Lecture Notes: Anatomy and Function of the Skin

Overview of Skin Structure

• Skin is the largest organ of the body.
• Composed of several layers:
  • Epidermis: Outer layer made of stratified squamous keratinized epithelium.
  • Dermis: Middle layer providing strength and elasticity.
  • Subcutaneous (Hypodermis) Fat Layer: Innermost layer offering insulation and protection.

Epidermis

• Stratified Squamous Epithelium: Composed of multiple layers, flat, and tough.
• Keratinocytes: Main cells producing keratin, a protein that hardens skin, hair, and nails.
• Layers of the Epidermis:
  • Stratum Basale (Germinativum): Deepest layer where cells divide and push upwards.
  • Stratum Spinosum: Cells begin producing keratin and appear spiny.
  • Stratum Granulosum: Cells start to die and create granules.
  • Stratum Lucidum: Only in thick areas like palms and soles.
  • Stratum Corneum: Outermost layer of dead cells.
• Special Cells in the Epidermis:
  • Merkel Cells: Mechanoreceptors for touch, especially in sensitive areas.
  • Melanocytes: Produce melanin for skin pigmentation, protecting DNA from UV damage.
  • Langerhans Cells: Immune cells acting as antigen-presenting macrophages.

Dermis

• Provides skin resistance and flexibility.
• Contains a lot of collagen and elastic fibers.
• Layers of the Dermis:
  • Papillary Layer: Contains peg-like structures anchoring the epidermis and increasing its surface area.
  • Reticular Layer: Deeper layer anchoring skin to the hypodermis.

Functions of the Skin

• Protection: Against mechanical, radiation, and chemical damage.
• Immune Defense: First line of defense, preventing pathogens from entering.
• Temperature Regulation: Through dilation/constriction of blood vessels.
• Water Balance: Prevents excess water loss.
• Sensory Functions: Detects pain, touch, temperature, and pressure.
• Communication: Skin can display emotions or reactions (e.g., turning pale or blushing).

Appendages of the Skin

• Sweat Glands: Help regulate body temperature and contain electrolytes.
• Sebaceous Glands: Produce sebum, an oily substance keeping skin and hair pliable.
• Hair: Provides protection, sensation, and temperature regulation.
  • Arrector Pili Muscle: Causes hair to stand up, creating goosebumps.

Nails

• Specialized formations of the epidermis.
• Aid in gripping and manipulating objects.
• Protects the tips of fingers and toes.

Additional Notes

• Understanding the different cells and layers of the skin helps in recognizing its role in protection, sensation, and regulation.
• Skin appendages play crucial roles in maintaining homeostasis and communication.
• Regular review of terminology and structure is important for exams.