Topic Outline
Topic Outline
Anatomy and Physiology
Topic Outline


The breast, or mammary gland, is the only organ not fully developed at birth. It undergoes four developmental stages: in utero, during the first two years of life, at puberty, and during pregnancy and lactation1 . During puberty, breast growth consists of ductwork, fat and connective tissue to support the ducts. The ultimate size of the breast is determined mainly by the amount of fatty tissue in the breast and is usually unrelated to milk production.

The nipple contains smooth muscle fibers and sensory nerve endings. Size and shape varies from woman to woman. Nipple pores are openings in the milk ducts on the face of the nipple and >90% of women have between 5 and 9 ductal openings on the face of the nipple2. The areola is the darker pigmented area from which the nipple protrudes in the center. The areola will enlarge and darken over the course of pregnancy. Within the areola are the Montgomery glands or tubercles. They secrete a lubricating substance that both conditions and protects the nipple and areola from infection. Occasionally milk can be expressed from these glands.

During pregnancy the placental hormones3 direct the breasts to develop alveolar tissue, usually resulting in a significant increase in size or fullness in the breasts. Alveoli within the glandular tissue are lined with milk-making cells called leptocytes that respond to prolactin by drawing nutrients from the mother’s blood in order to manufacture milk. Myoepithelial cells surround each alveolus and duct, and contract in response to oxytocin, creating the ‘let-down’ or milk ejection reflex (MER).




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