The hypothalamo-neurohypophyseal axis: posterior pituitary

Question 1

Name the hormones produced by the posterior pituitary gland

Answer 1

Oxytocin and Vasopressin (ADH)

Question 2

Name the artery located in the posterior pituitary gland

Answer 2

Inferior hypophysial artery add pic

Question 3

What is different about the nuerons coming from paraventricular nuclei and the supra-optic nuclei?

Answer 3

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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Question 4

What are the majority of the nuerones that are located in the supraoptic and paraventricular nuclei and secrete ADH and Oxytocin?

Answer 4

Magnocellular nuerones add pic

Question 5

Where are supraoptic nuerones located?

Answer 5

Supraoptic nuclei add pic

Question 6

What are herring bodies?

Answer 6

Herring Bodies - areas where the neurosecretions can be stored on the way down to the neurohypophysis.

Molecules can be released from the herring bodies .

Question 7

Where do supraoptic nuclie terminate?

Answer 7

Nuerohyophyis

Question 8

Where do the supraoptic nerurones pass through?

Answer 8

The median eminence-They don’t terminate there add pic

Question 9

What substances do supraoptic nuerones produce?

Answer 9

Oxytocin or vasopressin

Magnocellular nuerones in the supraoptic nuclie either express vasopressin or ocytocinergic

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Question 10

Where do paraventricular neurones originate from?

Answer 10

Paraventricular nuclei.

Question 11

Name the other places the parvocellular nurones terminate at?

Answer 11

Some (parvocellular) neurones pass to other parts of brain.

Some (parvocellular) VP neurones terminate in median eminence

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Question 12

Name the type of nurones found in the paraventricular nuclie?

Answer 12

Magnocellular ( Pass to the neurohypophysis).

Parvocellular (terminate in the brain or the median eminnance)

Question 13

Why do some parvocellular neurones pass to other parts of the brain?

Answer 13

Oxytocin and vasopressin effect behavior

Question 14

Where do magnocellular neurones terminate at?

Answer 14

neurohypophysis

Question 15

Vasopressin can be deposited in the nuerohypophysis and where else by the paraventricular nuerones?

Answer 15

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.

Question 16

State the difference between Vasopressin and Oxytocin in terms of their structure?

Answer 16

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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Question 17

What does the vasopressin prohormone break down into?

Answer 17

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

Question 18

List the steps for vasopressin synthesis.

Answer 18

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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Question 19

What is the difference between oxytocin synthesis and vasopressin synthesis?

Answer 19

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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Question 20

Name two nonapeptides

Answer 20

Oxytocin and vasopressin

Question 21

What is nuerophysin function?

Answer 21

The nuerophysin binds to the oxytocin or the vasopressin and prevents oxytocin and vasopressin diffusing out of the herring body.

Nuerophysin also prevents enzyme degregation of the hormones.

Question 22

What physiological actions on the body occurs when vasopressin binds to V1 receptors?

List what happens for V1a and V1b Receptors?

Answer 22

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Question 23

What physiological actions on the body occur when vasopressin binds to V2 receptors?

Answer 23

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Question 24

List the sequence of events within a cell when vasopressin binds to a V1 receptor

Answer 24

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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Question 25

List the sequence of events within a cell when vasopressin binds to a V2 receptor?

Answer 25

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

Question 26

Where does Vasopressin act in the kidney?

Answer 26

Renal collecting ducts where it stimulates water reabsorption

Question 27

How does vasopressin work in principle cells? Draw a diagram

Answer 27

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

Question 28

Name the minor effects of oxytocin?

Answer 28

Has unwanted effects in the cardiovascular system and kidney.

Question 29

Name the major effects of oxytocin?

Answer 29

add pic Uterine contraction ( myometrial cell contraction) and milk let down (myoeptithelial cell contraction).

Question 30

What supresses and enhances oxytocin action in the uterus.

Answer 30

Suppressed by progesterone Enhanced by oestrogen

Question 31

What does oxytocin stimulate the production of? This substance helps with uterine contraction.

Answer 31

Oxytocin stimulates the uterine muscles to contract and also increases production of prostaglandins, which increase the contractions further. add pic

Question 32

Name the effects of oxytocin on the uterus/

Answer 32

Rhythmic contraction; fundus to cervix. Increased local prostanoid production- they break down the collagen membrane that surrounds the baby. Dilation of cervix.

Question 33

Draw a graph showing contractile response to oxytocin in the y axis vs weeks of gestation?

Answer 33

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Question 34

What cardiovascular effects does oxytocin have

Answer 34

CARDIOVASCULAR - Pharmacological transient vasodilation & Tachycardia Constriction of umbilical arteries and veins

Question 35

Name the Reanal effects of oxytocin?

Answer 35

RENAL - pharmacological Anti-diuresis and secondary hyponatraemia, i.e. vasopressin-like

Question 36

List the clinincal uses of Oxytocin?

Answer 36

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Question 37

What is the stimulus for vasopressin release?

Answer 37

Increased plasma osmolarity

Question 38

What is the response of the body for increased vasopressin?

Answer 38

Decreased plasma osmolarity

Question 39

What is the stimulus that leads to Oxytocin release for women who have just given birth.

Answer 39

Stimulartion of the nipple by sucking

Question 40

Draw a diagram showing the oxytocin neroendocrine reflex arc

Answer 40

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Question 41

What is a lack of Vasopressin or an resistance to vasopressin called?

Answer 41

Diabetes Insipidus

Question 42

What is Central or cranial diabetes insipidus?

Answer 42

Absence or lack of circulating vasopressin

Question 43

What is nephrogenic diabetes insipidus?

Answer 43

End-organ (kidneys) resistance to vasopressin

Question 44

What are the signs for diabetes insipidus?

Answer 44

SIGNS Polydipsia (increased thirst). Polyuria (large volumes of urine). Urine very dilute (hypo-osmolar).

Question 45

List other effects of vasopressin?

Answer 45

Vasopressin is a POWERFUL VASOCONTRICTOR . Vasopressin released by parvocellular neurones in the median eminence is carried to the adenohypophysis and acts with corticotrophin releasing hormone (CRH) to control the release of corticotrophin. Some parvocellular neurones go to other parts of the CNS where vasopressin could act a hormone or a neurotransmitter and have an effect on behaviour . Vasopressin is involved in the synthesis of blood clotting factors (VII and Von Willbrandt) so vasopressin or vasopressin analogues can be used to treat certain blood clotting disorders. Hepatic Glycogenolysis - vasopressin is released by certain stressors such as dehydration so it is a stress hormone which has an effect on increasing blood glucose concentration.