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Epithelium: Tissue Structure, Classification & Functions

Learn about epithelium tissue, its structure, classifications like covering epithelium, glandular epithelium, and sensory epithelium, along with functions such as protection, secretion, absorption, and sensory reception. Dive into the detailed types of covering epithelium including simple squamous, cuboidal, columnar, and pseudostratified ciliated columnar epithelium, and stratified squamous and transitional epithelium. Explore the specializations of epithelial surfaces like microvilli, cell coat, and cilia.

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Epithelium: Tissue Structure, Classification & Functions

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  1. Chapter 2Epithelium

  2. What is epithelium? Conception: Epithelium is a tissue composed of closely aggregated polyhedral cells and very little extracellular matrix. Distribution: Cells cover body surfaces, line body cavities, and constitute glands.

  3. 1.General feature: 1) contain more cells and less extracellular ground substance 2) Polarisation(polarity): ---free outer surface: face air or other things ---basal surface: have basement membrane, to face underlying CT, --- lateral surface: between adjacent cells 3)  Avascularity, but innervation: ---no blood vessels ---rich in nerve terminals 4) Having functions of protection, secretion, absorption and sensory reception

  4. 2.Classification of Epithelium 1)Covering epithelium: the epithelium which cover body surface or line the inner surface of body cavities, tubes and sac. 2)Glandular epithelium: the epithelium which main function is secretion. 3)Sensory epithelium: the epithelium which has special sensory function.

  5. 3. Classification of covering epithelium According to the number of layer and shape of cells Simple epi.: ---simple squamous epi. ---simple cuboidal epi. ---simple columnar epi. ---pseudostratified ciliated columnar epi. Stratified epi.: ---stratified squamous epi. ---stratified columnar epi. ---transitional epi.

  6. 1)simple squamous epi: ---structural feature: /one layer flattened cells, cell border are interdigitate /with flattened ellipsoid nucleus

  7. ---distribution: Three types: 1.mesothelium:the simple squamous epi. which line the inner surface of body cavities such as thoracic, pericardiac and abdominal cavities. 2. endothelium:the simple squamous epi. which line the inner surface of cardiovascular and lymphatic system. 3. other place: alveoli, parietal layers of renal capsule.

  8. Mesothelium on abdominal cavity

  9. Vascular endothelium

  10. 2)  Simple cuboidal epi.: ---structural feature: • one layer of cells, with same height and width , hexagonal outline in surface view. • spherical centrally-located nucleus

  11. ---distribution: /the renal tubule /thyroid /the some ducts of glands ---function: covering and secretion renal tubule thyroid

  12. 3)      Simple columnar epi.: ---structural features: • one layer of columnar cells, with basally located ovoid nucleus

  13. ---distribution: gastrointestinal tract gallbladder uterus ---function: secretion and absorption goblet cell: scattered, secreting granules-mucinogen granules-mucus goblet cell simple columnar epi

  14. five types of cells 4) Pseudostratified ciliated columnar epi.: ---Structural feature: 1, Five types of cells columnar cell (ciliated); goblet cell fusiform cell; basal cell: pyramid-shaped diffuse neuroendocrine cell 2, Every cell locate on basement membrance: Simple epi.

  15. ---distribution: inner surface of large duct of respiratory trachea bronchi nasal The epithelium of trachea

  16. 5) Stratified squamous epi.: Three layers ---structural features: 1. Deepest (basal) cells: one layer of cuboidal cells 2. The cells in intermediate regions: several layers of polygonal –shaped cells 3. To the surface: more and more flattened cells

  17. ---distributon: • non-keratinised: mouth, pharynx, esophagus, and vagina • keratinised: the surface of body, make up the skin non-keratinised keratinised

  18. keratinised non-keratinised

  19. 6) Transitional epi.: • flexible-including the number of layers and shape of cells • Two condition: • in the distended bladder: there are two to three layers of cells. The cells become flattened. • in the contracted bladder : there are six to seven layers of cells.

  20. in the contracted bladder in the distendedbladder

  21. ---distribution:Urinary tract (ureters, bladder, urethra) The surface cells are very large and cuboidal in shape, covering several deep cells. Superficial cells

  22. Summary 1 General feature: 1) contain more cells and less extracellular ground substance 2) Polarisation: ---free outer surface: face air or other things ---basal surface: have basement membrane, to face underlying CT, 3)  ---no blood vessels ---rich in nerve terminals 4) Having many functions

  23. Classification of covering epithelium According to the number of layer and shape of cells Simple epi.: ---simple squamous epi. ---simple cuboidal epi. ---simple columnar epi. ---pseudostratified ciliated columnar epi. Stratified epi.: ---stratified squamous epi. ---stratified columnar epi. ---transitional epi.

  24. Exercise 1 for Histology • 1.The 4 basic types of tissue are ______________,______________,_________________and ________________. • 2. Describe the Classification of each covering epithelial type.

  25. 4. Epithelial specializations

  26. Specialisations of free surface specializations of the lateral surface specialization of basal surface

  27. 1)Specialisations of free surface Microvilli Cell coat Cilia

  28. ①microvilli: • defination:Microvilli are finger-like cytoplasmic projection on the free surface of most epithelial cells. • Distribution: striated border: intestinal epi. cell • brush border: proximal renal tubule

  29. structure: 0.1um in diameter, with different longth. surface: cell membrane with cell coat core: longitudinal microfilament-actin filament fixed on terminal web terminal web: made up of transverse-arranged filament at the apical side of cells Function: increase the surface areas for absorption

  30. ②cell coat: ---defination: a thick layer of extracellular glycoprotein ---function: adherence, supporting, protection, exchange of material and recognize

  31. ③     cilia: ---defination: elongated, motile projections of cell membrane and cytoplasm protruding from free surface

  32. ---structure: • 5-10um long, 0.2um in diameter • surface: cell membrane • core: microtubules, 9X2+2 • basal body: centrioles-connected with microtubules

  33. ---function: swing to produce a forward-moving wave ---distribution: epithelial cells of respiratory tract respiratory tract

  34. 2)specializations of the lateral surface

  35. ---intercellular connection of adjacent cells: • non-special: the minute space and cadherin（cell adherent molecules） • special: junctional structures

  36. junctional structures Tight junction (zonula occludens) Intermediate junction (zonula adherens) Gap junction (communication junction) Desmosome (macula adherens)

  37. ①Tight junction (zonula occludens): ---structure: • apical part • point-liked fused between adjacent cells • form anastomosing network ---function: seal the space between cells

  38. ② intermediate junction (zonula adherens): ---structure: • below the tight junction • a gap of 15-20nm in width with medium electron-density filament material • plaque of electron-dense materials, with attached microfilament-make up of terminal web ---function: /adherens /keep the cell shape /transfer cell contract force

  39. ③gap junction (communicating junction): ---structure: • the smallest gap of 2-3 nm • connexons: -consist of protein -7~9nm in diameter -composed of 6-subunits of proteins- connexin -2nm channel: hydrophilic channel ---function: provide a pathway between cells

  40. ④desmosome(macula adherens): ---structure: • plate or spot-shaped • a gap of 20-30 nm, with low electron-density filaments interdigitate • attachment plaque: with attached tonofilament-intermediate filament (karatin) ---function: firmly connection

  41. junctional complex: four types of junctional structures(at least two types) get together.

  42. 3)specialization of basal surface

  43. ①basement membrane: ---defination: a sheet of membrane-liked amorphous material interposed between epi. cells and underlying CT. ---structure: • HE: pink colour, hard to see

  44. ---function: • support, connection, fixation • semi-premeable membrane • induce the movement, proliferation and differentiation of epi.cell

  45. ② plasma membrane infolding (basal longitudinal striation): ---defination: the infolding of cell-membrane with many mitochondria at the basal surface of epi.cell

  46. ---function: • increase the basal surface areas • facilitate the passage of water and ions ---distribution: mainly in proximal and distal renal tubule.

  47. ③hemidesmosomes ---is half of desmosome.

  48. 2.Classification of Epithelium 1)Covering epithelium: the epithelium which cover body surface or line the inner surface of body cavities, tubes and sac. 2)Glandular epithelium: the epithelium which main function is secretion. 3)Sensory epithelium: the epithelium which has special sensory function.

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