The Integumentary System
The integumantary system contains the largest organ in the human body, the skin. It is also comprised of such extensions of the skin as hair and fingernails. The skin, however, is the most important of these. The skin protects and cushions the body's delicate organs. It also provides the body a physical barrier to keep out foreign materials and to prevent the body from drying out. The skin is made of three separate layers, each with its own particular function.
The epidermis, as its name suggests, is the outermost layer of the skin. It is comprised of four separate layers of epithelial tissue. The outermost layer of the epidermis is the stratum corneum. It is approximately 20-30 cells thick. The cells here are completely keratinized and dead, and this is what gives the skin its waterproof quality. The next two layers, the stratum granulosum and the stratum lucidum, are siimilar in that they represent an intermediate stage of keratinization. The cell here are not fully keratinized yet, but as the growth of the skin pushes them outward, they will increasingly move towards that state. The deepest layer of the epidermis is the stratum germinativum. The cells here are mitotically active-- that is, they are alive and reproducing. This is where the growth of skin takes place.
The dermis is the second layer of skin, directly beneath the epidermis. Unlike the epidermis, the dermis has its own blood supply. Because of the presence of this blood supply, more complex structures are able to exist here. Sweat glands are present to collect water and various wastes from the bloodstream, and excrete them through pores in the epidermis. The dermis is also the site of hair roots, and it is here where the growth of hair takes place. By the time hair reaches the environment outside of the skin, it is completely dead. The dermis also contains dense connective tissue, made of collagen fibers, which gives the skin much of its elasticity and strength.
The Subcutaneous Layer
Beneath the dermis lies the final layer of skin, the subcutaneous layer. The most notable structures here are the large groupings of adipose tissue. The main function of the subcutaneous layer is therefore to provide a cushion for the delicate organs lying beneath the skin. It also functions to insulate the body to maintain body temperature.
written by Lyle Mullican