1. HUMAN BODY SYSTEMS Skeletal Muscular Circulatory Lymphatic Digestive Excretory Endocrine Reproductive Skin Respiratory

2. SKIN SYSTEMS The skin has the largest surface area of any organ in the body and is the heaviest. On the surface are the sensitive papillae, and within are certain organs with special functions, the sweat glands, hair follicles, and sebaceous glands. The skin protects the internal organs of the body against infection, injury, and harmful sun rays. It also plays an important role in the regulation of body temperature. Although the skin of an average-sized adult may weigh as much as twenty pounds, it is only paper thin in some places and not much thicker in others.

3. The skin is composed of two tissues, an outer layer called the epidermis and an inner layer called the dermis or corium. The surface of the skin, or the epidermis, consists of dead cells, which are rubbed off as you move, wear clothes, and wash. This layer of dead cells is often refered to as "false" skin. Just below, in the dermis, the cells are very much alive. The cells of the dermis continually multiply to replace those cells that are worn away. The epidermis consists of four layers: the stratum basale, the stratum spinosum, the stratum granulosum, and the stratum corneum.

4. The hair follicle is a tunnel-like segment of the epidermis that extends down into the dermis. The follicle is a thin sac of epidermal tissue with a bulb at the bottom. The hair follicles produce the hair. Every hair follicle is nourished by a papilla. The root of a hair has a bulbous shape and is called the hair bulb. It is located deep in the hair follicle. The hair bulb is whiter in color, and softer in texture than the hair shaft.

5. Fingernails are simply another form of skin. They are formed by a hardened protein called keratin, which has a high sulfur content. The cuticle is the outermost layer of the epidermis (the stratum corneum) which protrudes a short way above the nail. The fatty pad of the skin is composed of adipose tissue (fat cells), which acts as a protective padding in the fingers. Adipose tissue also helps smooth out the contours of the fingertips. Fingerprints are the impression of the lines on the tips of the fingers. Fingerprints are composed of numerous papillary ridges that form their own unique pattern. Not only is the pattern unique for each individual, but also it never changes except to grow larger, which is why fingerprints are commonly used for identification.