histology

histology

1. epithelial: continuous sheets, cells packed closely together, avascular, high rate of cell division

   • simple
     • simple squamous: single layer of flat cells -- filtration, secretion, diffusion, osmosis [heart, lymph vessels, alveoli]
     • simple cuboidal: single layer of cube-shaped cells -- filtration, secretion, diffusion, osmosis [ovary, kidney tubules, ducts]
     • simple columnar: single layer of elongated cells
       • nonciliated: secretion, absorption -- [ducts, GI tract, glands]
       • ciliated: moves substances/mucus [bronchioles, uterine tubes, uterous]
   • pseudostratified columnar: secretion and movement of mucus, protection [respiratory tract, ducts]
     • ciliated pseudostratified columnar
     • nonciliated pseudostratified columnar
   • stratified
     • stratified squamous: flattened apical surface, cuboidal/columnar deeper layers -- protection
       • keratinized: apical cells are dead, filled with keratin [epidermis]
       • nonkeratinized: apical cells are alive [oral cavity, esophagus, vagina]
     • stratified cuboidal: apical cells are cuboidal -- protection, secretion [ducts of sweat glands, male urethra]
     • stratified columnar: irregularly shaped cells, only apical layer elongated -- protection, secretion [urethra, excretory ducts]
   • transitional: flat to cuboidal -- allows distention and relaxation [urinary bladder, ureters, urethra]
   • glandular epithelium: secretion -- exocrine or endocrine
     • endocrine gland: lacks ducts, directly into interstitial fluid and blood
     • exocrine gland: secrete into ducts