Epithelium

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Epithelium

  1. 1. Book Recommended: Basic HistologyLec. By Dr. Habib Qureshi
  2. 2.  Epithelium is the collection of cells with very little intercellular substance lining internal and external surfaces of body and performing similar function
  3. 3.  EPI = UPON THELE = NIPPLE DERIVED FROM ALL THREE EMBRYONIC GERM LAYERS Basal layer of epithelium rest on BASEMENT MEMBRANE
  4. 4.  Basement membrane consists of  Basal lamina proteoglycans, type 1V collagen, electron microscopic - Forms limit of cell - Secreted by epithelial cells  Reticular lamina - Consist of fine collagen fibers
  5. 5.  Simple Epithelium  Simple Squamous  Simple Cuboidal  Simple Columnar Stratified Epithelium Pseudostratified Epithelium Transitional Epithelim
  6. 6.  Single layer of flat cells. Rest on basement membrane Nucleus bulging Function: gas exchange, diffusion of fluids Endothelium = blood vessels Mesothelium = peritoneal, pleural and pericardial cavities Sites= bowman’s capsule, alveoli of lungs, mesothelium, endothelium, loop of Henle of kidney
  7. 7. Simple SquamousEpithelium
  8. 8.  SINGLE LAYER OF CUBOIDAL CELLS For secretion Sites=thyroid follicles, tubules of kidney, surface of ovary All cells of same height and width and rest on basement membrane
  9. 9.  Tall cells on basement membrane Nucleus near base For absorption and secretion ciliated = uterus Non ciliated = GIT, (has brush border – microvilli, folds of cell membrane to increase surface area
  10. 10.  S. sq. keratinized  Surface layer is squamous  In between 3-7 layers are polygonal to flat  Basal layer is cuboidal  There is layer of keratin at the the top  Sites. skin S. Sq. Non-keratinized  No keratin layer  Same as other  sites= esophagus, anal canal, vagina
  11. 11.  Stratified Cuboidal epithelium  Two to three layers of cells  Mostly present in ducts of salivary glands. Stratified Columnar epithelium  Two to three layers of cells  Present in ducts of salivary glands, Urethra.
  12. 12.  ALL LAYERS REACH BASEMENT MEMBRANE Nuclei at different levels Trachea Has goblet cells
  13. 13.  Empty urinary bladder Basal layer columnar Intermediate layers polygonal 2-3 layers Flask shaped layers Dome shaped( umbrella) at top Stretched urinary bladder 2-3 layers of flat cells
  14. 14.  Needed for cell aggregation and cohesion Marked in epithelial tissue Due to binding action of glycoproteins Lateral membranes have special junctions  For adhesion  Act as seals for flow of materials Present in definite order from apex to base
  15. 15.  Tight junctions – ZONULA OCCLUDENS  Most apical  Belt like , totally occluding (Closing)  Have ridges and grooves forming net like structure  Form tight seal (e.g Urinary bladder) to control paracellular pathway ZONULA ADHERENS  Belt like  Encircles cell  For adhesion of neighbouring cells  Forms terminal web on cytoplasmic surface of cell membrane
  16. 16.  Gap junctions –NEXUS  Present anywhere  Present in all tissues except skeletal muscle  There is gap of 2 nm in between opposing surfaces  Protiens of junction make connexons which control the flow  Permits molecules less than 1500 Da.  Eg. Heart muscle.
  17. 17.  DESMOSOMES:MACULA ADHERENS  Disc like structure  Membrane > 30 nm apart  Dense material in intracellular space DESMOSIN for adhesion  Attechment plaque protiens inside the cell membrane HEMIDESMOSOMES (Half Desmosomes) Are between basal surface of epithelial cells and basement membrane.
  18. 18.  Adhereing junctions  Z. Adherens  Hemidesmosomes  desmosomes Impermiable junctions  Zonula occludens Communicating Junctions  Gap junctions
  19. 19. For specific activities at the cell mambrane Microvilli  Fingerlike folds of cell membrane  Increase surface area  Present in absorptive cells e. g. small intestine where the make brush or striated border  1 um in height and 0.08 um wide  Within mv are clusters of actin microfilaments forming terminal web at the base
  20. 20.  STEREOCILIA  Long nonmotile processes of cell  Long microvill  Present in epididymis  Increase surface area for molecular movement CILIA AND FLAGELLA  Long, motile hair like structures  5-10 um long and 0.2 in dia  Surrounded by the cell membrane  Contain central pair of microtubule surrounded by9 pairs of microtubules  Inserted into basal body, inside the cell  Cilia eg. In trachea for movement of mucous  Flagela eg in sperms. Tail like movement
  21. 21.  The End

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