8. The hypothalamic pituitary axis Flashcards
Describe the location of the pituitary.
Beneath the hypothalamus in a socket of bone - the sella turcica.
What are the embryological origins of the anterior and posterior lobes of the pituitary.
anterior lobe: projection of ectoderm (Rathke’s pouch) growing upward from roof of mouth
posterior lobe: ectodermal tissue growing downwards from diencephalon of developing brain
Which structure connects the hypothalamus and pituitary?
infandibulum (pituitary stalk)
What does the posterior pituitary consist of?
- axons and terminals that originate in hypothalamus
2. specialised glial cells - pituicytes
Which 2 hormones are released from the posterior pituitary (and what hormone type are they)?
- oxytocin (peptide)
2. anti-diuretic hormone (peptide)
Where are oxytocin and ADH synthesised in the hypothalamus?
- ADH: supraoptic nucleus
- oxytocin: paraventricular nucleus
What stimulates oxytocin release from the posterior pituitary?
- suckling (milk let-down reflex) - stimulus is transmitted via neurons from the breast to the hypothalamus
- during childbirth: pressure on cervix and uterine wall
What is the effect of oxytocin release?
- activates oxytocin Rs on myoepithelial cells surrounding mammary alveoli… contraction to squeeze milk into duct system
- during childbirth: activates oxytocin Rs on uterine SM cells… powerful uterine contractions
Why is synthetic oxytocin (pitocin) often administered after birth?
increase uterine tone and control bleeding
What is the effect of ADH release?
reduction in urine production:
activates Rs on distal tubular epithelium of collecting ducts in kidneys… translocation of aquaporin water channels in plasma membrane of collecting duct cells (increased permeability)… reabsorption of water into blood
Why does drinking alcohol increase urination and lead to dehydration?
inhibits ADH release from posterior pituitary
How is blood osmolality regulated?
OsmoRs in hypothalamus detect changes in plasma osmolality…
- If high: stimulates ADH release from posterior pituitary (and stimulates thirst)… increased H2O reabsorption from collecting ducts
- If low: inhibits ADH release from posterior pituitary (and inhibits thirst)… decreased H2O reabsorption from collecting ducts
How is hypothalamus control of anterior pit. different to control of posterior pit.?
- posterior pit.: neuronal control
- anterior pit.: tropic hormone control
Where are hypothalamus hormones destined for AP stored?
median eminence just above AP
What are hormones stored in median eminence released into?
hypophyseal portal system
