## **Core Concept**
Milk ejection, also known as the letdown reflex, is a crucial process in lactation that involves the contraction of myoepithelial cells surrounding the alveoli and ducts of the mammary gland. This process is primarily facilitated by a neuroendocrine reflex. The hormone responsible for this reflex is released from the posterior pituitary gland.

## **Why the Correct Answer is Right**
The correct answer, **Oxytocin**, is a posterior pituitary hormone that plays a key role in the milk ejection reflex. When a baby suckles, it stimulates nerve endings in the nipple, which send signals to the hypothalamus. The hypothalamus then stimulates the release of oxytocin from the posterior pituitary gland. Oxytocin binds to receptors on the myoepithelial cells of the mammary gland, causing them to contract and express milk into the ducts, making it available for the baby to feed.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Prolactin is a hormone involved in lactation, but its primary role is in the stimulation of milk production (lactogenesis), not the ejection of milk. Prolactin levels increase during pregnancy and remain high during lactation, but it does not directly cause milk ejection.
- **Option B:** Progesterone is a steroid hormone involved in the menstrual cycle and in maintaining the early stages of pregnancy. It does not play a direct role in milk ejection.
- **Option C:** Luteinizing hormone (LH) is crucial for ovulation and the maintenance of the corpus luteum but is not directly involved in the process of milk ejection.

## **Clinical Pearl / High-Yield Fact**
A memorable point for exams is that the milk ejection reflex can be conditioned to auditory or visual cues, which is why some mothers may experience milk letdown when hearing a baby cry or seeing their baby. This reflex is essential for successful breastfeeding.

## **Correct Answer:** . Oxytocin