Posterior Pituitary

Question 1

Hypothalamic nuclei of Posterior Pituitary

Answer 1

• supraoptic nucleus (SON)

- paraventricular nucleus (PVN)

Question 2

magnocellular neurons

Answer 2

neurons in the SON and PVN that extend to and terminate at posterior pituitary

Question 3

the 2 peptides that magnocellular neurons in SON and PVN synthesize

Answer 3

• Oxytocin (OT)

- ADH

Question 4

OT is largely derived from the ___________.

Answer 4

PVN

Question 5

ADH is largely derived from the _________.

Answer 5

SON

Question 6

Synthesis and Secretion of Oxytocin

Answer 6

• preprooxyphysin (preprohormone) & neurophysin I (NPI)
• signal peptide cleaved from preprooxyphysin at the endoplasmic reticulum to yield prohormone
• prohormone then packaged into secretory granules in cell bodies of PVN & transported along axons through pituitary stalk towards axon terminals in Posterior Pituitary
• during axonal transport, prohormone cleaved to yield OT and NPI, along with C-terminal glycoproteins
• release of OT from nerve terminals into blood via exocytosis

Question 7

Synthesis and Secretion of ADH

Answer 7

• preprovasophysin (preprohormone) & neurophysin II (NPII)
• signal peptide cleaved from preprovasophysin at the endoplasmic reticulum to yield prohormone
• prohormone then packaged into secretory granules in cell bodies of SON & transported along axons through pituitary stalk towards axon terminals in Posterior Pituitary
• during axonal transport, prohormone cleaved to yield ADH and NPII, along with C-terminal glycoproteins
• release of ADH from nerve terminals into blood via exocytosis

Question 8

ADH is secreted from the posterior pituitary in response to…

Answer 8

an ↑ in plasma osmolality or a ↓ in plasma volume

Question 9

Functions of ADH: Kidneys

Answer 9

V2 receptor

collecting duct

↑ water reabsorption into blood
—produces more concentrated urine

Question 10

Functions of ADH: Arterioles

Answer 10

V1 receptor

vasoconstriction - ↑ blood pressure

Question 11

Central (Neurogenic) Diabetes Insipidus

Answer 11

• inadequate synthesis/release of ADH due to head injury/pituitary tumor/brain tumor
• production of large volumes of dilute urine (cannot concentrate urine)
• must ingest large volumes of water to maintain plasma osmolality

Question 12

Syndrome of Inappropriate ADH Secretion (SIADH)

Answer 12

• ↑ ADH synthesis and secretion due to brain tumor, anti-tumor agents, infection, pulmonary carcinoma
• water retention, concentrated urine, hyposmotic plasma if water intake not ↓

Question 13

What stimulates release of oxytocin?

Answer 13

• mechanical stimulation of uterine cervix by fetus near end of gestation
• uterine contraction during fetal expulsion reflex
• stimulation of tactile receptors in nipples of lactating breast

Question 14

2 major sites of action for Oxytocin

Answer 14

1. pregnant uterus

2. lactating breast

Question 15

Effects of Oxytocin: Pregnant Uterus

Answer 15

• produces rhythmic contractions to help induce labor

- promotes regression of uterus following delivery

Question 16

Effects of Oxytocin: Lactating Breast

Answer 16

-stimulates milk ejection by contracting the my-epithelial cells that line the alveoli and ducts in mammary gland