## Lactogenesis and Hormonal Control **Key Point:** Lactogenesis stage II (copious milk secretion) is initiated by the withdrawal of placental steroids and the unopposed action of prolactin after delivery. ### Mechanism of Lactogenesis Lactogenesis occurs in three stages: 1. **Stage I (Pregnancy):** Mammary gland development under estrogen and progesterone; milk secretion is inhibited by high placental steroid levels. 2. **Stage II (Postpartum):** Dramatic increase in milk production within 24–72 hours after delivery, triggered by sudden drop in estrogen and progesterone following placental expulsion. Prolactin (released by suckling stimulus via the pituitary) drives actual milk synthesis. 3. **Stage III (Galactopoiesis):** Maintenance of milk supply through continued suckling and prolactin secretion. **High-Yield:** Prolactin is the hormone that **stimulates and maintains** milk synthesis in the lactating breast. Oxytocin causes milk ejection (letdown reflex) but does not initiate milk secretion. ### Role of Each Hormone | Hormone | Role in Lactation | Timing | |---------|-------------------|--------| | Prolactin | Stimulates milk synthesis; maintains lactation | Postpartum onward | | Oxytocin | Causes milk ejection (letdown reflex) | During suckling | | Estrogen/Progesterone | Inhibit milk secretion during pregnancy | Pregnancy | | hPL | Supports fetal growth; does not regulate lactation | Pregnancy only | **Clinical Pearl:** Dopamine inhibits prolactin release; dopamine antagonists (metoclopramide, domperidone) can enhance lactation in mothers with low milk supply. [cite:Williams Obstetrics 26e Ch 37]
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