The female breast is made up of several types of structures designed to produce and deliver nutrition to an infant. Groups of glands called lobules produce milk which is carried by a series of hollow tubes, called ducts out through the nipple. The entire system of glands and ducts is embedded in fat and supportive tissues, with ligaments stretching from the skin to the chest wall to hold breast tissues in place. Blood vessels provide oxygen and carry away wastes. The pectoralis muscle lies against the chest wall underneath each breast.
Also present in the breast is a branch of the lymphatic system, a network of channels and lymph nodes that runs throughout the body. The lymphatic system provides a drainage system for tissue fluids: lymph fluid enters the lymph channels and is filtered through lymph nodes, where bacteria and foreign particles are trapped and destroyed by immune cells. The lymph nodes closest to the breast are found under the arm (axillary nodes) and under the breastbone (internal mammary nodes).
The breasts undergo many hormonally induced changes as a woman matures. During the reproductive years, breast tissues consist primarily of glands and swell with fluid on a cyclical basis. When pregnancy occurs, the lobules prepare to produce milk. After menopause, when hormone levels drop, the breasts lose their ability to produce milk, and much of the glandular tissue is replaced by less dense fatty tissue.
