1. EPITHELIUM
DR. SWATI PATIL

2. INTRODUCTION
Epi= upon; Thelia= nipple
DEVELOPMENT
Ectoderm- skin, mouth, nose and
anal canal.
Endoderm- GIT, glands, resp tract
Mesoderm-body cavities
(Mesothelium), endothelium.

3. Function of Epithelial Tissue
• Protection
• Absorption
• Filtration
• Secretion

4. Characteristics of Epithelial Tissue
• Form continuous sheets
(fit like tiles)

5. • Apical Surface
– All epithelial cells
have a top surface
that borders an
open space (lumen)

6. • Basement
Membrane
– anchors
epithelial cells
to underlying
connective
tissue

7. BASEMENT MEMBRANE
- visible under LM
- PAS +
- comprises of basal lamina
& reticular lamina

8.  BASAL LAMINA
- visible in EM
- 20-100 nm thick
- consists of dense and clear layers
- composed of macromolecules
1. Laminin
2. Type IV collagen
3. Entactin (Nidogen)
4. Proteoglycans

9. • Avascularity
– Lacks blood
vessels
– Nourished by
connective tissue
• Regenerate & repair
quickly

10. Classification of Epithelial Tissue

11. Classification of Epithelial
Tissue - Criteria
• Cell Shape
– Squamous – flattened
– Cuboidal - cubes
– Columnar - columns

12. • Cell Layers
– Simple (one layer)
– Stratified (many layers)
• Named after type of cell at apical surface

13. Simple Squamous Epithelium
• Structure
– Single Layer of flattened
cells
• Function
– Absorption, and filtration
– Not effective protection –
single layer of cells.
• Location
– Walls of capillaries, air sacs
in lungs
– Form serous membranes in
body cavity

15. Simple Cuboidal Epithelium
• Structure
– Single layer of cube
shaped cells
• Function
– Secretion and
transportation in glands,
filtration in kidneys
• Location
– Glands and ducts
(pancreas & salivary),
kidney tubules, covers
ovaries

17. Simple Columnar Epithelium
• Structure
– Elongated layer of
cells with nuclei at
same level
• Function
– Absorption, Protection
& Secretion
– When open to body
cavities – called
mucous membranes

19. Simple Columnar Epithelium
• Special Features
– Microvilli, bumpy
extension of apical
surface, increase surface
area and absorption rate.
– Goblet cells, single cell
glands, produce
protective mucus.
• Location
– Linings of entire digestive
tract

21. Features of Apical Surface of
Epithelium

22. Microvilli
 Finger-like extensions of
plasma membrane of apical
epithelial cell
 Increase surface area for
absorption
 Temporary or permanent
 1 µm : height, 0.8 µm : width
 BRUSH/STRIATED BORDER:
seen in LM
 Terminal web : supports
microvilli
 composed of actin filaments w/
fimbrin & villin
(eg.) in small intestine

23. Features of Apical Surface of
Epithelium
 Cilia: (eg.) respiratory tubes
 Whip-like, motile extensions
 Moves mucus, etc. over epithelial surface 1-way
 5-10 µm : length
 0.2 µm : diameter
* Flagella: (eg.) spermatozoa
 Extra long cilia
 Moves cell

24.  Stereocilia (eg.) epididymis & ductus deferens
 Longer but non motile, compared to microvilli
 Branched

25. Pseudostratified Epithelium
• Structure
– Irregularly shaped cells with
nuclei at different levels –
appear stratified, but aren’t.
– All cells reach basement
membrane
• Function
– Absorption and Secretion
– Goblet cells produce mucus
– Cilia (larger than microvilli)
sweep mucus
• Location
– Respiratory Linings &
Reproductive tract

26. Myoepithelial cells

27. Stratified Squamous Epithelium
• Structure
Many layers (usually cubodial/columnar at bottom
and squamous at top)
Function
– Protection
– Keratin (protein) accumulates in older cells near
the surface
• waterproofs and toughens skin.
Nonkeratinised
• Location
Keratinised

28. Stratified squmous keratinised

29. Stratified squamous non-keratinised

30. Stratified cuboidal epithelium

31. Stratified columnar epithelium

32. Transitional Epithelium
• Structure
– Many layers
– Very specialized
• cells at base are cuboidal or
columnar, at surface will
vary.
– Change between stratified &
simple as tissue is stretched out.
• Function
– Allows stretching (change size)
• Location
– Urinary bladder, ureters &
urethra

36. GLANDS
• One or more cells that make and secrete a product.
• Secretion = protein in aqueous solution: hormones, acids, oils.
• Endocrine glands
– No duct, release secretion into blood vessels
– Often hormones
– Thyroid, adrenal and pituitary glands
• Exocrine glands
– Contain ducts, empty onto epithelial surface
– Sweat, Oil glands, Salivary glands, Mammary glands.

37. Modes of Secretion
• (How the gland’s product is
released)
• Merocrine
- secretory products are released by
exocytosis
– Ex: Sweat glands and salivary glands
• Apocrine
-apical part is shed off to discharge –
secretion
- Ex:mammary glands

38. Modes of Secretion
• Holocrine
– Entire cell disintegrates
while discharging its
secretion
– Sebaceous (oil glands on the
face) only example

40. Classification of Exocrine glands
Branching
 Simple – single,
unbranched duct
 Compound – branched.

41. • Shape:
– tubular or alveolar
– Tubular – shaped like a tube
– Alveolar – shaped like flasks or sacs
– Tubuloalveolar – has both tubes and sacs in
gland

43. Cell Junctions & Cell-Cell Adhesion

44. Classification of cell contacts
• Unspecialised contacts
-cell adhesion molecule
-intermediate protein

45. Actin cytoskeleton dependent cell-cell and cell-ECM
adhesions
Cell-cell adherence junctions
1. Calcium-dependent
 Cadherins
 Selectins
 Integrins
2. Calcium-independent
 Neural cell adhesion molecule
 Intercellular adhesion molecule

46. • Specialized contacts
-Anchoring junctions
1.Adhesive spots or desmosomes or macula
adherens
2.Adhesive belts or zona adherens
3.Adhesive strips or fascia adherens
- Occluding junction or zonula occludens or tight
junction
-Communicating junctions or gap junctions

47. Desmosomes

48. Zonula adherens

49. Fascia adherens

50. Desmosomes
&
hemidesmosomes

51. Focal adhesion plaques

52. Tight Junctions

57. Types of Cell Junctions

58. Summary of cell junctions

59. Thank you