Epithelial tissue

1. The Diversity of Cells in the
Human Body

2. 2
¶ Despite its complexity, the human body is composed of only four basic
types of tissue:
● epithelial
● connective & supporting
● muscular & contractile
● nervous
¶ These tissues
● are formed by cells and molecules of the extracellular
matrix
● exist not as isolated units but rather in association with one
another and in variable proportions
● form different organs and systems of the body
¶ The main characteristics of these basic types of tissue are:
Tissue Cells Extracellular Matrix Main Functions
Nervous Intertwining elongated processes None Transmission of
nervous impulses
Epithelial Aggregated polyhedral cells Small amount Lining of surface
surface or body
body cavities,
glandular
secretion
Muscle Elongated contractile cells Moderate amount Movement
Connective Several types of fixed and
wandering cells
Abundant amount Support and
protection

3. 3
Prepared by:-Dr. Alazar Etana May/2023

4. Epithelial Tissue
• covers all free surfaces of the body (epi, on + thelium, surface).
• consists of cells attached to one another to form an uninterrupted layer of
cells that separates the underlying tissues from the outside world.
• consists of closely apposed cells without (or very little) intervening
intercellular substances.
• is avascular, but all epithelia "grow" on an underlying layer of vascular
connective tissue (CT).
CT and epithelium are separated by a basement membrane
• the body's epithelium - covers its obvious surfaces (such as the epidermis of the skin
and the linings of respiratory, urinary, and digestive tracts)
- extends into all of the complex invaginations which form
lungs, kidneys, sweat glands, digestive glands, liver, etc.
• provides the essential functions – protection
- containment of body fluids
- transport in and out across body surfaces
(absorption and secretion).
• Embryonically, most epithelial tissues are derived either from
ectoderm (e.g., epidermis) or
endoderm (e.g., epithelium of trachea and lung).

5. Ion transport Filtration Forms slippery surfaces

6. Special Characteristics of Epithelia
• Cellularity
– cells are in close contact with each other with little or no intercellular
space between them.
• Specialized contacts
– may have junctions for both attachment and communication.
• Polarity
– epithelial tissues always have specific apical, lateral and basal surfaces.
• Support by CT
– at the basal surface, both the epithelial tissue and the CT contribute to
the basement membrane.
• Avascularity (generally)
– nutrients must diffuse.
• Innervation
• Regeneration
– epithelial tissues have a high capacity for regeneration ; plasticity.
Epithelial tissue thus serves both as a protective barrier
for the body and as an active interface with the environment
● Great diversity of function

7. Special Characteristics of Epithelia

8. • Epithelial cells exhibit distinct polarity.
They have
• an apical domain,
• a lateral domain, and
• a basal domain.
• Specific biochemical characteristics are associated with
each cell surface.
• These characteristics and the geometric arrangements of
the cells in the epithelium determine the functional
polarity of all three cell domains.
●The free or apical domain is always directed toward
the exterior surface or the lumen of an enclosed
cavity or tube.
●The lateral domain communicates with adjacent cells
and is characterized by specialized attachment areas.
●The basal domain rests on the basal lamina
anchoring the cell to underlying CT.

9. Classification of epithelia
1. Surface epithelia
(Covering epithelia)
2. Glandular epithelia
3. Special epithelia

10. SURFACE
(Covering)
EPITHELIA

11. I. First name of tissue indicates
number of layers.
• Simple
–one layer of cells
• Stratified
–more than one
layer of cells
Classifications & Naming of Epithelia

12. Classification & Naming of Epithelia
II. Last name of tissue describes shape
of cells.
– Squamous – cells wider
than tall (plate or “scale” like)
– Cuboidal – cells are as wide
as tall, as in cubes
– Columnar – cells are taller than
they are wide, like columns

13. • Naming the epithelia includes both the layers
(first) and the shape of the cells (second).
– i.e. stratified cuboidal epithelium
• The name may also include any accessory
structures.
– Goblet cells
– Cilia
– Keratin
• Special epithelial tissues
(don’t follow naming convention).
– Psuedostratified
– Transitional
Classifications & Naming of Epithelia

14. Diagrams of simple epithelial tissue.
A: Simple squamous epithelium.
B: Simple cuboidal epithelium.
C: Simple ciliated columnar epithelium.
All are separated from the subjacent CT by a basement membrane.
In C, note the terminal bars that correspond in light microscopy to the zonula
occludens and the zonula adherens of the junctional complex.

15. Diagrams of stratified,
transitional and
pseudostratified epithelia.
A: Stratified squamous epithelium.
B: Transitional epithelium.
C: Ciliated pseudostratified
epithelium.
The goblet cells secrete mucus, which forms a
continuous mucous film over the ciliary layer.

16. Epithelium
Simple
Epithelium

17. Simple Squamous Epithelium
• Description
• single layer of flattened, scale- or plate-like
cells with disc-shaped nuclei.
(The nuclei are often flattened or ovoid, and they
are located close to the centre of the cells).
• Special types
– Endothelium (inner covering)
• slick lining of hollow organs: lines the internal
surfaces of blood and lymph vessels
– Mesothelium (middle covering) - lines the large
internal body cavities
• Lines peritoneal, pleural, and pericardial cavities
• Covers visceral organs of those cavities

18. • Function
– Passage of materials by passive diffusion and
filtration.
– Secretes lubricating substances.
• Location
– Renal corpuscles
– Alveoli of lungs
– Lining of heart, blood
and lymphatic vessels
– Lining of ventral body
cavity
…Simple Squamous Epithelium

19. Simple
squamous
lining the walls
…Simple Squamous Epithelium

20. Simple Squamous Mesothelium
Mesothelial cells

21. Simple Squamous – Endothelium (En)
Simple Squamous – Endothelium (Ed) by
TEM
Simple Squamous (Mesothelium) by TEM

22. Capillary (endothelial cell) by TEM

23. Simple Cuboidal Epithelium
• Description
– single layer of cube-like cells with large,
spherical central nuclei
• Functions
– secretion and absorption
• Location
– kidney tubules
(PCT,
DCT,
small CDs)
– secretory portions of
small exocrine glands,
surface of the ovary &
the follicles of the
thyroid follicles

24. Kidney Collecting Ducts: (cross section) Simple Cuboidal Epithelium (longitudinal section)

25. Simple cuboidal epithelium.
Cells vary in their height but are roughly as tall as they
are wide.
Their greater thickness often includes cytoplasm rich in
mitochondria providing energy for a high level of active
transport of substances across the epithelium.

26. Simple Columnar Epithelium
• Description
– single layer of column-shaped (rectangular) cells
with oval nuclei
– (cells are taller than they are wide)
• Some bear cilia at their apical surfaces
• May contain goblet cells
• Function
– absorption
– secretion of mucus,
enzymes, and other
substances
– Ciliated type propel
mucus in reproductive
cells by ciliary action

27. • Location
– Non-ciliated form
• Lines digestive
tract,
• gallbladder,
• ducts of some
glands
– Ciliated form
• Lines small bronchi,
uterine tubes,
uterus
…Simple Columnar Epithelium

29. Goblet Cell with
PAS stain (red)
Simple Columnar with
Goblet Cells (Mu) by TEM
(unicellular exocrine gland)

30. Absorbing cell:
Single cell layer of tall columnar cells with basal ovoid nucleus.
Although the cells appear retangular in this section, they are actually five- or six-sided
when they are cross-sectioned.
When underlying tissue folds or bends, these cells may have a pyramidal appearance.
Nucleus:
Ovoid situated in lower half of the columnar cell.
The nuclei in tightly packed cells may appear elongated and staggered at
different levels within the cell. (This is readily seen in pseudostratified ciliated columnar).
Brush border: (also know as the straited border).
Made up of fine, closely packed microvilli that vastly increase the surface area of the cell.
Characteristic of absorptive surfaces.
Adequate absorption of digestive products is dependent upon this cell surface
specialization of absorbing columnar epithelial cells.
Goblet cell:
Unicellular mucous glands scattered among the tall columnar cells appear empty
because mucin is extracted during tissue processing.
These unicellular gland cells are a specialization of simple epithelium and serve a
protective function for the principal epithelial cell type.
Basement membrane: Delicate in appearance but a firm support for the columnar cells.
Lamina propria: CT stroma.
Reticular framework containing a variety of wandering cells as well as vascular and
lymphatic channels.
Cells commonly found in the lamina propria include lymphocytes, plasma cells,
eosinophils, and mast cells.

31. Epithelium
Pseudo-
stratified

32. Pseudostratified Columnar Epithelium
• Description
– All cells originate at basement membrane
– Only tall cells reach the apical surface
– May contain goblet cells and bear cilia
– Nuclei lie at varying heights within cells
•Gives false impression of
stratification
• Function
– secretion of mucus
– propulsion of mucus by cilia

33. • Locations
– Non-ciliated type
• Ducts of male
reproductive
tubes
• Ducts of large
glands
– Ciliated variety
• Lines trachea
and most of
upper
respiratory tract
…Pseudostratified Columnar Epithelium
Cells appear to be in layers, but the basal ends of the cells are all
in contact with the basement membrane, which is often very thick.

34. Pseudostratified Ciliated
Epithelium with Goblet Cells
Respiratory epithelium

35. Pseudostratified Columnar Epithelium
(with microvilli)
Actually a single layer of columnar tissue but the nuclei do not line up making the
tissue layer appear stratified
Pseudostratified columnar epithelium
●All cells of this type of epithelium are in contact with the basement membrane,
but not all of them reach the surface of the epithelium.
● Nuclei of the epithelial cells are typically located in the widest part of the cell.
● Consequently, the nuclei of cells which do or do not reach the surface of the
epithelium are often located at different heights within the epithelium and
give the epithelium a stratified appearance.
● The epithelium will look stratified but it is not - hence its name "pseudostratified".
● Pseudostratified columnar epithelia are found in the excretory ducts of many glands.

36. ● Pseudostratified columnar epithelium of the trachea, formed by long and short cells.
● As some cells do not reach the surface of the epithelium their nuclei are present in
different heights of the epithelial layer.
● Mucus-secreting cells, called goblet cells (blue arrow), intermingle with ciliated lining

37. Epithelium
Stratified

38. Stratified Epithelia
• Contain two or more layers of cells.
– Many superficial layers of cells – squamous in shape.
– Deeper layers of cells appear cuboidal or columnar.
• Regenerate from below.
• Major role is protection.
• Thickest epithelial tissue.
• Are named according to the shape
of cells at apical layer.
Description

39. • Specific types
– Keratinized – contain the protective protein keratin.
• Surface cells are dead and full of keratin.
– Non-keratinized – forms moist lining of body openings.
• Function
– Protects underlying tissues
in areas subject to abrasion.
• Location
– Keratinized – forms epidermis
– Non-keratinized – forms lining of
• esophagus
• pharynx
• mouth
• anal canal, uterine cervix & vagina
…Stratified Squamous Epithelium

40. Stratified squamous
nonkeratinized (moist) epith.
of the esophagus.
The most superficial cells (arrow)
have the form of very thin scales.
PT stain. Medium magnification.
Oesophagus, human - H&E
The oesophagus is lined by a stratified squamous epithelium consisting of many
cell layers.
Basal cells often form a well defined layer at the border of the epithelium to the
underlying CT.
The underlying CT forms finger-like extensions towards the lumen of the
oesophagus, which are called papillae.
The border between epithelium and CT may appear quite irregular because of the
papillae.
This irregular border aids in anchoring of the epithelium to the CT.
If these extensions are not cut exactly along their long axis, they may look like
isolated small islands of CT and blood vessels within the epithelium.

41. Keratinized Stratified Squamous Epithelium
Stratum germinativum
(basale)
Str. spinosum
Str. granulosum
Str. corneum
Dermal ridge
Melanocytes

42. 42
Stratified cuboidal & columnar
epithelia are not common.
Stratified cuboidal epithelium
●is thin,
● usually consists of only
2-3 layers of cuboidal cells.
This type of epithelium is usually
confined to the lining of the larger
excretory ducts of exocrine glands
● the salivary glands
● ducts of sweat glands

43. STRATIFIED COLUMNAR EPITHELIUM
Mucous gland duct tongue
Stratified columnar epithelia are found in the excretory ducts
of the mammary gland and the main excretory duct of
the large salivary glands & Conjunctiva.

44. Transitional
Epithelium
(uroepithellum)
Epithelium

45. Transitional Epithelium
• Description
– Basal cells usually
cuboidal or columnar
– Superficial cells dome-
shaped or squamous
• Function
– stretches and permits
distension of urinary
bladder
• Location : Lines
- renal calyces & pelvis
– ureters,
– urinary bladder and
– part of urethra (prox)

46. Transitional epithelium
The shape of the cells in the surface layer of a transitional
epithelium varies with the degree of distension of the organs
whose lumen is lined by this type of epithelium.
[The term transitional epithelium does not imply that this
epithelium is in actual transition from one type to another, but
rather refers to the appearance of the cells, which change as
the organs with which they are associated are stretched or
relaxed].
✹ In the 'relaxed' state of the epithelium, it seems to be formed
by many cell layers.
The most basal cells have a cuboidal or columnar shape.
There are several layers of polyhedral cells, and, a layer of super-ficial
cells, which have a convex, dome-shaped luminal surface.
✹ In the distended state of the epithelium only one or two layers
of cuboidal cells are followed by a superficial layer of large,
low cuboidal or squamous cells.
In the distended state the epithelium will resemble a stratified
squamous epithelium.

47. Transitional Epithelium
When the tissue stretches the cells become thinner
and appear to be cuboidal or squamous.
(umbrella or dome cells U)

48. Epithelium
Special

49. SPECIAL EPITHELIA
A. Myoepithelium
1. Contractile, branched epithelial cells.
2. Located between glandular epithelial cells and basement membrane.
3. Contain contractile proteins like actin filaments; smooth muscle-like.
4. Facilitate glandular secretion.
B. Neuroepithelium
1. Non-neuronal
a. Receptor cells of taste buds
b. Hair cells of inner ear
2. Neuronal
a. Sensory cells of olfactory epithelium
b. Rods and cones of retina
C. Seminiferous epithelium
1. Surface epithelium of testis
a. Spermatogenic (germ) cells
b. Supporting (Sertoli) cells
i). Sertoli cells: simple epithelium
ii). Spermatogenic cells: stratified

50. Common types of covering epithelia in the human body.
Number of cell
layers
Cell form Examples of distribution function
Simple (one layer) squamous Lining of vessels
(endothelium).
Serous lining of cavities;
pericardium, pleura,
peritoneum
(mesothelium).
. Facilitates the movement
of the viscera
(mesothelium)
. active transport by
pinocytosis (mesothelium
and endothelium).
cuboidal Covering the ovary,
thyroid.
Covering
secretion.
columnar Lining of intestine,
gallbladder.
Protection, lubrication,
absorption, secretion.
Pseudostratified (layers of cells with nuclei
at different levels; not all cells reach
surface but all adhere to basal lamina)
Lining of trachea, bronchi,
nasal cavity.
Protection, secretion;
cilia mediated transport of
particles trapped in
mucus out of the air
passages.
Stratified (two
or more layers)
Squamous keratinized
(dry)
Epidermis Protection
prevents water loss.
Squamous nokeratinized
(moist)
Mouth, esophagus, larynx,
vagina, and anal canal.
Protection, secretion
prevents water loss
cuboidal Sweet glands, developing
ovarian follicles.
Protection
secretion
transitional Bladder, ureters, renal
calyces.
Protection
distensibility.
columnar Conjunctiva. Protection.