Integumentary System: Skin LayersEpidermis
The outermost layer of the skin is composed of epithelial tissue and is known as the epidermis. It contains squamous cells or keratinocytes, which synthesize a tough protein called keratin. Keratin is a major component of skin, hair and nails. Keratinocytes on the surface of the epidermis are dead and are continually shed and replaced by cells from beneath. This layer also contains specialized cells called Langerhans cells that signal the immune system of an infection.
The innermost layer of the epidermis contains keratinocytes called basal cells. These cells constantly divide to produce new cells that are pushed upward to the layers above. Basal cells become new keratinocytes which replace the older ones that die and are shed. Within the basal layer are melanin producing cells known as melanocytes. Melanin is a pigment that helps to protect the skin from harmful ultraviolet solar radiation by giving it a brown hue. Also found in the basal layer of the skin are touch receptor cells called Merkel cells.
The epidermis is composed of five sublayers.
- Epidermal Sublayers
- stratum corneum - top layer of dead, extremely flat cells. Cell nuclei are not visible.
- stratum lucidum - thin, flattened layer of dead cells. Not visible in thin skin.
- stratum granulosum - rectangular-shaped cells that become increasingly flattened as they move to the surface of the epidermis.
- stratum spinosum - polyhedral-shaped cells that flatten as they get closer to the stratum granulosum.
- stratum basale - innermost layer of elongated columnar (column-shaped) cells. Consists of basal cells that produce new skin cells.
Next > Skin Layers: Dermis and Hypodermis
SEER Training Modules, Module Skin Cancer: Melanoma. U. S. National Institutes of Health, National Cancer Institute. 3, March 2010 .