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Jehad Samhouri

Dana Ziyad Almanzalji and ru'aa Nade

Hanan Jaafer

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• Epithelium is an avascular “a means no “ → there aren’t any blood

vessels inside epithelium tissues.

So , how do they get food and Oxygen?

By connective tissue that located under epithelium tissues.

Epithelial tissue composed of cells ( packed together ) that cover the

exterior body surfaces and line internal closed cavities and tubes with

little intercellular material .

“No space between them, so it doesn’t have vascular”.

1. It forms the secretory portion of glands and their ducts. “Ducks are

coming out from glands ’’.

2. Specialized epithelial cells function as receptors for the special senses.

3. Covering the exterior body surface and lining the internal closed cavities.

• Epithelial cells are polarized ( different domains with different function )

and resting on basement membrane.

Can be derived from all embryonic germ layers:

( ectoderm , mesoderm , endoderm )

• Epithelium lining skin, mouth, nose and anus: ectoderm “most external

layer’’

• Epithelium lining respiratory system, digestive tract and glands of

digestive tract: endoderm “most internal layer”

• Epithelium lining blood vessels: mesoderm

Epithelial tissue could be found in :

General features:

Note:

The Epithelium that lines blood vessels are called Endothelium which is

derived from mesoderm.

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• We all came from Zygot , then it will divide then it will differentiate into

different kind of cells .

• Cells at day 16 , will arrange in 3 layers are called Germ Layer .

• Every layer has its own derivations .

• Epithelium can be deviated from any layers depending on its final

destination .

Cell Polarity :

Note : Apical surface always towards space

either Lumen or External Enviroment .

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The epithial cell shows two domains

1) Apical

2) Baso-lateral

➢ Each domain shows modifications to suit its functions

Function : • Protection

• Transcellular transport

• Secretion

• Absorption (selective permeability)

• Involved in sensation

According to number of layers

Simple : one layer of cells are resting over the Basal Lamina

Classifications & Naming of Epithelia :

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Stratified : more than one layer of cells “ multiple layers of cells”

According to shape of cells

o Squamous : cells wider than tall (plate or

“scale” like)

o Cuboidal : cells are as wide as tall, as in cubes

o Columnar : cells are taller than they are wide,

like columns

Naming Epithelia

• 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:

o Keratin” water resistance “

o Goblet cells “secreted mucus “

o Cilia

Note : not all the Basal Surfaces reaching the Basal

Lamina only the most basal is reaching the Basal

Lamina .

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➢ Special epithelial tissues (don’t follow naming convention)

o Pseudostratified

o Transitional

Epithelium

Simple

Squamous

Cuboidal

Columnar

Pseudostratifie

d

Stratified

Squamous

keratiniz

ed

nonkeratinize

dCuboid

al

Transitional

Columnar

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Simple Epithelium

Simple Squamous Epithelium Simple Cuboidal Epithelium

Ciliated Simple Columnar Epithelium

Note : This name for the right side

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Ciliated Pseudostratified

columnar Epithelium with Goblet

Cells. “Respiratory Tissue “

Stratified Epithelium

Stratified Squamous Stratified Cuboidal

Notice that its neither Keratinized always 2 layers

nor nonkeratinized

Note : all cells are resting on Basal Lamina

even though some cells are short and

can’t reach the Apical Tissue

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Stratified Columnar Transitional Epithelium

In this case we name This type of tissue is found

Depending on which in Urinary Bladder

Cell is nearer to Apical

Surface

Simple Squamous

Locations:

o Vascular system (endothelium)

o Body cavities (mesothelium)

o Bowman’s capsule (kidney)

Major function:

o Exchange

Simple Epithelia :

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Endothelium is the simple

squamous epithelium that

lines the lumen of the

cardiovascular system

Mesothelium is the simple

squamous epithelium that

lines serous cavities

(peritoneal “abdomen’’,

pleural ”lung” , and

pericardial cavities

“around heart’’) and coats

many of the organs in

these cavities

• Contain two or more layers of cells

• Regenerate from below

• Major role is protection

• Are named according to the shape of cells at apical layer

• Mitotic activity in stratified epithelium is limited to the basal

layer (under normal conditions)

• If cells in Apical die , the cell in Basal must divide in order to

regenerate them.

Stratified Epithelia

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❖ Stratified Squamous Epithelium

➢ Specific types

❖ Keratinized : contain the protective protein keratin

(keratin is water resistance protein and we need it in our skin )

→ 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 mouth, esophagus, and vagina

Nonkeratinized Stratified Squamous Keratinized Stratified Squamous

Note: the upper layer is sac full of

keratin

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Goblet cells produce mucus

Cilia (larger than microvilli) sweep mucus

Ciliated Pseudostratified Columnar

Epithelium with goblet cells

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