Epidermis

Functions: Protection from water, air, infection, chemicals, UV radiation. Sensations such as pressure, heat, cold, and pain. Temperature regulation - body can be heated or cooked by sweat and blood flow near surface. Excretion of waste through sweat. Production of Vitamin D.

The epidermis is the top layer of skin. It is composed of stratified squamous epithelial tissue.

Stratum corneum: layer of dead cells 20-30 thick. Thick, keratinized cells protects the deeper layers. Regularly shed from body.

Stratum lucidum: (clear layer) - a thin layer of translucent cells only found in the thick skin of the palm and soles of feet.

Stratum granulosm: cells here begin to flatten and disintegrate. Accumulate keratin granules, responsible for water-proofing the skin.

Stratum spinosum: “Spiny layer.” Named for the irregular shape of the cells. Several cells thick. Contains pre-keratin filaments.

Stratum basale: Constantly dividing and pushing up cells into the next layer.

Epidermis contains 4 types of major cells:

  • Keratinocytes

  • Melanocytes

  • Intraepidermal macrophages (langerhans cells)

  • Tactile epithelial cells (merkel cells)

Melanocytes are spider-shaped epithelial cells found in the bottom 2 layers of the epidermis. Melanocytes produce a pigment called melanin, which is absorbed by the nearby epidermal cells.

How do melanocytes differ in dark-skinned and light-skinned people? They have the same number of melanocytes. The difference is the amount of melanin produced.

Melanin protects the skin against harmful UV rays. When UV radiation mutates a skin cell’s DNA, the cells begin to divide uncontrollably. This is called skin cancer.

Types of skin cancer:

  • Melanoma - uncontrolled division melanocytes.

  • Basal cell carcinoma - uncontrolled division of cells in the stratum basale layer.

  • Squamous cell carcinoma - uncontrolled division of cells in the stratum spinosum layer.

Summary: The skin has several functions, but primarily protects the body. The epidermis is the top layer of the skin and it grows from the stratum basale towards the surface. Melanocytes produce melanin, protecting the body from UV radiation, which can cause mutations that result in cancer.