1. Chapter 2. Epithelial tissue Wang yang

2. Cells Tissue (fibers, ground substance, tissue fluid)
Extracellular matrix（non-cell component）
(fibers, ground substance, tissue fluid)
◆ Epithelial tissue are composed of closely apposed polyhedral cells with very little extracellular matrix.

3. Key points in this chapter
1. Features of epithelium
2. Types of epithelia
3. Classification of covering epithelium
4. Specific structures in epithelium

4. General features of epithelium
1、Contain more cells which tightly aggregate together and very little extracellular matrix. .
Apical surface
Vertical surface

5. Free surface Lateral surface Basal surface
2、Polarity: significantly structural and functional differences in cell’s opposite surface.
Free surface
Lateral surface
Basal surface 5

6. 3、Avascularity: no blood vessels 4、Innervation :rich in sensory nerve ending 5、Basement membrane: a layer of intercellular substance at the base of epithelium

7. Types of epithelia Two basic types
Covering epithelia form a continuous layer over all the free surfaces of the body:
the outer layer of the skin
the inner surface of cavities and vessels;
the ducts of the exocrine glands
Glandular epithelia:
* with main function for secretion
* make up most of the glands
Other types: sensory/germinal epithelium/myoepithelium

8. Type and distribution of epithelium
Name
Distribution
Covering Epi.
Surface of body, luminal organs and coelom (body cavity)
Glandular Epi.
Glands
Sensory Epi.
Sensory organs
Myoepithelium
Basal portion of the glands
Germinal Epi.
Sexual glands(gonad)

9. What are their functions?
-Protection (skin)
-Absorption (intestine)
-Lubrication (body cavity)
-Secretion (epithelial cells of gland)
-Sensation (neuroepithelium)
-Contractility (myoepithelial cells of gland)
-Reproduction (gonad)

10. Classification of covering Epithelia
Principle: based on the following features
Layers of cells
one layer: simple epi.
several layers: stratified epi.
Shape of cells on the vertical section
squamous epi.--flat/platelike
cuboidal epi. --having the shape of a cube
columnar epi.--column

11. Classification depends on layer
Simple layer
Stratify layers

13. .

14. 1、Simple squamous epithelium
BM————
CT—————
surface shape

15. border: interdigitate
Apical surface
Irregular or polygon
border: interdigitate
nucleus: round
Vertical surface
flat
cytoplasm: very thin
nucleus: oblate/oval

16. Simple squamous epithelium
one layer of flat cells (having one flat nucleus).
found in:
- alveoli of the lung
- kidney glomerulus
- heart, blood and lymphatic vessels
- body cavities
thinnest of all
- gas diffusion, nutrient absorption
- exchange of waste & metabolite
- keep organ surface smooth/antifriction

17. nuclei (one row of flat nuclei, long axis of the nucleus always parallel to the main axis of the cell)
lumen 1 1 1 2

18. The entire circulatory system (blood and lymph vessles) is lined by simple squamous epithelium that is called endothelium.
Longitudinal section
of the capillary

19. The major body cavities (peritoneum, pleura, pericardium) are lined by a mesodermally derived simple squamous
epithelium that is called mesothelium.
Function
To keep surface of vessels or organ smooth, reduce friction, facilitate the blood/lymph flow and movement of viscera.

20. 2、Simple cuboidal epithelium
--structural features:
one layer of cuboidal cells, with same height and width (in side view) and hexagonal outline in surface view.
round centrally-located nucleus

21. --Distribution: --Main function:
renal tubule, thyroid gland, ovary surface...
--Main function:
absorption, secretion and covering.

22. 3、Simple columnar epithelium
--structural features:
one layer of columnar cells, with basally located ovoid nucleus and hexagonal outline in surface view.
goblet cell: scattered, secreting granules-mucinogen +H2O=mucus: lubricate and protect epi.

23. Vertical section of duodenum
Simple columnar epi. Blue nuclei are almost at the same level, near to basal surface, goblet cells scattered among the epi.

24. 4、Pseudostratified ciliated columnar epithelium
Different types of cells
All cells rest on the BM
Not all can reach to the free surface
Columnar cell
Goblet cell
cilia on the columnar cell
Fusiform cell
Basal cell

25. PSEUDOSTRATIFIED
Appears layered but all cells touch the basement membrane
Stratified
Pseudostratified
B.M.

26. larger respiratory passages
Nuclei
Epithelium
Cilia
Lumen
Pseudostratified ciliated
columnar epi.
larger respiratory passages

27. 5、Stratified Squamous Epithelium
* Multi-layer cells
* squamous cells in outermost layers
* Large/polygonal cells in
intermediate regions
* deepest (basal) cells:
cuboidal / low columnar
resting on the BM
strong proliferation ability
* Basal surface is sinuate
not linear:
increase the contact area

28. -Keratinised
(skin:epidermis)
-Non-keratinised
(mouth, esophagus,vagina)
Keratinization: a process by which the superficial cells degrade, filled with keratin and become tough, hard squama.

29. 6、Transitional Epithelium
Main Feature:
The shape and layers of the epithelium are changeable, and are depend on the contraction or distention of organ.
Distribution:
Lining of bladder and ureters
surface epithelium
Basal epithelium

30. Structural feature of Transitional Epithelium
flexible-including the number of layers and shape of cells
In the nondistended bladder : there are six to seven layers of cells.
In the distended bladder: there are two to three layers of cells. The cells become flattened.
The surface cells are very large, dome-like or cuboidal in shape, covering several deep cells.
Basal surface almostly parallel to the free surface of the whole transitional epi.

31. Transitional epithelium
(in nondistented urinary bladder)
Epithelium is thicker
Large cuboidal
Low columnar cell

32. Transitional epithelium
(in distented urinary bladder)
The thickness of epithelium become thinner
Layer of epithelium is reduced
Cells become flat

33. Specialized Structures of Epithelial Cell
1)   specializations of free surface
2)   specializations of lateral surface
3)   specializations of basal surface

34. —cilia —microvillus ——BM
EM diagram of columnar cells
—cilia
—microvillus
Free surface—
Lateral
surface
Cell junction
—plasma membrane
infolding
Basal surface
——BM

35. Microvilli
—cell membrane
—cytoplasm
—microfilament
—terminal web

36. Definition of microvilli:
Delicate finger-liked projections of cell membrane and cytoplasm protruding from the free surface.

37. Function: increase the cell surface area,
better absorption
Distribution: absorptive cells
i.e.small intestine, proximal renal tubule

38. Striated border EM LM

39. Cilia
—cell membrane
—cytoplasm
—microtubule
——basal body

40. Definition of cilia:
Elongated, motile projections of cell membrane and cytoplasm protruding from free surface.

41. Function: Distribution:
Produce a forward-moving wave (rippling wheat field)
:cilia are motile, move back and forth, cilia movement is coordinated to push the fluid or particulate matter in one direction over the ciliated epithelium.
i.e. 1. Remove the inhale granules.　
2. Propell the ovum/ germ cells toward the uterus
in oviduct.
Distribution:
Respiratory system and
oviduct.

42. Cilia
SEM LM

43. Difference between microvilli & cilia
appearance
Small and short
Big and long
observation EM
LM/EM
Surface
Cell-membrane
Axes
Cytoplasm
Composition
Microfilament
Microtubule
Basal portion
Terminal web
Basal body
Function
Increase surface area
Movement

44. Specializations of the lateral surface
Cell junction：
Membrane-associated structures contribute to cohesion and communication between cells.
Distribution:
Present in most tissues:
i.e. muscle tissue and nerve tissue
Prominent in epithelial tissue

45. Tight junction or
zonula occludens
（紧密连接\闭锁小带）
Intermediate junction or
zonula adherens
（中间连接\粘着小带）
Desmosome or
macula adherens
（桥粒\粘着斑）
Gap junction or
communication junction
（缝隙连接\通讯连接）

46. Tight junction (zonula occluden)
* Located at the most apical of lateral surface
* Point-liked membrane fusions between adjacent cells
* Arranged in 2-4 thread-liked structures
* Non-fusion space:10-15nm gap
* Serves as a barrier,
form a seal that prevents
flow of materials between cells
= impermeable junction

47. Intermediate Junction (Zonula Adherens)
* located just below the tight j as a 'belt'
* a gap of 15-20nm in width with medium electron- density filament
* on cytoplasmic surface of junction membrane
electron-dense plaques of material
inserted with actin filament
to form terminal web
* Function
/adherent
/keep the cell shape
/transfer cell contract force
=adhering junction

48. Desmosome (Macula Adherens)
* plate or disk-shaped
* a gap of nm, with low electron-density filaments interdigitate to form intermediate line
* attachment plaque (made up of 12 proteins):
with attached tonofilament(10nm)
intermediate keratin filament
* Function
firmly adhesion/connection
=adhering junction

49. Gap/ Communication Junction
* At deep part of the lateral cell surface
* the smallest gap of 2-4nm
* narrow intercellular space spanned by connexon
Connexon
Cell membrane
Gap junction

50. = communicating junction
connexon:
-protein unit/individual unit of gap junction
-composed of 6-subunits of proteins--connexin
-hydrophilic pore---1.5nm width in the center
Function:
small molecular exchanges,
ions exchanges,
transmit electrical impulse,
provide a connective pathway
between adjacent cells
= communicating junction

51. Review of chapter 2 Features of epithelium Types of epithelium
Classification of covering epithelium
Cell junction

52. Which of the following specializations of the
apical surface of epithelial cells contain microtubules?
  Microvilli
  Cilia
  Stereocilia
  Both B and C are correct

53. 2.The portion of the junctional complex primarily
responsible for restricting the passage of molecules
between adjacent epithelial cells:
  Zonula occludens
  Zonula adherens
  Macula adherens
  Hemidesmosomes

54. ________ 3. Epithelial type that plays a protective function and is found lining the esophagus. ________ 4.  Epithelial type that is associated with distensible organs such as the urinary bladder. _______ 5.  Epithelial type found lining small capillaries where it modulates diffusion. ________ 6.  Epithelial type consisting of a single layer of square-shaped cells when viewed in tissue sections.
  Simple squamous
  Simple cuboidal
  Simple columnar
  Stratified cuboidal
  Stratified squamous
  Stratified columnar
  Pseudostratified columnar
  Transitional E H A B

55. 7. Cilia are commonly seen on cells in tissues that
A. line the blood vessels.
B. line the respiratory tract.
C. form the skin.
D. move from one place to another.
E. All of these are correct.

56. 8.The type of cell junction that prevents the contents of the stomach or urinary bladder from leaking into surrounding tissues is the
adherens junction.
gap junction.
hemidesmosome.
desmosome.
tight junction.

57. 9. One might expect to see microvilli on epithelial tissues whose principal function is
A. protection.
B. movement.
C. absorption.
D. mineral storage.
E. transmission of electrical impulses.

58. 10. Which of the following statements is NOT true
for the epithelium? A. Epithelium is avascular. B. Epithelium contains very little intercellular material C. Epithelial cells lack mitotic activity D. All epithelial cells of a pseudostratified
epitheliumlie on a basal lamina.

59. 11. Stratified squamous epithelia are characterized by always having: A. A keratinized layer B. Squamous cells in proximity to the basement
membrane C. Majority of cells that are squamous in shape D. Squamous cells at the free surface

60. 12. Pseudostratified epithelium differs from stratified epithelia because in the pseudostratified epithelium: A. Two or more than two layers of cells are present B. All cells reach the luminal surface but all cells do not
lie on the basal lamina C. All cells lie on the basal lamina but all cells do not
reach the luminal surface D. Blood vessels are numerous E. None of the above is correct

61. 13. Mesothelium can be defined as: A
13. Mesothelium can be defined as: A. A simple squamous epithelium lining the blood vessels B. A simple squamous epithelium lining the body cavities C. A transitional epithelium D. A pseudostratified epithelium E. None of the above is correct

62. 14. Cilia can be distinguished from microvili
because cilia: A. Are non-motile B. Are located at the basal lamina C. Always occur singly D. Lack 9+2 tubular arrangement E. Are associated with basal bodies

63. 15. Which of the following intercellular junctions would you expect to be most prevalent in an epithelium that is subject to much wear and tear?
Zonula occludens
Desmosome
Gap junction
Tight junction

64. End