Epithelial tissue forms protective linings and covers surfaces throughout the body. It is classified based on cell shape (squamous, cuboidal, columnar) and number of cell layers (simple or stratified). Simple epithelia are only one cell thick while stratified have multiple layers. Epithelial cells adhere together through junctions like desmosomes and tight junctions. Glands are classified as endocrine if they secrete into blood or exocrine if they secrete through ducts. Epithelial cells perform critical functions like protection, absorption, filtration, and secretion.

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