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EPITHELIAL TISSUES
College of Medical Laboratory Science

TOPIC OUTLINE
4
...
Diversity

4 Major types of tissue
1
...
Connective
3
...
Nervous

Cells in epithelia each have:
A
...
basal side (specialized for exocytosis) facing
a basement membrane and underlying
connective tissue
...

Principal functions of epithelial tissue:
1
...

3
...


Covering, lining and protecting surfaces (ex
...
intestines)
Secretion (ex
...
myoepithelial cells)

EPITHELIAL TISSUE

Characteristics:
1
...
Anchoring junctions/ (zonula adherens)
– Chains that mechanically binds adjacent epithelial cells
– site of adhesion
– Provides firm adhesion of one cell to its neighbours so that
they can function as a cohesive unit
...


EPITHELIAL TISSUE
b
...
BBB

INTERCELLULAR JUNCTIONS
• Tight or occluding junctions linear
arrangements of linked proteins surround the
apical ends of the cells and prevent
paracellular passage of substances

EPITHELIAL TISSUE
c
...
5 nm)
– More commonly found in embryo and low density tissues

INTERCELLULAR JUNCTIONS
• Gap or communicating
junctions are points of
cell contact where both
plasma membranes have
numerous
hexameric
complexes
of
transmembrane
connexons,

EPITHELIAL TISSUE
2
...
Basement membrane/ Basal lamina
– Semi solid structure that allows the diffusion of
materials from the underlying connective
tissue
...


BASEMENT MEMBRANE
• Thin
extracellular
layer of specialized
proteins,
usually
having two parts: a
basal lamina and a
more
fibrous
reticular lamina
...

• Reticular lamina contains type III collagen
and anchoring fibrils of VII collagen

EPITHELIAL TISSUE
4
...


Metaplasia
–
–
–
–

Adaptive transformation
A normal tissue is replaced by another normal tissue
...
Non-keratinized squamous epithelium replaces ciliated
columnar cells in the bronchi of smokers

Anaplasia
–
–

Normal to abnormal tissue
Malignant transformation

EPITHELIAL TISSUE
6
...


B
...


ectoderm
:skin,
sweat/oil
glands,
epithelium of the
mouth
mesoderm: blood vessels, reproductive
ducts- uterus, fallopian tubes, ducts of the
urinary system
endoderm: lining of the GIT –
stomach, intestines, liver, pancreas

EPITHELIAL TISSUE

Epidermal derivatives of embryonic germ layers
a
...

b
...
Endoderm
– Lining of esophagus: stratified squamous non-keratinized
– Lining of GIT: simple columnar
– Lining of the gall bladder: simple columnar
– Solid glands such as the liver and pancreas
– Lining of the respiratory system: pseudostratified columnar

Nomenclature
I
...
Flat, plate-like cells
– Squamous epithelium
– Ideal for protection, diffusion
– For exchange of gases (alveoli)

b
...
Tall/ height 2-3x greater the width
– columnar epithelium
– Ideal for absorption and transport of materials
(lining of the small intestines, trachea)

Nomenclature:
II
...
Single/ One layer: simple
b
...
Pseudostratified:
– Composed of a single layer of tall columnar cells
which may appear several layers
– False layers (due to the differences of the nucleus)

d
...

– Sometimes called umbrella cells
...

– Form of surface cells changes according to the degree
of distention of the bladder wall
...
Surface Modifications
1
...


3
...


Microvilli
– Cytoplasmic projection, finger-like extension/ folds that pursue a sinuous course
...


APICAL STRUCTURES OF EPITHELIAL CELLS
• Stereocilia are long microvilli with specialized
mechanosensory function in cells of the inner ear
and for absorption in tissues of the male
reproductive tract
...


MICROVILLI

STEREOCILLIA

CILLIA

KERATIN

IV
...
Mesothelium
– Membranes
– Prevents friction, acts as lubricants
b
...

Myoepithelium
– Muscle-like epithelium
– For contraction
– Found in the glands (mammary glands), skin (remodeling of scar)
d
...
Functional Classification
e
...
Glandular epithelium
– For secretion (glands)
– Formed by cells specialized to secrete
– Molecules to be secreted are generally stored in the cells in
small membrane bound vesicle called secretory granules
...
Based on the mode of secretion
a
...
Apocrine
• Partial destruction of the cell
• secretes with some of the apical cytoplasm containing cell product

c
...
Based on secretory products
a
...


Serous: watery secretions
Mucous: thick secretion (mucin)

EPITHELIAL SECRETION/GLANDS
• The major function in many epithelial cells is
synthesis and secretion of specialized products;
organs composed primarily of such epithelia are
called glands
...


EPITHELIAL SECRETION/GLANDS
• Endocrine glands lack
ducts;
secreted
substances
are
hormones
carried
throughout the body
by the interstitial fluid
and
blood
,with
specificity produced by
the hormone receptors
of target cells
...


Types of epithelia:
a
...
Simple cuboidal
–
Thyroid glands, kidney
c
...
Stratified squamous keratinized epithelium
– Skin/ epidermis
e
...

Stratified cuboidal
– sweat and salivary glands, seminiferous tubules
g
...
Pseudostratified columnar epithelium
– lining of the upper respiratory tract
i
...


Simple squamous

b
...


Simple columnar
–
Intestinal gland, goblet cells

d
...


Stratified squamous non-keratinized epithelium
– mouth, esophagus, vagina

f
...


Stratified columnar
– Male urethra, pharynx

h
...


Transitional epithelium
– Urinary bladder



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