Animal Tissues

In biology, tissue is a cellular organizational level between cells and a complete organ. A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Broadly tissues can be classified into two major groups : Plant tissue and Animal tissue.

In animals, organs are made up of four basic types of tissues - epithelial tissue, connective tissue, muscle tissue and nerve tissue. These tissues have distinctive features and specific functions which combine to form functioning organs.

In this lesson you will learn about different types of animal tissues :
1) Epithelial Tissue
2) Connective Tissue
3) Muscular tissue
4) Neural Tissue

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1. Animal Tissues

2. BiswarupMajumder| Bio-World
Introduction
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3. BiswarupMajumder| Bio-World
Animal Tissue -Types
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4. Polarity-Epitheliumisarrangedsothereisonefree
surface(apicalsurface)andoneattachedsurface
(basalsurface).
Cellularnature–Cellsinepitheliumfitcloselytogether
sidebysideandsometimesatopeachothertoformsheets
ofcells.Thesesheetsareheldtogetherbyspecialized
junctions.
Supportedbyconnectivetissue–Attachmenttoalayer
ofconnectivetissueatthebasalsurfaceformsalayer
calledthebasementmembrane,anadhesivelayerformed
bysecretionsfromtheepithelialcellsandtheconnective
tissuecells.
Avascular–Epitheliumtypicallylacksitsownbloodsupply.
Regeneration–Epitheliumcellscanregenerateifproper
nourished.
Absenceofnerves(exceptforafewaxonsinthedeeper
layers).
BiswarupMajumder| Bio-World 3
Epithelial Tissue
Anepitheliumisasheetofcellsthatcoversabodysurfaceor
linesacavity.
Epitheliumformsthecoveringsofsurfacesofthebodysuch
asSkin,Mouth,Nasalcavity(Ectodermal),Linesinternalbody
surfacesuchasGItract,Lungs,Urinarybladderandvagina
(Endodermal)andLiningofbloodvessels,lymphaticandheart
(EndothelialcellsderivedfromMesoderm).
Itservesmanypurposes,includingprotection,adsorption,
excretion,secretion,filtration,andsensoryreception.
Characteristics:

5. BiswarupMajumder| Bio-World
Epithelial Tissue -Types
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6. BiswarupMajumder| Bio-World
(a)Onthebasisofarrangementofcells
1.Simpleepithelium:
2.CompoundorStratifiedepithelium:
3.Pseudostratifiedepithelium:
4.Transitionalepithelium:
Cellsarefoundinasinglelayerattachedtothebasement
membrane.
Cellsarefoundin2ormorelayersstackedatopeachother.
Pseudostratifiedepitheliumappearstobemorethanone
cellthicksincethenucleilieatdifferentheights,butin
factitissinglelayerofcells,incontactwiththebasement
membrane.
Cellsareroundedandcanslideacrossoneanothertoallow
stretching.
Epithelial Tissue -Classification
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7. BiswarupMajumder| Bio-World
(b) On the basis of shape
1.Squamousepithelium:(Latin,squama-scale)
2.Cuboidalepithelium:
3.Columnarepithelium:
-Flat,thin,scale-likecells,
-Cellsthathaveabasiccubeshape.
-Typicallythecell’sheightandwidthareaboutequal.
-Tall,rectangularorcolumnshapedcells.
-Typicallycellsarelongerthanwidth.
Epithelial Tissue -Classification
Squamous Cuboidal Columnar
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8. Namesofepithelialtissuesincludeadescriptionofboththeirshapeandtheir
numberofcelllayers.Thepresenceofciliamayalsobeidentifiedintheir
names.Forexample,simplesquamousdescribesepitheliumconsistingofa
singlelayerofflatcells.Pseudostratifiedcolumnarciliatedepithelium
describesasinglelayeroftall,ciliatedcellsofmorethanonesize.
BiswarupMajumder| Bio-World
Simple Epithelium
Itconsistsofasinglelayerofepithelialcellsrestingona
basementmembrane,andispresentonthoseareaswhere
absorptionismore,butwearandtearisless.
Simpleepitheliumconsistsofthefollowingtypes:
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9. Stratifiedepitheliumisnamedaftertheshapeoftheoutermostcelllayer.Thus,stratified
squamousepitheliumhasoutermostlayersofsquamouscells,eventhoughsomeinner
layersconsistofcuboidalorcolumnarcells.
BiswarupMajumder| Bio-World
Compound Epithelium
Itconsistsofamanylayersofepithelialcellsofdifferent
shapesrepresentingnewlyformedandmaturecells.The
superficiallayergrowsoutwardfrombelow.Basement
membranesareusuallyabsent.Theirmainfunctionistoprotect
underlyingstructurefrommechanicalwearandtear.
Compoundepitheliumconsistsofthefollowingtypes:
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10. Thecellsofglandularepitheliumtissuearegenerallycolumnar
orcuboidal.Theglandularepitheliumtissuecanbeclassified
intotwotypes:
(a)Accordingtopresenceorabsenceofducts:
(b)Accordingtonumberofcells:
BiswarupMajumder| Bio-World
ExocrineGlands–Salivaryglands,Liveretc.
EndocrineGlands–Thyroidgland,Pituitaryglandetc.
MixedGlands–Pancreas.
Glandular Epithelium
Unicellular–Gobletcells.
Multicellular–Salivaryglands.
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11. BiswarupMajumder| Bio-World
Types of Exocrine Glands
(a) According to their structure:
(b) According to their function:
MerocrineSecretion
ApocrineSecretion
HolocrineSecretion
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12. BiswarupMajumder| Bio-World
Connective Tissue
Characteristics:
Connectivetissuerangesfromavasculartohighlyvascular.
Composition:Composedmainlyofnonlivingextracellular
matrixthatseparatesthecellsofthetissue.
Location:Itispresentinbetweendifferenttissueand
organs.Itcanbefoundinandaroundthebodyorgans.
skeletaltissuepresentintheformofboneandcartilage,
andfluidconnectivetissueasbloodandlymphare
connectivetissue.
Functions:
Establishingthestructuralframeworkofthebody.
Transportingfluidanddissolvedmaterials.
Protectingorgans.
Supporting,surroundingandconnectingothertissues.
Storingenergy.
Defendingthebodyfrommicroorganisms.
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13. BiswarupMajumder| Bio-World
Connective Tissue -Types
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14. BiswarupMajumder| Bio-World
Connective Tissue Proper
Looseconnectivetissue:
Denseconnectivetissue:
Thecellsinthematrixarewidelydistributedandthe
fibresarelooselywoven.
Itgenerallyconnectsandsupportvarioustissuesand
organsandhelpsthemtoresiststrainanddisplacement.
Thefibresdominateoverthecellsandthematrixin
quantity.
Thefibresmayberegularlyorirregularlyarranged.
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15. AreolarTissue
Theybindstissuestogether.
Theyengulfbacteriaanddamagedanddeadcells.
Theysecreteheparinandhistamine.Heparinisan
anticoagulantwhilehistaminecausesinflammationreaction.
Theyproducesantibodies.
Structure:
Functions:
Thesearesimplestandmostwidelydistributedconnective
tissues.
Ithashomogenous,transparent,semi-fluidandgelatinous
matrix.
Matrixcontainvarioustypesofcells(fibroblast,
macrophages,mastcells,lymphocytes,fatcells,plasma
cells)andfibres(whitecollagenfibres,yellowelastic
fibres).
Fibresarelooselyarrangedandthereisspacebetween
fibres,areolae,whichderivesitsname.
Foundincontinuouslayersbeneathskin,spacebetween
manyorgans,betweenmuscles,peritoneumand
mesenteries.
BiswarupMajumder| Bio-World
Location:
Areolartissue makes the skin elastic and
helps it to withstand pulling strain.
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16. Adipose Tissue
Asitsynthesize,storesandmetabolizesfat,itisa
considerablesourceofenergy.
Itactsasashockabsorbersaroundkidney,heart,andeye
balls.
Itpreventheatlossbyforminginsulatinglayer.
Structure:
Functions:
Itisamodifiedformofareolartissuethatcontainlarge
numberoffatcells(Adipocytescells).
Adipocyteisalarge,sphericalorovalshapedcell,with
largefatdropletcausingshiftingofnucleustoperipheryof
thecell.
2typesofadipocytes-whiteadipocyte-containasingle
largefatdropletandBrownadipocyte-containnumberof
smallfatdroplets.
Foundbeneathskinindermis,mesenteries,aroundkidney,
heartandeyeballs.
BiswarupMajumder| Bio-World
Location:
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17. Reticular Tissue
Theyaremostlyphagocyticcells,helpsindefense
mechanismofthebody.
Structure:
Functions:
Itisamodifiedareolartissuethatcontainslargenumber
ofstellateshapereticularcellsfloatinginfluidmatrix.
Reticularcellshasnumberofcytoplasmicprocesseswhich
areinterconnectedtoformreticularnetwork.
Reticularcellssecretesreticularfibres.
Found-lymphglands,spleen,liver,bonemarrow,thymusand
tonsils.
BiswarupMajumder| Bio-World
Location:
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18. White Fibrous Tissues
Structure:
Itcontainsfibroblastcellsandcollagenfibresandvery
fewamountofmatrix.
Thedensenetworkofcollagenfibresgivesgreatstrength.
Itoccurintwoforms-(i)tendonand(ii)Sheath
Tendonisthethickbundleofcollagenfibresrunning
paralleltoeachother,givingstrong,flexiblebut
inextensiblestrength.Itjoinsskeletalmusclestobones.
Sheathisthebundlesofcollagenfibresliesinacriss-cross
manner.Itispresentinpericardiumofheart,duramatter,
cornea,capsuleofkidney,spinalcord.Italsoforms
coveringofcartilageandbones.
BiswarupMajumder| Bio-World
Yellow Fibrous Tissues
Structure:
Thesetissuescontainsnumerousandcloselypackedyellow
elasticfibres.
Elasticfibresarelong,straightandbranched,theyare
elasticandflexible.
TheyarepresentinLigament,alsopresentinwallofblood
vessel,vocalcords,respiratorypassageandlungs.
Ligament–Itiscomposedofyellowelasticfibresandsome
collagenfibres.Itjointwobonetogether.
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19. BiswarupMajumder| Bio-World
Supportive Connective Tissue
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20. BiswarupMajumder| Bio-World
Carilage
Itistough,hardbutaflexibleconnectivetissue.Itcan
resiststrainandcanabsorbmechanicalshock.
Itconsistsofsolidorsemisolidmatrixinwhichcartilage
cell(chondrocytes)andfibresareembedded.
Cartilageisenclosedinasheathofwhitefibrous
connectivetissuecalledBelowtheperichondrium,there
islayerchondroblastcell,whichformchondrocytes.
Chondrocytesaredispersedinthematrixandoccurin
thefluidfilledspacecalledlacunae.
Eachlacunaecontain2-4chondrocytes.Each
chondrocytesisalarge,angularcellwithdistinct
nucleus.
Thematrixlacksthebloodvessels.
Structure:
Depending upon matrix, cartilage are of 3 types :
Types:
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21. BiswarupMajumder| Bio-World
Bone
Itissupportiveandprotectivetissue.
Thematrixissolidandcalcified(70%saltsofcalciumand
phosphate:hydroxyapatite,30%fibrousprotein;Ossein).
Bonecell(Osteocyte)andcollagenfibreareembeddedin
solidmatrix.
Eachboneisenclosedinalayerofwhitefibrous
connectivetissue,calledperiosteum.
Matrixisarrangedinconcentriccirclescalledlamellae.
Numberofosteoblastcellandosteocytesarearranged
inbetweenthelamellae,inthefluidfiledspacecalled
Lacunae.
Eachlacunaehasfinecytoplasmicprocesses
calledcanaliculi,whichconnectwithotherlacunae.
Osteoblastareactivebonecell,whileosteocytesare
inactiveosteroblats
Structure:
Types:
1. Compact bone
Outsideofthebone.
Supportivetissueofthebody.
Isthepartwecalltheskeleton.
2.Spongybone
Tissueinsidethebone.
Strong,butlightweight.
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22. BiswarupMajumder| Bio-World
Fluid Connective Tissue
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23. BiswarupMajumder| Bio-World
Blood
Composition:
Functions:
Bloodiscalledafluidconnectivetissuebecauseitdevelops
fromthemesodermoftheembryolikeanyothertypical
connectivetissueandconnectsalltheorgansystemsofthe
bodybytransportingoxygen,nutrients,hormones,etc.,and
removingwastesfromtheseorgans.
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24. BiswarupMajumder| Bio-World
Lymph
Lymphatic System
Lymphactsasa“middleman”whichtransportsoxygen,foodmaterials,
hormones,etc.tothebodycellsandbringscarbondioxideandother
metabolicwastes,fromthebodycellstobloodandthenfinallypoursthe
sameintothevenoussystem.
Lymphissimilarincompositiontobloodplasmaexceptthatit
lacksredbloodcells,platelets,plasmaproteinrequiredfor
clottingandothermacromoleculesfoundinblood.
Thelymphatictissueincludesthelymphnodes,spleen,tonsils,
adenoidsandthethymus(anorganinthechestthatis
particularlylargeduringinfancy).
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25. BiswarupMajumder| Bio-World
Summary Table
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26. BiswarupMajumder| Bio-World
Muscular Tissue
Musclesaremadeupofhighlyspecializedthinand
elongatedcellscalledmusclefibres.
Themusclefibrescontainsspecializedcytoplasm
calledsarcoplasmthatcontainnetworkofthe
membranecalledsarcoplasmicreticulum.
Themusclefibresmaybeboundedbythecell
membranecalledsarcolemma.
Eachmusclefibremaycontainnumerouslongitudinal
fibrilscalledmyofibrils.
Basic Physiological Property of Muscular Tissue
Contractibility
Excitability
Extensibility
Elasticity
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27. BiswarupMajumder| Bio-World
Muscular Tissue -Types
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28. BiswarupMajumder| Bio-World
Skeletal Muscle Tissue
Skeletalmuscleiscalled"striated"becauseofits
appearanceconsistingoflightanddarkbandsvisible
usingalightmicroscope.
Asingleskeletalmusclecellislongand
approximatelycylindricalinshape,withmanynuclei
locatedattheedges(periphery)ofthecell.
Movementoftheskeletonunderconsciouscontrol,
includingmovementoflimbs,fingers,toes,neck,etc.
Movementoftissuesoffacialexpressionunder
consciouscontrol,e.g.abilitytosmileandtofrown.
Structure:
Function:
Skeletal or striated muscles constitute about 50% of the body
weight.
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29. BiswarupMajumder| Bio-World
Smooth Muscle Tissue
UnlikeSkeletalandCardiacmuscletissue,Smoothmuscle
isnotstriated.
Smoothmusclefibersaresmallandtapered-withthe
endsreducinginsize,incontrasttothecylindricalshape
ofskeletalmuscle.
Eachsmoothmusclefiberhasasinglecentrallylocated
nucleus.
Contractionsofsmoothmuscleconstrictthevesselsthey
surround.
Thisisparticularlyimportantinthedigestivesystemin
whichtheactionofsmoothmusclehelpstomovefood
alongthegastrointestinaltractaswellasbreakingthe
fooddownfurther.
Smoothmusclealsocontributestomovingfluidsthrough
thebodyandtotheeliminationofindigestiblematter
fromthegastrointestinalsystem.
Structure:
Function:
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30. BiswarupMajumder| Bio-World
Cardiac Muscle Tissue
Cardiacmusclefibersarestriated,branched
(sometimesdescribedasY-shaped),andhaveasingle
centralnucleus.
Thesefibersareattachedattheirendstoadjoining
fibersbythickplasmamembranes called
intercalateddiscs.
Pumpingofbloodthroughtheheart:Alternate
contractionandrelaxationofcardiacmusclepumps.
Structure:
Function:
De-oxygenatedbloodthroughtheRightAtriumandRight
Ventricletothelungs,and
OxygenatedbloodthroughtheLeftAtriumandLeft
Ventricletotheaorta,thentherestofthebody.
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31. BiswarupMajumder| Bio-World
Nervous Tissue
Nervoustissueisthemaintissuecomponentofthetwo
partsofthenervoussystem;thebrainandspinalcordof
thecentralnervoussystem(CNS),andthebranching
peripheralnervesoftheperipheralnervoussystem(PNS),
whichregulatesandcontrolsbodilyfunctionsandactivity.
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32. BiswarupMajumder| Bio-World
Neuron
Structure:
Thecellbodyistheenlargedportionoftheneuronsthat
containsthenucleus.Itisthe“nutritionalcentre”ofthe
neuronwheremacromoleculesareproduced.Thecellbody
alsocontainsdenselystainingareasofroughendoplasmic
reticulumknownasNisslBodiesthatarenotfoundinthe
dendritesoraxon.
Dendrites(fromtheGreekdendron=treebranch)arethin,
branchedprocessesorstructurethatextendfromthe
cytoplasmofthecellbody.Dendritesprovideareceptive
areathattransmitselectricalimpulsestothecellbody.
Theaxonisalongerprocessthatconductsimpulsesaway
fromthecellbody.Axonsvaryinlengthfromonlya
millimeterlongtouptoameterormore(forthosethat
extendfromtheCNStothefoot).Theoriginoftheaxon
nearthecellbodyisanexpandedregioncalledtheaxon
hillock;itisherethatnerveimpulsesoriginate.Side
branchescalledaxoncollateralsmanyextendfromthe
axon.
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33. BiswarupMajumder| Bio-World
Myelinated& Non-myelinatedAxons
Myelinatednerves, which are the most common type in humans, conduct
action potential much faster than the unmyelinatednerves.
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34. BiswarupMajumder| Bio-World
Synapse
Synapseisajunctionbetweentheaxonterminalofoneneuron
andthedendriteofthenextneuron.Itisseparatedbyasmall
gapknownassynapticcleft.
Asynapseisformedbythemembranesofapre-synaptic
neuronwhichmayormaynotbeseparatedbyagapcalled
synapticcleft.Chemicalsinvolvedintransmissionofimpulses
atchemicalsynapsesarecalledneurotransmitters.
Therearetwotypesofsynapses:
a)Electricalsynapses
b)Chemicalsynapses
Inelectricalsynapses,thepreandpostsynapticneuronsliein
closeproximitytoeachother.Hencetheimpulsecanmove
directlyfromoneneurontoanotheracrossthesynapse.This
representfastermethodofimpulsetransmission.
Inchemicalsynapses,thepreandpostsynapticneuronsare
notincloseproximity.Theyareseparatedbyasynapticcleft.
Thetransmissionofnerveimpulsesiscarriedoutbychemicals
suchasneurotransmitters.
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35. BiswarupMajumder| Bio-World
Neuron -Types
(a) On the basis of the structure
(b) On the basis of function
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36. BiswarupMajumder| Bio-World
Neuroglia
Neuroglia(neuro=nerve;glia=glue)orneuroglialcellsare
specializedcellsfoundinthebrainandspinalcordsupporting
theneuronsandtheirfibres.
About50percentofallbraincellsareneuroglialcells.
Theyprovideavarietyoffunctionsforbraintissue.They
supportthemetabolicandsignalingfunctionsofneurons.
Neurogliaalsocontributetotheorganizationandformationof
abarrierbetweenthebloodandthebrain.Theotherfunction
ofneurogliaisparticipationincreatinganinflammatory
responseininjuredneuraltissues,includingphagocytosisof
cellulardebris.
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37. BiswarupMajumder| Bio-World
Ependymalcells
Thesecellsarearrangedasanepitheliallayer,onecell
thick,whichlinestheventricles(cavitiesofthebrain)and
thecentralcanalofthespinalcord.
Thecellsvaryfromsquamoustocolumnaraccordingto
theirlocation.Theirfreesurfacebearsnumerous
microvilliandcilia.
Themicrovillihelpintheabsorptionofcerebrospinalfluid.
Themovementsoftheciliacontributetheflowofthe
cerebrospinalfluid.
Theependymalcellspossessoneormorelongprocesses
towardsoppositesidewhichpenetratethenervoustissue.
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38. BiswarupMajumder| Bio-World
Neurosecretorycells
Neurosecretorycell,atypeofneuron,ornervecell,whose
functionistotranslateneuralsignalsintochemicalstimuli.
Suchcellsproducesecretionscalledneurohormonesthat
travelalongtheneuronaxonandaretypicallyreleasedinto
thebloodstreamatneurohemalorgans,regionsinwhich
theaxonendingsareinclosecontactwithbloodcapillaries.
Neurosecretorycellsarepresentinmostmulticellular
animalsandareusuallydistinguishedfromotherneurons
bytheunusuallylargesizeofthecellnucleus,axon
endings,andthecellitself.
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39. BiswarupMajumder| Bio-World 38
Animal Tissues -Summary