mod 3

• Epithelial tissues are arranged very closely with very little intercellular substances in between
• Epithelial tissues include both surface epithelia and solid organs
• Surface epithelia cover or line all body surfaces, cavities, and tubes
• Epithelial cells are bound to adjacent cells by various cell junctions
• All epithelia are supported by a basement membrane
• Epithelial cells are polarised, with one side facing the basement membrane and the other facing outwards
• Epithelium primarily involved in secretion is often arranged into structures called glands
• Glands are invaginations of epithelial surfaces formed during embryonic development
• Some solid organs are composed largely of epithelial cells with a supporting tissue framework
• Exocrine glands are connected to the surface epithelium of the gastrointestinal tract by a branching system of ducts
• Endocrine glands release their secretions directly into the blood
• Classification and Distribution of Epithelial Tissue:

  • Surface epithelia
  • Simple epithelium: composed of one layer of cells attached to the basement membrane
  • Simple squamous epithelium: found in Bowman’s capsule of the kidney, endothelium, mesothelium
  • Simple cuboidal epithelium: non-ciliated in collecting tubules of the kidney, ciliated in bronchioles and thyroid gland
  • Simple columnar epithelium: non-ciliated in pyloric end of stomach, gallbladder, small/large intestines, ciliated in fallopian tube, uterine tube, lungs
• • Pseudostratified columnar epithelium: non-ciliated in male urethra, ciliated in trachea, larynx, bronchi, oviduct
  • Stratified epithelium: composed of more than one layer of cells, where only the basal cells are attached to the basement membrane
  • Stratified squamous epithelium: keratinized type in epidermis of the skin, non-keratinized type in the opening of the mouth, esophagus, vagina
  • Stratified cuboidal epithelium: found in sweat gland ducts
• • Stratified columnar epithelium: part of male urethra, conjunctiva of the eye, some large ducts of exocrine glands
  • Transitional epithelium (Urothelium): found in excretory passages of the urinary tract (renal calyces, ureter, urinary bladder, proximal segment of urethra)
  • Glandular or Pyramidal epithelia
  • Serous glandular epithelium: found in pancreas, parotid glands
  • Mucous glandular epithelium: found in sublingual glands
  • Mixed glandular epithelium: found in submaxillary glands