The hypothalamo-neurohypophyseal axis: posterior pituitary Flashcards
Name the hormones produced by the posterior pituitary gland
Oxytocin and Vasopressin (ADH)
Name the artery located in the posterior pituitary gland
Inferior hypophysial artery add pic
What is different about the nuerons coming from paraventricular nuclei and the supra-optic nuclei?
Some of the neurons which originate in the paraventricular nucleus terminate on the walls of the primary capillary plexus in the median eminence whilst the nuerons in the supra-optic nuclei only terminate in the posterior pituitary gland.
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What are the majority of the nuerones that are located in the supraoptic and paraventricular nuclei and secrete ADH and Oxytocin?
Magnocellular nuerones add pic
Where are supraoptic nuerones located?
Supraoptic nuclei add pic
What are herring bodies?
Herring Bodies - areas where the neurosecretions can be stored on the way down to the neurohypophysis.
Molecules can be released from the herring bodies .
Where do supraoptic nuclie terminate?
Nuerohyophyis
Where do the supraoptic nerurones pass through?
The median eminence-They don’t terminate there add pic
What substances do supraoptic nuerones produce?
Oxytocin or vasopressin
Magnocellular nuerones in the supraoptic nuclie either express vasopressin or ocytocinergic
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Where do paraventricular neurones originate from?
Paraventricular nuclei.
Name the other places the parvocellular nurones terminate at?
Some (parvocellular) neurones pass to other parts of brain.
Some (parvocellular) VP neurones terminate in median eminence
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Name the type of nurones found in the paraventricular nuclie?
Magnocellular ( Pass to the neurohypophysis).
Parvocellular (terminate in the brain or the median eminnance)
Why do some parvocellular neurones pass to other parts of the brain?
Oxytocin and vasopressin effect behavior
Where do magnocellular neurones terminate at?
neurohypophysis
Vasopressin can be deposited in the nuerohypophysis and where else by the paraventricular nuerones?
Median eminance
These neurones also synthesize corticotropin-releasing factor (CRF), which acts synergetically with vasopressin to stimulate release of adrenocorticotropin (ACTH) from the pituitary gland
The CRF and ADH is released at the same time.
State the difference between Vasopressin and Oxytocin in terms of their structure?
VP has Phenylalanine instead of Isoleucine.
VP has Arginine instead of Leucine. They differ by TWO AMINO ACIDS.
Because they have similar structures VP can have similar effects to oxytocin and vice versa. These effects however are not as strong.
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What does the vasopressin prohormone break down into?
Vasopressin (Arginine Vasopressin - AVP) .
Neurophysin (large protein which is specific to the provasopressin molecule).
Glycopeptide (may be a prolactin releasing factor but little is known about it) . add pic
List the steps for vasopressin synthesis.
Pre-Prohormone- the signal peptide is cleaved.
Then it is a prohormone.
Then it is cleaved again to make Vasopressin and Neurophysin and glycopeptide.
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What is the difference between oxytocin synthesis and vasopressin synthesis?
Same sequence for oxytocin synthesis, except that the neurophysin differs slightly and the glycopeptide is absent
Pre-prooxytocin splits into TWO.
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What physiological actions on the body occurs when vasopressin binds to V1 receptors?
List what happens for V1a and V1b Receptors?
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What physiological actions on the body occur when vasopressin binds to V2 receptors?
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List the sequence of events within a cell when vasopressin binds to a V1 receptor
Linked via G proteins to phospholipase C.
Which acts on membrane phospholipids to produce inositol triphosphate IP3 (and diacyl glycerol, DAG) which increase cytoplasmic [Ca2+] and other intracellular mediators (PKC) which produce cellular response
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List the sequence of events within a cell when vasopressin binds to a V2 receptor?
Linked via G proteins to adenyl cyclase which acts on ATP to form cyclic AMP which activates protein kinase A which in turn activates other intracellular mediators which produce cellular response (aquaporins, AQP2). add pic
How does vasopressin work in principle cells? Draw a diagram
V2 receptors are found in the basolateral membrane. Vasopressin binds to the V2 receptor and activates adenylate cyclase . Adenylate cyclase converts ATP to cAMP . cAMP activates protein kinase A which stimulates the synthesis of AQUAPORIN 2 molecules . All cells need aquaporins to allow the movement of water across the cell membrane . There are 9 types of aquaporin but AQUAPORIN 2 is the vasopressin dependent aquaporin. Aquaporins assemble into accumulations called Aggraphores. Under the influence of vasopressin, aggraphores migrate to the apical membrane (facing the inside of the collecting duct). Once the channels are inserted into the membrane, then water can move into the cells. Water is transported out of the cells and into the blood via AQP3 and AQP4 . An osmotic gradient is needed for the movement of water from the collecting duct, through the principal cells and into the blood . add pic add pic
Name the major effects of oxytocin?
add pic Uterine contraction ( myometrial cell contraction) and milk let down (myoeptithelial cell contraction).
What does oxytocin stimulate the production of? This substance helps with uterine contraction.
Oxytocin stimulates the uterine muscles to contract and also increases production of prostaglandins, which increase the contractions further. add pic
Draw a graph showing contractile response to oxytocin in the y axis vs weeks of gestation?
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List the clinincal uses of Oxytocin?
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Draw a diagram showing the oxytocin neroendocrine reflex arc
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What are the signs for diabetes insipidus?
SIGNS Polydipsia (increased thirst). Polyuria (large volumes of urine). Urine very dilute (hypo-osmolar).
