1. I. General Features and Considerations
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. II. Classification of Epithelia
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. IV. Surface Specializations
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