Chapter 2 Epithelium

1. Chapter 2Epithelium

2. 1.General feature: 1) contain more cells and less extracellular ground substance 2) Polarisaton: ---free surface: face air or other things ---basal surface: have basement membrane, to face underlying connective tissue (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 contractedbladder 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, e.g. 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

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

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

30. 2)specializations of the lateral surface

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

32. 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

33. 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 terminal web

34. cilia Tight junction desmosome intermediate junction

35. 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

36. 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

37. connexons

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

39. 3)specialization of basal surface

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

41. Under EM: --basal lamina: 20-300 nm, electron-dense, thread-liked and amorphous ground substance, produced by epi. cell --reticular lamina: reticular tissue + ground substance, produced by CT

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

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

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

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

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

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

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

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