## The Letdown (Milk Ejection) Reflex **Key Point:** The letdown reflex is a neuroendocrine reflex mediated by oxytocin, which causes contraction of myoepithelial cells surrounding the alveoli and ducts, propelling milk toward the nipple. **High-Yield:** This is a frequently tested mechanism in pediatrics and physiology. Understanding the letdown reflex is essential for counseling mothers on breastfeeding success. ## Mechanism of Letdown Reflex 1. **Stimulus:** Infant's suckling on the nipple stimulates mechanoreceptors 2. **Neural pathway:** Sensory impulses travel via the spinal cord to the hypothalamus 3. **Hormone release:** The posterior pituitary releases oxytocin in response to hypothalamic stimulation 4. **Effector response:** Oxytocin circulates in the blood and binds to receptors on myoepithelial cells surrounding the alveoli 5. **Result:** Myoepithelial cell contraction increases intramammary pressure, ejecting milk into the ducts and toward the nipple **Clinical Pearl:** The letdown reflex can be conditioned — mothers may experience letdown in response to the cry of their infant or even thinking about breastfeeding. Conversely, stress, anxiety, and pain can inhibit the reflex through sympathetic inhibition of oxytocin release. **Mnemonic:** **OXY-LETDOWN** — **OXYtocin** causes **Letdown** by contracting myoepithelial cells. ## Comparison: Oxytocin vs. Prolactin | Hormone | Function | Timing | | --- | --- | --- | | **Oxytocin** | Milk ejection (letdown reflex) | During and after feeding | | **Prolactin** | Milk production/synthesis | Increases with each feeding | **Warning:** Do not confuse prolactin (which stimulates milk production) with oxytocin (which causes milk ejection). Both are essential, but they have distinct roles. [cite:Guyton & Hall Textbook of Medical Physiology Ch 82]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.