February 07, 2007

Anatomy of the Skin


Facts about the skin:
The skin is the body's largest organ, covering the entire outside of the body and weighing approximately six pounds. In addition to serving as a protective shield against heat, light, injury, and infection, the skin also:

regulates body temperature.
stores water, fat, and vitamin D.
can sense painful and pleasant stimulation.

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

fat layer

epidermis The epidermis is the thin outer layer of the skin. The epidermis itself is made up of three sub-layers:
status corneum (horny layer)

This layer contains continually shedding, dead keratinocytes (the primary cell type of the epidermis). The keratin, a protein formed from the dead cells, protects the skin from harmful substances.
keratinocytes (squamous cells)

This layer contains living keratinocytes (squamous cells), which help provide the skin with what it needs to protect the rest of the body.
basal layer

The basal layer is the inner layer of the epidermis, containing basal cells. Basal cells continually divide, forming new keratinocytes and 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 is made up of the following:
blood vessels
lymph vessels
hair follicles
sweat glands

The dermis is held together by a protein called collagen, made by fibroblasts (skin cells that give the skin its strength and resilience). This layer also contains pain and touch receptors.

subcutis The subcutis is the deepest layer of skin and is also known as the subcutaneous layer. The subcutis, consisting of a network of collagen and fat cells, helps conserve the body's heat while protecting other organs from injury by acting as a "shock absorber."

Adapted from: University of Maryland Medical Center