3 - Hypothalamo-neurohypohysial system Flashcards
What is the posterior pituitary gland also known as?
Neurohypophysis
What 2 hormones are secreated from the posterior pituitary gland?
Vasopressin
Oxytocin
What does vasopressin do?
Vasoconstriction
It stimulates water reabsorption in the renal collecting ducts.
It has an antidiuretic effect.
ADH is vasopressin
What are the 5 other effects of vasopressin?
- Vasoconstriction
- Corticotrophin release (together with CRH)
- CNS effects (acts as a neurotransmitter)
- Synthesis of blood clotting factors (VIII and Von Willbrandt factor)
- Hepatic glycolgenolysis
What are the 2 types of vasopressin receptors?
V1 and V2
How do V1 receptors work?
USED FOR VASOCONSTRICTION
- Linked via G proteins to phospholipase C
- which acts on membrane phospholipids
- to produce IP3 (and diacyl glycerol) which increase cytoplasmic [Ca2+] and other intracellular mediators
- which produce cellular response.
How do V2 receptors work?
USED FOR WATER REABSORPTION
- Linked via G proteins to adenyl cyclase
- ATP —> cyclic AMP
- Activates protein kinase A —> activates other intracellular mediators
- which produce cellular response - aquaporins (AQP2)
What are the 2 types of hypothalamic nuclei that send messages to the posterior pituitary?
Paraventricular nuclei
Supra-optic nuclei
Draw a diagram showing the hypothalamo-neurohypophysial axis.
Draw picture
What are magnocellular neurones?
Which cell bodies do they come from?
Neurones that travel from the cell bodies of…
-Paraventricular nuclei
-AND supra-optic nuclei
Directly to the posterior pituitary.
What are parvocellular neurones?
Which cell bodies do they come from?
Neurones that come from…
Paraventricular nuclei
That go to the median eminence (or other parts of the brain).
Where are herring bodies found and what is their function?
Along supra-optic neurones.
Function is to store oxytocin and vasopressin on the way.
How do supra-optic neurones secrete hormones?
3 steps
- Hormones are stored in the hypothalamic supra-optic nuclei.
- They pass down the magnocellular neurone through the median eminence.
- Neurone terminates in neurohypophysis.
They are EITHER vasopressinergic OR oxytocinergic.
How do messages from paraventricular nuclei travel?
How do they travel down the paraventricular neurones?
- The majority of neurones are magnocellular, these terminate in the neurohypophysis.
- Some neurones are parvocellular. These terminate in either the median eminence (VP only) or other parts of the brain.
- Paraventricular neurones are EITHER vasopressinergic OR oxytocinergic.
Describe the structures of vasopressin and oxytocin.
What is the difference
BOTH: NONAPEPTIDES (9 amino acids) Ring structure of 6 3 attached to ring. Disulphide bond between 2 adjacent cysteine's in the ring.
Differences:
Arginine Vasopressin (AVP) has Phe and Arg
Oxytocin has Ile and Leu
(All other amino acids are the same)
How is vasopressin synthesised?
- Pre-provasopressin is made in the nucleus. Its has a signal peptide
- Provasopressin moves all the way down the neurone with neurophysin attached (important stability properties in axon) and glycopeptide.
- Neurophysin and glycopeptide are cleaved at the end of the neurone. Vasopressin is produced.
NOTE ** exactly the same for oxytocin but neurophysin differs and there is no gylcopeptide.
What are the 2 types of V1 receptors and what do they do?
V1a
- Found in arteriole smooth muscle for vasoconstriction
- Found in hepatocytes for glycogenolysis
- Found in CNS neurones for behaviour
V1b
- Found in corticotrophs for ACTH production.
What do V2 receptors do?
- Collecting duct walls for water reabsorption
- Other effects elsewhere
What is the main physiological action of vasopressin?
clue - What is an antidiuretic effect?
In the renal collecting duct.
Stimulates water reabsorption.
It therefore has an antidiuretic effect.
Draw a flowchart of the physiological action of vasopressin (antidiuretic hormone) in the kidney.
Picture
What are the physiological effects of oxytocin?
MAJOR- (therapeutic advantage)
Uterus
Mammary gland - myoepithelial cells
MINOR - (unwanted effects)
Cardiovascular system - constriction of umbilical arteries and veins
Kidneys
Additional
CNS - behavioural (tend and befriend)
How does oxytocin lead to milk ejection?
What cells are involved?
Oxytocin
- Breast during lactation
- Myoepithelial cells
- Contration
- Milk ejection
How does oxytocin lead to delivery of a baby?
What cells are involved?
Oxytocin
- Uterus at parturition
- Myometrial cells
- Contraction, increased prostanoid production
- Breakdown of collagen & dilation of cervix
- Delivery of baby
What surpasses and enhances the uterine actions of oxytocin?
Enhanced by oestrogen
Surpassed by progesterone
(marked late in pregnancy as more oxytocin receptors nearer the end)
