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Milk ejection and uterine contraction

End hormone or mediator · Myoepithelial Myometrial Gq Spiral artery clamp

Myoepithelial contraction ejects milk into the ducts within seconds of suckling, while coordinated myometrial contraction advances labour and clamps the placental bed afterwards.

Traced from the start

  1. Tuberoinfundibular dopamine (prolactin-inhibiting factor)Thyrotrophin-releasing hormone (paraventricular nucleus)
  2. Supraoptic and paraventricular magnocellular neurones
  3. Lactotroph — prolactinPosterior pituitary — oxytocin release
  4. Mammary alveolus and myometrium
  5. Milk ejection and uterine contraction

Detail

Let-down
A neuroendocrine reflex that can be conditioned by the infant's cry and inhibited by pain or anxiety through catecholamines
Haemostasis
Myometrial contraction compresses the spiral arteries — the mechanical, not coagulation, control of bleeding after delivery

When it goes wrong

Active management of the third stage with prophylactic oxytocin

Roughly halves the risk of postpartum haemorrhage compared with expectant management

Failure of let-down from pain or anxiety

The breast stays full despite adequate milk production; managed with positioning, analgesia and skin-to-skin contact rather than hormones

Practise this structure

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