Structure of the Breast
The mammary gland (breast) is a modified sweat gland situated in the superficial fascia of the pectoral region. It is found in both sexes but remains rudimentary in males; in females it becomes well developed at puberty. It consists of three structural components: skin, stroma, and parenchyma.
Skin
Nipple
- Conical projection below the centre of the breast, at the level of the 4th intercostal space (10 cm from the midline)
- Pierced by 15–20 lactiferous ducts
- Contains circular and longitudinal smooth muscle fibres — can make the nipple stiff/erect or flatten it
- Richly innervated by sensory nerve endings — the most sensitive part of the breast
- No fat subjacent to the nipple
- Contains a few modified sweat and sebaceous glands
Areola
- Circular area of pigmented skin surrounding the base of the nipple
- Contains large numbers of modified sebaceous glands (particularly at outer margin)
- These glands produce oily secretion → lubricates nipple and areola → prevents cracking during lactation
- Colour varies with complexion; darkens and enlarges during pregnancy
Montgomery’s tubercles: The sebaceous glands of the areola enlarge during pregnancy and lactation, appearing as small nodular elevations at the outer margin of the areola.
The areola also contains some sweat glands and accessory mammary glands (BD Chaurasia).
Stroma
Forms the supporting framework of the breast. Consists of:
Connective Tissue — Suspensory Ligaments of Cooper
- Fibrous strands/septa condensed from connective tissue
- Arranged radially, like spokes of a wheel
- Connect dermis of overlying skin → ducts of breast → pectoral fascia
- Maintain the protuberance (shape) of the breast
- Atrophy with ageing → breast becomes pendulous in old age
Clinical significance: Cancer infiltrating the suspensory ligaments → shortens them → causes skin retraction/dimpling and breast fixation. Also causes peau d’orange if lymphatics are blocked.
Fat
- Forms the main bulk of the breast
- Distributed all over the breast except beneath the areola and nipple
- The posterior surface of the breast is relatively avascular (BD Chaurasia)
Parenchyma (Glandular Tissue / Mammary Gland Proper)
- A compound tubulo-alveolar gland (BD Chaurasia)
- Secretes milk to nourish the newborn
Lobes
- Consists of 15–20 lobes arranged radially (like spokes of a wheel), converging toward the nipple
- Each lobe = cluster of lobules
- Each lobule = cluster of acini (alveoli)
- Each lobe is drained by a lactiferous duct
Lactiferous Ducts
- Each lobe is drained by one lactiferous duct
- Ducts from different lobes converge toward the nipple and open separately on its surface
- Near the nipple, each duct expands into a lactiferous sinus — a reservoir for milk during lactation
Epithelium
- Alveoli are lined by secretory alveolar epithelium
- Cuboidal in the resting phase
- Columnar during lactation
- In distended alveoli cells appear cuboidal (stretched)
- Smaller ducts → lined by columnar epithelium
- Larger ducts → two or more layers of cells
- Terminal parts of lactiferous ducts → stratified squamous keratinised epithelium
Myoepithelial Cells (Basket Cells)
- Found around alveoli and smaller ducts, lying between epithelium and basement membrane
- Their contraction facilitates passage of milk from alveoli into and along the ducts
Control of Milk Secretion
- Milk secretion is NOT under neural control
- Controlled by the hormone prolactin secreted by the pars anterior of the hypophysis cerebri (anterior pituitary)
- Sensory nerve endings in nipple and areola stimulate prolactin release in response to suckling by the infant
Viva Pearls
- Breast = modified sweat gland in the superficial fascia
- Nipple at the level of 4th intercostal space
- 15–20 lobes converge radially toward the nipple
- Lactiferous sinus = reservoir of milk, at the base of the nipple
- Suspensory ligaments of Cooper connect skin to pectoral fascia
- Fat is absent beneath the nipple and areola
- Milk secretion controlled by prolactin (not neural)
- Montgomery’s tubercles = enlarged sebaceous glands of areola in pregnancy