Where it is
Over the pectoralis major muscle, from the second to the sixth rib. Each breast has 15–20 lobes draining through lactiferous ducts to the nipple, supported by suspensory ligaments; the upper outer quadrant extends toward the axilla (tail of Spence).
What it does
Prolactin stimulates milk production and oxytocin triggers the let-down reflex during breastfeeding.
Clinical relevance
- Most breast cancers start in the upper outer quadrant.
- Mastitis causes a red, painful, warm area, often with fever, during breastfeeding.
Nursing focus
- Encourage continued breastfeeding or pumping with mastitis, along with prescribed antibiotics.
- Examine breast tissue in a pattern that includes the tail of Spence and axillary nodes.