Epidermis Cell Types and Functions

keratinocytes

• Found in epidermis

• Produce keratin protein

• Provide physical protection from abrasions, heat, microbes, UV light

melanocytes

• Found in epidermis

• Produce melanin pigments

• Transfer melanin to keratinocytes (through long arms that project from the cells)

• UV protection

intraepidermal macrophages (Langerhans cells)

• Found in epidermis

• Form in bone marrow and move to epidermis

• Immune responses against invading microbes

• Destroy microbes and make antigens to share with other immune cells

Merkel complexes

• Found partially in epidermis

• Two cells that work together to function as a tactile nerve ending

  • Tactile epithelial cell -> associated Merkel disc

• Provide tactile sensation

keratinocytes

• Main function is physical protection

• Fill with keratin as they mature

• Keratin: tough protein 

  • Hair and nails

• How:

  • 1. Interlocking cell layers

  • 2. Frequent replacement

    • Outer cells sloughed off by friction/abrasion

• Cycle

  • 4-6 weeks

  • Born at deep part of epidermis and pushed superficially

  • Keratinization

    • Generated via mitosis

    • Accumulates keratin

    • Apoptosis (programmed cell death) -> also die off due to lack of nutrients and resources

    • Shed

  • Positive feedback loop

    • Cells replaced at same rate they are shed

melanocytes

• Function in UV protection

  • Produce melanin

    • Pigment particles

  • Weak against UV light by themselves

• How: Melanin transfer

  • Passed to keratinocytes

  • Surround nucleus

  • Shield DNA

intraepidermal macrophages (langerhans cells)

• Have immunological function

• How:

  • Destroy microbes in skin

  • Present antigens to T cells

Vitamin D synthesis

• What is this function of epidermal cells?

  • Vitamin D (calcitriol): Hormone

    • Calcium absorption

    • Bone growth/muscle activation

  • 7-dehydrocholesterol (7-DHC)

    • Precursor to Vitamin D

    • Synthesized by keratinocytes

• How: Exposure to UVB

  • 7-DHC -> D3

  • D3 activated by liver and kidneys

Merkel complexes

• Function in tactile sensation

• How:

  • Tactile epithelial cell in epidermis

  • Cell in dermis

    • Cluster:

      • Around hair follicles

      • Palms of hands

      • Soles of feet

      • Lips

      • Genital mucosa

    • Free nerve endings are also another cell in the dermis that function in sensation

      • Pain, temperature