Epidermis Layers

Stratum corneum

Stratum lucidum (variable)

Stratum granulosum

Stratum spinosum

Stratum basale

layers from superficial to deep

stratum basale

Which layer of epidermis?

• 2-4 layers

• Cells:

  • Keratinocytes

    • Alive -> supplied by vessels in the dermis

      • Functioning nucleus and organelles

  • Melanocytes

  • Merkel complexes

• Desmosomes: bind neighboring cells (mainly keratinocytes)

  • Anchor cells together so they travel up at the same rate

stratum spinosum

Which layer of epidermis?

• 8-10 layers

• Cells:

  • Keratinocytes - mainly

    • Alive

      • Functioning nucleus and organelles

    • Appearance:

      • Deep: large and round

      • Superficial: flat

  • Intraepidermal macrophages (Langerhan’s cells) - a few in this layer

• “Spinos” = thorn-like

• Histological prep:

  • Deflates cells

  • Pulls cells apart

• Desmosomes and intermediate keratinous filaments = spikes

thin skin

Thin or thick skin?

• Characterized by:

  • Thin stratum corneum (still thickest layer though)

  • No stratum lucidum

• Where: everywhere except palms and soles

• Hair: Yes

• Ridges: No

thick skin

Thin of thick skin?

• Characterized by:

  • Thick stratum corneum

  • Stratum lucidum present

• Where: palms of hands and soles of feet

• Hair: No

• Ridges: Yes

stratum granulosum

Which layer of epidermis?

• 3-5 layers

• Cells: 

  • Keratinocytes

    • Apoptosis begins -> due to lack of nutrients

      • Nucleus fragments

      • Organelles degenerate

      • No longer metabolically active

    • Appearance:

      • Continue to flatten

• Granules

  • Keratohyalin

    • Protein involved in assembling keratin

    • Stains darkly

  • Lamellar granules

    • Secrete glycolipid into intercellular spaces of stratum granulosum, stratum lucidum, stratum corneum

    • Water resistant

      • Prevents loss of fluids

stratum lucidum

Which layer of epidermis?

• Only on palms and soles

• 4-6 layers

• Cells:

  • Keratinocytes

    • Dead

    • Appearance:

      • Flat

      • Clear

      • Thick plasma membranes

      • Large amount of keratin (very tough)

stratum corneum

Which layer of epidermis?

• 24-30 layers in thin skin

• Up to 50 layer in thick skin

• Cells:

  • Corneocytes

    • Final product of keratinocyte apoptosis

      • No nucleus or organelles

      • Tight junctions between cells

    • Appearance:

      • Thin, flat, enclosed in plasma membrane

• Calluses = abnormal thickening of this layer due to constant friction which activates positive feedback loop