What are you going to learn?

  • What are oxytocin's effects?
  • How is oxytocin secreted?
  • How is oxytocin regulated?
  • terms: milk ejection (letdown)

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Oxytocin is responsible for milk ejection from the breasts after pregnancy. The milk is stored in alveoli in the mammary gland. When a baby suckles, sensory receptors in the nipple get stimulated and this stimulus is then transported to hypothalamus, which causes neurohypophysis to release oxytocin. Then, oxytocin in transported by blood to the breasts and here it causes contraction of myoepithelial cells around the alveoli and this contraction forces the milk into milk ducts and eventually into the nipple. This process is called milk ejection or milk letdown.

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Milk ejection mechanism:
1) stimulus in the sensory receptors of the nipple
2) hypothalamus
3) neurohypophysis
4) oxytocin is released and transported to the breasts
5) myoepithelial cells contract
6) milk is transported to the nipple

Oxytocin also causes uterine contractions or more specifically, contractions of uterine smooth muscle. These contractions are believed to be at least partially responsible for causing birth of the baby. And for that reason, oxytocin is also used for inducing labour.

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Oxytocin causes uterine contractions and therefore the birth of the baby (at least partially).

Regulation

The major stimulus for oxytocin's secretion is suckling. However, there are also other factors that cause oxytocin's secretion: the sight, sound, or smell of the baby or even the dilation of the cervix during labour or orgasm.

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The most important stimulus for oxytocin's secretion is suckling.


References:
Costanzo, L. S. (2018). Physiology. Elsevier.
Hall, J. E., Hall, M. E., & Guyton, A. C. (2021). Guyton and Hall Textbook of Medical Physiology. Elsevier.