Epithelial Sheets and Cell Junctions

Epithelial Sheets and Cell Junctions

1. Structure

   • come together and are arranged side by side

2. epithelial sheets

   • structure
     • apical surface free and exposed
     • basal surface sitting on some support
   • example
     • intestinal epithelium

3. types

   • simple
     • Kidney
   • stratified
     • skin
   • shape
     • squamous, cuboidal, columnar

4. tight junctions

   • Function
     • tight seal
     • mechanical strength
     • communication between each other
   • Claudins and occludins
     • appear like a string of pearls
     • these are the proteins that form the junction

5. Cytoskeletal junctions

   • adheren junctions, hemidesmosomes, cadherins, desmosomes
   • Adherens junctions
     • bind with actin
     • can form adhesion belt around the apical end of the cell
     • adherins will bind together
   • Hemidesmosomes
     • located on the basal side and attach epithelial cells to the basal lamina
     • bind to integrins
   • Desmosome junctions
     • attach to the intermediate filaments and join them together
     • attach to keratin
     • found in the dermis
   • cadherins
     • transmembrane part of the junction

6. Gap Juncions

   • pretty small junctions usually 2-4nm in size
   • gap junctions can open or close depending on extracellular signals
   • connexins are the protein ends that fill the gap
     • connexins will make pores between the cells so they can exchange water and molecules, cytosol becomes uniform