There’s a lot going on underneath the surface of our boobs. According to Johns Hopkins University, the entire structure of the breast is specialized for its primary function—milk production—the anatomy and system is a bit more complex than just that. It’s not all milk, or fat, or tissue—rather, it’s a combination of those and other components.

Lobules and Ducts

Healthy breasts have 12-20 lobes, which are sections made up of 20-40 smaller lobules (think: a bunch of grapes), according to the National Breast Cancer Foundation. The lobules branch out from the nipple and hold mini, hollow sacs called the alveoli, according to the Mayo Clinic. They’re linked together by a network of ducts, which are responsible for carrying the milk through the breast during breastfeeding.

Fat and Tissue

The areas surrounding the lobules and ducts are made up of a combination of fat, ligaments, and connective tissue, according to Mayo Clinic. The fat tissue in breasts is called adipose tissue, and typically, larger breasts contain more fat while smaller breasts have less. That said, the fat level may also vary based on life stage. Older women who have already gone through menopause tend to have more fatty breast tissue than younger women whose breasts are denser with tissue and ligaments. A thin layer of connective tissue, called fascia, surrounds the breast tissue, and sits on top of the pectoralis muscle.


Technically, there’s no muscle tissue inside the actual breast, according to Mayo Clinic. But, it—specifically, the pectoralis muscle—does sit right underneath all of that other stuff, separating your boobs from your ribs.

Capillaries and Arteries

These thin blood vessels are the path through which blood containing oxygen and nutrients travel to your breasts, according to Mayo Clinic. Specifically, the internal mammary artery runs under the main breast tissue and is the primary source blood supply, according to Johns Hopkins University.

Lymph Nodes and Ducts

Also known as the lymphatic system, this network of nodes and ducts is situated behind the breastbone, as well as under the armpit and above the collarbone. The lymph nodes play an important role in trapping harmful substances and draining them from the body to avoid infection, according to the Mayo Clinic.

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