Oxytocin is a nine-amino acid peptide hormone synthesized by neurons in the hypothalamus and released into the circulation from the posterior pituitary. It promotes contraction of uterine smooth muscle during childbirth and contraction of cells around mammary secretory units, ejecting milk. Milk ejection is distinct from producing the milk.[ref]
Anatomy and Physiology 2e by J. Gordon Betts and others. Section 17.3, Oxytocin
Childbirth illustrates positive feedback: stretching of the cervix stimulates a neural pathway that increases oxytocin release; stronger uterine contractions can increase the stretch until delivery removes the initiating stimulus. During suckling, sensory input similarly couples an external event to hormone release and milk ejection. These circuits connect sensory neurons, endocrine signaling and mechanical action.[ref]
Anatomy and Physiology 2e by J. Gordon Betts and others. Section 17.3, Oxytocin, childbirth and milk-letdown feedback
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