Hypothalamo-neurohypophysial Axis Flashcards
What are the two main origins of hypothalmic nuclei that project into posterior pituitary?
Paraventricular nuclei
Supra-optic nuclei
What is the posterior pituitary made up of?
Mainly nerve axons that originate in the hypothlamua
What two molecules is the posterior pituitary mainly associated with?
Oxytocin
Vasopressin
What are the two types of Hypothalamic nuclei?
Magnocellular:
- Large
- All terminate in Posterior pituitary
Parvocellular:
- Average sized
- Terminate in median eminence or other parts of the brain
What are the areas on magnocellular neurones where neurosecretions can be stored on the way down to the neurohypophysis?
Herring bodies
What is the difference between Supra-optic and Paraventricular neurones?
Supra-optic are exclusively magnocellular
Paraventricular have magnocellular and parvocellular components
Where can a paraventricular neurone terminate?
Neurohypophysis, Median eminence, or other parts of the brain
Describe the overall stages of oxytocin and vasopressin synthesis:
Preprohormone
Prohormone
Hormone + other products
What can provasopressin be broken down into?
Arginine Vasopressin (AVP)
Neurophysin (specific to provasopressin)
Glycopeptide
What can prooxytocin be broken down into?
Oxytocin
Neurophysin
NO GLYCOPEPTIDE
What are the differences between oxytocin and vasopressin?
They differ by only 2 amino acids
How long are vasopressin and oxytocin?
9 amino acids
Nonapeptides
What is the main effect of vasopressin?
Stimulates water reabsorption in the renal collecting ducts
Anti-diuretic
What are the four other effects of vasopressin?
Vasoconstriction
Stimulates corticotrophin release in anterior pituitary
Involved in synthesis of clotting factor VII and Von Willbrandt factor
Stimulates hepatic Glycogenolysis
What are the 3 main types of vasopressin receptor?
V1a: Arterial smooth muscle, Hepatocytes, CNS neurones
V1b: Adenohypophysial corticotrophs
V2: Renal collecting ducts, (Blood clotting factors)
What type of receptor is V1?
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)
What type of receptor is V2?
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)
Where on a collecting duct cell are V2 receptors found?
Basolateral membrane
What does cAMP in renal collecting duct cells cause synthesis of?
Aquaporin 2 (AQP 2)
After Aquaporin 2 is synthesised, what happens to it?
Assembles into accumulations called Aggraphores
Under influence of vassopressin, migrate to apical surface
Inserted into membrane to allow water to move into the cells
What two main things stimulate Vasopressin release, and how are they detected?
Dehydration (increase in plasma osmolality)
- Detected by osmoreceptors
Fall in blood pressure
- Detected by baroreceptors/volume receptors
What does oxytocin cause?
Contraction
What are the two main fucntions of oxytocin?
Contraction of uterus during birth
Contraction of breast muscle tissue during lactation
What cells do oxytocin act on?
Myometrial cells (uterus) Myoepithelial cells (breast)
What stimulates release of oxytocin?
Suckling (same afferent pathway as prolactin)
Uterine wall stress
What two conditions do vasopressin cause?
Diabetes insipidus
Syndrome of inappropriate ADH (SIADH)
What are the two types of diabetes insipidus?
Central - No vasopressin produced
Nephrogenic - tissue insensitivity
