Histo.1

• Microvilli


  • Small membrane projections with cores of actin filaments that generally function to increase epithelial cells' apical surface area for absorption

  
• Stereocilia


  • Long microvilli with specialized mechanosensory function in cells of the inner ear and for absorption in tissues of the male reproductive tract

  
• Cilia


  • Larger projecting structures with a well-organized core of microtubules (in a 9 + 2 arrangement called the axoneme) in which restricted, dynein-based sliding of microtubules causes ciliary movement that propel material along an epithelial surface

  
• Celiac disease is a disorder of the small intestine in which one of the first pathologic changes is loss of the microvilli brush border of the absorptive cells

  
• The immotile cilia syndrome (Kartagener syndrome) is caused by several mutations in the proteins of the cilia, whose symptoms are chronic respiratory infections caused by the lack of the cleansing action of cilia in the respiratory tract and immotile spermatozoa, causing male infertility
• Types of epithelia


  • Covering (or lining) epithelia
  • Secretory (glandular) epithelia

  
• Simple epithelium


  Contains one cell layer and all cells contact the basement membrane
• Stratified epithelium


  Contains two or more layers of cells and only the lowest layer of cells contact the basement membrane
• Cell morphology in the outer layer of covering epithelia


  • Squamous (thin cells)
  • Cuboidal (cell width and thickness roughly similar)
  • Columnar (cells taller than they are wide)
• Simple squamous epithelium


  • Interior surface of Bowman's capsule
  • Lining of blood vessels
  • Mesothelium covering the mesentery

  
• Simple cuboidal epithelium


  • Tubules around renal corpuscles
  • Ducts in the pancreas
  • Outer surface of the ovary
• Simple columnar epithelium


  • Lining of the small intestine villi
  • Lining of the bile duct
  • Lining of the oviduct
• Ciliated simple columnar epithelium


  • Lining of the trachea
• Pseudostratified columnar epithelium


  • Lining of the trachea
• Stratified squamous keratinized epithelium


  • Thick skin on palms and soles
  • Thin skin on other body parts

  
• Stratified squamous non-keratinized epithelium


  • Lining of the esophagus

  
• Stratified cuboidal epithelium


  • Large ducts from exocrine glands

  
• Transitional epithelium


  • Multiple layers of cells, with large dome-shaped umbrella cells on the surface that become elongated and flattened when the epithelium is stretched
• In chronic vitamin A deficiency, epithelial tissues of the type found in the bronchi and urinary bladder may gradually be replaced by stratified squamous epithelium
• Polarity of epithelial cells


  Apical surface faces the lumen or external environment, lateral surface faces adjacent cells, basal surface attaches to the basement membrane
• Cells of most epithelia exhibit continuous renewal, with the locations of stem cells and rates of cell turnover variable in various specialized epithelia