The third lecture in a series for the module Endocrinology. This lecture covers the basics of the posterior pituitary gland from it's main secreted hormones, role in the body and more. A great way to start your understanding of the module or to miss a lecture or two.
L3 – Posterior Pituitary Gland Function
Keywords:
Polydipsia, neurohypophysis (posterior pituitary gland, secretes ADH and oxytocin),
adenohypophysis (anterior pituitary) infundibulum region (floor of the third ventricle)
Lecture:
Posterior pituitary gland is formed by proliferated CNS cells from infundibulum region
Magnocellular neurons
o Cells found in paraventricular and supraoptic nuclei
o Vasopressin/ADH cells stained by fluorescent green
o Oxytocin cells stained with florescent red
Magnocellular neurons = large cell body 30um
o Prohormone packaged into secretary vesicle in Golgi -fast axonal transport 2mm/h
→ vasopressin/oxytocin
Precursors molecule of vasopressin/oxytocin
o First synth in RER – w/neuropeptide sequence,
o Vasopressin – neurophysin II + glycopeptide + signal peptide
o Oxytocin = neurophysin I + oxytocin protein coding + glycopeptide
Oxytocin (neuropeptide)
o A nonapeptide (9 AAs)
o Ringed structure w/disulfide bridges
o Oxys ∙ tokos = swift ∙ childbirth
o Uterine smooth muscle contraction = delivers baby/placenta
o Used in lactation = milk ejection reflex (smooth muscle contraction in alveoli of
mammary glands)
o Oxytocin receptor = activated PLC pathway →↑ PI turnover = ↑ Ca2+ to promote
muscle contraction
o Requires tactile stimulation of nipple (sensory nerves → oxytocin producing
magnocellular neurons in hypothalamus)
Transport to myo-epithelial cells lining mammary glands (smooth muscle
cells) to contract alveolus to milk ducts
Myoepithelial cells (extending contractile mesh for contraction) – respond to
oxytocin
Epithelial milk-secreting cells respond to prolactin
o Lactation caused by touch or conditioned reflex (activate oxytocin eg baby crying or
rattling bucket in dairy cows)
o Stress can inhibit reflex (eg postnatal depression)
o Rat lactation experiment
Electrode in rats brain – stimulation and record magnocellular neuron
Pressure transducer on the nipple
Jugular catheter to take blood samples
Results
10s delay between APs at oxytocin neuron and the intramammary
pressure increase (constriction of myoepithelial)
Pups sense the ↑ intramammary pressure
+ feedback loop (also activate prolactin release w/feedback loop)
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