(Basal layer) This layer consists of a single row of mostly stem cells representing the youngest keratinocytes. These cells divide rapidly. About 10% to 25% of the cells in the stratum basale are spider-shaped melanocytes which make the dark skin pigment melanin. Melanocytes also secrete a variety of signaling molecules in response to ultraviolet radiation.

This layer is several cell layers thick. Mitosis occurs here but less often then the basal layer. The layers name comes from the spinelike extensions of its keratinocytes. These spinelike extensions do not exist in living cells as they are created during tissue preparation.

Occurs in thick skin but not in thin skin. It appears as a thin translucent band and consists of a few rows of flat, dead keratinocytes. The cells are identical to those at the bottom of the stratum corneum.

Consists of one to five layers of flattened keratinocytes along with abundant pre-keratin intermediate filaments. These cells also contain keratohyalin granules and lemellar granules. The keratohyalin granules help form keratin in the more superficial layers. The lamellar granules contain waterproofing glycolipid that is secreted into the extracellular space. The glycolipid and tight junctions plays a major role in slowing water loss across the epidermis.

The most external part of the epidermis. Stratum corneum is many cells thick. Much thicker in thick skin than in thin skin. Its dead keratinocyes are flat sacs completely filled with keratin. Both keratin and the thickened plasma membranes of cells in the stratum corneum protect the skin against abrasion and penetration.

Protection: Skin cushions and insulates the deeper body organs and protects the body from bumps, scrapes and cuts. Skin also protects the body from chemicals and invading microorganisms.

Body temperature regulation: The skin's rich capillary networks and sweat glands regulate the loss of heat from the body, helping to control body temperature.

Excretion: The skin acts as a miniature excretory system when urea, salts and water are lost through sweat.

Production of vitamin D: The epidermal cells use UV radiation to syntheszie vitamin D, a molecule necessary for absorbing calcium from the digestive tract.

Sensory reception: The skin contains sense organs called sensory receptors that are associated with nerve endings. By sensing touch, pressure, temperature and pain these receptors keep us aware of conditions at the body surface.

Hypodermis: Just deep to the skin is the fatty hypodermis the hypodermis consists of both areolar and adipose connective tissue but adipose dominates. The hypodermis anchors the skin to the underlying structures which mostly are muscles but loosely enough the skin can slide relatively freely over these structures. The hypodermis also acts as insulation.