epithelial tissue

• Epithelial Tissues


  • Cover the external body surfaces
  • Provide lining of the internal surfaces
  • Cells are arranged very closely with little intercellular substance between
  • Arranged as sheets covering or lining surfaces as masses of cells as in glands
  • Composed of closely aggregated polyhedral cell
  • Strongly adhering to one another
• Epithelial cells


  Aggregated polyhedral
• Extracellular matrix


  Small amount
• Epithelial tissues


  Avascular (has no blood supply)
• Functions of epithelial tissues

  • Covering, lining and protecting
  • Absorption
  • Secretion: process of producing or releasing substances by cells or glands
• Categories of epithelial tissues

  • Simple epithelium
  • Stratified epithelium
  • Glandular or pyramidal epithelium
• Apical Region


  • Outermost part of the tissue
  • Nearest to the top
  • Cilli
  • Microvilli
• Basement Membrane


  • Extracellular part
  • No cells
  • Entire structure beneath the epithelial tissue
  • Composed of: basal lamina and reticular fibers
  • Basal lamina is nearest to the epithelial cells
  • Reticular fibers are beneath the basal lamina
• Cell Junctions


  • Tight junction (occluding junction / zonula occludens)
  • Adherens junction (anchoring junction / zonula adherens)
  • Desmosome (anchoring junction / macula adherens)
  • Intermediate filament
  • Gap junction (communicating junction / nexus)
  • Hemidesmosome (anchoring junction / half desmosome)
• Tight junction


  Forms a seal between adjacent cells to control the passage of molecules between each cell
• Adherens junction

  Site of strong cell adhesion, strengthens and stabilizes the nearby tight junction and helps hold cells together
• Desmosome

  Spot-like, disk-shaped, for adhesion but supplements the adherens junction to maintain the integrity of the epithelium
• Gap junction

  Allow the direct transfer of small molecules and ions from one cell to another
• Hemidesmosome

  Half, usually anchors the cytoskeleton to the basal lamina
• Specialized structures


  • Microvilli (for absorption, demonstrate uniformity, visible like brushborder or striated, contain microfilaments)
  • Cilia (hair-like, for propelling fluid (mucous), longer than microvilli, motile, contain internal arrays (microtubules))
• Classification of epithelial tissues

  • Number of cell layers: Simple (one layer attached to basement membrane), Stratified (two or more layers)
  • Morphological structure (shape): Squamous (thin, flat cells), Cuboidal (cube-like shape), Columnar (brick-like, taller than wide)
• Types of simple epithelium

  • Simple squamous epithelium
  • Simple cuboidal epithelium
  • Simple columnar epithelium
  • Pseudostratified columnar epithelium
• Simple squamous epithelium


  • Endothelium (lining of vessels)
  • Mesothelium (lining of cavities)
• Simple cuboidal epithelium


  • Common in glands and ducts (e.g. ovaries, thyroids, kidney tubules)
• Goblet cell

  Column-shaped cell found in respiratory and intestinal tracts, secretes the main component of mucus (mucin), cup-like shaped, creates a protective mucus layer
• Pseudostratified columnar epithelium

  Layers of cells with nuclei at different levels, not all cells reach the surface but all are attached to the basal lamina
• Pseudostratified ciliated columnar epithelium

  Lines the respiratory tract and parts of the reproductive tract, functions include protection, secretion, movement of mucus, and transport of sex cells
• All epithelium with mucus and goblet cells is pseudostratified ciliated columnar epithelium
• Types of stratified epithelium

  • Stratified squamous epithelium (keratinized and non-keratinized types)
  • Stratified cuboidal epithelium
  • Stratified columnar epithelium
  • Transitional epithelium
• Stratified squamous (non-keratinized)


  • Opening of the mouth, esophagus, vagina
• Stratified squamous (keratinized)


  • Epidermis of the skin
• Stratified cuboidal epithelium


  • Sweat gland ducts
• Stratified columnar epithelium


  • Male urethra, conjunctiva, excretory ducts
• Transitional epithelium


  • Excretory passage of urinary tract (ureter, urinary bladder, urethra)
• Transitional epithelium


  Mix of cuboidal and columnar cells, capable of stretching
• Types of glandular or pyramidal epithelium

  • Serous glandular epithelium (e.g. pancreas, parotid glands, synthesize proteins)
  • Mucous glandular epithelium (e.g. sublingual glands, produce mucous fluids and digestive enzymes)
  • Mixed glandular epithelium (e.g. submaxillary glands)
• Exocrine glands


  Have tubular ducts
• Endocrine glands


  Have no ducts
• pseudostratified columnar epitehelium

  
• SIMPLE COLUMNAR EPITHELIUM

  
• SIMPLE CUBOIDAL EPITHELIUM

  
• SIMPLE SQUAMOUS EPITHELIUM

  
• SIMPLE SQUAMOUS EPITHELIUM

  
• STRATIFIED COLUMNAR EPITHELIUM

  
• STRATIFIED CUBOIDAL EPITHELIUM