The female breast is made up of several types of structures, most of which are related to its ability to produce milk. Groups of glands known as lobules produce the milk. A breast has some fifteen to twenty lobules, all connected by a series of hollow tubes called ducts. The ducts carry the milk produced by the lobules forward to small storage areas called milk sinuses, found underneath the areola. The milk travels from these sinuses via channels through the nipple.
Tissues
The entire system of glands and ducts is embedded in fat and supportive tissues. Ligaments stretching from the skin to the chest wall hold the breast tissues in place. Blood vessels provide oxygen and carry away wastes. The pectoralis muscle lies flush with the chest wall underneath each breast.
The Lymphatic System
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 the bean-shaped lymph nodes, where bacteria and foreign particles are trapped and destroyed by specialized immune system cells. The lymph nodes closest to the breast are found under the arm and under the breastbone.
Hormones
During a woman's reproductive years, monthly hormonal changes will cause her breast tissues to swell with fluid, often causing tenderness. If pregnancy occurs, that month 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.
