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AN9.1-3 | Pectoral region — Summary & Reflection

REFLECT

Kolb Reflection — Pectoral Region

Take 5 minutes to work through these four steps:

  1. CE (Concrete Experience): Stand in front of a mirror. Place your hands together at chest level and push hard — you will feel pectoralis major contract. Trace where the muscle goes: from your collarbone and breastbone, converging into your upper arm. Feel your armpit — the front wall is pectoralis major, the back wall is latissimus dorsi.
  1. RO (Reflective Observation): Which part of the breast anatomy surprised you most? Why is the lymphatic drainage more clinically important than the blood supply in the context of cancer spread?
  1. AC (Abstract Conceptualisation): Connect what you learned today to your Physiology topic (nerve and muscle physiology). The medial and lateral pectoral nerves emerge from the brachial plexus — damage at different spinal levels produces predictable patterns of pectoral weakness. How would you test this clinically?
  1. AE (Active Experimentation): Before tomorrow's lecture, look at a chest X-ray (posteroanterior view). Can you identify the silhouette of pectoralis major on the X-ray? Where is the axillary tail of Spence in relation to the apex of the lung shadow?

Forward reference: You will revisit pectoral anatomy in your surgical posting (Year 3) when you observe or perform breast examination. The anatomy you learn today is the foundation for every breast examination you will conduct for the rest of your career.

KEY TAKEAWAYS

Key Takeaways — Pectoral Region (AN9.1–AN9.3)

  1. Pectoralis major (AN9.1): Fan-shaped; clavicular head (C5–7 via lateral pectoral nerve) + sternocostal head (C8–T1 via medial pectoral nerve); inserts on bicipital groove of humerus; adducts and medially rotates the arm.
  1. Pectoralis minor (AN9.1): Deep to pectoralis major; ribs 3–5 to coracoid process; depresses and protracts the scapula; KEY landmark for axillary lymph node levels (I = lateral, II = behind, III = medial).
  1. Clavipectoral fascia (AN9.1): Between clavicle and pectoralis minor; pierced by LCTA — Lateral pectoral nerve, Cephalic vein, Thoracoacromial artery, Axillary lymphatics.
  1. Breast location (AN9.2): 2nd to 6th rib, sternal edge to mid-axillary line; nipple at 4th intercostal space; axillary tail of Spence projects into axilla.
  1. Breast structure (AN9.2): 15–20 lobes each via lactiferous duct to lactiferous sinus to nipple; Cooper's ligaments support breast — invaded in cancer causing skin dimpling.
  1. Blood supply (AN9.2): Lateral thoracic artery (dominant), internal thoracic perforators (medial), intercostal perforators (lateral).
  1. Lymphatic drainage (AN9.2): 75% axillary Levels I–III; 25% internal mammary. Sentinel node biopsy guides dissection. Quadrant rule: upper outer = Level I axillary first.
  1. Breast development (AN9.3): Mammary ridge week 6; oestrogen = puberty; prolactin = lactation; oxytocin = milk ejection.
  1. Congenital anomalies (AN9.3): Polythelia/polymastia most common; NEW nipple inversion in adult = malignancy until proven otherwise.
  1. Cross-subject links: Calcium (BI) drives pectoral muscle contraction; nerve physiology (PY) explains pectoral nerve innervation patterns; ECM collagen (BI) forms Cooper's ligaments and clavipectoral fascia.