mammary gland
Meaning of mammary gland: Not simply another word for the breast: the glandular working part inside it, and a distant relative of the sweat gland.
Definition of mammary gland
The mammary gland is the milk-producing organ of the breast, built from clusters of tiny sacs that make milk and a branching set of ducts that carry it to the nipple. It is a modified sweat gland, present in both sexes, but it develops fully only under the hormones of puberty and pregnancy. Its lining is where most breast cancers begin.
Is it the same thing as the breast?
Not quite, although the two words are often swapped. The breast is everything in that part of the chest wall: skin, the nipple and the darker ring around it, fat, fibrous strands that anchor the whole structure to the chest, blood vessels, lymph channels and the gland itself. The mammary gland is only the working tissue within it. That difference explains something people find surprising, which is that breast size mostly reflects how much fat is present rather than how much glandular tissue there is, and it says nothing about how much milk can be made. After menopause the glandular part shrinks and fat gradually replaces it.
How is it put together?
| Part | What it does |
|---|---|
| Alveoli | Sacs of milk-making cells, the end of the line |
| Lobule | A cluster of alveoli draining into one small duct |
| Lobe | A group of lobules; a breast holds roughly fifteen to twenty |
| Ducts | Branching tubes carrying milk toward the nipple |
| Myoepithelial cells | A muscular net around the sacs that squeezes milk out |
What switches it on?
Hormones, in a fixed order. Estrogen at puberty lengthens and branches the ducts. Progesterone, in far greater amounts during pregnancy, drives the lobules to grow so that the gland becomes crowded with milk-making sacs. Prolactin from the pituitary gland then starts actual milk production, which is held back until after delivery by the high hormone levels of pregnancy. Suckling triggers oxytocin, which makes the muscular net contract and pushes milk down the ducts. In males the same structure exists in miniature and stays dormant, which is why it can still become swollen or, rarely, cancerous. A gland of this kind is classed as exocrine, meaning it empties onto a surface through a duct rather than releasing into the blood.
Also known as
Used in a sentence
The specimen showed normal mammary gland tissue with no evidence of malignancy.
Good to know
The mammary gland is the glandular portion of the breast rather than a synonym for it, and because the gland shrinks with age, the proportion of glandular to fatty tissue seen on imaging changes across a lifetime.
Word origin
Where “mammary gland” comes from
Mammary comes from the Latin mamma, meaning breast, the same root behind mammal, an animal that feeds its young on milk.