Milk comes out of the nipple through multiple tiny openings called milk duct orifices, which typically number between four and twenty per breast
. The process begins in the mammary glands inside the breast, where milk is produced in small grape-like sacs called alveoli. These alveoli are grouped into lobules, which connect to larger structures called lactiferous ducts. Milk flows from the alveoli into these ducts, which converge and open at the nipple through the multiple duct orifices
. When a baby suckles, it stimulates the nipple, triggering the release of oxytocin, which causes myoepithelial cells around the alveoli to contract and push milk through the ducts and out of the nipple openings
. Milk is not sucked out directly from the alveoli but is secreted into the ducts and then ejected through the nipple. In summary, milk is produced in the alveoli of the mammary glands, travels through lactiferous ducts, collects briefly in lactiferous sinuses behind the nipple, and exits the breast through multiple small openings in the nipple itself
