During breastfeeding, two hormones act sequentially on the mammary gland. The correct pairing of stimulus, hormone and action is:

• A Suckling stimulates oxytocin, which contracts myoepithelial cells and ejects milk ✓
• B Suckling stimulates oxytocin, which promotes further milk secretion
• C Suckling stimulates prolactin, which ejects stored milk from the alveoli
• D Suckling stimulates progesterone, which maintains alveolar proliferation

Explanation

Suckling afferents from the nipple reach the hypothalamus and trigger two separate neuroendocrine responses. Oxytocin released from the posterior pituitary contracts myoepithelial cells surrounding alveoli, producing milk ejection, the let-down reflex. Prolactin released from the anterior pituitary drives milk secretion for the next feed, so option C reverses the actions. Progesterone falls after delivery and its withdrawal permits lactation rather than maintaining it.

Reference: Ganong Review of Medical Physiology, 26th ed.

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