1. Department of Histology & Embryology
Chapter 2
Epithelial Tissue
Guanhua Huo
Department of Histology & Embryology
BMU

2. I. OUTLINE Epithelial Tissue is commonly named Epithelium
Epithelium: In Greek ("epi") means "on" or "upon", and ("thēlē") means "nipple“
Epithelium: is made up of cells closely packed and ranged in one or more layers; forms the covering or lining of all internal and external body surfaces, as well as cavitys and lumen of organs.

5. 1. Construction features have more cells(arranged tightly)，
only a small amount of intercellular substance,
ranged in one or more layers;
the cell have polarity
basement membrane: provides structural support for the epithelium and also binds it to neighbouring structures.
no blood vessels-avascular: nutrients and precursors of products of the epithelial cells diffuse across BM and are taken up through the baso-lateral surface of the epithelial cells through the basement membrane
rich in nerve endings: conea, epidermis
2. Distribution features
line cavities and surfaces of structures throughout body
body surface-covering ep.
inner surface of various kinds of tubes, cavities and sacs
Free (apical) surface –apical pole
Basal surface -basal pole

6. B. glandular epithelium C. special epithelium 4. Function
3. Classification
A. lining epithelium (covering epi.):lines both the outside (skin) and the inside cavities and lumen of bodies.
B. glandular epithelium
C. special epithelium
4. Function
protection: physical / chemical / microorganism /desiccation
secretion: mainly for glandular epi.
absorption: small intestine / renal tubule
excretion: sweat gland / renal tubule
others: Sensation/ produce germinal cells,
transcellular transport
myoepithelium
germinal epi.
sensory epi.

7. II. Covering epithelium
Principles of classification:
Tissues are generally classified by the morphology of their cells,
and the number of layers they are composed of.

10. Simple epi.
Stratified epi.
Stratified epi.
Simple epi.

11. 2. Classification & structure
s. squamous epi.
s. cuboidal epi.
s. columnar epi.
pseudostratified ciliated columnar epi.
Simple
epi.
st. squamous epi.
st. columnar epi. transitional epi.
Stratified
epi.

12. A. simple squamous epithelium
Top view: scales-like; have an irregular shape with a serrated border
side view: flat

13. Location: Endothelium: inner lining of blood vessels, heart, and lymphatic vessels Mesothelium: walls of pericardia, pleura, and peritoneal cavities, secrete a lubricating fluid, called serous['sɪrəs] fluid Others: walls of alveoli of the lungs , parietal [pə'raɪətəl] layer of Bowman's capsule some renal tubule

14. alveoli of the lungs

15. visceral layer
parietal layer
Renal Corpuscle: Note the flattened cells of the parietal layer of Bowman's capsule.

16. B. Simple cuboidal epithelium
Top view: hexagonal; side view: square
Location: thyroid follicles; renal tubules

17. C. Simple columnar epithelium
Top view: polygonal [pə'lɪɡənl] ;
side: column-like，prismatic form
Special structure: striated ['straɪeɪtɪd] border,
brush-like border
Cytoplasmic projections
Location: gastrointestinal tract; gall bladder; uterus

20. D. Pseudostratified ciliated columnar epithelium
Taller simple epithelial cells (see columnar, below) are viewed in cross section with several nuclei appearing at different heights, they can be confused with stratified epithelia. This kind of epithelium is therefore described as "pseudostratified" epithelium.
4 types of ell,
Nu. at different
levels
fusiform cell
pyramidal cell

22. c b c f

23. Location: respiratory passages & epididymis.

24. E. Stratified squamous epithelium
Basal layer: low columnar on B.M.;
Middle layers: polygonal and larger;
Top layers: flat / largest and scale-like
platycyte
polygonal cell
basal layer cell
B.M.

25. Location: Nonkeratinized: mouth / pharynx/ esophagus/ vagina; Keratinized: epidermis

27. stratified columnar epithelium
Columnar cells
Columnar cells +
Layers of polygonal cells
Location: ocular conjunctiva, large ducts of salivary glands

28. F. Transitional epithelium
Different functional state has different cell layer & cell-shape.
surface layer: cap cell
Contracted
Distended

29. Location: urinary bladder Full state: 2-3 layers empty state: 5-6 layers

31. III. Glandular epithelium & gland
1. Definition
Glandular epithelia.: The epithelia specialized
for secretion
Glands: The organs composed mainly of
glandular epi.
2. Classification
Exocrine gland
Endocrine gland

32. Derived from the localized covering epithelium
3. Development
Derived from the localized covering epithelium
retain
obliterate
The agglomerated cells form anastomosing cords interspersed between dilated blood capillaries. The others, cells line a vesicle or follicle filled with noncellular material.

33. 4. Exocrine gland Classification：Depend on number of cells
Unicellular glands: goblet cell
Multicellular glands
secretory unit
duct system

34. Section of large intestine showing goblet cells secreting mucus to the extracellular space. The mucus precursor stored in the cytoplasm of the goblet cells is also stained in a dark color. PAS-PT stain. Medium magnification.

35. Apical portion: Large, lightly staining granules containing strongly hydrophilic glycoproteins-mucin.
mucous acini

36. Parotid Gland, Human and Sublingual Gland, Human - H&E
serous acini

37. Electron micrograph of a pancreatic cell
Electron micrograph of a pancreatic cell. Note the nucleus, mitochondria, Golgi complex, secretory (zymogen) granules in various stages of condensation, and rough endoplasmic reticulum. x13,000.

38. Depend on shape: Tubular glands Alveolar glands Tubulo-alveolar glands

39. Depend on function: Serous glands, mucous glands, mixed glands

40. 5. Endocrine gland
Consist of endocrine cells; the secretions (hormone) enter bloodstream directly . To be discussed more detail late.

41. IV. Special structure of epithelium
1. Cellular free surface
cell coat
microvillus
cilium
A. Cell coat:
extracellular glycoprotein layer

43. B. Microvilli
LM:
striated borders
brush-like borders
EM:
finger-like projections (cell-membrane & cytoplasm) (0.1/1.4 μm)
microfilaments (actin filaments): interconnect terminal web
Function: increase the surface area of absorption

44. Cell coat
Electron micrograph of the apical region of an intestinal epithelial cell. Note the terminal web composed of a horizontal network that contains mainly actin microfilaments. The vertical microfilaments that constitute the core of the microvilli are clearly seen. An extracellular cell coat (glycocalyx) ['glaɪkoʊ'kælɪks] is bound to the plasmalemma of the microvilli. x45,000.

45. C. Cilium LM: elongated & mobile projections(0.2/5-10μm);
EM: 9+2 microtubules
connected to the basal
body (the centrioles)

46. inner dynein arm microtubule radial spoke central microtubule
outer dynein arm
radial spoke
central microtubule
Cilia have a rapid back-and-forth movement-
permit a current of fluid or particular matter
to be propelled in one direction over the ciliated epithelium--ATP

47. Ciliary ultrastructure, Left, Normal cilium from a healthy individual in which both inner and outer dynein arms can clearly identified. Right, the absence of outer and inner dynein arms in a patient with primary ciliary dyskinesia [dɪskɪ'ni:ʒə] .

48. 2. Lateral surfaces A. Tight junction B. Intermediate junction
C. Desmosome
D. Gap junction

49. A. Tight junction (zonula occludens )
Location:
around the apex of cells
Structure:
belt-shaped
anastomosing network
of ridges
formed by fused protein
in adjacent cellular
membrane
Function: form a seal
& a barrier to prevention.
Zonula:form a band completely encircling
occludens: membrane fusion that close off the intercellular space

51. B. Intermediate junction, zonula adherens
Location: around adjacent cells,
just below T.J.
Structure:
a gap: 15-20nm, amorphous
material (glycoprotein)
electron-dense material:
on the cytoplasmic faces
filaments: numerous, being
continuous terminal web
Function: hold adjacent cells
Firmly, maintain the cell shape,
and pass cellular contract forces

52. Desmosome, macula adherens
Location:
along the intercellular
faces, widely distributed,
plate-shaped
Structure:
a gap: 20-30nm, filled with
extracellular material &
an intermediate line
attechment plaque: electron dense,
on inner surface of cell-membrane
tonofillaments: a great number,
inserted into the plaque, hairpin
loop-like
Function: “spot weld [weld] ” type
attachment, provide a firm adhesion

54. D. gap junction Location: deep part Structure:
a narrow gap: 2-3nm, spanned
by connexons in opposing
cell membranes
connexons（D=7-8nm):
6 subunits of protein ,
a central channel (2nm)；
Function:
communication (transfer the impulses; passion
& molecules) ;
rich in cardiac muscles and neurons.

56. E. Junction complex
2 or more types of junction present collectively in same area

58. 3. Basal face
A. Basement membrane
B. Plasma membrane infolding
C. Hemi-desmosome

59. A. Basement membrane Location: between epi. & underlying C.T.
50-300nm thick, PAS +, argyrophilia

60. Structure: Lamina lucida Basal Lamina densa lamina reticular lamina
Basal lamina: glycoprotein; produced by epi. cells.
Reticular lamina: reticular fibers + matrix, formed
by fibroblasts in C.T.
Main chemical components: polysaccharide &
glycoprotein (Laminin, type Ⅵ collagen etc.)
reticular lamina
Basal
lamina
Lamina lucida
Lamina densa

61. reticular
lamina
lamina lucida
lamina densa
basal
Function:
support, connection, serve as a semi-permeable membrane, facilitate the proliferation and differentiation of cells

62. B. Hemidesmosome hemidesmosome basal lamina reticular lamina
Function: enhance the cell adhesion to the B.M.

63. Hemidesmosome
& Desmosome

64. C. Plasma membrane infolding
Structure: infolding membrane mitochondria,
Location: renal tubules
Function: increase the basal
surface area & enhance
the reabsorption of water
& ions

66. Proximal tubule kidney. Basal membrane is highly infolded
Proximal tubule kidney. Basal membrane is highly infolded. Note fenestrated capillary at right.