Regarding the physiology of lactation and milk production, all of the following statements are TRUE EXCEPT:

Explanation

## Physiology of Lactation: Hormonal Control ### Prolactin and Milk Synthesis **Key Point:** Prolactin is synthesized by lactotroph cells of the anterior pituitary and is the primary hormone driving milk synthesis and secretion from mammary acinar cells. ### Oxytocin and the Milk Letdown Reflex **Key Point:** Oxytocin, released from the posterior pituitary in response to nipple stimulation, causes contraction of myoepithelial cells surrounding the alveoli and ducts, propelling milk toward the nipple (milk ejection reflex). ### Stages of Lactogenesis | Stage | Timing | Features | |-------|--------|----------| | **Lactogenesis I** | Late pregnancy to 2–3 days postpartum | Colostrum production; high protein, low lactose | | **Lactogenesis II** | 2–3 days to 2 weeks postpartum | Transition milk; increased lactose, decreased protein | | **Lactogenesis III (Galactopoiesis)** | Beyond 2 weeks | Mature milk; maintenance phase | ### Prolactin-Inhibiting Factor (Dopamine) **High-Yield:** Dopamine, released by the hypothalamus, is the primary prolactin-inhibiting factor (PIF). When dopamine is suppressed (e.g., by suckling, TRH, or certain drugs), prolactin levels rise and milk production increases. **The Trap in Option 3:** The statement says "Suppression of prolactin-inhibiting factor (dopamine) leads to **decreased** milk production." This is **FALSE**. Suppression of dopamine (the inhibitor) leads to **increased** prolactin and **increased** milk production — the opposite of what the option claims. ### Why the Other Options Are Correct - **Option 0:** Prolactin is indeed the primary hormone for milk synthesis. ✓ - **Option 1:** Oxytocin-mediated myoepithelial contraction is the mechanism of milk letdown. ✓ - **Option 2:** Lactogenesis stage I does begin in late pregnancy and continues until 2–3 days postpartum. ✓ [cite:Williams Obstetrics 26e Ch 37]