Breast Anatomy and Physiology

Breast Anatomy and Physiology

Breast Anatomy and Physiology

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Gross Anatomy - The Breast Blueprint

  • Extent: Vertically 2nd-6th ribs; horizontally sternum to mid-axillary line. Axillary Tail of Spence pierces deep fascia, extends into axilla.
  • Layers: Skin → Subcutaneous fat → Mammary gland (parenchyma & stroma) → Retromammary space (loose areolar tissue) → Pectoralis major fascia.
  • Parenchyma: 15-20 lobes, each with a lactiferous duct opening at nipple. Lobes → lobules → Terminal Duct Lobular Unit (TDLU).
  • Stroma:
    • Fibrous: Cooper's ligaments (suspensory ligaments from clavicle/pectoral fascia to dermis, provide support).
    • Fatty: Fills interlobular spaces. Sagittal view of female breast anatomy

⭐ The Tail of Spence is a common site for breast cancer due to its glandular tissue content.

Microscopic Anatomy - Tiny Tissue Tales

  • Terminal Duct Lobular Unit (TDLU): Key functional unit; origin of most breast diseases.
    • Consists of lobule & extralobular terminal duct.
  • Epithelium (Bilayered): Lines ducts & acini.
    • Luminal (inner): Cuboidal/columnar cells; milk production.
    • Myoepithelial (outer/basal): Contractile cells; milk ejection.
  • Stroma: Connective tissue.
    • Intralobular: Loose, cellular, hormonally sensitive.
    • Interlobular: Dense, fibrous, adipocytes.
  • Cooper's Ligaments: Fibrous septa (fascia to skin).

Female Breast Anatomy with Histology

⭐ Myoepithelial cell layer: intact = benign/in-situ; disrupted/absent = invasive carcinoma.

Vascular & Nerves - Lifelines & Drains

Breast vascular supply and lymphatic drainage

  • Arterial Supply:
    • Internal Thoracic A. (medial perforators)
    • Lateral Thoracic A. (from axillary a.)
    • Thoracoacromial A. (pectoral br.)
    • Posterior Intercostal A. (2nd-4th)
  • Venous Drainage:
    • Follows arteries.
    • Axillary V. (main)
    • Internal Thoracic V.
    • Post. Intercostal V. → Batson's (vertebral mets)
  • Lymphatic Drainage:
    • Key for staging/spread.

    ⭐ Axillary LNs: ~75% of breast lymph drainage.

    • Axillary nodes (~75%): Levels I-III.
    • Internal Mammary nodes (~20%): Medial.
    • Supraclavicular nodes (~5%).
  • Nerves (Surgical Importance):
    • Long Thoracic N. (Serratus Ant.; injury → winged scapula). 📌 C5-7: "Wings to Heaven".
    • Thoracodorsal N. (Latissimus Dorsi).
    • Intercostobrachial N. (T2; upper arm sensation).
    • Medial/Lateral Pectoral N. (Pectoralis major/minor).

Physiology & Development - Hormonal Harmony

  • Pubertal Development (Thelarche):
    • Estrogen: Primary driver for ductal elongation, branching, and fat deposition.
    • Progesterone: Synergistic with estrogen for lobuloalveolar budding.
  • Cyclical Changes (Menstrual Cycle):
    • Follicular (Estrogen): Ductal proliferation, ↑epithelial activity.
    • Luteal (Progesterone): Alveolar differentiation, stromal edema, breast tenderness.
  • Pregnancy & Lactation:
    • High Estrogen, Progesterone, Prolactin, hPL: Full lobuloalveolar maturation, colostrum formation.
    • Prolactin (PRL): Milk synthesis. 📌 Suckling reflex maintains high PRL.
    • Oxytocin: Milk ejection ("let-down") via myoepithelial cell contraction.
  • Involution (Post-Lactation/Menopause):
    • Hormonal withdrawal → apoptosis, glandular atrophy, connective tissue & fatty replacement.

⭐ Prolactinomas are the most common hormone-secreting pituitary tumors, often presenting with galactorrhea.

Hormonal control of breast development and lactation

Clinical Anatomy - Exam Room Essentials

  • Quadrants & Clock Face: Standard for lesion localization.
  • Axillary Tail of Spence: Extends into axilla; common site for breast tissue & cancer.
  • Palpable Lymph Nodes:
    • Axillary: Levels I, II, III (pectoralis minor landmark).
    • Supraclavicular & Infraclavicular.
  • Nerves at Risk (Axillary Dissection):
    • Long Thoracic (serratus anterior → winged scapula).
    • Thoracodorsal (latissimus dorsi).
    • Intercostobrachial (upper arm numbness).
  • Cooper's Ligaments: Skin dimpling/retraction if infiltrated by cancer. Breast Lymphatic Drainage and Lymph Node Levels

⭐ Most breast cancers (≈50%) occur in the Upper Outer Quadrant (UOQ).

High‑Yield Points - ⚡ Biggest Takeaways

  • Cooper's ligaments maintain breast shape; their involvement causes skin dimpling in cancer.
  • Main blood supply: Internal mammary artery (medial) & lateral thoracic artery (lateral).
  • Lymphatic drainage: Primarily to axillary nodes (pectoral group, 75%); also internal mammary nodes (25%).
  • Nerve injury risks: Intercostobrachial nerve (arm numbness); long thoracic nerve (winged scapula); thoracodorsal nerve (weak adduction).
  • Milk line remnants can lead to accessory nipples (polythelia) or breast tissue (polymastia).
  • Montgomery tubercles are sebaceous glands on the areola, prominent during pregnancy/lactation.
  • Terminal Duct Lobular Unit (TDLU) is the functional unit and common origin site for most breast cancers and benign proliferative diseases.
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Practice Questions: Breast Anatomy and Physiology

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Which of the following stages of Breast Cancer corresponds to the following features: a breast mass of 6 x 3 cm, ipsilateral supraclavicular lymph node involvement, and distant metastasis that cannot be assessed?

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Flashcards: Breast Anatomy and Physiology

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What breast sx involves removal of all of breast + Nipple areola complex + overlying skin + level I+II+/-III axillary lymph nodes (Pec. minor removed)?_____

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What breast sx involves removal of all of breast + Nipple areola complex + overlying skin + level I+II+/-III axillary lymph nodes (Pec. minor removed)?_____

Patey's Modified radical mastectomy

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