vasopressin and oxytocin?

Answer 12

9 amino acids

Nonapeptides

Question 13

What is the main effect of vasopressin?

Answer 13

Stimulates water reabsorption in the renal collecting ducts

Anti-diuretic

Question 14

What are the four other effects of vasopressin?

Answer 14

Vasoconstriction

Stimulates corticotrophin release in anterior pituitary

Involved in synthesis of clotting factor VII and Von Willbrandt factor

Stimulates hepatic Glycogenolysis

Question 15

What are the 3 main types of vasopressin receptor?

Answer 15

V1a: Arterial smooth muscle, Hepatocytes, CNS neurones

V1b: Adenohypophysial corticotrophs

V2: Renal collecting ducts, (Blood clotting factors)

Question 16

What type of receptor is V1?

Answer 16

Gq protein linked receptor:
Linked via G protein to Phospholipase C (PLC)
PLC converts PIP3 to IP3 and DAG which increases cytoplasmic Ca2+ and activates other mediators such as Protein Kinase C (PKC)

Question 17

What type of receptor is V2?

Answer 17

Gs Protein Linked Receptor:
Linked via G protein to Adenylate cyclase
Which converts ATP to cAMP
cAMP activates Protein Kinase A (PKA) which activates other intracellular mediators (e.g. recruitment of aquaporins)

Question 18

Where on a collecting duct cell are V2 receptors found?

Answer 18

Basolateral membrane

Question 19

What does cAMP in renal collecting duct cells cause synthesis of?

Answer 19

Aquaporin 2 (AQP 2)

Question 20

After Aquaporin 2 is synthesised, what happens to it?

Answer 20

Assembles into accumulations called Aggraphores

Under influence of vassopressin, migrate to apical surface

Inserted into membrane to allow water to move into the cells

Question 21

What two main things stimulate Vasopressin release, and how are they detected?

Answer 21

Dehydration (increase in plasma osmolality)
- Detected by osmoreceptors

Fall in blood pressure
- Detected by baroreceptors/volume receptors

Question 22

What does oxytocin cause?

Answer 22

Contraction

Question 23

What are the two main fucntions of oxytocin?

Answer 23

Contraction of uterus during birth

Contraction of breast muscle tissue during lactation

Question 24

What cells do oxytocin act on?

Answer 24

Myometrial cells (uterus)
Myoepithelial cells (breast)

Question 25

What stimulates release of oxytocin?

Answer 25

Suckling (same afferent pathway as prolactin)

Uterine wall stress

Question 26

What two conditions do vasopressin cause?

Answer 26

Diabetes insipidus

Syndrome of inappropriate ADH (SIADH)

Question 27

What are the two types of diabetes insipidus?

Answer 27

Central - No vasopressin produced

Nephrogenic - tissue insensitivity