The nipples contain the outlets of the milk ducts (lactiferous tubules). Each nipple is situated in the center of the mammary gland. It generally has a conical shape and is a light rosy colour that deepens during pregnancy. Nipples vary in size and shape and may be smooth, protruding, or inverted. The nipples enlarge during pregnancy, followed by enlargement of the entire mammary gland. The
nipples usually point upward and somewhat to the sides, a position that is believed to have evolved because it is most convenient for the sucking infant. The nipple and areola contain smooth muscle fibres that can contract in response to cold, to sexual stimulation, or to the baby's suckling, causing the areola to shrink and the nipple to become erect. The involuntary action squeezes the ducts and, during breast-feeding, helps release milk. Research Nipples
Abbreviations
Medicine
Research Nipples