The integument, which is the skin covering the body and its supportive structures, is the largest organ of the body. It is designed to cover and protect the other organs of the body. There are different layers that make up the integument. They comprise the outer layer or epidermis which is made of squamous epithelium and which is thinner in rats due to the covering of hair over most of the body. The underlying layer which is the dermis a broad layer of connective tissue composed of course collagen fibers and containing blood and lymph vessels, nerves, sebaceous glands, and hair roots, and below the dermis, the subcutis (subcutaneous) which anchors skin to muscle and bone, and is composed of some connective tissue interlaced with fat.

Parts of the integument serve different functions. The hair helps to serve as thermal insulation. The glands which are the sebaceous glands give an oily secretion to the space between hair follicle and hair shaft and helps to keep the skin pliable, and the sweat glands which in rats are located only in the feet pads may help to reduce elevated ambient temperature.

The skin functions to protect against bacterial invasion and foreign matter, to prevent water and electrolyte loss , to keep the tissues from drying out, and to help with thermal regulation.

Changes that occur in the integument, can be due to spontaneous changes of aging, infections, or disease processes.