L3.4: Structure of the Skin

• 2 kinds of tissue compose the skin

  • epidermis
  • dermis
• • Anchors the skin to underlying organ
  • Not technically part of the integumentary system
  • Composed mostly of adipose tissue
  • Serves as a shock absorber and insulates deeper tissues


  Hypodermis (subcutaneous layer)
• • Capable of being hard and tough
  • “Stratified squamous epithelium”
  • Avascular
  • Keratinocytes
  • Most common cell
  • Produce a fibrous protein called “keratin”

  Epidermis (outer layer)
• • Composed of 5 layers (strata) - from deepest to most superficial:
  • Stratum Basale
  • Stratum Spinosum
  • Stratum Granulosum
  • Stratum Lucidum
  • Stratum Corneum


  Epidermis (outer layer)
• • Deepest layer of the epidermis
  • Lies next to dermis
  • Wavy borderline with the dermis anchors the two together
  • Cells undergoing mitosis
  • Daughter cells are pushed upward to become the more superficial layers
  • Stem cells are constantly dividing
  • New cells are produced daily
  • “Stratum germinativum” (germinating layer)


  Stratum Basale
• • Cells contain thick bundles of intermediate filaments made of pre-keratin
  • Cells become increasingly flatter and more keratinized


  Stratum Spinosum
• • Cells are flattened
  • Organelles are deteriorating
  • Cytoplasm full of granules


  Stratum Granulosum
• • Formed from dead cells of the deeper strata
  • Not present in all skin regions
  • Occurs only where the skin is hairless and extra thick
  • Palm of the hands
  • Soles of the feet


  Stratum Lucidum
• • Outermost layer
  • 20 to 30 cell layers thick
  • Cornified/Horny cells
  • Cornu = horn
  • Shinglelike dead cells
  • Filled with keratin
  • Protective protein prevents water loss from skin
  • Cells are dead, flat membranous sacs filled with keratin
  • Glycolipids in extracellular space make skin water resistant


  Stratum Corneum
• Alert and activate immune cells to a threat (bacterial or viral invasion)


  Epidermal Dendritic Cells
• • Associated with sensory nerve endings
  • Merkel discs
  • Serve as touch receptors


  Merkel Cells
• 2 layers of dermis

  • Papillary layer
  • Reticular layer
• • Dense irregular tissue (connective tissue)
  • Underlies the epidermis
  • OTHER DERMAL FEATURES:
  • Cutaneous sensory receptors
  • Phagocytes
  • Blood vessels
  • Collagen and elastic fibers


  Dermis
• • Upper dermal region
  • Dermal papillae - contains projections
  • Indent in the epidermis above
  • Many projections contain capillary loops, and others house pain and touch receptors
  • On palm and sole surfaces, papillae increase friction and gripping ability
  • Fingerprints are identifying films of sweat


  Papillary layer
• • Deepest skin layer
  • Blood vessels
  • Sweat and oil glands
  • Lamellar corpuscles - deep pressure receptors


  Reticular layer
• 1. epidermis
  2. dermis
  3. papillary layer
  4. reticular layer

  A) 1

  B) 2

  C) 3

  D) 4