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Epithelial Tissue (Covering and lining epithelia - forms outer covering…

- - - - Endothelium lining blood vessels
      - Mesothelium lines pericardial, pleural and peritoneal cavities
    - - Lines kidney tubules and ducts of glands
    - - Ciliated - have cilia and goblet cells; assist motility of mucus, foreign objects oocytes
        
        Line parts of the upper respiratory tract, Fallopian tubes and brain ventricles
      - Non-ciliated - have microvilli on apical surface, which increases the surface area for absorption
        
        Line gastrointestinal tract from stomach to anus
  - - - Keratinised - apical cells are packed with keratin, making surface tough and waterproof e.g. skin
      - Non-keratinised - no keratin in apical cells; protect from abrasion, defense from microbes, require secretions e.g. lining of mouth and oesophagus
  - - - Ciliated - goblet cells secrete mucus and cilia move it; lines airways of most of the upper respiratory tract
      - Non-ciliated - no goblet cells so functions in absorption and protection; larger ducts of sweat glands
- - - - e.g. pituitary gland
  - - - e.g sweat and salivary glands
      - Single cell glands
        
        individual secretory cells called mucous cells - secrete mucin; apical cytoplasm is filled with (large) secretory vesicles that look clear/foamy in a light micrograph
      - Multicellular glands
        
        Simple glands - single duct that does not divide on its way to the gland cells
        
        Simple tubular - glandular cells form straight tubes e.g. intestinal glands
        
        Simple coiled tubular - glandular cells form coiled tubes e.g. merocrine sweat glands
        
        Simple branched tubular - glandular cells form tubes and several secretory areas share a common duct e.g. gastric glands
        
        Simple alveolar (acinar) - glandular cells from sac-like pockets e.g. embryonic stage in development of simple branched glands
        
        Simple branched alveolar - glandular cells form sac-like pockets and share a common duct e.g. sebaceous (oil) glands
        
        Compound glands - duct divides one or more times on its way to gland cells
        
        Compound tubular - glandular cells form tubes e.g. mucous glands in mouth
        
        Compound alveolar (acinar) - glandular cells form sac-like pockets e.g. mammary glands
        
        Compound tubuloalveolar - secretory cells form both tubes and sacs e.g. salivary glands and pancreas
- - - - The basement membrane is thus found between the epithelium and connective tissue
- - - - Cadherins span gap/space between cells; catenins link cadherins to actin in microfilaments in cell cytoplasm
    - - 6 connexin molecules form connexons that connect neighbouring cells
        
        Narrow intercellular gap - small molecules/ions diffuse through - allow cell communication and nerve impulses to spread
    - - Electrically tight; transmembrane proteins fuse adjacent plasma membranes together - claudins and occludins
    - - Transmembrane glycoprotein cadherin links to intermediate filaments containing keratin in adjacent cells
  - - - Connects epithelia to basement membrane
        
        Integrin linker protein binds to laminin in the basement membrane and keratin intermediate filament in cytoplasm