# Breast Anatomy and Development

> NEET-PG Obstetrics and Gynaecology notes on breast anatomy and development, covering lobes, blood and lymph supply, mammary line and hormones of lactation.

- Canonical URL: https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/breast-anatomy-and-development
- Exam / course: NEET-PG · Subject: Obstetrics and Gynaecology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Bailey and Love's Short Practice of Surgery; Gray's Anatomy for Students; Williams Obstetrics
- How to cite: "Breast Anatomy and Development", PrepElephant, https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/breast-anatomy-and-development

## Direct answer

The breast is a modified apocrine sweat gland of about 15 to 20 lobes, resting on the pectoral fascia and draining through lactiferous ducts to the nipple. It develops from the ectodermal mammary line and grows at puberty under oestrogen, while pregnancy hormones prepare it for lactation. Lactation begins after delivery of the placenta, when falling progesterone allows prolactin to drive full milk secretion.

## What you must remember

- **Lobes and ducts:** 15 to 20 lobes, each drained by a lactiferous duct that opens separately on the nipple, with a lactiferous sinus beneath the areola.
- **Suspensory support:** Cooper ligaments run from the skin to the deep fascia, and their stretching contributes to sagging.
- **Arterial supply:** the internal thoracic (mammary) artery, with lateral thoracic, thoracoacromial and intercostal perforating branches.
- **Lymphatics:** most drainage goes to the axillary nodes, with the remainder to parasternal internal thoracic nodes, the basis of nodal staging.
- **Innervation:** anterior cutaneous branches of the 4th to 6th intercostal nerves, with the nipple lying at the T4 dermatome.
- **Mammary line:** an ectodermal ridge from the axilla to the groin in the embryo, where supernumerary nipples or breast tissue can persist.
- **Puberty:** oestrogen drives ductal elongation and fat deposition, progesterone adds lobules and alveoli, and growth hormone supports both.

## Stages of breast development

Breast development is a sequence of hormonal stages, each with its own signal. The steps follow that sequence from the embryo to established lactation.

1. **Embryonic milk line:** ectodermal thickening forms along the mammary line from axilla to groin, and most of it regresses, leaving the pectoral region.
2. **Ductal tree at birth:** a rudimentary ductal system is present in the newborn and lies dormant until puberty.
3. **Puberty:** oestrogen elongates the ducts and deposits fat, while progesterone adds lobules and alveoli.
4. **Pregnancy:** placental oestrogen and progesterone expand the lobuloalveolar tissue, but high levels of these hormones suppress milk secretion until delivery.
5. **Lactogenesis:** after the placenta is delivered, falling progesterone lets prolactin trigger full milk secretion, and oxytocin then drives milk ejection.

A failure at any of these steps leaves the breast unable to feed, so lactation questions are answered by working through the sequence. Exam vignettes often describe the step that has gone wrong, such as absent placental delivery or low prolactin.

## Where the exam tries to catch you

Breast questions in NEET-PG usually test segmental supply and lymph drainage.

- **Trap:** Placing the nipple at T10. — **Correct:** The nipple lies at the T4 dermatome, which is the level taught for breast sensation and dermatome questions.
- **Trap:** Assuming most breast lymph goes to the internal thoracic chain. — **Correct:** Most lymph drains to the axillary nodes, so axillary staging dominates the assessment of breast cancer.
- **Trap:** Expecting milk production to start at puberty. — **Correct:** Puberty builds the ducts and lobules, but full lactogenesis needs the fall in progesterone after placental delivery.

## Frequently asked questions

### Which nerves supply the nipple and areola?
The nipple and areola are supplied by anterior cutaneous branches of the intercostal nerves, with the nipple at the T4 dermatome. This segmental supply is the basis of dermatome questions in breast anatomy.

### Which hormone triggers milk ejection in lactation?
Oxytocin triggers milk ejection by contracting the myoepithelial cells around the alveoli and ducts. Prolactin drives milk production rather than ejection, and it works alongside the fall in progesterone after delivery.

### Where does breast cancer spread first through lymphatics?
Breast cancer commonly spreads first to the axillary lymph nodes, so axillary staging guides treatment decisions. Parasternal internal thoracic nodes form the other important group of drainage.

### What is the mammary line?
The mammary line is an ectodermal ridge that runs from the axilla to the groin in the embryo. Most of it regresses, but remnants can form supernumerary nipples or breast tissue along its course.