Epidermis

Layers of the Skin

Beauty might be skin deep, but the skin has many layers. The three main sets of layers are:

• Epidermis: The outermost layers (five layers)

• Dermis: The middle layers (two layers)

• Subcutaneous Tissue/Hypodermis: The innermost layer

🧍 The Epidermis

The epidermis is the most superficial layer of the skin. It's composed of five layers or strata.

Stratum Basale (Basal Layer)

• The deepest layer of the epidermis, sitting right above the dermis.

• Primary function: Production of keratinocytes.

• Characterized by rapid cell division.

• Contains melanocytes, which produce melanin (the pigment responsible for skin color).

  Melanocytes determine skin color, but the amount of melanin produced, not the number of melanocytes, determines the darkness of skin.

Stratum Spinosum (Spiny Layer)

• Sits above the stratum basale.

• Characterized by desmosomes, connections between keratinocytes that give the layer a spiny appearance under a microscope when dehydrated.

  A desmosome is a structure that connects two cells together.

• Contains Langerhans cells, immune cells that seek out and engulf foreign invaders and pathogens.

Stratum Granulosum (Granular Layer)

• More superficial layer above the stratum spinosum.

• Named for the abundant keratohyalin granules found in the keratinocytes.

  Keratohyalin granules contain proteins that handle keratin.

• Releases lamellar bodies containing lipids that form a water-tight, impermeable layer at the skin's surface, preventing pathogen entry.

Stratum Lucidum (Lucid Layer/Clear Layer)

• Layer where keratinocytes have died, resulting in a clear or lucid appearance.

• Lacks nuclei and organelles, which are usually responsible for the color of the cell.

  The keratinocytes in this layer are effectively "zombie keratinocytes."

Stratum Corneum

• The topmost layer of the epidermis.

• Composed of stacked layers of dead keratinocytes (15-20 layers).

  Think of it as the "coroner's layer," where dead cells reside.

• The cells in this layer continuously slough off, making way for newer cells.

  Reptiles molt this entire layer in one piece.