The biggest part of the breast consists of lobes, which produce milk, and milk ducts, which bring the milk to the nipple.
One third of the breasts is made up of fat.
The breasts also contain arteries, veins and nerves. The connective tissue holds it all together.
Every month hormones give a signal to your breasts to prepare for pregnancy. New cells are made in the glands and ducts, enlarging the breasts and making them more sensitive than usual before your period starts. After your period your breasts are back to normal again.