Lecture Notes: The Epidermis

Overview of the Epidermis

• The epidermis is the outermost layer of skin.
• Characteristics: Avascular, strong, flexible, and waterproof.
• Protective role through different types of cells.

Major Cells of the Epidermis

1. Keratinocytes

• Location: Most abundant in the epidermis.
• Function: Provide structure and toughness due to keratin, a fibrous structural protein.
• Development: Begin as pre-keratinocytes in the stratum basale, become more keratinized, and die as they move outward.
• Etymology: The root "cyte" means cell.

2. Tactile Cells (formerly Merkel Cells)

• Location: Associated with sensory nerve endings.
• Function: Sensitive to touch and pain.
• Note: In textbooks, now referred to as tactile cells, not Merkel cells.

3. Dendritic Cells (formerly Langerhans Cells)

• Location: Identified as purple cells in diagrams (note: recognize by shape, not color for tests).
• Function: Act as macrophages to consume pathogens and activate the immune system.

4. Melanocytes

• Function: Produce melanin, a pigment that provides protection by accumulating on the keratinocyte nucleus.
• Sun Exposure: Increases melanin output.
• Variability in Skin Color: Differences are due to the type and amount of melanin output, not the number of melanocytes.

Additional Notes

• Tests will have black and white photocopies of figures; recognize cells by shape, not color.
• Melanocytes are relatively the same in number across different people, variations in skin color arise from melanin activity and production.