What triggers the breast to produce large amounts of milk after delivery?

The production of large amounts of milk after delivery is primarily triggered by the sudden withdrawal of progesterone. During pregnancy, high levels of progesterone play a crucial role in preparing the breasts for milk production; however, progesterone levels drop significantly after the placenta is delivered. This dramatic decrease allows prolactin, the hormone responsible for milk production, to take effect. As a result, the ducts and alveoli in the breast are stimulated to produce and secrete milk, leading to the establishment of lactation.

Other hormones, such as oxytocin, contribute to the milk ejection reflex, and while insulin and estrogen have roles in overall reproductive health and metabolism, they do not directly stimulate the large-scale production of milk post-delivery as the withdrawal of progesterone does. Therefore, understanding the hormonal shifts that occur after childbirth is essential for comprehending the biological mechanisms behind the onset of lactation.