Histology
Team
Lecture 2
Clinical Pharmacy
Cairo University
/Clinical2020CU
2014/2015
Lecture II: Epithelial Tissue

I.
There are four types of tissues:
1. Epithelial Tissue
2. Connective tissue
3. Nervous tissue
4. Muscular tissue
Epithelial tissue (epithelium)
a. Structure: Consists of crowded cells with very little
intercellular space
b. Site:
It covers outer surface of the body & lines cavities.
c. Origin
It may be derived from ectoderm, mesoderm or
endoderm
d. Main characteristics
i. Has a high power of regeneration
(i.e. high capacity for repair after damage)
ii. Cells rest on basement membrane (BM)1 that separates them from the
underlying connective tissue (C.T.).
iii. Avascular tissue (i.e. blood and lymph vessels don’t penetrate between
epithelial cells and so, receives nutrition by diffusion from the connective
tissue while some nerves can penetrate.)
epithelium
connective tissue
blood capillaries
tissue ‫ آخر حتة فى الـ‬1
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e. Classification
According to functions:
According to the number of layers:
a. Surface epithelium:
cover outer surface or line inner surfaces and
grooves
b. Glandular epithelium:
modified cells have secretory function.
c. Neuroepithelium:
Modified cells acting as receptors e.g. taste buds
in the tongue to accept the taste of the food.
d. Myoepithelium:
modified cells can contract around the glands
a. Simple epithelium:
consists of one layer of cells resting
basement membrane
b. Stratified epithelium:
consists of more than one layer of
cells where only the basal layer
rests on BM.
Having the surface epithelium topic under study, we are gonna see the different subtypes of it
according to the number of layers:
Simple Surface Epithelium
they will be represented gradually according to their thickness
1. Simple Squamous2 Epithelium:
a. Description
One layer of flattened cells resting on BM with
flat nucleus and very little amount of cytoplasm
b. Site and function
i. Give a smooth surface: in heart lining
and blood vessels (CVS), known as endothelium ‫تجويف القلب و الشعيرات الدموية‬
→ for blood flow and to prevent blood clotting
ii. Provide a thin surface
1. Alveoli of lungs → to allow gas exchange
2. Bowman's capsule in kidney (renal corpuscle)
→ help in filtration of the blood
2. Simple Cubical Epithelium:
a. Description
One layer of cubical cells with central rounded nuclei resting on BM.
2
squama = scale
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b. Site and function
i. Thyroid follicles →
secretions of thyroid gland.
ii. Tubules of kidney → re-absorption of the
important substances in blood.
Simple Cubical
3. Simple Columnar Epithelium:
a. Description
One layer of columnar (tall) epithelium cells, with basal oval nuclei resting on BM.
They are classified into two groups which are:
i. Ciliated: which contain cilia on the free surface “cilia can push fluids & particles
in one direction”
ii. Non-ciliated “its surface doesn't contain cilia”
Simple Ciliated Columnar Epithelium
Simple Columnar Epithelium
b. Site and function of Ciliated Columnar Epithelium:
i. Female genital system especially lining the uterus and the fallopian tubes:
→ to help the movement of the fertilized ovum from the fallopian tube to be
implanted in the uterus.
ii. Respiratory system especially in bronchioles of lungs → to push mucus.
c. Site of Non-ciliated Columnar Epithelium:
They are mainly found in the digestive system (G.I.T) as the lining in stomach & intestine. .
4. Pseudo-stratified Columnar Epithelium:
a. Description
One layer of columnar cells resting on BM. They are very crowded that some cells don't
reach the free surface. The nuclei are arranged at different levels gives pseudostratification (i.e. false impression)3. It’s also classified into two groups
i. Ciliated
ii. Non-ciliated.
3
Actually it's simple epithelium not stratified as it consists of only one layer of crowded cells all of them are on the
basal membrane but with different heights some are short and some are long
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Simple Pseudo-stratified
Columnar Epithelium
Simple Pseudo-stratified Ciliated Columnar Epithelium
b. Site of Non-ciliated pseudo-stratified epithelium:
They found mainly in the male genital system especially lining the vas deference &
membranous male urethra.
c. Ciliated pseudo-stratified epithelium:
Description
the free surface of the columnar cells is covered by motile cilia with goblet cells.
Site and Function
they are lining the nasal cavity and the upper respiratory tract as trachea & bronchi.
Goblet cells → cells specialized in synthesis & secretion of mucous.
* Mucous secreted by the goblet cells lining the trachea get away from this cells to reach the surface of
the cells to make the cilia wet so it can attract any foreign body & the dust which penetrates our
respiratory system with gases during inhalation then cilia will move in irregular movements to get rid of
the mucous with the dust (coughing).
* Fats & mucous dissolves by H&E die. So goblet cells will appear empty cells in L.M as they are all
stained by this die.
Stratified Surface Epithelium
they will be represented according to the shape of superficial layer
This epithelium is characterized by the presence of more than one layer of cells divided as:
1. Basal Layer: mostly columnar cells resting on BM.
2. Intermediate several layers: polyhedral cells
3. Superficial Layer: vary in shape according to the stratified epithelial type
The only function of Stratified Epithelium is Protection.
1. Stratified Squamous Epithelium:
a. Number of layers: formed of 5-30 layers (thickest type of epithelium)
b. Characteristics of Basement Membrane:
it rests on a clear wavy BM.
c. Basal cells description:
columnar cells with basal oval nuclei known as
stem cells because they are mitotically active
d. Intermediate cells description:
polyhedral tightly connected cells with central
round nuclei
e. Superficial cells description: flat cells with
flattened nuclei
Note: Cells are getting smaller towards the surface
f.
Classification
Stratified Squamous Epithelium
i. Keratinized
1. Top layer is covered with keratin as the flat
Functions of keratin:
superficial cells die; lose their nucleus which
1. Strong cover
contains tough protein material “Keratin”.
2. Resist friction and infection
2. Sites: Dry Exposed Surfaces: such as Skin.
3. Water proof
ii. Non-keratinized
1. No Keratin on surface.
2. Tissue is kept moist by secretions.
3. Sites: Present in wet inner surfaces as: cornea, oral Cavity, anal canal
and vaginal canal.
Keratin
Keratinized Stratified Epithelium
Non-keratinized Stratified Epithelium
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2. Stratified Columnar Epithelium:
similar to squamous stratified epithelium, but the surface cells are columnar. It may be:
a. Non-ciliated: as in a penile pare of male urethra
b. Ciliated: as in fetal esophagus
3. Transitional Epithelium (Uroepithelium):
a. Site: The lining of urinary tract (ureter & urinary bladder)
Suitable for urinary tract as it can change its thickness acc. to the state of distension of
bladder (empty or full).Cells can stretch and flatten to increase the internal volume of
the organ e.g. full bladder.
b. Function: Protection & Distensibilty
c. Number of layers: formed of 5-8 layers (strongest type of epithelium)
d. Characteristics of Basement Membrane:
it rests on a non- clear BM.
e. Basal cells description:
short columnar cells with basal rounded nuclei
f. Intermediate cells description:
polyhedral cells with central round nuclei
g. Superficial cells description: large with convex surfaces, may be bi-nucleated
-
-
Cells have wide intercellular spaces containing mucus-like substance which helps in gliding of
cells over each other.
Top layer: “Dome Cells: large cubical cells with convex surface & rounded nuclei.
Some are Binucleated.
In case of full bladder, the epithelium flattens
out (the cells become squamous) with
apparent decrease in number of cell layers.
Changes are due to gliding of cells over each
other (mucous).
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