Lactiferous ducts

Lactiferous ducts are the major excretory ducts of the mammary gland that transport milk from the lobular units to the nipple surface. Each breast contains approximately 15–20 lactiferous ducts, each draining a corresponding lobe of the breast. These ducts converge toward the nipple, where they open as separate orifices on the nipple surface.

Anatomy and Structure

The ductal system of the breast is organized hierarchically. Terminal ductules within lobules (the terminal ductal lobular units, or TDLUs) drain into subsegmental ducts, which merge into segmental ducts, and ultimately into the main lactiferous ducts. Near the nipple, each lactiferous duct may widen slightly into a region historically referred to as the lactiferous sinus (or ampulla), though modern ultrasound studies have questioned the consistent presence of a true sinus in all individuals.

Histology

The lactiferous ducts are lined by a double-layered epithelium: an inner layer of luminal (secretory) epithelial cells and an outer layer of myoepithelial cells, surrounded by a basement membrane. The myoepithelial cells contract under the influence of oxytocin to propel milk toward the nipple during lactation.

Clinical Significance

• Ductal carcinoma: The majority of breast cancers arise from the epithelial lining of the ductal system, including ductal carcinoma in situ (DCIS) and invasive ductal carcinoma.

• Duct ectasia: Dilation and inflammation of the lactiferous ducts, often presenting with nipple discharge.

• Galactorrhea and nipple discharge: Pathologic or physiologic secretions travel through these ducts.

• Intraductal papilloma: A benign tumor arising within a lactiferous duct, commonly causing bloody nipple discharge.