II. Anatomy

  1. GynBreastAnatomyGeneral.jpg
  2. GynBreastAnatomyLobes.gif
  3. GynBreastAnatomyLobules.gif
  4. gynBreastLobuleGrayBB1172.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)

III. Anatomy: Surrounding landmarks

  1. Underlying foundation to Breast tissue
    1. Pectoralis major Muscle
    2. Serratus anterior border (laterally, inferior)
  2. Lateral border
    1. Latissimus dorsi Muscle (axilla)
  3. Inferior Breast border
    1. Inframammary ridge
  4. Superior Breast border
    1. Second rib (inferior to clavicle)
  5. Medial Breast border
    1. Sternum

IV. Anatomy: Organization

  1. Structural Components
    1. Peri-Nipple structures
      1. Areola
      2. Areolar glands
      3. Nipple
    2. Cooper's Ligaments
      1. Add structure to Breast
      2. Attached to underlying fascia
  2. Key Lactation Components: Ducts and Lobules
    1. Lobules
      1. Composed of acini and ducts
    2. Lobes
      1. Composed of Lobules
    3. Lactiferous ducts
      1. Drain lobes to ducts at nipple surface (6-10 major ducts drain to surface)

V. Physiology: Development

  1. Pre-Puberty
    1. Breasts in resting state
    2. Nonfunctional ducts
  2. Puberty: Stage 1 Mammogenesis
    1. Ovulation starts
      1. Menstrual Cycle related increase in Estrogen and Progesterone
    2. Ducts elongate due to Estrogen
    3. Type 1 Breast lobules develop
    4. Breast alveolar buds form
      1. Appear as retroareolar mass (Do not excise as mass! - halts Breast development)
    5. Type 2 and 3 Breast lobules form from the alveolar buds
      1. Side branches of ducts and lobular elements form
  3. Maturity (end of Puberty)
    1. Further Breast development stops at the end of Puberty (until pregnancy)
    2. Breasts become pendulous
    3. Lobular elements well formed in resting state
  4. Pregnancy
    1. General Changes
      1. Areolar pigmentation
      2. Vascular engorgement
        1. Mammary Blood Flow increases 180%
        2. Breast doubles in weight
        3. May result in bloody Nipple Discharge
          1. Second and third trimester and early Lactation
          2. Resolves spontaneously in most cases
    2. Stage 2 Mammogenesis (first half of pregnancy)
      1. Breast alveoli develop in response to increased Estrogen and Progesterone levels
      2. Proximal ducts grow and branch
      3. Type 3 Breast lobules form in response to HCG in early pregnancy
        1. Breast lobulesn as well as the overall Breast increase in size during pregnancy
    3. Stage 1 Lactogenesis or Secretory Initiation (second half of pregnancy)
      1. Increased Progesterone from the placenta inhibits Prolactin and milk production
      2. Small amounts of milk and colostrum form
    4. Stage 2 Lactogenesis or Secretory Activation (after delivery)
      1. Progesterone levels fall (without placenta)
        1. Proalctin is no longer inhibited by Progesterone, and Lactation occurs
      2. Prolactin
        1. Stimulates copious milk production
        2. Prolactin secretion is inhibited by Dopamine activity at D2 receptors on the Hypothalamus
      3. Other Lactation triggers
        1. Cortisol
        2. Insulin
        3. Nipple stimulation
        4. Emptying of the Breast (by Breast Feeding or pumping)
      4. Oxytocin
        1. Stimulates milk let down, myoepithelial cell contraction and milk ejection
  5. Perimenopausal
    1. Lobules begin to recede
    2. Leaves residual ducts and fibro-connective tissue
    3. Breast cysts commonly develop during this stage
  6. Postmenopausal
    1. Residual ducts and fat
    2. Easiest time for Clinical Breast Exam

VI. References

  1. Pillay (2022) Lactation Physiology, Stat Pearls, Treasure Island, Fl, accessed 2/24/2023
    1. https://www.ncbi.nlm.nih.gov/books/NBK499981/

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