Epithelial tissue

• Epithelial tissues line every body surface and all body cavities

  • organs are lined on the outside and inside
  • lining of digestive tract organs and other hollow organs including skin surface (epidermis)
  • little to no extracellular matrix
• tissue


  group of similar cells and extra cellular products that perform a common function
• Extracellular matrix


  different tissues varying in structure and function

  • composed of H20, protein fibers, dissolved molecules
• Function of epithelial tissue

  • physical protection
  • selective permeability
  • secretion
  • sensation
• Epithelial cells


  Composed of almost entirely of cells, little extracellular matrix
• Epithelial cells

  • Cellularity
  • Polarity
  • Attachment
  • Avascularity
  • Innervation
  • High regeneration capacity
• Polarity


  Epithelial cells have an apical and basal surface. Apical surface = facing forward. Basal surface = attached to connective tissue
• Apical surface


  Facing forward
• Basal surface


  Attached to connective tissue
• Attachment


  Basal surface attaches to basement membrane
• Lack of blood vessels
• Innervation

  Lots of nerves, nervous system involved
• High regeneration capacity


  Lots of mitosis replacing damaged cells. Too much mitosis - cancer
• Intercellular junction hold cells together.
• Intercellular junctions

  1). Tight junctions

  2). Adhering junctions

  3). Desmosomes

  4). Gap junctions
• Tight junctions


  “gate-keepers“ between external/internal environments

  • near apical surface
  • creates a barrier
  • prevent molecules from traveling between cells

  
• Adhering Junctions 


  Surround whole cell, deep to tight junctions

  
• Desmosomes 


  Appear where there is movement

  • hemidesmosomes - anchor basal epithelial cells to basement membrane
• Gap junctions 


  Opening so that adjacent cells can communicate with each other by the flow of ions and small molecules
• Classification of epithelial tissue

  • simple epithelial
  • stratified epithelial
  • simple squamous
  • stratified squamous
  • simple cuboid
  • simple columnar
  • pseudostratified columnar
• Simple epithelial 


  one layer
• Simple squamous

  • Flat
  • allows for rapid exchange (ex. breathing)
• stratified epithelial 


  multiple layers
• stratified squamous

  • multiple layers
  • protection (ex. skin)
• simple cubodial

  • square/circle
  • length/width are equal
  • allows for absorption/secretion (ex. kidneys)
• simple columnar

  • rectangle
  • taller than wide
  • involved in absorption/secretion
• Pseudostratified columnar

  • Single layer of narrow cells with varying heights
  • Protection; secretes mucin, moves mucin (ex. respiratory tract)
  • Cilated, to move things
• What are the function of epithelial tissues?

  Cellularity, polarity, attachment, avascularity, innervation, high regeneration capacity