1. Epithelial Tissue
BIOL241

2. Epithelial Tissue Overview: Characteristics and functions of epithelia
Cell junctions
Classification of epithelia
Exocrine glands

3. Four tissue types in the body
Groups of cells similar in structure and function
The four types:
Epithelial
Connective
Muscle
Nerve

4. Remember the levels of organization

5. What is an Epithelium? Epi = “on” or “around” Thele = “nipple”
Covers the external body surface (epidermis), lines cavities and tubules, and generally marks off our insides from our outsides
Other examples?

6. Epithelial Tissues – two types
layers of cells covering internal or external surfaces
Glands:
structures that produce secretions

7. Characteristics of Epithelia
Cellularity: composed of cells bound by cell junctions
Polarity: apical and basal surfaces
Attachment: via basal lamina to underlying connective tissue
Avascularity: no blood vessels (but richly innervated)
Regeneration: germinative cell division

8. Free Surface and Attached Surface
Polarity:
apical and basolateral surfaces
Figure 4–1

9. Repairing and Replacing Epithelia
Epithelia are replaced by division of germinative cells (stem cells)
Near basal lamina

10. Functions of Epithelial Tissue
Provide physical protection
Control permeability
Move fluids over the surface
Provide sensation (e.g. neuroepithelia)
Produce specialized secretions (glandular epithelium)

11. Specializations Microvilli increase absorption or secretion
Cilia (ciliated epithelium) move fluids

12. Indentations & Protrusions Increase Surface Area

13. More Examples

14. Effective Barriers Physical integrity is maintained by:
intercellular connections
attachment to basal lamina
maintenance and repair

15. Cell Junctions

16. Cell junctions Tight Junctions – surround cells, waterproof
Isolates wastes in the lumen
Gap junctions – allow rapid communication
Desmosomes – tie cells together with great strength (like rivets)
Hemidesmosomes attachment
Figure 4–2b

17. Desmosomes
CAMs, dense areas, and intercellular cement
Figure 4–2d

18. Attachment to Basal Lamina
Hemidesmosomes
Figure 4–2e

19. Classification of epithelia
Cell shape
Squamous: flat “square”
Cuboidal: cubes (2-D: “square”)
Columnar: tall
Layers of cells
Simple: one layer of cells (what is a function?)
Stratified: many layers of cells (what is a function?)

20. Classes of Epithelia
Based on shape and layers
Table 4–1

21. Classification of Epithelia
Simple or stratified
Figure 4.1a

22. Classification of Epithelia
Squamous, cuboidal, or columnar
Figure 4.1b

23. Simple Squamous Epithelia
Single layer of flattened cells with disc-shaped nuclei and sparse cytoplasm
Look like a fried egg from the top
most delicate
Diffusion, friction reduction
Special names
Mesothelium:
lines body cavities (e.g. peritoneum, pleura)
Endothelium:
lines heart and blood vessels

24. Epithelia: Simple Squamous
Figure 4.2a

25. Simple Squamous Epithelium
Figure 4–3a

26. Epithelia: Simple Cuboidal
Single layer of cube-like cells with large, spherical central nuclei
Function in secretion and absorption
Present in kidney tubules, ducts and secretory portions of small glands, and ovary surface

27. Epithelia: Simple Cuboidal
Figure 4.2b

28. Simple Cuboidal Epithelium
Kidney tubules
Figure 4–4a

29. Epithelia: Simple Columnar
Single layer of tall cells with oval nuclei
May have microvilli
Goblet cells are often found in this layer
Function in absorption and secretion
Line digestive tract and gallbladder, small bronchi, uterine tubes, and some regions of the uterus

30. Epithelia: Simple Columnar
Figure 4.2c

31. Epithelia: Simple Columnar
Intestinal lining

32. Epithelia: Pseudostratified Columnar
Single layer of cells with different heights; all touch the basal lamina but some do not reach the free surface
Nuclei are seen at different layers
Function in secretion and propulsion of mucus
Present in the male sperm-carrying ducts (nonciliated) and trachea (ciliated)

33. Epithelia: Pseudostratified Columnar
Figure 4.2d

34. Pseudostratified Columnar Epithelium
Trachea
Figure 4–5b

35. Epithelia: Transitional
Several cell layers, basal cells are cuboidal, surface cells are dome shaped (or flat)
Stretches to permit the distension of the urinary bladder
Lines the urinary bladder, ureters, and part of the urethra

36. Epithelia: Transitional
Figure 4.2f

37. Epithelia: Transitional
Urinary bladder
Figure 4.2f

38. Stratified epithelia

39. Epithelia: Stratified Squamous
Thick membrane composed of several layers of cells (the only one with more than 2 or 3 true layers)
Functions in protection of underlying areas subjected to abrasion
Forms the external part of the skin’s epidermis (keratinized cells), and linings of the esophagus, mouth, and vagina (nonkeratinized cells)

40. Epithelia: Stratified Squamous
Figure 4.2e

41. Epithelia: Stratified Cuboidal
Quite rare in the body
Found in some sweat and mammary glands
Typically two cell layers thick
Only top layer is cuboidal

42. Stratified Cuboidal Epithelium
Sweat gland ducts
Figure 4–4b

43. Epithelia: Stratified Columnar
Limited distribution in the body
Found in the pharynx, male urethra, and lining some glandular ducts
Also occurs at transition areas between two other types of epithelia

44. Stratified Columnar Epithelium
Rare
Salivary gland duct
Figure 4–5c

45. Epithelia: Glandular
A gland is one or more cells that makes and secretes an aqueous fluid
Classified by:
Site of product release – endocrine or exocrine
Relative number of cells forming the gland – unicellular or multicellular

46. Glandular Epithelia
Endocrine and exocrine glands
Figure 4–6

47. Glands Endocrine Exocrine More numerous than endocrine glands
Ductless glands that produce hormones
Secretions include amino acids, proteins, glycoproteins, and steroids
Exocrine
More numerous than endocrine glands
Secrete their products onto body surfaces (skin) or into body cavities via ducts
Examples include mucous, sweat, oil, digestive, and salivary glands
The most notable unicellular gland is the goblet cell
EXAMPLES?

48. Goblet Cell
Figure 4.3b

49. Glands are classified based on mode of secretion - 3 types

50. Modes of Secretion
Merocrine – products are secreted by exocytosis (e.g., pancreas, sweat, and salivary glands)
Holocrine – products are secreted by the rupture of gland cells (e.g., sebaceous glands)
Apocrine – products accumulate in the top of the cell and then it breaks down

51. Summary Epithelial tissue structures and functions Cell junctions
Classification by cell shape and layers
Glands