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Structure and Function

You may not think of the skin as an organ, but it is actually the largest organ of the body. Let’s take a look at the structure and function of the integumentary system.

The skin consists of three layers (Fig. 4-1). The epidermis is the thin outer layer that is constructed mostly of nonliving, keratinized (hardened) cells. It is waterproof and provides protection for the deeper layers. The epidermis is thickest on the palms of the hands and the soles of the feet. The base of this layer, aptly named the basement membrane, is where new, living epidermal cells are produced. These cells are pushed upward as even newer cells form beneath them. Eventually, they rise to the top, away from blood vessels and nerve endings, and die, thus becoming keratinized tissue. This is why cells on the top layer of your skin can be scraped away without causing pain.


The prefix epi- means above or upon; so the name epidermis, which means above or upon the dermis, tells you exactly where it is located.

image Learning Style Tip

Look carefully at the illustrations and photos in this book. Draw and label what you see.

The dermis lies just beneath the epidermis and is much thicker. It is made of fibrous connective tissue containing elastin, which provides elasticity, and collagen, which provides strength. It also contains a good blood supply and numerous other structures, including hair follicles, nerves, sweat glands, oil glands, and sensory receptors.

Beneath the dermis is the subcutaneous layer. This layer contains fat tissue as well as deeper blood vessels, nerves, the lower part of hair follicles, elastin, and collagen. The subcutaneous layer provides insulation for deeper structures.

Accessory structures of the skin include the sudoriferous (sweat) glands, sebaceous (oil) glands, hair, and nails. Sudoriferous glands are located throughout the body but are more concentrated in some areas, such as the soles of the feet and palms of the hands. Sebaceous glands are found at the base of hair follicles all over the body; they secrete an oily substance called sebum.

image Learning Style Tip

It can be helpful to speak and hear the information you are learning multiple times. Find a study partner or join a study group whenever possible. Take turns “teaching” each other the information by saying it aloud. Listeners should pay close attention and be prepared to discuss information they feel is incorrect or incomplete.

The skin (and its accessory structures) serve several important functions in the body. Its major functions are protection and temperature regulation. The skin protects your body from bacteria and other microorganisms, harmful ultraviolet light from the rays of the sun, and extreme temperatures. ...

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