CLASSIFICATION OF EPITHELIAL TISSUES

CLASSIFICATION OF EPITHELIAL TISSUES

1. Covering and lining epithelia

   • SIMPLE
     • Simple cuboidal epithelium
       • Cytoplasm: boundaries clear and visible
       • Nuclei: round and centrally placed
       • Presence of Microvilli
       • Presence of organelles and secretory vesicles (less than in columnar epithelium
       • LOCATION: thyroid follicles, small ducts of exocrine glands, ovary, kidney
       • FUNCTION: protection, barrier, secretory and absorptive activity
     • Simple columnar epithelium
       • Cytoplasm: abundant, basophilic, indistinct boundaries
       • Nuclei: oval-shaped, hypochromatic
       • Have microvilli and may have cillia
       • LOCATION: small intestine, colon, stomach, gallbladder, salivary glands
       • COMPLEX FUNCTION: protection, absorption and secretion
     • Simple squamous epithelium
       • Nuclei: prominent, elongated, hyperchromatic
       • Cytoplasm: Scant, dense, few organelles
       • Poor metabolic activity
       • FUNCTION: Protection and barrier
       • LOCATION: endothelium, alveoli, Bowman's capsule, loop of Henle, mesothelium (pleural, pericardial cavities)
     • Pseudostratified epithelium
       • Nuclei: positioned in different heights
       • Cytoplasm: boundaries indistinct
       • Cells present: basal cells, goblet cells, ciliated cells, neuroendocrine cells
       • Can be or not ciliated
       • LOCATION: trachea and bronchi, urethra, epididymis, ductus deferens
   • STRATIFIED
     • Non-keratinized stratified squamous epithelium
       • 1. BASAL LAYER
         • 1 row cuboidal stem cells
         • Mitotic capacity
       • 2. SPINOUS LAYER
         • several rows of polygonal cells
         • Visible boundaries
         • great number of desmosomes and lateral infoldings
       • LOCATION: oral cavity, esophagus, anal canal, vagina
       • 3. SUPERFICIAL LAYER
         • several layers of flattened (squamous) cells
         • Cytoplasm: pale or absent
         • Nucleus: smaller and darker, eccentric
       • FUNCTION: protection
     • Keratinized stratified squamous epithelium
     • Stratified cuboidal epithelium
       • LOCATION: sweat gland ducts, large ducts of exocrine glands
     • Stratified columnar epithelium
     • Urothelium