Development of the Breast
Embryological Origin
The breast develops from ectodermal thickening (the mammary ridge / milk line / line of Schultz).
- Appears during the 4th week of intrauterine life
- Extends as a ridge from the axilla to the groin on each side
- In humans, it disappears over most of its extent, persisting only in the pectoral region
Steps of Development
- Mammary ridge persists in the pectoral region → converted into a mammary pit (ectodermal thickening becomes depressed)
- The mammary pit gives off 15–20 solid ectodermal cords that grow into the underlying mesenchyme
- These cords proliferate to form the lobes of the gland
- Cords are initially solid; they later canalise to form the lactiferous ducts
- At birth, the depressed ectodermal thickening (pit) is everted/raised to form the nipple
- The stroma of the breast develops from surrounding mesoderm
Summary: Gland (parenchyma) = ectodermal origin; Stroma = mesodermal origin.
Postnatal Development
At Birth
- Mammary gland is rudimentary in both sexes
- The nipple is everted at birth
At Puberty (Female)
- Growth stimulated by oestrogens (from ovaries)
- Progesterone (from corpus luteum) stimulates development of secretory alveoli
- Prolactin (from pars anterior of hypophysis) stimulates milk secretion during lactation
During Pregnancy
- Areola darkens and enlarges
- Montgomery’s tubercles become prominent
- Secretory alveoli fully develop under combined hormonal influence
Developmental Anomalies
| Anomaly | Description |
|---|---|
| Amastia | Complete absence of the breast |
| Athelia | Absence of the nipple |
| Polymastia | Development of more than one breast along the milk line (supernumerary breasts) |
| Polythelia (supernumerary nipples) | Extra nipples appearing along the milk ridge; often mistaken for moles |
| Retracted / inverted nipple | Occurs if nipple fails to evert from the ectodermal pit at birth; infant cannot suckle; nipple prone to infection |
| Gynaecomastia | Development of breast tissue in males; mainly at puberty; usually bilateral; due to hormonal imbalance (oestrogen excess / androgen deficiency); associated with Klinefelter’s syndrome |
Viva Pearls
- Breast parenchyma = ectodermal origin; stroma = mesodermal origin
- Milk line extends from axilla to groin (appears at 4th week IUL)
- Nipple formed by eversion of mammary pit at birth
- 15–20 secondary buds → lobes of the breast
- At puberty: oestrogen causes breast growth
- Milk secretion: prolactin (not oestrogen)
- Gynaecomastia = breast development in males; hormonal imbalance; bilateral; Klinefelter’s syndrome
- Polythelia = supernumerary nipples along milk line; mistaken for moles