9 layers of the epidermis

Sep 9, 2024

Lecture Notes on the Integumentary System

Introduction

  • Focus on the epidermis, the most superficial layer of the integument (skin).
  • Integument (skin) is the largest organ in the body, composed of two main layers: epidermis and dermis.
  • Hypodermis supports the skin but is not part of it.

The Epidermis

  • Described as the "buttercream frosting" of the skin.
  • Composed of 4 or 5 distinct layers.
  • Made of keratinized stratified squamous epithelial tissue:
    • Keratinized: contains keratin, a protein unique to the skin.
    • Stratified: many layers.
    • Squamous: cells are flat and irregular.

Layers of the Epidermis

  1. Stratum Basale
    • Deepest layer; mitotically active cells (stem cells).
    • Contains keratinocytes (soon-to-be), melanocytes.
    • Desmosomes link cells tightly together.
  2. Stratum Spinosum
    • Prickly layer containing mature keratinocytes.
    • Cells start producing keratin protein.
  3. Stratum Granulosum
    • Cells look granular due to keratin accumulation.
    • Cells begin to die due to lack of nutrients.
  4. Stratum Lucidum (only in thick skin such as palms and soles)
    • Clear, protein-filled layer.
    • Contributes to resistance; not present everywhere.
  5. Stratum Corneum
    • Outermost "horny" layer with dead keratinocytes.
    • Provides a durable barrier; about 20-30 layers thick.

Cell Types in the Epidermis

  • Keratinocytes: Produce keratin, form the bulk of the epidermis.
  • Melanocytes: Produce melanin, provide pigmentation.
  • Dendritic (Langerhans) Cells: Part of the immune system, act as macrophages.
  • Merkel (Tactile) Cells: Sensory receptors, part of the nervous system.

Function and Importance

  • Stratum corneum serves a critical role in the immune response as a barrier.
  • Melanocytes protect against UV radiation and aid in Vitamin D synthesis.
  • Desmosomes are essential for cell adhesion and structural integrity.

Conclusion

  • The epidermis is a complex system vital for protection, sensation, and various bodily functions.
  • Understanding its structure and function is crucial for grasping skin's role in the body.