Lecture on Skin: The Largest Organ

Introduction

• Skin is the largest organ of the body.
• Functions: Protects against infection, regulates temperature, maintains fluid balance, synthesizes vitamin D.
• Contains nerve endings, sweat glands, and blood vessels for sensing, cooling, and communicating.
• Comprises the integumentary system alongside hair, nails, and glands.

Structure of Skin

• Layers of Skin:
  • Epidermis: Outer visible layer, made of stratified squamous epithelial tissue.
  • Dermis: Below epidermis, where most skin functions occur (sweating, blood circulation).
  • Subcutis/Hypodermis: Bottom layer, composed mainly of adipose tissue.

Cells in the Skin

• Epidermal Cells:
  • Keratinocytes: Build keratin, die and replace frequently, form the majority of epidermis.
  • Melanocytes: Produce melanin, determining skin color.
  • Dendritic (Langerhans) Cells: Immune cells that protect against invaders.
  • Merkel Cells: Combine with nerve endings for touch sensation.

Thick vs Thin Skin

• Thick Skin: Found on palms and soles, has five layers.
• Thin Skin: Covers the rest of the body, has four layers.

Epidermal Layers (Thick Skin)

1. Stratum Corneum: Outermost, dead keratinocytes.
2. Stratum Lucidum: Clear, found only in thick skin.
3. Stratum Granulosum: Contains living keratinocytes.
4. Stratum Spinosum: Spiny layer, active mitosis.
5. Stratum Basale: Deepest layer, cell production.

Dermis

• Two Layers:
  • Papillary Layer: Areolar connective tissue, forms fingerprints.
  • Reticular Layer: Dense connective tissue, contains nerves and vessels.

Hypodermis

• Adipose tissue for insulation, energy storage, and shock absorption.

Skin’s Interactions

• Sunlight: UV radiation can damage DNA, cause skin cancer, and degrade collagen.
• Tattoos: Ink must reach the dermis to be permanent.

Conclusion

• Importance of understanding skin structure and function.
• Upcoming topics: effects of lotion, deodorant, and hair care.

Credits

• Written by Kathleen Yale, edited by Blake DePastino, with consultant Dr. Brandon Jackson.
• Directed and edited by Nicholas Jenkins, sound design by Michael La Ronda.