Lactiferous duct
Lactiferous ducts are ducts that converge and form a branched system connecting the nipple to the lobules of the mammary gland. When lactogenesis occurs, under the influence of hormones, the milk is moved to the nipple by the action of smooth muscle contractions along the ductal system to the tip of the nipple. They are also referred to as "galactophores", "galactophorous ducts", "mammary ducts", "mamillary ducts" or "milk ducts". Structure. Lactiferous ducts are lined by a columnar epithelium supported by myoepithelial cells. Prior to 2005, it was thought within the areola the lactiferous duct would dilate to form  the lactiferous sinus in which milk accumulates between breastfeeding sessions. However past studies have shown that the lactiferous sinus does not exist. Function. The columnar epithelium plays a key role in balancing milk production, milk stasis and reabsorption. The cells of the columnar epithelium form tight junctions which are regulated by hormones and local factors like pressure and casein content. Prolactin and/or placental lactogen are required for tight junction closure while progesterone is the main hormone preventing closure before birth. Clinical significance. The majority of breast diseases either originate from lactiferous ducts or are closely related. The high susceptibility to  benign and malignant diseases is in part a consequence of the cycling hormonal growth stimulation resulting in a high cell turnover and accumulation of defects and complicated hormonal equilibrium which is highly sensible to disturbance. Lactiferous Duct Dysmorphia (LDD). Lactiferous Duct Dysmorphia (LDD) is the deformity or abnormality in the shape or size of a milk duct negatively affecting milk flow (also known as Milk Duct Dysmorphia). Typical causes include: nipple clamps, piercings, or most commonly, ill fitting breast pump flanges.