Breast tissue is the thin layer of cells that lies over the breast. It is made up of fat, connective tissue, and epithelial tissue. The cells that make up the breast tissue are called lobules. The lobules have a rich blood supply and are made up of fat, connective tissue, and epithelial cells. The mastectomy removes all breast tissue from the chest wall. After surgery, there is no longer any breast tissue to nourish or support the newly-removed skin flap that is left to cover the chest wall. If a nipple-sparing mastectomy has been performed, then some lobules remain in place to provide nourishment for this flap of skin. Mastectomy can be done for many reasons - for example: cancer treatment or as part of a reconstruction process after an accident such as a car crash or firework injury.