EPITHELIAL TISSUE.pdf.pdfffchncxfghjjhhh

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1. EPITHELIAL TISSUE Vincent Daktari,
Kenyatta University MBChB
2025

2. OBJECTIVES Definition
Characteristics
Classification
Functions
Adaptation of various types in different organs
Steps in identifying epithelial slides
Revision

3. DEFINATION These are adjacent cells with a free surface
set on a basement membrane.
Epithelioid cells-cells aggregated in close
apposition but lack a free surface.

4. CHARACTERISTICS Close apposition since the cells are connected by strong
intercellular matrix
Avascular
Minimal/ absent intercellular material hence tight
intercellular cohesion
Presence of a basement membrane/basal lamina
Polaritythey have distinct apical, lateral and basal surface
domains
Surface specialization i.e. cilia, Stereocilia, keratin and goblet
cells

5. CLASSIFICATION Mainly into
a)Surfaceepithelia/epithelial tissue proper

Lines external and internal tissue of organs
b) Glandular epithelia/secretory epithelium

Secrets various macro molecules in our blood
stream

6. SURFACE EPITHELIAL Further classified according to
Shape
Squamous
centered nucleus
width greater than height and contain ovoid,

7. 2. Cuboidal

width and height are equal and contain round,
centered nucleus.SURFACE EPITHELIAL

8. 3.

Columnar
Heightgreaterthan widthSURFACE EPITHELIAL

9. Number of cell layers
Simple-onecell layer
Stratified-more than one layerSURFACE EPITHELIAL

10. SURFACE SPECIALIZATION 1.Ciliated/non ciliated
2.Sterocilia
3.Microvilli
4.Keratinized
5. kinocilia

12. STEPS IN IDENTIFYING
EPITHELIAL SLIDES 1.
Defining characteristics of epithelia is that they have a free apical
space unlike other tissues and so the first step in identifying
epithelium on a slide is to look for an appical free apical space
/surface
Finding a free apical/surface space

13. 2.

Determining the number of cell layers
Once you have mastered finding appropriate free surface,
the next step is to determine the number of cell layers in the
epithelium.
If it is one cell thick then it is simple epithelium and if it is
more than one layer thick, then it is stratified.STEPS IN IDENTIFYING
EPITHELIAL SLIDES

14. 3.Determining apical cell shape

That is determining the shape of the cells on the surface
Determining the shapes of the nucleus of the apical cells can also be
important in determining the shape
They can either be
Squamous
Columnar
CuboidalSTEPS IN IDENTIFYING
EPITHELIAL SLIDES

15. SIMPLE CUBOIDAL In renal tubules,thyroidfollicles,surface of ovaries

16. SIMPLE CUBOIDAL

17. SIMPLE COLUMNAR Instomach,intestines,gallbladder,trachea, male reproductive system, bronchioles

18. SIMPLE COLUMNAR

19. STRATIFIED SQUAMOUS
KERATINIZED Skin – keratin prevents dehydration

20. STRATIFIED SQUAMOUS
KERATINIZED Skin – keratin prevents dehydration

21. STRATIFIED SQUAMOUS
NON KERATINIZED

22. STRATIFIED CUBOIDAL Duct of sweat glands

23. STRATIFIED CUBOIDAL

24. STRATIFIED COLUMNAR

25. OTHER SPECIAL TYPE
OF EPITHELIA 1.Pseudostratified columnar epithelium

Itisasimpleepitheliumthoughthecellsappear stratified since the
nuclei areplaced atdifferent levelshencethe name.
Most of the cells don’t extend between apical surface and basal surface
Can either be ciliated or non ciliated,withgoblet cells or without
Found in trachea, bronchi, nasal cavity.

27. PSEUDOSTRATIFIED
COLUMNAR
Prostate, vas deferens(non ciliated)

28. 2.TRANSITIONAL
EPITHELIUM
Form ofstratifiedepitheliumthough different from other stratified since it allows a
considerable stretch
The apical cells vary in appearance; they appear cuboidal when the organ is not
stretched, and wherestretchedthey appear to be squamous.
Lines organs of urinary system such as bladder, urethra, ureters and hence known as
urothelium

29. 2.TRANSITIONAL
EPITHELIUM

30. 2.TRANSITIONAL
EPITHELIUM

31. FUNCTIONS OF EPITHELIAL Receptors of sensory organs i.e. organ of corti in
the ear
Absorption i.e. ileum
Tissue environment barrier i.e. skin
Secretion i.e. in glands
Contractility i.e. in bladder

32. ADAPTATION OF VARIOUS TYPES
IN DIFFERENT ORGANS Microvilli
Made of actinbinding protein and are capable of movement thus stirring luminal content to
increase absorption.
Found in small intestine.
Finger like projections found on the surface of simple epithelia with the role of absorption

33. ADAPTATION OF VARIOUS TYPES
IN DIFFERENT ORGANS cilia
Theseare short hair like structures emanating from cells involved intransport.
Made of tubulin
Found in fallopian tubes, respiratory tract and lining of brain cavities

34. ADAPTATION OF VARIOUS TYPES
IN DIFFERENT ORGANS Stereocilia
These are long, non motile irregular cytoplasmic processes extending from
apical of the cell.
They are taller and largerthan cilia
Are limited to epididymis, as deferens(where they inc.S.A for resorption) and
organ of corti in the inner ear(signal transduction)

35. ADAPTATION OF VARIOUS TYPES
IN DIFFERENT ORGANS

36. ADAPTATION OF VARIOUS TYPES
IN DIFFERENT ORGANS Keratin
Fibrous protein known as sceleroprotein.
It protects epithelial cells from damage or stress
Also limits dehydration
Its also the key structural material making up hair, nails, outer layer of skin.

37. ALL THE BEST THANK YOU Always learn to apply the
principle of when they sit I
stand, when they stand I
standout, When they standout I
set the standards