Lecture on Skin Structure

Introduction

• Beauty and Skin: Common saying is "beauty is only skin deep."
• Outer Layer: Composed entirely of dead cells.
• Purpose of Lecture: Explore the different layers of the skin.

Layers of the Skin

1. Epidermis: Topmost layer with five sub-layers or "strata."
2. Dermis: Located beneath the epidermis, consists of two layers.
3. Subcutaneous Tissue (Hypodermis): The deepest layer.

Detailed Study of the Epidermis

1. Stratum Basale

• Location: Deepest layer of the epidermis.
• Function:
  • Generation of keratinocytes.
  • Rapid cell division.
  • Melanocytes here produce melanin, determining skin color.
• Melanin:
  • Not the number of melanocytes, but the amount of melanin determines skin darkness.

2. Stratum Spinosum

• Characteristics:
  • Contains desmosomes connecting keratinocytes.
  • Desmosomes give cells a spiny appearance when moisture is lost.
• Langerhans Cells: Immune cells present to fight pathogens.

3. Stratum Granulosum

• Characteristics:
  • Presence of keratohyalin granules (keratin-handling proteins).
  • Production of lamellar bodies.
• Function:
  • Forms a lipid layer, making the skin impermeable and waterproof.

4. Stratum Lucidum

• Characteristics:
  • Composed of dead keratinocytes ("zombie keratinocytes").
  • Cells in this layer are clear due to loss of nuclei and organelles.

5. Stratum Corneum

• Characteristics:
  • Outermost layer.
  • Contains 15-20 layers of dead keratinocytes.
  • Cells slough off randomly and continuously.
• Additional Note: In reptiles, this layer molts as a single piece.

Conclusion

• The epidermis consists of both living (bottom three) and dead layers (top two).
• No blood vessels in the epidermis; nutrients and oxygen diffuse from deeper layers.

This summary provides an overview of the layers of the skin, focusing on the structure and function of the epidermis.