HISTO LAB EPI

• Epithelial tissues


  Composed of closely aggregated polyhedral cells adhering strongly to one another and to a thin layer of ECM, forming cellular sheets that line the cavities of organs and cover the body surface
• Epithelial tissues line all external and internal surfaces of the body and all substances that enter or leave an organ must cross this type of tissue
• Common features of epithelia

  • Formed entirely of adherent cells
  • Contains less amounts of intracellular substances
  • Fitted closely by cell junction
  • Avascular - it lacks blood supply and is nourished by diffusion
  • Nerve supply has free-nerve endings
• Functions of epithelial tissues

  • Covering, lining, and protecting surfaces (resists abrasive influence of environment)
  • Absorption (intestinal lining)
  • Secretion (glands)
  • Selective barrier that aids in transferring substances into and out of the body
• Surfaces of epithelial tissues

  • Apical surface
  • Lateral surface
  • Basal surface
• Basement membrane


  The thin extracellular layer that consists of two layers: Basal lamina and Reticular lamina
• Types of epithelia


  • Covering epithelia
  • Secretory epithelia or Glandular
• Arrangement of cells in layers

  • Simple epithelium
  • Pseudostratified epithelium
  • Stratified epithelium
• Cell shape of epithelial tissues

  • Squamous cells
  • Cuboidal cells
  • Columnar cells
  • Transitional cells
• Simple squamous epithelium


  Single layer of thin cells, specializes in lining of vessels and cavities, regulates the passage of substances
• Simple cuboidal


  Cells are roughly tall as they are wide, functions mostly for secretion and excretion
• Simple columnar epithelium


  Cells are always taller than they wide, with apical cilia or microvilli, and are often specialized for absorption
• Types of stratified epithelium

  • Stratified squamous epithelia
  • Stratified cuboidal and columnar epithelia
• Stratified squamous epithelium


  Can be keratinized (dry) or non-keratinized (moist), provides protection, secretion, and protection from water loss
• Stratified cuboidal


  1. 3 layers thick, found in large ducts of exocrine glands, more protection than simple epithelium
• Stratified columnar


  1. 3 layers thick, very rare, more protection, found in conjunctive of eye
• Transitional epithelium (urothelium)


  Stratified and lines much of the urinary tract, superficial cells are rounded or dome-shaped with specialized membrane features
• Pseudostratified epithelium


  Appear to be in several layers, but their basal ends all rest on the basement membrane, functions mostly by protection
• Glands


  Epithelial cells that function mainly to produce and secrete various macromolecules
• Types of glands


  • Exocrine glands
  • Endocrine glands
• Key points in exocrine glands

  • Glands can be simple or compound
  • Secretory portions can be tubular or acinar
  • Secretory units may be branched, even if the duct is not branched
  • Compound glands can have branching ducts and multiple tubular, acinar, or tubuloacinar secretory portions
• Three basic mechanisms of exocrine glands

  • Merocrine secretion
  • Holocrine secretion
  • Apocrine secretion
• Epithelial tissues


  Composed of closely aggregated polyhedral cells adhering strongly to one another and to a thin layer of ECM, forming cellular sheets that line the cavities of organs and cover the body surface
• Epithelial tissues line all external and internal surfaces of the body and all substances that enter or leave an organ must cross this type of tissue
• Common features of epithelia

  • Formed entirely of adherent cells
  • Contains less amounts of intracellular substances
  • Fitted closely by cell junction
  • Avascular - it lacks blood supply and is nourished by diffusion
  • Nerve supply has free-nerve endings
• Functions of epithelial tissues

  • Covering, lining, and protecting surfaces (resists abrasive influence of environment)
  • Absorption (intestinal lining)
  • Secretion (glands)
  • Selective barrier that aids in transferring substances into and out of the body
• Surfaces of epithelial tissues

  • Apical surface
  • Lateral surface
  • Basal surface
• Basement membrane


  The thin extracellular layer that consists of two layers: Basal lamina and Reticular lamina
• Types of epithelia


  • Covering epithelia
  • Secretory epithelia or Glandular
• Arrangement of cells in layers

  • Simple epithelium
  • Pseudostratified epithelium
  • Stratified epithelium
• Cell shape of epithelial tissues

  • Squamous cells
  • Cuboidal cells
  • Columnar cells
  • Transitional cells
• Simple squamous epithelium


  Single layer of thin cells, specializes in lining of vessels and cavities, regulates the passage of substances
• Simple cuboidal


  Cells are roughly tall as they are wide, functions mostly for secretion and excretion
• Simple columnar epithelium


  Cells are always taller than they wide, with apical cilia or microvilli, and are often specialized for absorption
• Types of stratified epithelium

  • Stratified squamous epithelia
  • Stratified cuboidal and columnar epithelia
• Stratified squamous epithelium


  Can be keratinized (dry) or non-keratinized (moist), provides protection, secretion, and protection from water loss
• Stratified cuboidal


  1. 3 layers thick, found in large ducts of exocrine glands, more protection than simple epithelium
• Stratified columnar


  1. 3 layers thick, very rare, more protection, found in conjunctive of eye
• Transitional epithelium (urothelium)


  Stratified and lines much of the urinary tract, superficial cells are rounded or dome-shaped with specialized membrane features
• Pseudostratified epithelium


  Appear to be in several layers, but their basal ends all rest on the basement membrane, functions mostly by protection