Oxytocin and Prolactin: Hormonal Coordination of Milk Production and Let-Down

The video provides an in-depth look at two key hormones, oxytocin and prolactin, and how they coordinate milk production and milk ejection during pregnancy, childbirth, and breastfeeding. It explains where these hormones are produced in the hypothalamus and pituitary, how prolactin is inhibited by dopamine and stimulated by prolactin releasing hormone, and how oxytocin travels from the hypothalamus to the posterior pituitary to trigger milk let-down and support labor. The content covers how pregnancy prepares the breasts, the positive feedback loops in labor, and the breastfeeding-driven maintenance of milk production, including how prolactin can suppress ovulation. The explanation is framed around the Osmosis module on lactation endocrinology.

Overview

In this Osmosis module, the endocrinology of lactation is explored through two key hormones, oxytocin and prolactin. The video explains how these hormones are produced in the hypothalamus and pituitary, travel to the mammary glands, and coordinate milk production, storage, and ejection. It details how dopamine from the hypothalamus inhibits prolactin release while prolactin releasing hormone can stimulate it, and how oxytocin promotes milk let-down by acting on myoepithelial cells surrounding the alveoli. The narrative also covers the pregnancy context, where estrogen and progesterone prepare the breast tissue but inhibit milk production until birth, and how labor and breastfeeding trigger positive feedback loops that sustain lactation. It ties these processes to clinical relevance for students and clinicians alike.

Breast Structure and Hormone Action

Each breast contains lobules with milk-secreting alveolar cells and lactiferous ducts lined by myoepithelial cells. Prolactin and oxytocin act on receptors in these cells to promote milk production and milk ejection, respectively. Alveolar development during pregnancy is driven by a combination of placental hormones and ovarian steroids, while high estrogen and progesterone levels prevent milk production until after delivery.

Labor and Milk Ejection

Labor is described as a positive feedback cycle where cervical dilation increases oxytocin release, enhancing contractions and further dilation. After birth, the fall in estrogen and progesterone allows prolactin to promote milk production. Suckling triggers pulsatile oxytocin release, causing milk to be ejected in a rhythmic pumping pattern, and supportive feedback mechanisms ensure continued milk supply during nursing.

Breastfeeding and Reproductive Hormones

Breastfeeding maintains elevated prolactin levels, which suppress GnRH and downstream LH and FSH, reducing ovulation and menstruation during lactation. The video highlights how tactile nipple stimulation leads to brain signals that reinforce the lactation cycle, aligning infant nutrition with maternal physiology.

Clinical Context

Across these sections, the Osmosis module emphasizes the integrated hormonal control of lactation and its relevance to medical education, illustrating how hypothalamic and pituitary signals coordinate milk production and reproductive physiology.