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Histology(MLHS-201)

Lecture 4Tissue types

(Epithelial tissue)

Dr. Afaf Mousaad• Department of Medical Laboratory Technology• Faculty of Allied Medical Sciences

Learning objectives

• How to Identify the keratinized, basal and apical layers in stratified epithelium.

• Distinguish between simple and stratified.

• Describe the shapes of stratified epithelial cells.

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All epithelial cells are in contact with the basement

membrane, but not all of them reach the surface of the

epithelium. The nuclei are often located at different

heights give the epithelium a stratified appearance.

Ciliated e.g. epithelium of respiratory tract

(Nasal cavity ,larynx, trachea, bronchi,....)

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a.keratinized stratified epithelium:

The mammalian skin epidermis (cornified epithelium) :

-A protective type of epithelium

containing a tough, resistant keratin

protein . Protects underlying tissues from, dehydration, chemicals, and bacterial invasion.

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Stratified epithelium

The outermost layers of cells are flattened squamous, filled with Keratin.

-protects delicate tissues in areas

subjected to abrasion.

The thickness of the cornified layer of the skin varies greatly,

being thickest on the soles and palms.

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Keratinized

stratified

squamous

epithelium

e.g epidermis of the

skin

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This type of stratified epithelium is constantly renewing itself.

Cells in the bottom layer divide, and the daughter cells move

towards surface maturing and then degenerating.

There are around 8-10 layers of cells.

The cells become more flattened towards the top (apical) layer

and have flattened nuclei - these cells are dying.

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Horny cells are constantly shed

from this part of the stratum

corneum.

Variations in the thickness of the

epidermis are mainly the result

of variations in the thickness of

the stratum corneum(~0.1 mm

in thin skin and 1 mm or more

in thick skin).

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The stratum spinosum:

The cells become irregularly

polygonal. The cells have

spine-like cytoplasmatic

extensions (hence the name

of the layer and of its cells:

spinous cells), which

interconnect the cells of this

layer. 

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Elongated keratinized structures derived from invaginations of epidermal epithelium.

Nail plate is divided into:

1-The body of the nail :

Broad pink part, appears pink because it is semi-

transparent (blood capillaries in the dermis shows through).

It shows a crescent-shaped area, Lunula best seen on the thumb and absent

from the little fingers

2- The root of the nail:It lies beneath the skin (invisible part). Nails grow

at a rate of 0.5 mm/week. A finger nail grows faster than toe nail 13

Horny hard plates made up of

cornified cells containing keratin.

b.Non keratinized type: the

most common stratified type

consists of many layers of

closely held cells with the

outermost layer consisting of

flattened cells . e.g. covers

the tongue and lines the

mouth cavity, throat,

esophagus, anus, & vagina. 14

- non-keratinized, mucousal cell layer

lining the esophagus

- protection of the esophagus from

stomach acid,

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Stratified squamous

epithelium.There are 10-

20 layers of cells present,

which by definition makes

this a "stratified"

epithelium; and that the

cells at the free surface are

flattened, squamous

shaped ones.The cells in

the deeper layers are

cuboidal.

The lumen of the esophagus is lined with stratified squamous epithelium.

Rare-found in ducts of e.g.

Sweat glands which are coiled

tubular glands.

Their ducts consisting of

two layers of small cuboidal

cells16

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Stratified cuboidal epithelium is a rare type

of epithelial tissue

cube-shaped

commonly cells make up two layers

sweat glands in the skin

mammary gland in the breast

salivary glands in the mouth

composed of cuboidal shaped cells arranged

in multiple layers.

Stratified cuboidal epithelium : the ducts of the parotid gland

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Transitional epithelium:

e.g. Urinary bladder ,

ureter, urethra .

Control the amount of

water and salts that are

absorbed back into the

blood and what is taken

out as waste.

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•Multilayered

•Surface cells varying in shape

from round to flat if stretched

•Lines hollow organs of the urinary

tract that expand

Transitional epithelium

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3.Transitional epithelium is a stratified epithelium in which the shape of

the surface cells changes (undergoes transitions) depending on the degree

of stretch. Empty:Unstretched cells :rounded

superficial cells bulge out

1.When a transitional epithelium is not stretched (in an empty bladder)

the cells of the surface layers are large and rounded.

2.When a transitional epithelium is stretched (in a full bladder) the cells of

the surface layers are pulled into a flatter shape.

"transitional“ = ability to change its shape

from cuboidal to squamous when stretched.

 e.g. Urinary bladder , ureter, urethra.

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Empty bladder, consists of 4 -8 layer of cells .

When the bladder is distended with urine the cells at the top become flat , the number of layers is reduced to 2 - 3 glide on each other.

a. distended urinary

bladder (full with urine).

The epithelium is very thin

with fewer layers of cells

and the top layer become

flattened. The cells of the

intermediate layers glide

on each others. and reduced

to 2 or 3 layers .  23

Transitional epith. thickness

depends on the state of distension

(full) or contracted (empty).

b. Empty urinary bladder-

the epithelium consists of

more than five layers of

cuboidal cells.The surface

cells facing the lumen of

the bladder are dome-

shaped which

characterizes on the apical

surface the transitional

epithelium.on the apical surface

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Neuroepithelial Cells

The tongue is a muscular organ covered with mucosa. Tiny

bumps called papillae give the tongue its rough texture.

Thousands of taste buds cover the surfaces of the papillae.

Taste buds contain neuroepithelial cells

embedded in the stratified squamous

epithelium of each papilla that are

the receptors for taste.

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We all have about 10,000 taste buds, mainly on the tongue.

Most highly concentrated in certain regions of the

tongue's surface.

Sweet receptors on the tip of the tongue .

Sour receptors occur along the sides of the tongue .

Salt receptors most common in the tip and upper front portion

of the tongue.

Bitter receptors :located toward the back of the tongue.

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Receptor cells live for only 1 to

2 weeks and then replaced by

new receptor cells.

Each receptor responds to one

of the basic tastes.

The four common tastes are

sweet, sour, bitter, and salty.

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2.What type of epithelium has dome shaped cells on the apical surface?a. Epithelioid tissueb. Mesotheliumc. Endotheliumd. Transitionale. Pseudostratified

3.Keratinized stratified squamous epithelium forms the epidermis.

1.Keratinization is a characteristic of the cells in the epidermis of the skin.

Questions

04/21/23

AssignmentsAssignment tittles األسم I.D م

Nucleus

رمضان عادل اسالم

على ابراهيم51012018 1

السالم عبد محمد اسالم

محمد 51012019 2

كمال إبراهيم اسماء

بسيوني 51012020 3

وادي النقراشي اسماء

احمد51012021 4

عبد مصطفى الشيماء

العاطي 51012022 5

احمد احمد محمد امل

سويدان51012023 6

يوسف اسعد اميرة

االسكندراني51012024 7

عبد مرشدي صالح أميرة

السالم51012025 8

Smoking & Lung cancer

احمد فتوح احمد محمد

سعده51012109 1

قاقا محمد احمد محمد 51012110 2

الغنى عبد انور محمد

هالل السيد51012111 3

عبد اسماعيل خالد محمد

العال51012112 4

صابر السيد صالح محمد

سعيد51012113 5

جامع الدين صالح محمد

الباب فتح51012114 6

خضر عادل محمد

إبراهيم51012115 7

علي رمضان علي محمد

النقيب51012116 8