Epithelial Specializations

Epithelial Specializations

1. Intracellular

   • Tight Junctions (Zona occludens)
     • Blood brain, blood ocular and blood testes barriers
       • Water can't even pass that easily
   • Adhering Belt (Zona adherens)
     • Cadherin outside bound to B-catenins in cytoplasm. Actin filiaments
       • When cadherins unbind, beta catenins come off and tells nucleus something is wrong
   • Desmosomes (Macula adherens)
     • Cadherins and intermediate filaments
       • Very high tensile strength (cardiac muscles)
   • Gap Junctions
     • Hexameric connexons
       • Allows direct passage of small signaing molecules between adjacent cells

2. Apical

   • Cilia
     • Mobile extensions of cell surface
       • Outgrowth from basal bodies
         • 9+2 microtubule core, dynein
   • Microvilli
     • Increase surface area for absorption
       • Core of cross-linked actin filaments extends to a supporting terminal web
   • Stereocilia
     • Very long specialized microvilli
       • Epididymis and inner ear

3. Basal

   • Hemidesmosomes
     • Integrins of cells associate with laminin of basement membrane