Lecture Notes: Layers of the Epidermis

Introduction

• Focus on the epidermis, the thin, superficial layer of skin.
• Layers are visible in histological slices.

Overview of Epidermis Layers

1. Stratum Basale

   • Deepest layer, attached to dermis.
   • Single cell layer thick.
   • Contains young keratinocytes, melanocytes (10-25%), and Merkel cells.
   • Cells are vital and mitotic.

2. Stratum Spinosum

   • Several cell layers thick.
   • Appears web-like and spiny due to fixative process.
   • Contains primarily young, still-living keratinocytes.
   • Presence of melanocytes and dendritic cells.

3. Stratum Granulosum

   • 3 to 5 cell layers thick.
   • Keratinocytes flatten and secrete lipids for waterproofing.
   • Important for keeping fluids inside the body and external fluids out.
   • Polar substances like water have difficulty passing through.

4. Stratum Lucidum

   • Translucent band, few cells thick.
   • Clear, flat, dead keratinocytes.
   • Found only in thick skin (palms, soles).

5. Stratum Corneum

   • Outermost and thickest layer, 15-20 cell layers thick.
   • Comprises 3/4 of epidermis thickness.
   • Contains completely dead keratinocytes.
   • Provides protection from abrasion and is waterproof due to lipids from the stratum granulosum.

Cellular Movement and Function

• Cell Lifecycle: Begins in stratum basale where cells are mitotic and vital.
• Migration: Cells push outward through layers as they grow and proliferate.

Key Points

• Epidermal layers provide a barrier and protection for underlying structures.
• The process of keratinocyte proliferation and migration is crucial for skin regeneration.
• Each layer has distinct characteristics and functions contributing to the skin's protective role.