Epithelia

Epithelia

1. Simple epithelia

   • 4 types
     • Simple squamous
       • flattened with large SA
       • nucleus bulges from cell
       • ideal for rapid transport across barrier
         • low friction
     • Simple cuboidal
       • cube shaped
       • central nucleus
       • beads of a necklace
       • restricted to internal protected surfaces
         • form walls of ducts
           • form wall of thyroid follicle
     • Simple Columnar
       • column shape
       • all nuclei lying at same level towards base of cell
       • engage in cellular activity but restricted to internal surfaces
         • absorption
         • secretion
         • moving material over the surface
           • Brush border on LM
             • cilia on their apical surfaces
               • goblet cells secrete mucus
                 • numerous in intestinal epithelium
     • Pseudostratified columnar
       • similar shape to simple columnar
         • BUT nuclei lie at different levels in the lower half of cell
         • appears stratified but with EM it is simple
           • all make contact with the basal lamina
       • in the airways
         • mucus, goblet cells, and cilia
         • resp. epithelium is pseudostratified ciliated columnar with goblet cells
   • found on internal protected surfaces

2. Stratified epithelia

   • SQUAMOUS
     • Stratified squamous
       • multiple layers of cells
       • cells in basal are rough cuboidal
         • flattened squamous as they move up the layers
       • defence against mechanical damage
       • line oral cavity & oesophagus
         • withstand coarse food
       • desmosomes between cells
       • attatchment to connective tissue
         • RETE PEGS
           • from lowest cell layer into connective tissue
     • Keratinised stratified squamous
       • more squamous up the layer
         • accumulate granules of KERATOHYALIN
           • stain dark blue
         • in superficial layer - red stain keratin
       • forms epidermis - protects from....
         • DESMOSOMES & RETE PEGS
         • mechanical, chemical and dessication
     • Parakeratotic stratified squamous
       • only found in compartments of ruminant forestomach
       • similar to stratified squamous
         • superficial layer shows cellular detail and keratinisation
       • protects from coarse ingest
         • allows absorption of VFA
   • TRANSITIONAL
     • variable, multiple cell layers
     • move up - fatter and rounder
       • balloon shape
         • great for lateral stretching
     • some 2 nuclei
     • no keratin
     • ONLY in urinary system
       • variable volume of fluid- no rupture
         • modified superficial membrane
       • as bladder fills, cells take on squamous shape
     • always examine in the trough of folds