The Postpartum Period Quiz

See Definition. Option B is correct. Milk is made by secretory cells in tiny sacs called alveoli, and it is carried towards the nipple along ducts. Wrapped around the alveoli and ducts are myoepithelial cells, contractile cells that behave like small muscles. When they contract they squeeze the milk out of the alveoli into the ducts. The trigger is oxytocin. Suckling sends sensory signals from the nipple to the brain, and oxytocin, made in the hypothalamus, is released from the posterior pituitary (the back part of the small hormone gland beneath the brain). It travels in the blood to the breast and causes the myoepithelial cells to contract. This is the milk ejection or let-down reflex, which can also be triggered by the sight, sound or smell of the baby. It is separate from milk production, which depends on prolactin released from the anterior pituitary in response to suckling. A simple way to remember it: prolactin makes the milk, oxytocin moves it.

• Cells: Myoepithelial cells around the alveoli and ducts contract to squeeze milk into the ducts.
• Trigger: Oxytocin, released from the posterior pituitary in response to suckling.
• Distinction: Prolactin makes the milk and oxytocin moves it, in the milk ejection (let-down) reflex.