Final answer:
Oxytocin stimulates the release of breast milk during breastfeeding, while prolactin is responsible for milk production. Oxytocin is released from the posterior pituitary gland in response to the baby's suckling.
Step-by-step explanation:
The hormone which stimulates the release of breast milk when a baby nurses is oxytocin. While prolactin is responsible for the production of milk, oxytocin promotes the release or letdown of milk from the mammary glands. Both hormones play crucial roles in the process of lactation. Prolactin is synthesized in the anterior pituitary gland and is instrumental in the establishment and maintenance of milk supply, and oxytocin is synthesized in the hypothalamus but stored and released by the posterior pituitary.
During breastfeeding, the baby's suckling triggers nerve signals that stimulate the hypothalamus to release oxytocin, which in turn causes the muscles around the alveoli in the mammary glands to contract and eject milk through the ducts and out of the nipple. Frequent breastfeeding helps to maintain high prolactin levels and thus a plentiful milk supply. Over time, with continued nursing, baseline prolactin levels will gradually return to pre-pregnancy levels.