it 4 as1PAUL LILLY
TEREASA KATYNSKI
UNIT 4 STUDY 1
Overcoming the perils of Canoe Lake * Describe the general structure of skin
Epidermis, and Dermis

The epidermis is the relatively thin, tough, outer layer of the skin. Most of the cells in the epidermis are keratinocytes. They originate from cells in the deepest layer of the epidermis called the basal layer. New keratinocytes slowly migrate up toward the surface of the epidermis. Once the keratinocytes reach the skin surface, they are gradually shed and are replaced by newer cells pushed up from below.

The outermost portion of the epidermis, known as the stratum corneum, is relatively waterproof and, when undamaged, prevents most bacteria, viruses, and other foreign substances from entering the body. The epidermis also protects the internal organs, muscles, nerves, and blood vessels against trauma. In certain areas of the body that require greater protection the outer keratin layer of the epidermis is much thicker.

Scattered throughout the basal layer of the epidermis are cells called melanocytes, which produce the pigment melanin, one of the main contributors to skin color. Melanin's primary function, however, is to filter out ultraviolet radiation from sunlight which damages DNA, resulting in numerous harmful effects, including skin cancer.

The epidermis also contains Langerhans cells, which are part of the skin's immune system. Although these cells help detect foreign substances and defend the body against infection, they also play a role in the development of skin allergies.

The dermis, the skin's next layer, is a thick layer of fibrous and elastic tissue that gives the skin its flexibility and strength. The dermis contains nerve endings, sweat glands and oil glands, hair follicles, and blood vessels.

The nerve endings sense pain, touch, pressure, and temperature. Some areas of the