Your breasts are designed to make milk after pregnancy. The breast tissue extends almost to the collar bone at the top and to the armpit at the side. Lying beneath the breasts are the chest muscles and ribs.
Breast tissue is made up of milk glands, connective tissue, and fat. The milk glands consist of milk sacs (lobules) where milk is made, and ducts which take the milk to the nipple.
In your breast area and armpit there are lymph glands or nodes which are connected by a system of lymph ducts. These glands and ducts are part of the lymphatic system, which helps your body to fight infection.
Your breasts do not stay the same throughout your adult life. Your monthly period, pregnancy, age, and weight changes can all alter their shape. Some women find their breasts feel more tender and lumpy before their period. This tenderness and lumpiness disappears after the period ends. This is quite normal.