A small raised projection at the center of the areola through which milk is delivered from the mammary gland.
Structure
The nipple contains the openings of about fifteen to twenty lactiferous ducts. Smooth muscle fibers in the surrounding tissue can contract to make it erect.
Function
During breastfeeding, contraction of the smooth muscle and stimulation of nerve endings trigger milk ejection from the underlying ducts through the let-down reflex.
Clinical note
Changes in nipple shape, retraction, or discharge can be early signs of breast disease and warrant evaluation.
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