Topic Outline
Topic Outline
Anatomy and Physiology
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Topic Outline

Anatomy/Physiology

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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References

  1. Inman JL, Robertson C, Mott JD, Bissell MJ Mammary gland development: cell fate specification, stem cells and the microenvironment Development (2015) 142 1028-1042
  2. Love, S. M. and Barsky, S. H. (2004), Anatomy of the nipple and breast ducts revisited. Cancer, 2004 101: 1947–1957
  3. Napso T, Yong HEJ, et al The Role of Placental Hormones in Mediating Maternal Adaptations to Support Pregnancy and Lactation Frontiers in Physiology August 2018 Vol 9 Article 1091
  4. Truchet S, Hono-Houeto E. Physiology of Milk Secretion Best Practice & Research Clinical Enocrinology & Metabolism 31 (2017) 367-384
  5. Phillipps, HR, YIP SH, Grattan DR. Patterns of prolactin secretion Molecular and Cellular Endocrinology 2020 Vol 502,  15 Feb 2020
  6. Stuebe AM, Meltzer-Brody S, Pearson B, Pedersen C Grewen K. Maternal Neuroendocrine Serium Levels in Exclusively Breastfeeding Mothers Breastfeeding Med 10(4) 2015 p. 197-202
  7. Cox DB, Owens RA, Hartmann PE. Blood and Milk Prolactin and the Rate of Milk Synthesis in Women Experimental Phys (1996) 81, 1007-1020
  8. Weaver SR, Hernandez LL Autocrine-paracrine regulation of the mammary gland J Dairy Sci 99:842-853
  9. Nagasawa M, Okabe S, Mogi K, Kikusui T. Oxytocin and mutual communication in mother-infant bonding Front Hum Neurosci 28 Feb 2012