Hypothalamic nuclei of Posterior Pituitary
- supraoptic nucleus (SON)
- paraventricular nucleus (PVN)
magnocellular neurons
neurons in the SON and PVN that extend to and terminate at posterior pituitary
the 2 peptides that magnocellular neurons in SON and PVN synthesize
- Oxytocin (OT)
- ADH
OT is largely derived from the ___________.
PVN
ADH is largely derived from the _________.
SON
Synthesis and Secretion of Oxytocin
- 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
Synthesis and Secretion of ADH
- 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
ADH is secreted from the posterior pituitary in response to…
an ↑ in plasma osmolality or a ↓ in plasma volume
Functions of ADH: Kidneys
V2 receptor
collecting duct
↑ water reabsorption into blood
—produces more concentrated urine
Functions of ADH: Arterioles
V1 receptor
vasoconstriction - ↑ blood pressure
Central (Neurogenic) Diabetes Insipidus
- 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
Syndrome of Inappropriate ADH Secretion (SIADH)
- ↑ ADH synthesis and secretion due to brain tumor, anti-tumor agents, infection, pulmonary carcinoma
- water retention, concentrated urine, hyposmotic plasma if water intake not ↓
What stimulates release of oxytocin?
- 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
2 major sites of action for Oxytocin
- pregnant uterus
2. lactating breast
Effects of Oxytocin: Pregnant Uterus
- produces rhythmic contractions to help induce labor
- promotes regression of uterus following delivery
Effects of Oxytocin: Lactating Breast
-stimulates milk ejection by contracting the my-epithelial cells that line the alveoli and ducts in mammary gland
