Integumentary System: Epidermis Overview

Integumentary System: Epidermis

• The epidermis is the outermost layer of skin.
• It is comprised of multiple layers of stratified epithelium.
• The epidermis is avascular, meaning it lacks blood vessels.
• Nutrients and oxygen reach the epidermis via diffusion from the dermis.
• The epidermis is a protective barrier, shielding the underlying tissues from injury.

Epidermal Cell Types

• Keratinocytes:
  • These are the most abundant cell type (about 90%).
  • Keratinocytes produce keratin, a tough fibrous protein that strengthens the epidermis.
  • They also produce lamellar granules, releasing lipids to create a water-repellent barrier.
  • Keratinocytes are continually produced by stem cells in the deepest layer and migrate upwards, eventually dying and being shed.
• Melanocytes:
  • About 8% of epidermal cells.
  • Located in the basal layer.
  • Produce melanin, a pigment that gives skin its color.
  • Melanin granules containing melanin are carried to surrounding keratinocytes by melanocyte dendrites, creating a protective shield against UV radiation damage.
• Intraepidermal Macrophages (Langerhans Cells):
  • Small fraction of epidermal cells.
  • Function as immune cells, recognizing invading microbes and destroying them.
• Tactile Epithelial Cells (Merkel Cells):
  • Least numerous of the epidermal cells.
  • Found in the basal layer.
  • Have contact with tactile/Merkel discs of sensory neurons.
  • Function in detecting touch sensations.

Dermis

• The dermis is the layer beneath the epidermis.
• It is thicker than the epidermis.
• It contains connective tissues with collagen and elastic fibers.
• The dermis provides structural support and strength to the skin.
• The dermis houses blood vessels, nerves, hair follicles, sebaceous glands, and sudoriferous glands.
• Papillary region and Reticular region are two main layers of the dermis.
• Papillary region contains nipple-shaped dermal papilla to increase surface area for nutrient uptake by epidermis via capillary loops and nerve endings for sensory perceptions like touch, pressure, pain, tickling, and itch. Reticular region is the deeper layer with thick collagen and elastic fiber bundles allowing the skin to resist stretching.

Accessory Structures

• Hair:
  • Consists of dead, keratinized cells.
  • Provides limited protection and assists in detecting light touch.
• Skin Glands:
  • Sebaceous glands: Produce sebum, a lipid mixture, to lubricate the skin.
  • Sudoriferous (sweat glands): Produce dilute salt fluid to cool and regulate body temperature.
  • Apocrine glands: Release secretions related to emotional or stress, producing body odor.
  • Ceruminous glands: Modified sweat glands found in the ear. Produce a waxy secretion (cerumen) to lubricate the ear canal and protect from foreign bodies.
• Nails

Hypodermis

• The layer beneath the dermis.
• Consists of loose connective tissue with collagen and elastin fibers, adipose cells, some fibroblasts and macrophages.
• It serves as energy storage and insulation.
• Not part of the skin.