Lecture on Skin and the Integumentary System

Introduction

• Common associations with organs usually exclude the skin.
• Skin is the largest organ and plays numerous vital roles:
  • Protects against infection and extreme temperatures.
  • Maintains fluid balance and synthesizes vitamin D.
  • Sensory functions via nerve endings.
  • Regulation of temperature and communication via sweat glands and blood vessels.
• Skin accounts for about 3-5 kg of body weight; covers roughly 2 square meters.
• Part of the integumentary system, along with hair, nails, and glands.

Structure of the Skin

• Epidermis: Outermost layer, visible, made of stratified squamous epithelial tissue.
• Dermis: Below epidermis; responsible for circulation, sensation, and more.
• Hypodermis (Subcutis): Bottom layer, composed mainly of fatty tissue.

Epidermis

• Keratinocytes: Main cells, produce keratin for durability and waterproofing.
  • Constantly replaced; complete turnover every 4-6 weeks.
• Melanocytes: Produce melanin, the skin pigment.
  • Skin color differences due to cellular extensions, not the number of cells.
• Langerhans Cells: Immune cells that originate in bone marrow.
  • Engulf invaders that penetrate the skin.
• Merkel Cells: Sensory cells for touch located at the epidermis-dermis boundary.
• Thick vs. Thin Skin: Varies in epidermal layers; thick skin has five layers, thin skin has four.

Layers of the Epidermis

1. Stratum Corneum: Outermost, rough, dead keratinocytes; provides protection.
2. Stratum Lucidum: Clear, flat dead cells; found only in thick skin.
3. Stratum Granulosum: Grainy layer with active keratin-producing cells.
4. Stratum Spinosum: Spiny layer; active cell regeneration.
5. Stratum Basale: Deepest layer; single columnar cells, major cell production.

Dermis

• Contains collagen and elastin fibers for strength and elasticity.
• Rich in capillaries, blood vessels, nerve fibers, and parts of hair follicles and glands.
• Papillary Layer: Thin areolar connective tissue, forms fingerprints in thick skin.
• Reticular Layer: Dense, irregular connective tissue; houses dynamic parts of the dermis.

Hypodermis (Subcutis)

• Composed mainly of adipose tissue.
• Functions: Insulation, energy storage, shock absorption, skin anchoring.

Skin Care and Protection

• Importance of sunscreen to protect against UV radiation.
  • UV can damage epidermis, affect immune cells, and alter DNA leading to skin cancer.
• Tattoos must reach the dermis to be permanent.

Conclusion and Future Topics

• Overview of the functions and structures within the integumentary system.
• Upcoming topics include skincare products, deodorants, and hair care.

Acknowledgements

• Contributions by Kathleen Yale, Blake DePastino, Dr. Brandon Jackson, Nicholas Jenkins, Michael La Ronda, and the Dot Cafe graphics team.