Epithelial tissue

Epithelial tissue

1. Specialised cell junctions

   • Occluding
     • A link forming an impermeable barrier
   • Anchoring
     • Links cytoskeleton of 1 cell to the cytoskeleton of an adj. cell
   • Communicating
     • Selective diff. of molecules between adj. cells

2. Ultrastructure

   • Zona adherens
     • Mech. stab. between epi. cells
   • Zona occludens
     • Transmemb. CHONs
     • JAMs
   • Desmosome
   • Gap junction/ nexus
     • Allows direct passage of ions
     • Connexins --> Connexons
   • Focal contacts
   • Hemidesmosomes

3. Classification

   • Function
     • Respiratory
     • Absorptive
       • Simple: cuboidal, columnar
         • Cuboidal: pancreas, ducts of glands Columnar: single-layered, non-ciliated
     • Sensory
       • Photoreceptors
         • Rods
           • Pigment: rhodopsin More sensitive to light
         • Cones
           • Pigment: iodopsin Receives RGB colours
       • Chemoreceptors
       • Mechanoreceptors
       • 1° cells
         • Axon= rods, cones, olfactory
       • 2° cells
         • No axon= hair + taste sensory cells
     • Secretory (glands)
       • Serous
         • CHON secreting cell Basophilic staining cytoplasm
       • Mucus
         • Staining: PAS rxn, Alcian blue  Produce mucus (and its precursors...mucin?)
       • Exocrine
       • Endocrine
     • Myoepithelium
       • Contractile- contain actin and myosin fil.
       • Surrounds glandular epithelial cells
     • Germinal
     • Covering
       • Simple
       • Stratified
       • Transitional
   • Arrangement
     • Reticular
       • 3D network
     • Trabecular
       • Cord/ plate arrangement
     • Planar
       • Tight cohesive sheets

4. Rich Innervation

5. Renewal

   • Rate of renewal is variable
     • Fast: Intestinal epi.
     • Slow: Liver
   • Metaplasia: one tissue type may transform into another type

6. Avascular

7. Small ECM quantity

8. Tissue types

   • Simple
     • Cuboidal
     • Columnar
   • Stratified
   • Transitional
   • Ciliated psuedostratified