The hormonal mechanism
The most important hormones in regulating breastfeeding are prolactin and oxytocin.
Their production begins during pregnancy and is then regulated by the newborn's suckling, creating a perfect alchemy between mother and baby.
Prolactin owes its name precisely to this function: it is pro-lactation, it promotes and regulates milk production. It is produced by the pituitary gland, an endocrine gland located at the base of the skull, roughly above the nasal cavities, in a bony cavity called the sella turcica. A characteristic of this hormone, which also comes into play in the stress mechanism with relaxing effects, is its ability to disrupt the ovulation mechanism, which tends to be less regular when the mother breastfeeds exclusively.
This inhibition is not total or constant in every case, so it is not wise to rely on it to avoid further pregnancies.
Oxytocin, on the other hand, regulates the squeezing of the milk ducts, that is, the release of milk.
Its production regulates uterine contractions during childbirth and those induced by early breastfeeding, which play an important role in reducing blood loss and helping the uterus return to its pre-pregnancy state. It is also produced simply at the thought of the baby to be breastfed; in fact, it performs the fundamental function of generating and maintaining the psychosomatic parental behaviors (maternal but also paternal) that allow for the reduction of fear and instinctive self-interest at the basis of the beginning of the couple's relationship and the social bond among mammals. (See The hormones that shape paternal caregiving.)
(To learn more: bnews.unimib.it.)