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The Epidermis

Objectives:
  1. Identify the functions of the epidermis.
  2. Identify the cells forming the epidermis and their function.
  3. Understand the function of melanin.
  4. Understand the structure and characteristics of the epidermal layers found in thick and thin skin.
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Epidermis Stratum basale- deepest layer of the epidermis formed by a single layer of cells. Stem cells within this layer can undergo mitosis giving rise to new keratinocytes, replacing those lost at the apical surface. Melanocytes in this layer produce melanin. Stratum spinosum- layer composed of keratinocytes with a spiny appearance due to cytoplasmic projections formed during slide preparation. This layer also contains dendritic cells and melanocytes.Stratum spinosum- layer composed of keratinocytes with a spiny appearance due to cytoplasmic projections formed during slide preparation. This layer also contains dendritic cells and melanocytes.Melanocyte- pigment producing cell located in the epidermis. These cells provide protection against ultraviolet radiation to keratinocytes with the movement and positioning of their pigments over the nuceli of keratinocytes. Sensory neuron- neuron relaying sensory information towards the central nervous system.Tactile (Merkel) cell- specialized cell closely associated with sensory neurons. Dead keratinocytes - Keratinocytes that have each lost their nucleus; seen at the most apical surface of the skin Lamellar granules - Aggregations of lipid accumulated in keratinocytes making the skin waterproof Keratinocyte - The predominant cells of the epidermis; capable of producing keratin, making cells tough and resistant to damage Dermis- deep portion of the skin, located just below the epidermis. Stratum corneum- the most superficial layer of the epidermis. Consists of keratin and dead keratinocytes. Stratum lucidum- layer found in thick skin consisting of translucent, dead keratinocytes. Stratum granulosum- layer consisting of keratinocytes containing granules (precursors of keratin). Keratinocytes being to die in this layer as the nucleus is pushed out with the accumulation of keratin precursor.

Epidermis

The epidermis is the superficial layer of the skin and consists of stratified squamous epithelium that is keratinized (containing the protein keratin). It forms the tough outer covering of our body allowing us to withstand physical, chemical, and thermal insults.  Because the epidermis is avascular, it relies on the underlying dermis for nutrient and gas exchange.

Cells
There are four basic cells forming the epidermis:

  1. Keratinocytes
  2. Melanocytes
  3. Dendritic (Langerhans) cells
  4. Tactile (Merkel) cells
Layers
The epidermis is composed of five layers in thick skin, the skin located at the soles of the feet and palms of the hands.
The layers include:
  1. stratum corneum,
  2. stratum lucidum
  3. stratum granulosum
  4. stratum spinosum
  5. stratum basale.

The skin located throughout the rest of the body is categorized as thin skin. It lacks the stratum lucidum seen in thick skin.

Bluedoor Publishing 2011