epithelial tissue

• Epithelial tissues

  • Tightly packed cells
  • Little or no extracellular matrix
  • Always for surface layers
  • Not covered by another tissue
• Epithelial tissue has no blood vessels
• Epithelial tissue is always found immediately adjacent to blood vessel-rich tissue
• Epithelial tissue enables exchanges with blood necessary for the delivery of oxygen and removal of wastes
• Epithelial tissue


  Consists of cells arranged in continuous sheets, in either single or multiple layers
• Epithelial tissue functions

  Selective barrier<|>Secretory surface<|>Protective surface
• Apical surfaces of epithelial cells

  • free surface
  • May contain specialized structures
  • Face a body cavity or lumen
  • exposed and not attached to other cell
• Epithelial tissue is not covered by another tissue, so it always has a free surface
• Basal surface


  The surface of an epithelial cell that adheres to the basement membrane
• Lateral surfaces


  The surfaces of an epithelial cell that face adjacent cells
• Junctions in epithelial cells

  • Tight junctions
  • Adherens junctions
  • Desmosomes
  • Gap junctions
• Apical layer


  The most superficial layer of cells in multiple-layered epithelia
• Basal layer


  The deepest layer of cells in multiple-layered epithelia
• The basal surfaces of the deepest layer of epithelial cells adhere to extracellular materials such as the basement membrane
• The lateral surfaces of an epithelial cell may contain tight junctions, adherens junctions, desmosomes, and/or gap junctions
• major function

  • protecting underlying structures
  • acting as a barrier
  • permitting the passage of substances
  • secreting substances
  • absorbing substances