During pregnancy, hormones prepare the mammary gland to produce milk, increasing glandular tissue and breast volume.
The pituitary gland produces various hormones including prolactin which is responsible for milk production.
At every attachment to the breast, the stimulation of the nerve endings of the nipple, sends a message to the pituitary gland for the production of prolactin, which reaches the breast through blood activating the production of milk, therefore the more the newborn is attached to the breast, the more milk is produced.
The milk supply arrives after about 3 days after delivery, favored by adequate stimulation of the breast.
For the continuity of milk production there are 2 main factors essential:
the stimulation of the breast with sucking and/or breast pumping
Milk production is directly proportional to breast stimulation with sucking (or breast pump). With exclusive, on-demand breastfeeding, the breasts will produce enough milk for the infant's needs.
More stimulation (sucking and/or breast pumping) = more milk production
Less stimulation = less milk production
For continuity of milk production, it is necessary to drain the breasts; if this does not happen, the breasts will tend to produce less milk. The remaining milk presses on the glandular cells limiting their secretion.
There is a factor called FIL (feedback inhibiting factor) that accumulates in the milk inside the mammary gland that blocks the production of more milk, this explains the possible differences in milk production between the 2 breasts.
The more drained breast produces more milk because the FIL is removed.
The less drained breast produces less milk because the FIL is not removed.
Returning to the 2 main essential factors: the stimulation of the breast with suction and/or breast pump and the drainage of the breast, it must be said that they are independent, for example, if an infant no longer attaches to a breast, it will stop producing milk even if it attaches to the other breast stimulating the production of prolactin.
Natural milk ejection
The mammary gland is surrounded by muscle cells that contract and increase the pressure of the milk that is "pressed" outward along the ducts and galactophorous sinuses until it reaches the nipple. Oxytocin, a hormone secreted by the pituitary gland, is responsible for the contraction of muscle cells, its production is stimulated by the sucking of the newborn and acts during the feeding to allow the ejection of milk. This process, constitutes the reflex of milk ejection, which together with sucking serves for the intake of the right quantity of milk.
Emotional factors and moods can influence the ejection reflex, favoring or hindering it.
The crying of the newborn baby can favor the ejection reflex, feeling a pressure inside the breast with possible leakage of milk even before feeding.
Conditions in which the mother is worried for any reason, or in which breastfeeding is difficult or painful, or when there is little confidence in her ability to breastfeed, can hinder the ejection reflex.