Epithelial Specializations

Epithelial Specializations

1. Intracellular

   • Tight Junctions (Zonula occludens)
     • Attach adjacent cells, act as a barrier to solutes, boundary between apical and basolateral membrane
       • Blood Brain Barrier, Blood Ocular Barrier, Blood Testes Barrier
   • Adhering Belts (Zonula adherens)
     • Deep to tight junctions
       • Continuous belt of cadherin around cells
         • Cadherin binds to B-catenin inside cytoplasm of cell
           • Associated with actin filaments
   • Desmosomes (macula adherens)
     • Cell-Cell Adhesions via cadherins
       • Connect to tonofilaments (intermediate keratin filaments)
         • In cardiac muscle = desmin filaments
   • Gap Junctions
     • Clusters of closely packed connexoms (Transmembrane Channels)
       • Connexon hemichannel+ connexon hemichannel back to back
         • Connexons are hexameric: 6 channel protein subunits

2. Apical

   • Cilia
     • 10-12 micrometers
       • outgrowth of basal bodies like centrioles
         • 9+2 microtubule arrangement, dynein driven
           • Respiratory system, reproductive tract
   • Microvilli
     • Stereocilia
       • Different than cilia, found in inner ears and epididymus
     • Rigid
       • Increase absorption surface area
         • Actin filaments to support terminal web below PM

3. Basal

   • Hemi-Desmosomes
     • anchors basal domain to basal lamina
       • cytoplasmic side + keratin (tonofilaments)
         • outer = integrins and laminin in basement membrane