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Epithelial Tissue

Epithelial Tissue. I. General Features and Considerations. A. Characteristics. Lines internal and external surfaces Single or multiple layers of cells Little or no intercellular space Avascular Polarization Keratin Cell junctions Basement membrane. 1. Protection. 2. Absorption.

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Epithelial Tissue

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  1. Epithelial Tissue I. General Features and Considerations

  2. A. Characteristics • Lines internal and external surfaces • Single or multiple layers of cells • Little or no intercellular space • Avascular • Polarization • Keratin • Cell junctions • Basement membrane

  3. 1. Protection

  4. 2. Absorption

  5. 2. Absorption

  6. 3. Secretion

  7. 3. Secretion

  8. 4. Excretion

  9. 5. Sensation

  10. 6. Contraction

  11. Epithelial Tissue II. Classification of Epithelia

  12. A. Terminology • Classification by number of layers: - simple - stratified • Classification by shape of surface cells: - squamous, cuboidal, or columnar • Classification by structural specializations: - pseudostratified - transitional (urinary) - surface structures

  13. B. Simple epithelia • Simple squamous • Simple cuboidal • Simple columnar

  14. Simple Squamous Epithelium

  15. Simple Squamous Epithelium

  16. Endothelium

  17. Mesothelium

  18. Simple Cuboidal Epithelium

  19. Simple Cuboidal Epithelium

  20. 3. Simple columnar epithelium • in profile are rectangular with nuclei usually approximately the same level • most likely to show polarity • often function in absorption, secretion or both • may show extensive surface specializations such as cilia and microvilli • “pseudostratified” columnar - all cells touch the basement membrane (so it’s “simple) but all do not reach the free surface so it looks like it is multilayered

  21. Simple Columnar Epithelium

  22. B. Stratified epithelia • Stratified squamous epithelium - Non-keratinized - Keratinized • Stratified columnar (or cuboidal) epithelium

  23. 1. Stratified squamous epithelium • usually 5-25 cell layers thick • cuboidal cells on the basement membrane and squamous cells at free surface • found on surfaces subject to injury, wear & tear • non-keratinized - lining inside surfaces - all cells including the surface cells viable - surface cells possess functional nuclei • keratinized - surfaces exposed to external world - surface cells non-viable and do not possess nuclei - surface cells contain almost only keratin (eosinophilic)

  24. Non-Keratinized Stratified Squamous

  25. Keratinized Stratified Squamous

  26. 2. Stratified columnar (or cuboidal) epithelium • deep cells small, irregularly polyhedral while superficial cells cuboidal or columnar • located at sites of transition from one type of epithelium to another • provides more robust lining than a simple type of epithelium

  27. Stratified Columnar Epithelium

  28. D. Specialized epithelia • Pseudostratified columnar epithelium • Transitional (urinary epithelium)

  29. 1. Pseudostratified Columnar • all cells contact the basement membrane but not all cells reach the free surface • nuclei aligned at two or more levels

  30. Pseudostratified Epithelium

  31. 2. Transitional Epithelium • form of stratified epithelium that changes in thickness due to the stretch of the organ it lines • when relaxed, the surface cells cuboidal and when distended, the surface cell become more squamous in shape • found in organs of the urinary system

  32. Transitional Epithelium

  33. Epithelial Tissue IV. Surface Specializations

  34. A. Microvilli • Large numbers on a cell surface constitute a brush or striated border by light microscopy • 1.0 mm X 0.1 mm evaginations of the luminal plasmalemma

  35. A. Microvilli • Composed of actin filaments, terminal web extends into cytoplasm • Usually covered with a glycocalyx (sugar coat) • Functions - increase surface area for absorption

  36. Microvilli

  37. Stereocilia

  38. B. Cilia • Actively motile evaginations of luminal plasmalemma, 2-10 mm long

  39. B. Cilia • Core of longitudinal microtubules called an axoneme (9+2) • Basal bodies • at base of cilia • nine triplet microtubules • Function in transport

  40. Cilia

  41. Epithelial Tissue V. Basal Lamina

  42. A. Components • Acellular supportive structure that can be up to 100 nm thick • Composed mainly of type IV collagen, laminin, and proteoglycans

  43. B. Basement membrane vs.basal lamina

  44. Basement Membrane vs.Basal Lamina

  45. C. Functions • Barrier and support • Contains recognition and regulatory factors • Carries a positive charge - thromobogenic

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