Lecture Notes: The Epidermis
Overview
- The epidermis is the outermost layer of skin.
- It is avascular, strong, flexible, and waterproof.
- Contains four major types of cells, each providing different types of protection.
Key Cell Types in the Epidermis
1. Keratinocytes
- Description: Most abundant cells in the epidermis.
- Location: Begin in the stratum basale (bottom-most layer of the epidermis).
- Function: Produce keratin, a fibrous structural protein that provides strength and toughness.
- Development: Start as pre-keratinocytes with underdeveloped keratin, become more keratinized and die as they move outward.
2. Tactile Cells (formerly Merkel Cells)
- Description: Spiky cells associated with sensory nerve endings.
- Function: Sensitive to touch and pain, contribute to the sensation.
- Naming: Now referred to as tactile cells in most textbooks.
3. Dendritic Cells (formerly Langerhans Cells)
- Description: Macrophages capable of consuming pathogens like bacteria and viruses.
- Function: Activate the immune system when pathogens are detected.
- Identification Tip: Learn to recognize by shape as test figures are in black and white.
4. Melanocytes
- Description: Spider-shaped cells that produce melanin pigment.
- Function: Melanin provides protection by accumulating on the sunny side of keratinocyte nuclei.
- Pigment Type: Dark brown or black, varies by type and amount produced.
- Sun Exposure: Increases melanin output.
- Skin Color Variations: Differences in skin color are due to the type and amount of melanin, not the number of melanocytes, which are relatively the same across different people.
Important Notes
- Melanin spots are often visible in deeper layers of the epidermis on the sunny side of the nucleus.
- Differences in skin tone are due to activity levels of melanocytes, not their number.
These notes summarize the key points about the structure and function of the epidermis, focusing on the major cell types and their roles.