The Integumentary System: Your Skin

Introduction to Skin as an Organ

• Skin is the body's largest organ.
• Functions of the skin:
  • Protects against infection and extreme temperatures.
  • Maintains fluid balance.
  • Synthesizes vitamin D.
  • Sensory reception and temperature regulation through nerve endings, sweat glands, and blood vessels.
• Skin's physical properties:
  • Weighs about 3-5 kg.
  • Surface area of up to 2 square meters.
  • Stretchy, waterproof, self-repairing.
• Part of the integumentary system, which includes hair, nails, sweat, and oil glands.

Structure of the Skin

• Three Main Layers of Skin:
  1. Epidermis
     • Outer visible layer.
     • Made of stratified squamous epithelial tissue.
     • Contains keratinocytes and melanocytes.
  2. Dermis
     • Below the epidermis.
     • Responsible for most skin functions like sweating and blood circulation.
     • Contains dense connective tissue and nerve endings.
  3. Hypodermis (Subcutis)
     • Innermost layer.
     • Composed mostly of adipose tissue (fat).
     • Provides insulation, shock absorption, and energy storage.

The Epidermis

• Contains four main types of cells:
  1. Keratinocytes:
     • Produce keratin for structure, durability, and waterproofing.
     • Continuously replaced every 4-6 weeks.
  2. Melanocytes:
     • Produce melanin, the pigment for skin color.
  3. Langerhans cells:
     • Part of the immune response, they ingest pathogens.
  4. Merkel cells:
     • Combine with nerve endings to create sensory receptors for touch.
• Layers of the Epidermis:
  • Thick skin (palms, soles) has 5 layers; thin skin has 4.
  • From outermost to innermost:
    • Stratum corneum: Dead keratinocytes, provides protection.
    • Stratum lucidum: Clear layer, found only in thick skin.
    • Stratum granulosum: Living keratinocytes producing keratin, appear grainy.
    • Stratum spinosum: Spiny appearance, active in mitosis.
    • Stratum basale: Single layer, cell factory, connects epidermis to dermis.

The Dermis

• Two layers:
  1. Papillary Layer
     • Areolar connective tissue, dermal papillae form friction ridges (fingerprints).
  2. Reticular Layer
     • Dense irregular connective tissue, contains various dynamic parts like nerve fibers and capillaries.

Hypodermis (Subcutis)

• Contains adipose connective tissue.
• Functions include:
  • Insulation
  • Energy storage
  • Shock absorption
  • Anchoring the skin

Important Notes

• Skin Regeneration:
  • Takes place in the lower layers of the epidermis.
• Sunscreen:
  • Important to protect against UV radiation which can damage the skin, depress the immune system, and cause DNA alterations leading to cancer.
• Tattooing:
  • Tattoos must reach the dermis to be permanent.

Conclusion

• Overview of skin structure, function, and layers.
• Importance of skin care and protection.
• Next topics: Effects of products like lotion and deodorant on skin and hair.