There are several hormones that regulate the making and ejection of milk from human breasts as well as from the breasts of all female mammals after childbirth.

The initiation of breastfeeding in all mammals including humans is an effort from both the mother and the baby. For example while human mothers hold their baby close to their breast while attempting to feed the baby, several animals like rats do not transport their newborn pups which are blind and deaf at birth, to the nipple.

Instead the mother rat assists newborns by assuming a special squatting posture that allows the pups to find the nipple. On the other hand babies of rhesus monkeys are able to move to their mother’s nipple without the mother assisting them.

Among all mammals the specific maternal behaviours that help to initiate breastfeeding and the subsequent maintenance of lactation that is continued flow of milk according to the nutritional needs of the baby.

There are alveolar cells within the breast that make breast milk. During the latter half of the pregnancy the breasts gear up to make milk after childbirth.

Hormones

• A hormone called Prolactin secreted by the pituitary gland in the brain is responsible for the alveoli making milk. Prolactin rises when the baby suckles.
• There is another hormone called Oxytocin that causes tiny muscles around the alveoli to squeeze the milk via small tubes called milk ducts. These milk ducts progressively enlarge to end in the nipple and eject the milk from the nipple. Oxytocin also causes the muscles of the uterus to contract during and after birth. Before childbirth this may induce labour and after childbirth it helps uterus to get back to its original size and reduces the bleeding after childbirth.
• Both prolactin and oxytocin help the mother form an emotional bond with her baby.

Neuroendocrine mechanisms

Lactation begins and is maintained by neuroendocrine mechanisms. This involves the neural component mediated by the nerves in the breast (especially nipples) that are stimulated by the baby’s sucking.

The neural component also includes the emotional factors in the brain like hearing the baby cry or thinking of the baby. The endocrine component refers to the hormones related to let down reflex.

In addition there are other signals that allow maintenance of lactation. One of these is smell. Smell helps the baby recognize its mother and helps in forming social attachment and an emotional bond with the mother.