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Chapter 2 Epithelium

Learn about the different types of epithelium, their structural features, functions, and specialized adaptations. Explore the classifications of covering epithelium and discover unique features of free and lateral cell surfaces.

richardwillie
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Chapter 2 Epithelium

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  1. Chapter 2Epithelium

  2. 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)  Avascularity, but innervation: ---no blood vessels ---rich in nerve terminals 4) Having functions of protection, secretion, absorption and sensory reception

  3. 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.

  4. 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.

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

  6. ---distribution: • mesothelium: the simple squamous epi. which line the inner surface of body cavities such as thoracic, pericardiac and abdominal cavities. • endothelium: the simple squamous epi. which line the inner surface of cardiovascular and lymphatic system. • other place: alveoli, parietal layers of renal capsule. ---function: a) transport of materials b) facilitates movement of viscera

  7. Vascular endothelium

  8. Mesothelium on abdominal cavity

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

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

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

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

  13. four types of cells 4)pseudostratified ciliated columnar epi.: ---Structural feature: 1, Four types of cells columnar cell (ciliated); goblet cell fusiform cell; basal cell:pyramid-shaped 2, Every cell locate on basement membrance: Simple epi.

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

  15. 5)stratified squamous epi.: ---structural features: • deepest (basal) cells: one layer of cuboidal cells • the cells in intermediate regions: several layers of polygonal –shaped cells • to the surface: more and more flattened cells

  16. ---distributon: • non-karatinised: mouth, pharynx, oesophagus, urethra and vagina • karatinised: the surface of body, make up the skin karatinised non-karatinised

  17. 6)transitional epi.: • flexible-including the number of layers and shape of cells • 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. • The surface cells are very large and cuboidal in shape, covering several deep cells.

  18. ---distribution: bladder

  19. in the contracted bladder in the distendedbladder

  20. 4. Epithelial specializations

  21. 1)Specialisations of free surface

  22. ①microvilli: ---defination: delicate finger-liked projections of cell-membrane and cytoplasm protruding from the free surface

  23. ---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

  24. ---function: increase the surface areas ---distribution: /striated border: intestinal epi. cell /brush border: proximal renal tubule

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

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

  27. ---structure: • 5-10um long, 300-500nm in diameter • surface: cell membrane • core: microtubules, 9X2+2 • basal body: centrioles-connected with microtubules

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

  29. 2)specializations of the lateral surface

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

  31. ①Tight junction (zonula occludens): ---structure: • apical part • point-liked fused between adjacent cells • arranged in 2-4 thread-liked structures • form anastomosing network ---function: seal the space between cells

  32. 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

  33. ③desmosome (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

  34. ④gap 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

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

  36. 3)specialization of basal surface

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

  38. EM: --basal lamina: 20-300 nm, electron-dense, thread-liked and amorphous ground substance, produced by epi. Cell --reticular lamina: RT+ground substance, produced by CT

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

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

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

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

  43. 5. Glandular epi. and gland • glandular epi.: epi are specialized for secretion • gland: organs composed mainly of glandular epi.

  44. 1)classification: exocrine gland: discharge the secretion through a duct system endocrine gland: release the secretion directly into blood steam

  45. 2) structure of exocrine gland: ①acinus (secreting unit): according the nature of secretion a.serous acinus: serous secretory cells

  46. ---structure: • pyramid-shaped cell • basally-located round nucleus • acidophilic cytoplasm-eosinophilic zymogen granules-contain enzymes • EM: RER,Golgi complex ---function: produce a serous secretion

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