Mammary alveolus and myometrium
Target gland or tissue · Prolactin receptor Oxytocin receptor Myoepithelium
Prolactin acts on alveolar epithelium through JAK2 and STAT5 to make milk; oxytocin acts on the myoepithelial cells wrapped around those alveoli and on myometrial smooth muscle through Gq and calcium.
Traced from the start
Detail
- Two hormones, two jobs
- Prolactin fills the alveolus and oxytocin empties it — milk is still made without oxytocin, it simply cannot be ejected
- Timing
- High placental oestrogen and progesterone prime the breast but block milk secretion; their fall after delivery of the placenta releases lactogenesis II at about 30-72 hours
- Myometrial signalling
- Gq coupled: IP3, calcium release and myosin light chain kinase activation, with a rise in uterine prostaglandins
When it goes wrong
Retained placental fragments
Progesterone stays high and lactogenesis is delayed; the same fragments cause secondary postpartum haemorrhage
Uterine atony after delivery
The commonest cause of primary postpartum haemorrhage: rub up a contraction, empty the bladder, give oxytocin, then ergometrine, then carboprost or misoprostol
Practise this structure
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