Milk ejection is facilitated by: March 2007, March 2013
**Core Concept**
Milk ejection, also known as the letdown reflex, is a physiological process during lactation where the muscles surrounding the ducts of the mammary glands contract, releasing milk from the alveoli into the ducts. This process is essential for successful breastfeeding and is primarily regulated by the hormone oxytocin.
**Why the Correct Answer is Right**
The correct answer is facilitated by the hormone oxytocin, which is released from the posterior pituitary gland in response to suckling. Oxytocin binds to oxytocin receptors on the myoepithelial cells surrounding the mammary ducts, causing them to contract and release milk. This process is crucial for effective milk ejection and is often referred to as the "letdown reflex."
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because oxytocin is the primary hormone responsible for milk ejection, not prolactin. Prolactin stimulates milk production, but it does not facilitate milk ejection.
**Option B:** This option is incorrect because dopamine is actually an inhibitor of milk ejection. High levels of dopamine can suppress the release of oxytocin, making it more difficult to facilitate milk ejection.
**Option C:** This option is incorrect because vasopressin is a hormone involved in water reabsorption in the kidneys and is not directly involved in milk ejection.
**Clinical Pearl / High-Yield Fact**
It's essential for healthcare providers to understand the importance of oxytocin in milk ejection, as this hormone can be used to stimulate milk production in women with difficulty breastfeeding.
**Correct Answer:** B. Dopamine.