Your breasts are made up of tissues that produce milk (glandular tissue), connective tissue, and fat. Younger women tend to have more glandular tissue in their breasts than older women, making their breasts more dense.
Each breast is arranged into 15-20 sections called lobes, and each lobe contains a number of milk-producing glands called lobules. Milk produced by the lobules is carried through a network of passageways called ducts, which eventually join together and exit the breast through the nipple.
Connective tissue helps to provide support and give shape to your breasts. Your breasts also have a small amount of muscle. Muscle tissue in the nipple allows it to become erect in response to stimulation or breastfeeding. Muscle tissue around the lobules helps squeeze milk into the ducts. Glands on the areola secrete small amounts of fluid to lubricate the nipple when breastfeeding.
Your breasts also contain lymph nodes joined by a network of lymph vessels, blood vessels, and nerves which provide feeling to the breast.1
1.Canadian Breast Cancer Foundation (now Canadian Cancer Society) The Healthy Breast