Posterior Pituitary Hormones and general pit

The posterior pituitary releases what 2 hormones

ADH/Vasopressin Oxytocin

What is the pathway for posterior pituitary hormone release?

Hypothalamus makes ADH/oxytocin axons transport them posterior pituitary stores them nerve terminals release them into blood.

What does ADH do?

Helps the kidneys retain water So you lose less water in urine Helps conserve body water

What does oxytocin do?

Causes uterine contractions during labor Causes milk ejection/letdown during breastfeeding

ADH and Oxytocin are __

neurohormones meaning they’re made by neurons

PVN nuclei

paraventricular nucleus about 4,000 cell bodies most produce oxytocin (think p - pregnancy)

SON nuclei

supraoptic nucleus about 14,000 cell bodies most produce vasopressin/ADH (think s - save water)

How are oxytocin and vasopressin first produced?

As larger precursor proteins called preprohormones.

What happens to the preprohormone after it is made?

It is processed and cleaved into smaller secretory products.

What does the oxytocin precursor produce?

Oxytocin + neurophysin I.

What does the vasopressin precursor produce?

Vasopressin + neurophysin II + copeptin.

Which neurophysin is paired with oxytocin?

Neurophysin I.

Which neurophysin is paired with vasopressin?

Neurophysin II.

Which precursor contains copeptin?

The vasopressin precursor.

What may neurophysins do for these hormones?

Help prevent hormone degradation in blood.

Where are the oxytocin and vasopressin genes located?

Chromosome 20.

How similar are the oxytocin and vasopressin precursor structures?

Their gene structure and peptide processing are very similar.

Posterior pituitary peptides evolved through ___

gene duplication + small amino-acid substitutions.

Which peptide is shown as the ancestral starting point?

Arginine vasotocin.

What process created separate related peptide genes?

Gene duplication.

What causes individual amino-acid substitutions?

Point mutations.

Which two major hormones evolved as closely related peptides?

Arginine vasopressin and oxytocin.

At position 3, what differs in vasopressin vs oxytocin?

Vasopressin has Phe; oxytocin has Ile.

At position 8, what differs in vasopressin vs oxytocin?

Vasopressin has Arg; oxytocin has Leu.

What peptide can arise from a later substitution of vasopressin?

Phenypressin.

What other vasopressin form is shown after duplication/substitution?

Lysine vasopressin.

What is the oxytocin positive-feedback pathway during labor?

1. Cervix stretches 2. Stretch receptors send sensory signals to hypothalamus 3. Posterior pituitary releases oxytocin into blood 4. Oxytocin causes uterine contractions 5. Baby pushes harder on cervix 6. More cervical stretch causes more oxytocin release

What stops the oxytocin positive-feedback loop during labor?

Delivery of the baby removes cervical stretch, so the stimulus for oxytocin

What are the steps of the breastfeeding hormone pathway?

1. Suckling stimulates nipple/areola nerves 2. Signals travel to hypothalamus 3. Posterior pituitary releases oxytocin and anterior pituitary releases pr 4. Oxytocin causes milk letdown 5. Prolactin stimulates milk production.

How does oxytocin cause milk letdown

Oxytocin causes myoepithelial cells around the mammary glands to contract,

What is the general oxytocin release pathway?

PVN of hypothalamus → oxytocin stored in neurohypophysis nerve endings → exocytosis → oxytocin-neurophysin I enters blood → dissociates → free oxytocin binds target receptors.

What stimulates oxytocin release and what are its main effects?

Cervical distension and suckling stimulate release. Oxytocin causes uterine contractions and milk ejection; in testes it decreases testosterone synthesis.

How does pregnancy prepare the uterus to respond to oxytocin?

Near term, progesterone falls and estrogen rises → oxytocin receptors increase → uterus becomes more responsive to oxytocin and contractions.

neurohypophyseal hormones (postpitu, oxy and vaso) are produced as

preprohormones

What are the steps of ADH release during dehydration or low blood volume?

1. Dehydration or low blood volume is detected.

2. Osmoreceptors/baroreceptors stimulate ADH-producing neurons in the hypothalamus.

3. The posterior pituitary releases ADH into the blood.

4. ADH acts on the kidneys to retain more water.

5. Urine output decreases, blood volume rises, and blood pressure increases.

What happens to ADH when the body is overhydrated or blood volume is high?

Osmoreceptors are inhibited → ADH secretion decreases or stops → less water is retained.

What happens when plasma tonicity increases?

1. Osmoreceptors detect ↑ plasma tonicity 2. Thirst increases 3. AVP/ADH increases 4. Water intake increases and water excretion decreases 5. Water is retained 6. Plasma tonicity returns toward normal.

What happens when plasma tonicity decreases?

1. Osmoreceptors detect low plasma tonicity.

2. Thirst decreases.

3. AVP/ADH secretion decreases.

4. The kidneys excrete more water.

5. Plasma tonicity returns toward normal.

What inputs regulate vasopressin/AVP neurons?

• Osmoreceptors monitor plasma tonicity/osmolality.

• Baroreceptors monitor blood pressure/volume.

• Adrenergic neurons provide stress/sympathetic input.

What are the steps of AVP synthesis and release?

1. AVP precursor is made in hypothalamic neurons.

2. It is processed in the RER and Golgi.

3. It is packaged into secretory vesicles.

4. It travels down the axon to the posterior pituitary and is processed into AVP + neurophysin II + copeptin.

5. An action potential causes Ca²⁺ influx at the nerve terminal.

6. AVP is released from the posterior pituitary into the blood. like whats the diff between all these

What is AVP, and how is it related to ADH?

AVP = arginine vasopressin. It is the same hormone as ADH and helps the body retain water.

What is the overall AVP/ADH pathway during water loss?

Water loss/high salt raises plasma tonicity

Osmoreceptors are stimulated

AVP/ADH is released from the posterior pituitary

Kidneys reabsorb more water

Plasma tonicity moves back toward normal.

How does AVP increase water reabsorption in the kidney? (KIDNEY SIGNALING PATHWAY)

1. AVP/ADH binds to the V₂ receptor in the kidney.

2. V₂ activates Gs protein.

3. Gs activates adenylyl cyclase.

4. Adenylyl cyclase increases cAMP.

5. cAMP activates PKA.

6. PKA causes aquaporin-2 (AQP2) water channels to move into the cell membrane.

7. More water is reabsorbed into the blood → less urine is produced.

Why AVP is released and main effect

water loss/high salt → ↑ plasma tonicity → osmoreceptors → ↑ AVP

Main effect: kidneys retain water → less water excreted → plasma tonicity moves back toward normal

What other inputs can regulate AVP

baroreceptors detect blood-pressure changes, and adrenergic neurons provide sympathetic/stress input

What protein travels with AVP, and what half-life is shown?

AVP is associated with neurophysin II; the slide shows a blood half-life of 5-20mmin

Vasopressin V1a receptor with PLC coupling system, G protein, effect, and target

Coupling system: PLC G protein: Gplc Effect: Stimulation Target tissue: Smooth muscle (blood vessel constriction), liver, CNS

Vasopressin V1a receptor with AC coupling system, G protein, effect, and target

Coupling system: AC G protein: Gi Effect: Inhibition Target tissue: Liver

Vasopressin V1b receptor coupling system, G protein, effect, and target

Coupling system: PLC G protein: Gplc Effect: Stimulation Target tissue: Pituitary

Vasopressin V2 receptor coupling system, G protein, effect, and target

Coupling system: AC G protein: Gs Effect: Stimulation Target tissue: Distal and collecting tubule of kidney

Oxytocin receptor coupling system, G protein, effect, and target

Coupling system: PLC G protein: Gplc Effect: Stimulation Target tissue: Uterus, CNS

What is central diabetes insipidus?

ADH is not produced/released properly, so the kidneys cannot retain enough water → excessive dilute urine.

What is nephrogenic diabetes insipidus?

ADH is present, but the kidneys fail to respond to it → excessive dilute urine.

Why does alcohol increase urine production?

Alcohol inhibits ADH release → kidneys reabsorb less water → more water stays in the urine → urine output increases.

The anterior and posterior pituitary are also known as?

Anterior: Adenohypophysis Posterior: Neurohypophysis

The posterior pituitary is a __ organ

Neurohemal

neurons terminate on blood vessels

Components of posterior pituitary

• Pars nervosa – Stores and releases oxytocin and ADH/AVP from nerve terminals.

• Infundibulum – Pituitary stalk connecting the hypothalamus to the posterior pituitary; contains axons that transport hormones.

• Median eminence – Region at the base of the hypothalamus where releasing/inhibiting hormones enter the portal blood vessels to regulate the anterior pituitary.

The pituitary gland collectively is known as __

hypophysis

The neurohypophysis originates from _

neuroectoderm

The median eminence is _

at base of pituitary stalk contains cells that produce hormones that are released into portal system fibers pass through to posterior pituitary

Layers of median eminence from outside to inside

1) Pars tuberalis – “sheath” around pituitary stalk

2) Capillary networks

3) Fibers of SON/PVN

4) Ependymal layer – membrane around ventricle

5) Infundibular recess – contiguous with 3rd ventricle and cerebrospinal fluid