epithelial tissue 2003

8/14/2019 Epithelial Tissue 2003

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THE TISSUES OF THEBODY -

THE EPITHELIUM

DR IRAM IQBAL


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TISSUES

Tissues are aggregates or groups of

cells organized to perform one or

more specific functions.4 types ofbasic tissues

Epithelium

Connective tissue

Muscle tissue

Nerve tissue


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EPITHELIUM

Epithelium is an avasculartissue.

Composed of cells that cover the exterior

body surfaces and line internal closed

cavities (including the vascular system)

and body tubes that communicate withthe exterior(the alimentary, respiratory,and genitourinary tracts).


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EPITHELIAL TISSUE


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CONNECTIVE TISSUE

Cell

A. LOOSE CONNECTIVE TISSUE(under the skin)

Collagenfiber

Otherfibers

B. ADIPOSE TISSUE

Fatdroplets

Cellnucleus

C. BLOOD

White bloodcells

Red bloodcells

Plasma

D. FIBROUS CONNECTIVE TISSUE(forming a ligament)

Cellnucleus

Collagenfibers

E. CARTILAGE

(at the end of a bone)

Cells

Matrix

F. BONE

Centralcanal

Matrix

Cells


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MUSCULAR TISSUE

Muscular tissue is characterized by

aggregates ofspecialized , elongated

cells arranged in parallel array whose

primary role is contraction.


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SKELETALMUSCLE

CARDIACMUSCLE

SMOOTHMUSCLE

MUSCULAR TISSUE


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Nervous Tissue

Densely packed tissue having

Two main cell types

Neurons transmit electrical signals

Support cells (neuroglial cells) nonexcitable

Surround and wrap neurons


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NERVOUS TISSUE

Nucleus

Cell body

Cellextensions


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CHARACTERISTICS

Avasculartissue

Forms the secretary portion

(Parenchyma) of Glands and Ducts

Receptors for certain Sensory Organs

Closely opposed adhere to each other

byjunctions


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Simplesquamous

Epithelium lines

alveoli in lungs.

Simple cuboidal

Epithelium

Forms tubes in

kidneys.

Simple columnar

Epithelium lines

the intestine.

Stratified

squamous

Epithelium

lines the

esophagus.

Epithelium is found everywhere


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In addition, specialized epithelial cells function as

receptors for the special senses (smell, taste,

hearing, and vision).


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Epithelium also forms the secretory

portion (parenchyma) of glands and their

ducts.


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EPITHELOID TISSUES

Certain special situations

Epithelial cells lack free surface

Found aggregated in to each other

Closed apposition and BM is present but no free surfacehence epithelial like

Examples

- Interstitial cells of leydig (testis)

- Luteal cells (ovary)- Parenchyma ofadrenal glands

- Epithelioreticular cells (thymus)

- Pathologic responses to injury and tumors


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FUNCTIONS

Depend upon the activity of cell type

Selective barrier

- Forms a continuous sheet like

investment separating CT frominternal and external environment

- Fascilitates or inhibits certain substancesbetween the two compartments

(metabolites and waste material passthrough it not between them)

- Impervious barrier (urinary bladder)


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Secretory (Stomach)

Both Secretory and Absortive (intestine)

Transport system through motile Cilia

on its surface (particulates/mucus in

Trachea and Bronchi)

Serve to receive Sensory Stimuli (Taste

Buds of Tongue or Retina of Eye)


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How are epithelia

classified?Depends on number of layers

One layer 2 or more

layers

SIMPLE

Special

STRATIFIED

PSEUDOSTRATIFIED

TRANSITIONAL


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The individual cells that compose

an epithelium


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Importance of layering


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Simple squamous epithelium

Locations

Vascular system

(endothelium)

Body cavities

(mesothelium)

Bowmans capsule(kidney)

Respiratory spaces

in lungs

Major functions

Exchange, barrier in

CNS

Exchange &

lubrication

Barrier

Exchange


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Mesothelium


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Respiratory spaces


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Bowmans capsule


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Simple Squamous Epithelium 100X

1 cell

Adjacent cell

membranes held

together with tight

junctions

Nucleus

Methylene blueSingle layer of flat

cells


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Simple Squamous Epithelium 400X

1 cell

Silver Single layer of flat


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Simple cuboidal epithelium

Locations

Small ducts ofexocrine glands

Surface of ovary

(germinal

epithelium)

Kidney tubule

Major functions

Absorption, conduit

Barrier

Absorption & secretion


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Ducts of exocrine glands


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Simple Cuboidal Epithelium 400X

Cells

Single layer of cube shaped cells; large


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Simple columnar epithelium

Locations

Small intestine &

colon

Stomach lining &gastric glands

Gallbladder

Major functions

Absorption & secretion

Secretion

Absorption


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Simple Columnar Epithelium 400X

Single layercolumnar cells

nuclei in a line

Kidney collecting duct


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Single layer of cube shaped cells; large nucleus


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Stomach


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SPECIAL CATEGORIES OF

EPITHELIUM

PSEUDOSTRATIFIED EPITHELIUM

Actually a simple epithelium

All rest on BM

Some cells do not reach the surface

Appearance of being stratified

Limited distribution


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Pseudostratified epithelium

Locations

Trachea &

bronchial tree

Ductus deferens

Efferent ductules of

epididymis

Major functions

Secretion, conduit

Absorption, conduit


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Trachea (monkey) 400XGoblet cell

Smooth muscle

Lamina propria

Seromucous glands

Pseudostratified ciliated

columnar epithelium


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Stratified squamous

epitheliumLocations

Epidermis

Oral cavity &

oesophagus

Vagina

Major functions

Barrier

Protection


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St tifi d S E ith li 400X


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Stratified Squamous Epithelium 400X

(keratinized)

Squamous cells

Skin epidermis

Outermost layers of cells are

squamous shape

Dermis


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Stratified cuboidal epithelium

Locations

Sweat gland ducts

Large ducts of

exocrine glands

AnorectaljunctionGrowing follicles in

ovary

Major functions

Barrier

Conduit


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Stratified Cuboidal Ovary follicle


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Stratified columnar epithelium

Locations

Largest ducts of

exocrine glands

Anorectal junction

Major functions

Barrier

Conduit

St tifi d C l t l d


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Stratified Columnar, sweat gland

duct


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Transitional epithelium

(urothelium)Locations

Renal calyces

Ureters

Bladder

Urethra

Major functions

Barrier

Distensible

property


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Distended

bladder

Empty bladder


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CELL POLARITY

Cells whose apex differs from it,s base regarding

the modification of plasmalemma and function is

called as polarized cell.

Epithelial cells exhibit distinct polarity

They have an;

Apical domain

Lateral domainBasal domain


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APICAL DOMAIN & ITS

MODIFICATIONSStructural surface modifications include

microvilli, stereocilia & cilia.

Apical domain may contain specific

enzymes (e.g., hydrolases), ion

channels & carrier proteins (e.g.,glucose transporters).


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MICROVILLI

Finger-like cytoplasmic projections on thesurface of most epithelial cells.

Vary widely in appearance.Short, irregular, bleb-like projections

Tall, closely packed, uniform projections

Number & shape of the microvilli of a given

cell type correlate with its absorptive capacity.

Intestinal absorptive cells/striated


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Intestinal absorptive cells/striated

border


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Molecular structure of microvilli


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Molecular structure of microvilli


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STEREOCILIA

Unusually long, immotile microvilli.

Also termed stereovilli.

Not widely distributed among epithelia.

Limited to:

Epididymis

Proximal part of the ductus deferens of the

male reproductive system

Sensory (hair) cells of the ear

Electron micrographs showing


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Electron micrographs showing

variations in stereovilli of different cell

types


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Sterocilia of the sensory epithelium of the ear are uniform indiameter and possess an internal structure similar to that of

genital duct sterocilia however they lack both erzin and a-

actinin, and serve as sensory receptors rather than absorptive

structure


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CILIA

Motile cytoplasmic structures capable

of moving fluid & particles along epithelial

surfaces.Hair like structures .25um in diameter and

2um-10um in length.

Location:Trachea

Bronchi

Oviducts


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Cilia contain an organized core of


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g

microtubules arranged in a 9+2 pattern

Molecular structure of cilia


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Molecular structure of cilia

Microtubule-associated motor protein

Cilia develop from procentrioles


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p p

Electron micrograph of the cilia


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Electron micrograph of the cilia


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Microvillia vs cilia, SEM


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EPITHELIAL CELL ADHESIONS


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EPITHELIAL CELL ADHESIONS

Epithelial cell not only in close apposition but

also adherent (with exceptions)

Before electron microscopy it was referred as

intercellular cement and called Terminal BarJUNCTIONAL COMPLEX

Specific structural components that make up the

barrierand attachment device

Creat a long term behavior, compartmentalize

and effects passage from and through the cells

-

LATERAL DOMAIN & ITS


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SPECIALIZATIONS

3 types of junctional complexes in lateraldomain i.e.,

occluding junctions

anchoring junctions

communicating junctions.

In addition, lateral cell surface membrane in

some epithelia may form folds & processes,

invaginations & evaginations that createinterdigitating & interleaving tongue-and-

groove margins between neighbouring cells.


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Zonula occludens


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Also called tight junctions.

Located at the most apical point.

Forms a ring or circumferential band

Created by localized sealingof adjacent plasma

membranes.

Separates Luminal space from intercellular

space and CT

Limitthe movement of water & other molecules.

Maintain the integrity of apical & lateral surfaces.

At high resolution


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At high resolution , Zonula occludens appear not as a continuous

seal but as a series of focal fusion b/w the

cells.

These focal fusions are created by

transmembrane proteins of adjoining cellsthat join in the intercellular space.

Best visualized by freeze fracture technique.

The ridges & grooves are arranged as a

network of anastomosing particle strands thus

creating a functional seal within the

intercellularspace.

Molecular organization of zonula


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occludens

Junctional adhesion molecule,

associated with claudin ,involved in

formation of occl dens j nction in


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formation of occludens junction in

endothelial cells

Claudin formbackbone of each

strand

Junctional adhesion molecule,

associated with claudin ,involved in



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endothelial cells

Freeze fracture preparation of zonula


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occludens

E-face reveals complementary grooves

P-face reveals ridge like structures for junctional

proteins

The zonula occludens separates theluminal space from the intercellular space


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luminal space from the intercellular space

& connective tissue compartment

It is now evident that the zonula occludens play a

essential role in selective passage of substances


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essential role in selective passage of substances

from one side of epithelium to the other.

Creating a diffusion barrierwhich is controlled by2 pathways.

The transcellular pathway

Occur across the plasma membrane of the epithelial cell

Requires specialized energy-dependent membranetransport proteins and channels

The paracellular pathway

Occur across the zonula occludens b/w 2 epithelial cells

T ll l thParacellular pathway


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Transcellular pathway


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ANCHORING JUNCTIONS


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ANCHORING JUNCTIONSProvide lateral adhesions between epithelial

cells, using proteins that link into the cytoskeletonof the adjacent cells.

Band orbelt like configuration around the cell

2 types of anchoring cell-to-cell junctions can be

identified on the lateral surface.

Zonula adherens,

Which interacts with the network ofactin filaments

inside the cell.

Macula adherens/desmosomes

Which interacts with intermediate filaments inside

the cell.


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ZONULA ADHERENS


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ZONULA ADHERENS

Heterotypic binding, If the

binding occur b/w diff type

of CAMs

Homotypic binding, occur b/w

CAMs of the same type

The integrity of the epithelial surface depends in large

t th l t l dh i f th ll ith


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part on the lateral adhesion of the cells with one

another and their ability to resist separation.

Homotypic binding

The morphologic andfunctional integrity of zonula

adherens is Ca dependent15 20


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adherens is Ca dependentCAMs 15-20nm

Fuzzy plaque


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MACULA ADHERENS/


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MACULA ADHERENS/

DESMOSOMES

Molecular structure of macula


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adherens


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COMMUNICATING


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COMMUNICATING

JUNCTIONSGap junctionsornexus.

Present in wide variety of tissues, includingepithelia,smooth & cardiac muscle, & nerves.

Consist of an accumulation oftransmembrane

channels or pores in a tightly packed array.

Also called low resistance junctions.


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Open & closed states of gap junctions


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Gap junctions allow cells to exchange ions,

regulatory molecules & small metabolites


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regulatory molecules, & small metabolites

through the pores


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MORPHOLOGICAL

SPECIALIZATIONS OF LATERAL


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SPECIALIZATIONS OF LATERAL

SURFACELateral surface folds (plicae) create

interdigitating cytoplasmic processes of

adjoining cells.

Increase lateral surface area of the cell.

Particularly prominent in epithelia that are

engaged in fluid & electrolyte transport, such as

intestinal & gallbladder epithelium.


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BASAL DOMAIN & ITS


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BASAL DOMAIN & ITS

SPECIALIZATIONSBasement membrane: Located next to basal surface

Cell-to-extracellular matrix junction: Anchor cell to

extracellular matrix

Plasma membrane infoldings: Increase surface area &

facilitate morphological interactions between adjacent

cells.

B l l i


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Basal lamina

EM examination of the site of the basement

membranes reveals a discrete layer of electron

dense matrix material 40-60nm thick between the

epithelium & adjacent connective tissue called thebasal laminaor, sometimes lamina densa.

Between the basal lamina & the cell is a relativelyclear or electron-lucent area, the lamina lucida

(also about 40nm wide).

LAMINA DENSA & LAMINA

LUCIDA


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LUCIDA


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BASEMENT MEMBRANE


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BASEMENT MEMBRANE Epithelium attached to underlying CT

Layer of variable thickness at the basal surfaces Periodic acid Schiff technique is implied

BASAL LAMINA (LAMINA DENSA) Discrete layer of electron dense material between

epithelium and adjacent CT

BY ELECTRON MICROSCOPY Between Basal lamina and cell is Lamina Lucida Between Basal lamina and CT is Microfibrils (Type VII

collagen) attached to the Reticular fibres of CT

RETICULAR LAMINA

Reticular fibres (Type III Collagen) beneath Basal Lamina Part of CT Some investigators contend that its part of Basal Lamina


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COMPONENTS OF BASAL


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LAMINAConsists of at least five components

Collagen (type IV collagen) provide structuralintegrity to Basal lamina

Proteoglycans much of the bulk volume of

Basal lamina Laminin (glycoprotein molecule) bridges the

Lamina Lucida to the overlying epithelial cells Enactin and Fibronectinrole not clear

Anchoring filaments(Type VII collagen) linkBasal Lamina to underlying CT (ReticularLamina


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Several structures are responsible for attachment

f th b l l i t th d l i ti


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of the basal lamina to the underlying connective

tissue.


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FUNCTION

N f ll ll id d


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Not fully ellucidated

Structural attachment site for the overlyingcells and underlying CT

Compartmentalization Separations/isolation of

CT from epithelia ,Nerves ,muscle tissue

Filtration movement of substances to and from

the tissues (ionic charges and integral

spaces), kidney

Tissue scaffolding serves as a guide duringregeneration. Newly formed cells help to

maintain original tissue architecture


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Cell-to-extracellular matrix


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junction2 major anchoring junctions are;

Focal adhesions: Anchor actin filaments ofthe cytoskeleton into the basement membrane.

Hemidesmosomes:Anchor intermediatefilaments of the cytoskeleton into the basementmembrane.

FOCAL ADHESIONS


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FOCAL ADHESIONS


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HEMIDESMOSOMES


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HEMIDESMOSOMES


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References:


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References:

Text And Atlas Of Histology By MICHAEL

H. ROSS 5th Edition

BAILEYS Textbook Of MicroscopicAnatomy 18th Edition

Textbook Of Histology By LEESON,

LEESON, PAPAROGoogle search results for images

anatomy.iupui.edu/.../cell.f04/cellf04.html


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epithelial tissue 2003

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