Breast Anatomy

The diagrams to the right shows some basic anatomical structures of the breast. These structures are of interest in a discussion about DCIS.

Macro Normally, there are two mammary glands, one on either side of the sternum but breast tissue or nipples may occur anywhere along the embryonic milk lines. The adult female breast normally extends from the second rib superiorly to the 6th or 7th rib inferiorly and from the sternal border to the midaxillary line laterally. Rarely breast tissue may extend well beyond those landmarks The breast develops within the superficial fascia and is retained in place by suspensory ligaments (Cooper's ligaments) The breast rests on the major chest muscle, the pectoralis major Fat surrounds and permeates the gland. Fat contributes to the size and shape of the breast.

Micro

• Each breast, or mammary gland, contains 15-20 lobes and each lobe is comprised of 20-40 terminal ductal lobular units (TDLU). The TDLU is the functional unit of the breast.
• TDLUs consists of:
  • extralobar terminal duct (ETD) which attaches the lobule to the ductal system
  • intralobar terminal duct (ITD) continues the duct system into the lobule
  • clusters of 10-100 sac-like acini that open into the ITD.
• Acini and the terminal duct are the source of milk production.
  • "The epithelium throughout the ductal-lobular system is bilayered, consisting of an inner (luminal) epithelial cell layer and an outer ( basal ) myoepithelial cell layer".
  • Visual, auditory and areola stimulation trigger a neuroendocrine reflex which releases oxytocin from the posterior pituitary. Oxytocin travels in the blood to the mammary gland where it stimulates specific receptors on myoepithelial cells, causing them to contract and expel milk into the ducts and on toward the nipple.
• Each lobe empties into a lactiferous duct.
• Lactiferous ducts merge into 5-10 main lactiferous ducts that open at the nipple.
• The majority of pathologic changes in the breast, including DCIS and invasive carcinomas, are believed to arise from the TDLU.

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