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Development of Breast

  1. During the fourth week of gestation 2 ectodermal thickenings called milk lines develop on the ventral surface extending axillae to the medial thigh.
  2. It the level of the fourth intercostal space these ridges persists subsequently developing into mammary gland.
  3. This primary bud gives rise to several secondary buds that develop into the lactiferous ducts and their branches that make up the mammary gland. The lobules are comprised of acini that consist of layers of two types of cells (epithelial and myoepithelial) that surround a lumen. Q
  4. The surrounding areola is formed by the ectoderm during the fifth month. The areola also contains other epidermal glands, including glands of Montgomery (sebaceous glands for lubrication of the areola).
  5. At term, approximately 15-20 lobes of glandular tissue are there, each containing a lactiferous duct. The supporting fibrous connective tissue, Cooper ligaments, and fat of the mammary gland develop from the surrounding mesoderm.
  6.  It reaches normal size between 16 to 19 years. During pregnancy the breast assumes its complete morphologic maturation and functional activity.
  7. During pregnancy cellular proliferation occurs under the influence of estrogen and progesterone, plus placental lactogen, prolactin and chorionic gonadotropin.
  8. At delivery, there is a loss of estrogen and progesterone, and milk production occurs under the influence of prolactin.
  9. The lactiferous ducts drain into retroareolar ampullae that converge into a depressed pit in the overlying skin.
  10. Each of the 15-20 lobes of the mammary gland has an ampulla with an orifice opening into this mammary pit.
  11. Stimulated by the inward growth of the ectoderm, the mesoderm surrounding this area proliferates, creating the nipple with circular and longitudinally oriented smooth muscle fibers.
  12. The normal breast lobules and ducts are lined inner secretory epithelial cells and outer myoepithelial cells. The inner epithelial cells changes its shape from cuboidal to columnar shape under the hormonal influence.
  13. Under active hormonal stimulation, the cells maintain tall shape and abundant cytoplasm. Myoepithelial cells are under the epithelial cells and they have contractile protein which contracts the duct and push the secretory product outside.
  14. Congenital breast malformations may vary from absence to supernumerary breast (at milk line).
    Amastia (Absence of breast), micromastia (Small breast), macromastia (Large breast), polymasita (extra breasts), athelia (nipple deficiency), microthelia (small nipple), polythelia (extra nipple).  
  15. Amastia is complete absence of glandular tissue, nipple, and areola.
  16. Athelia is absence of nipple (rarest).
  17. Hypoplasia is the presence of very small rudimentary breasts (most common form of congenital breast malformations).
  18. Amastia and hypoplasia may be associated with: Finlay-Marks syndrome (Autosomal dominant. Nodules of raw hairless scalp/ Small ears/ sparse pubic hair and renal hypoplasia) and Turner syndrome. Q
  19. Poland syndrome is characterized by aplasia, the absence of glandular tissue in the presence of a nipple and areola and is often accompanied by musculoskeletal deformities of the chest wall and ipsilateral upper extremity.
  20. Polythelia is presence of more than 2 nipples (90% of supernumerary nipples are in the inframammary region)
  21. Polymastia is the presence of accessory glandular tissue. It is second most common form of supernumerary breast tissue and the most common location is in axilla).

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