Mammary gland

Glandula mammaria

Endocrine & glandsGlandsThoraxLeft and right

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Shown on the female body.

What it is

The milk-producing tissue of the breast: 15–20 lobes arranged like the spokes of a wheel around the nipple, each lobe a cluster of lobules of tiny alveoli, embedded in fat and supported by suspensory (Cooper's) ligaments over the pectoralis major muscle. Shown here as 17 lobes of three lobules each, larger towards the edge of the breast, with one long lobe reaching towards the armpit.

Function

Under prolactin the alveoli secrete milk; oxytocin makes the muscle-like cells around them contract to eject it. Between pregnancies the gland is mostly quiescent ducts.

Size

Glandular tissue spread through a breast of ~10–12 cm diameter; adult breast 150–500 g, roughly half of it gland

Clinical note

Most glandular tissue — and about half of breast cancers — lies in the upper outer quadrant, which also sends an axillary tail (of Spence) towards the armpit; this is why the axillary lymph nodes are examined.