Anatomy of the skin

Facts about the skin:

The skin is the body's largest organ, covering the entire body. In addition to serving as a protective shield against heat, light, injury, and infection, the skin also:

• regulates body temperature
• stores water and fat
• is a sensory organ
• prevents water loss
• prevents entry of bacteria

Throughout the body, the skin's characteristics vary (i.e., thickness, color, texture). For instance, the head contains more hair follicles than anywhere else, while the soles of the feet contain none. In addition, the soles of the feet and the palms of the hands are much thicker.

The skin is made up of the following layers, with each layer performing specific functions:

• epidermis
• dermis
• subcutaneous fat layer

Epidermis

The epidermis is the thin outer layer of the skin which consists of the following three parts:

• stratum corneum (horny layer)
  This layer consists of fully mature keratinocytes which contain fibrous proteins (keratins). The outermost layer is continuously shed. The stratum corneum prevents the entry of most foreign substances as well as the loss of fluid from the body.
• keratinocytes (squamous cells)
  This layer, just beneath the stratum corneum, contains living keratinocytes (squamous cells), which mature and form the stratum corneum.
• basal layer
  The basal layer is the deepest layer of the epidermis, containing basal cells. Basal cells continually divide, forming new keratinocytes, replacing the old ones that are shed from the skin's surface.

The epidermis also contains melanocytes, which are cells that produce melanin (skin pigment).

Dermis

The dermis is the middle layer of the skin. The dermis contains the following:

• blood vessels
• lymph vessels
• hair follicles
• sweat glands
• collagen bundles
• fibroblasts
• nerves

The dermis is held together by a protein called collagen, made by fibroblasts. This layer also contains pain and touch receptors.

Subcutaneous fat layer

The subcutis is the deepest layer of skin. The subcutis, consisting of a network of collagen and fat cells, helps conserve the body's heat and protects the body from injury by acting as a "shock absorber."