Nipple

The nipple (papilla mammaria) is a cylindrical or conical projection located at the apex of the breast, typically situated at the level of the fourth intercostal space in the non-pendulous breast. It serves as the terminal point of the ductal system, containing 15–20 lactiferous duct openings through which milk is delivered during lactation.

The nipple is composed of dense connective tissue and smooth muscle fibers arranged both circularly and longitudinally. Contraction of these smooth muscle fibers causes nipple erection in response to tactile, thermal, or sympathetic stimulation. The nipple is surrounded by the areola, a pigmented circular area of skin containing sebaceous glands (Montgomery glands/tubercles) that provide lubrication during breastfeeding.