Tissues - Copy - Copy

8/6/2019 Tissues - Copy - Copy

1/47

EPITHELIA


2/47

INTRODUCTION The outer surface of the body and

the luminal surface of the cavities

within the body are lined by one ormore layers of cells that completelycover them, such layers of cells are

called epithelia


3/47

The term epithelium is derived fromthe greekepi, upon; thele, nipple

Upon referred, to covering andnipple referred, the connective

tissue papilla


4/47

Epithelial and Connective

Tissues

Epithelial tissues

Classes Junctions

Glands


5/47

Simple: just onelayer or cellshape

Stratified:multiple layersand cell shapes

Classes of Epithelia


6/47

Simple Epithelia

Type Cell shape Example

Squamous Squashed Endothelium (lines blood

vessels), mesothelium

(serous lining of celom)

Cuboidal Cubed Walls of glands

Columnar Columns Lining of gut tube;sometimes w ith cilia likelining of uterine tube

Pseudo-stratified Flat cells give riseto columns

With cilia in respiratorytubes to move

mucous/particles out oflungs


7/47

SIMPLE SQUAMOUSSingle layer

Squamous shape

Lining of body cavity,lungs, blood vessels


8/47

That line alveoli of lungs- pleura

Peritonium mesothelium

Inside lining of heart- endocardium

Blood vessels and lymphatics endothelium also line renal tubules

and some parts of the ear.


9/47

SIMPLE CUBOIDALSingle layer

Cuboidal shaped

Kidney tubules, glands


10/47

EPITHELIAL TISSUE

SIMPLE COLUMNARSingle layer

Columnar shape

Lining of digestive tract

Modified by presence of

cilia

Straited borders or

brush borders is seen

in small intestine.


11/47

Columnar epithelium is seen inrespiratory tract, uterus and the

uterine tubes, auditory tube , part ofmiddle ear ,central canal of spinalcord and ventricles of brain.


12/47

EPITHELIAL TISSUE

STRATIFIED SQUAMOUSMulti layer

Outer most layer- squamous

cellsInner- cuboidal or columnar

Lining of mouth,

esophagus, skin


13/47

EPITHELIAL TISSUE

PSEUDOSTRATIFIEDCOLUMNAR

One layer

Appears stratifiedRespiratory tract


14/47

These cells oftenvary in height.

Because the heights

vary, it gives offfake (pseudo)looking layers.

Secretes and

absorbs along thelungs.


15/47

Stratifies Squamoushas many differentlayers.

Usually found inplaces that aremore likely to tear

It is used for

protection

Stratified Squamous


16/47

It can be keratinize epithelium andnon keratinized

Non keratinized epithelium forms thelining of the mouth

Under pathological conditions the

epithelium in any of these situationsmay become keratinized.


17/47

Very rare in thehuman body

They are sometimes

found in ducts andin larger glandssuch as sweatglands and

mammary glands.

Stratified Cuboidal


18/47

Can be found in thelining of glandularducts, pharynx, and

the male urethra. Occurs as

transitional areasbetween other

types of epithelia

Stratified Columnar


19/47

` Its basal layer iscuboidal andcolumnar.

`

It is found in theurinary organs andstretches as urine isproduced.

`When urine ispresent it stretchesfrom six layers toabout three.

Transitional Epithelial


20/47


21/47

Cell Junctions Desmosome: binding spots

between cells with proteins called

cadherins Tight junctions: impermeable

E.g. gut tube, doesnt let enzymes from

gut into blood stream Gap junctions: tubes that let small

molecules pass between cells


22/47


23/47

(Tight junction)

Controls the passage throughintercellular spaces

Permeability of tight junctions in sometissues may be regulated by certainneurotransmitters and hormones.

Occluding junctions


24/47

If this extend around the entire perimeter of cell,called

Zonula occludens or Continuous tight junctionex. Intestinal epithelial cells.

Complementary protein particle of two opposed cellmembrane establish mutual contact & becomeinterlocked across the intercellular gap like teeth of azipper.


25/47

Fascia occludens: Similarto zonula occludensexcept that they are strip

or band shaped.ex. Endothelial lining

of blood vessels (Braincapillaries are exception,here endothelial cells are

joined by zonulaoccludens forming BBB)

Seal effect is interrupted. Itenables capillary toproduce tissue fluid. Alsoprovide escape route toleukocytes.


26/47

Strongly bond contiguous epithelialcells.

Are of two types- a) Zonula adherens

b) Maculaadherens(desmosomes)

Zonula adherens:

Present b/w intestinal epithelial cells justbelow occludens

Extend around entire perimeter

Below it macula adherens are also

present

Adhesive Junctions


27/47

So Zonula adherens is also called as Intermediatejunction or Belt desmosome.

Wide intercellular gap (20 nm) is filled with the finefilamentous material of moderately low electrondensity. It is believed to constitute the strong bond

b/w apposed cell membrane.

Apical constriction of its component cells so that

their microvilli fan out & provide regions of cellmembrane between the bases of their microvilliwith free access to luminal content


28/47

Also called Desmosome

Circular or spot like in shape

Most abundant in epithelial membranethat are adapted to withstand wear &tear

Present as a part of junctional complex

Macula adherens


29/47

In desmosomes, bundles of tonofilaments areanchored to disc like plaque.

These tonofilaments are type of intermediatefilaments made of Prekeratin.

Plaque is a mass of electron dense material

that adheres to cytoplasmic aspect of eachopposed area of cell membrane.

It is made of protein desmoplakin &

plakoglobin.

Also an electron dense line is seen extendingalong midline intercellularly (30 nm wide, filledwith Glycoprotein)


30/47


31/47


32/47


33/47

On each cell membrane, the proteinparticles appear as rings of sixdumbbell shaped subunits thatenclose one half of central channel.

A slight left hand twist in the way thesubunits are arranged, keep thecentral channel open.

When subunits assume moreperpendicular orientation, channel

closes.


34/47

In physiologic conditions intracellularcalcium concentration is well below ofextra cellular fluid which maintainthese channel open.

Cell damage result in massive influx ofextra cellular calcium, which causesthese channel to close.

Also Gap junction permeabilitydecreases as pH increases.


35/47

c-AMP increases Gap junctionpermeability by creating new junctions &

also by adding new connexons to oldgap junctions.

Gap junctions are commonly present in

b/w embryonic cells

Gap junctions also communicate or relay

cell recognition signals, positionalinformation or other signals require todirect the normal course of developmentof embryo.


36/47

It is a thin layer of specialized intercellular matrixpresent at interface between connective tissue &various tissues.

Name basement membrane because it was firstnoticed beneath basal surface of epithelium.

Under electron microscope , the layer appearsmuch thinner and is then termed the Basal Lamina.

All the major products of the basal lamina appears tobe synthesized by the epithelial cells.

BASEMENT MEMBRANE


37/47

In Light microscopy- appearhomogenous, PAS positive due toGlycoproteins

In Electron microscopy- electron denselayer, seldom more than 100 nm

Basement membrane follow thecontour of cell surface at a distance ofup to 60 nm from cell membrane.


38/47

Functions:

a) Bond cell to underlying connective tissue.

b) Provide these cells with flexible support,which is particularly evident in lens capsule.

c) Permeable to low molecular weightsubstances & impede passage ofmacromolecules.

d) May act as a substance capable ofdirecting cell growth & migration duringmorphogenesis & regeneration & repair.


39/47

`


40/47

Structure of BM:

Now it clear that electron dense layerseen under EM represents only a part ofBM.

This electron dense layer, formerly knownas basal lamina now called Lamina

densa, varies in thickness from 20 to 300nm depending on location.


41/47

On cellular side, it is called as lamina raraexterna or lamina lucida.

Other side which lie in intimateassociation of reticular fibers ofunderlying connective tissue is calledlamina rara interna or laminafibroreticularis.

Lamina densa contains very finemeshwork of type IV collagen .

This type IV collagen along withconstituent glycoproteins are producedby cells that BM .


42/47

The nature of lamina lucida is less firmly established.This region is traversed by delicate cords that extendfrom lamina densa to cell membrane.

These cords are similar to anastomosing cords thatmake up lamina densa except that they are looselyarranged.

In both, these cords possess an axial core filament oftype IV collagen, encased by sheath containingadhesive glycoprotein, Laminin.


43/47

Immunocytochemical studies haveconfirmed that laminin is an universal,

major constituent of BM.

Laminin is crucifix shaped glycoproteinmolecule which bind to type IV collagen

& also to receptor on cell membrane so laminin attaches cell to basement

membrane

Fibronectin is another glycoprotein withV shaped molecule. It has collagenbinding domains on both arms.


44/47

Fibronectin binds to collagen, proteoglycans,heparin & other GAGs & to cell membrane

receptors.

So it has dual role attaching the basementmembrane to its underlining matrix of reticular

fibers and act in conjugation with laminin topromote cellular adhesion to basementmembrane.

In addition to it basement membrane containEntactin which is a sulfated glycoprotein andalso Heparan sulphate proteoglycan.


45/47


46/47

Hams Histology 9th edition David H.Cormack

Textbook of histology- 4th edition ;InderbirSingh

REFERENCES


47/47

THANK YOU

Tissues - Copy - Copy

Documents

Transcript of Tissues - Copy - Copy