Skin Anatomy: Epidermis and Dermis

Skin Layers

• The epidermis is the most superficial layer of the skin, composed of epithelial tissue, and contains keratinocytes.
• It protects against dehydration, UV radiation, and pathogens.

Epidermal Layers

• Stratum Corneum: outermost, protective layer composed of corneocytes.
• Stratum Lucidum: layer of dead keratinocytes that are not yet differentiated into corneocytes, only present in palms and soles.
• Stratum Granulosum: contains keratinocytes that form a water barrier.
• Stratum Spinosum: contains keratinocytes with long extensions (“spines”), important for strength (desmosomes).
• Stratum Basale (Germinativum): precursor keratinocyte stem cells proliferate here, site of light touch sensation (Merkel cells) and melanin synthesis (melanocytes).

Dermis

• Located just below the epidermis, the dermis supports the epidermis and cushions against injury.
• Composed of two layers: papillary dermis (more superficial and thin, high surface area) and reticular dermis (deeper and thick, made of connective tissue).

Hair

• Made of keratin, generated from hair follicles.
• Stands up via erector pili muscles, and offers sun and hypothermia protection.
• Only mammals have true hair.

Glands

• Sudoriferous (Sweat) glands:
  • Eccrine glands (sweat glands) are located on the entire body surface and are important in thermoregulation.
  • Apocrine glands are located at specific sites and secrete into a hair follicle, producing earwax (ceruminous) or milk (mammary), depending on their location.
• Sebum-producing glands:
  • Sebum (oils + wax) is secreted into a hair follicle.
  • Located over the entire body except at the palms of hands and soles of feet.

Hypodermis

• The hypodermis (subcutaneous layer) is the deepest layer and contains larger nerves and blood vessels.
• Composed of connective tissue and primarily functions to store fat.