oral histo ,, first lec

8/3/2019 Oral Histo ,, First Lec

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EARLY EMBRYOLOGICALEARLY EMBRYOLOGICAL

DEVELOPMENTDEVELOPMENT

Oral HistologyOral Histology

Dent 206Dent 206Dr Ashraf ShaweeshDr Ashraf Shaweesh


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IntraIntra--uterine stagesuterine stages

PrePre--embryonic (proliferative period)embryonic (proliferative period) 00 2 weeks2 weeks

FertilizationFertilization

ImplantationImplantation

Bilaminar embryonic discBilaminar embryonic disc

EmbryonicEmbryonic 22 8 weeks8 weeks

Different types of tissues developDifferent types of tissues develop

Formation of organ systemsFormation of organ systems FetalFetal

8 weeks until birth8 weeks until birth

Increase in body wt & sizeIncrease in body wt & size


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PrePre--embryonic period (1st week)embryonic period (1st week)

FertilizationFertilization zygote, 0.1zygote, 0.1--0.2 mm0.2 mm

Cleavage (Mitotic) divisionsCleavage (Mitotic) divisions

2 cell (blastomere) stage2 cell (blastomere) stage

4 cell stage4 cell stage

1212--16 cell stage (morula, 0.116 cell stage (morula, 0.1--0.2mm)0.2mm)

BlastocystBlastocyst

100100--150 cells, 0.1150 cells, 0.1--0.2 mm0.2 mm

BlastocoelBlastocoel

Zona pellucidaZona pellucida

Inner cell massInner cell mass

embryo properembryo proper

Outer cell massOuter cell mass

Future trophoblastFuture trophoblast

AttachmentAttachment

ImplantationImplantation


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PrePre--embryonic period (2embryonic period (2ndnd week)week)

Bilaminar EmbryoBilaminar Embryo

Inner cell mass becomes 2 layeredInner cell mass becomes 2 layereddisc (7disc (7--12 days)12 days) Embryonic EpiblastEmbryonic Epiblast

Columnar cellsColumnar cells

Face the cytotrophoblastFace the cytotrophoblast

Future ectodermFuture ectoderm Embryonic hypoblastEmbryonic hypoblast

Flattened cellsFlattened cells

Face the blastocoelFace the blastocoel

Future endodermFuture endoderm

Amniotic cavityAmniotic cavity

Exocoelomic membraneExocoelomic membrane Continuous with endodermContinuous with endoderm

With endoderm enclose:With endoderm enclose:

Primitive yolk sac (exocoelomic cavity)Primitive yolk sac (exocoelomic cavity)

Still 0.1Still 0.1--0.2 mm0.2 mm


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Bilaminar embryoBilaminar embryo

ExtraExtra--embryonicembryonic

mesodermmesoderm

FromFrom

cytotrophoblastscytotrophoblasts

Secondary yolk sacSecondary yolk sac

Connecting stalksConnecting stalks

Placental circulationPlacental circulationestablishedestablished


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Embryonic period (3Embryonic period (3rdrd week)week) Prochordal (cephalic) plateProchordal (cephalic) plate

Slight thickening of endodermSlight thickening of endoderm

Indicates the future head endIndicates the future head end

Buccopharyngeal membraneBuccopharyngeal membranelaterlater

Caudal end (cloacalCaudal end (cloacalmembrane)membrane)

IntraIntra--embryonic mesodermembryonic mesoderm Appears from ectoderm at 17Appears from ectoderm at 17

daysdays

Rounding up toward caudalRounding up toward caudal

midlinemidline

Spreading between ectodermSpreading between ectodermand endodermand endoderm

Formation leavesFormation leaves

Primitive streakPrimitive streak

Primitive (Hensens) nodePrimitive (Hensens) node


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Trilaminar embryo (Gastrula)Trilaminar embryo (Gastrula)

Three germ layersThree germ layers EctodermEctoderm

MesodermMesoderm

EndodermEndoderm Primitive streak & nodePrimitive streak & node

Notochordal processNotochordal process BlindBlind--ended tubeended tube

From primitive nodeFrom primitive node

Up to the prochordal plateUp to the prochordal plate

Progenitor of the backbone andProgenitor of the backbone andthe vertebral columnthe vertebral column

Mesoderm separatesMesoderm separates

ectoderm & endoderm except inectoderm & endoderm except in Prochordal plateProchordal plate

NotochordNotochord

Cloacal membraneCloacal membrane


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Germ layersGerm layers

These cells are consideredThese cells are considered pluripotentpluripotent: each is capable of: each is capable of

producing descendants representing all of the hundreds ofproducing descendants representing all of the hundreds ofdifferentiated cell typesdifferentiated cell typesEctodermEctoderm MesodermMesoderm EndodermEndoderm

Skin and appendagesSkin and appendagesBone & MuscleBone & Muscle

Lingual tonsilsLingual tonsils

Oral and anal mucosaOral and anal mucosaConnective tissueConnective tissue Linings of lungsLinings of lungs

Linings of nose andLinings of nose and

sinusessinuses

All dental tissuesAll dental tissues

except enamelexcept enamelDigestive systemDigestive system

EnamelEnamelLymphatic tissue &Lymphatic tissue &

spleenspleen

Linings of excretoryLinings of excretory

systemsystem

Nervous systemNervous systemBlood cells, heart &Blood cells, heart &

lungslungs

Pituitary & mammaryPituitary & mammary

glandsglandsReproductive systemReproductive system

Lens of the eyeLens of the eye Excretory systemExcretory system


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Notochordal processNotochordal process

From the primitive knot,From the primitive knot,mesoblastic cells migratemesoblastic cells migrate

toward the prochordal platetoward the prochordal plate Acts as a template for theActs as a template for the

notochordnotochord

Cannot go through theCannot go through theprochordal plateprochordal plate

Some cells migrate aroundSome cells migrate aroundthe prochordal platethe prochordal plate(cardiogenic area)(cardiogenic area)

In prochordal plate, theIn prochordal plate, theembryonic endoderm andembryonic endoderm andectoderm layers are fusedectoderm layers are fused


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Further developmentFurther development

NotochordNotochord Fusion with endodermFusion with endoderm

Rounding up and separationRounding up and separationfrom endodermfrom endoderm

MesodermMesoderm Paraxial mesoderm (Somites)Paraxial mesoderm (Somites)

Pairs on each side ofPairs on each side ofnotochordnotochord

Cuboidal masses, mould theCuboidal masses, mould theectodermal surfaceectodermal surface

4242 45 pairs by the end of 545 pairs by the end of 5thth

weekweek Intermediate mesodermIntermediate mesoderm

Urinary systemUrinary system

Adrenal cortexAdrenal cortex

Much of reproductive systemMuch of reproductive system

Lateral plate mesodermLateral plate mesoderm


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Further developmentFurther development

Lateral plate mesodermLateral plate mesoderm More widespread thanMore widespread thansomitessomites

Spreads cephalic (ahead) toSpreads cephalic (ahead) toprochordal plateprochordal plate

Intraembryonic coelomIntraembryonic coelom Forms by coalescence ofForms by coalescence of

vacuoles within lateral platevacuoles within lateral platemesodermmesoderm

U shapedU shaped

Anterior partAnterior part Primitive pericardial cavityPrimitive pericardial cavity

Cephalic (ahead) to primitiveCephalic (ahead) to primitivepericardial cavity lies what willpericardial cavity lies what willbecomebecome septum transversumseptum transversumin which liver later developsin which liver later develops

Lateral part is primitiveLateral part is primitivepleural & peritoneal cavitiespleural & peritoneal cavities


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SomitesSomites

Differentiation of somitesDifferentiation of somites

DermatomeDermatome

Dermis of the skinDermis of the skin

Lamina propria of oral mucosaLamina propria of oral mucosa

MyotomeMyotome

Vertebral musculatureVertebral musculature

Intercostal musculatureIntercostal musculature

Some limb musculatureSome limb musculature

SclerotomeSclerotome

Vertebrae, ribs and sternumVertebrae, ribs and sternum

Head somitesHead somites Prootic somites (3 pairs)Prootic somites (3 pairs)

MyotomeMyotome -- eye muscleseye muscles

Metotic (occipital) somitesMetotic (occipital) somites

Myotome of 3Myotome of 3rdrd --66thth metotic somitesmetotic somites tonguetonguemusclesmuscles


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NeurulationNeurulation

Formation of CNSFormation of CNS Neural plateNeural plate: thickened mass forms in: thickened mass forms in

the overlying ectoderm. and becomesthe overlying ectoderm. and becomesknown as theknown as the

Neural grooveNeural groove

A crease or fold soon appears in thisA crease or fold soon appears in thisplateplate

Rapidly deepensRapidly deepens -- precursor of theprecursor of theembryos CNS, the first organs toembryos CNS, the first organs todevelopdevelop

Neural foldsNeural folds: arch over and fuse with: arch over and fuse witheach other at several points along theeach other at several points along thelength of the neural tubelength of the neural tube

Neural tube:Neural tube:

zippered closed as byzippered closed as bythe neural folds, concomitant with thethe neural folds, concomitant with the

buddingbudding somitessomites

Anterior & posterior neuroporesAnterior & posterior neuropores

The entire embryo is lengthening asThe entire embryo is lengthening asthis happensthis happens


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Neural crestNeural crest

Junction of neural plateJunction of neural platewith ectodermwith ectoderm

Unite then pinched off asUnite then pinched off as

neural tube separatesneural tube separatesfrom ectodermfrom ectoderm

Neural crest cellsNeural crest cellsmigrate withinmigrate within

mesodermmesoderm

So far embryo is 1.5So far embryo is 1.5--33

mmmm


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Neural crestNeural crest

Ectomesenchyme tissue in head regionEctomesenchyme tissue in head region Dermis of head regionDermis of head region

All dental tissue except enamelAll dental tissue except enamel

Branchial archesBranchial arches SkeletonSkeleton

Part of musculaturePart of musculature

Pigment cellsPigment cells MelanocytesMelanocytes

MeningesMeninges

Spinal & cranial nerve gangliaSpinal & cranial nerve ganglia

Sympathetic & parasympathetic systemsSympathetic & parasympathetic systems Adrenal medullaAdrenal medulla

Schwann cellsSchwann cells


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Folding of embryonic plateFolding of embryonic plate

Embryonic plate bulges upwards into amniotic cavityEmbryonic plate bulges upwards into amniotic cavity

Folding turns the plate into a portion of a spheroidFolding turns the plate into a portion of a spheroid

CausesCauses Most of growth happens in the upper surfaceMost of growth happens in the upper surface

Neural tube growth exceeds that of the rest of the embryonicNeural tube growth exceeds that of the rest of the embryonicplateplate

ConsequencesConsequences Buccopharyngeal & cloacal membranesBuccopharyngeal & cloacal membranes

Folded under cephalic & caudal ends, respectivelyFolded under cephalic & caudal ends, respectively

Their ventral surfaces become dorsalTheir ventral surfaces become dorsal

Part of the yolk sac becomes incorporated in the embryo asPart of the yolk sac becomes incorporated in the embryo asforegut, midgut and hindgutforegut, midgut and hindgut

Primitive pericardial cavity lies beneath the foregutPrimitive pericardial cavity lies beneath the foregut

The most cephalic lateral plate mesoderm (septum transversum)The most cephalic lateral plate mesoderm (septum transversum)lies caudal to the pericardial cavity in which liver will formlies caudal to the pericardial cavity in which liver will form


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FoldingFolding


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Development of epithelialDevelopment of epithelial

structuresstructures EpidermisEpidermis surface ectodermal cellssurface ectodermal cells

DermisDermis underlying mesoderm of somitesunderlying mesoderm of somites

Ectodermal cells thicken into 4 layers by 11Ectodermal cells thicken into 4 layers by 11--1212

weeksweeks Basal layerBasal layer superficial layer of epitheliumsuperficial layer of epithelium

Melanocytes invade epidermisMelanocytes invade epidermis

Structures developing from a combination ofStructures developing from a combination of

dermal and epidermal tissuesdermal and epidermal tissues Mammary, sebaceous, salivary glandsMammary, sebaceous, salivary glands

Teeth, nails, hairTeeth, nails, hair


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Development of connective tissueDevelopment of connective tissue

CN develop from somites as migrating fromCN develop from somites as migrating fromeither side of neural tubeeither side of neural tube

SomiteSomite SclerotomeSclerotome

Medial portionMedial portion mesenchymal cellsmesenchymal cells Osteoblasts, chondroblasts, fibroblastsOsteoblasts, chondroblasts, fibroblasts

MyotomeMyotome Skeletal musclesSkeletal muscles

Smooth muscles & mesenteriesSmooth muscles & mesenteries

DermatomeDermatome DermisDermis

Visceral mesodermVisceral mesoderm lamina propria of GITlamina propria of GIT


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Development of cartilage & boneDevelopment of cartilage & bone

Cartilage is the initial skeletal componentCartilage is the initial skeletal component Functions in supporting the soft embryoFunctions in supporting the soft embryo

Maintains its 3Maintains its 3--D configurationD configuration

Cartilage migrate to surround notochord froming spinalCartilage migrate to surround notochord froming spinal

columncolumn Cartilage growthCartilage growth

AppositionalAppositional new layers on the surfacenew layers on the surface

InterstitialInterstitial proliferation & expansion of cellsproliferation & expansion of cells

HyalineHyaline elasticelastic fibrous cartilagefibrous cartilage

Bone formationBone formation IntramembranousIntramembranous

EndochondralEndochondral E.g. long boneE.g. long bone


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EndoEndo--chondral bone Formationchondral bone Formation

Deposition of bone matrix on a preDeposition of bone matrix on a pre--existing cartilage matrixexisting cartilage matrix

Mesenchymal tissueMesenchymal tissue CartilageCartilage BoneBone

The primary transitional

cartilage is a hyalinecartilage whose shaperesembles a smallversion of the bone to beformed


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IntraIntra--membranous Bone Formationmembranous Bone FormationDirect mineralisation of matrix secreted by osteoblastsDirect mineralisation of matrix secreted by osteoblasts

Mesenchymal tissueMesenchymal tissue

(Condensed)(Condensed)

BoneBone


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Epiphyseal growthEpiphyseal growth

EndoEndo--chondral ossification in a long bonechondral ossification in a long bone

IntraIntra--membranous bone collar formsmembranous bone collar formswithin the perichondrium of the cartilagewithin the perichondrium of the cartilagemodelmodel

Cartilage degeneration (by hypertrophy)Cartilage degeneration (by hypertrophy)and calcification starting at the centraland calcification starting at the centralportion of diaphysisportion of diaphysis

Blood vessels penetration bringingBlood vessels penetration bringing

osteoblastsosteoblasts Continuous primary bone deposited overContinuous primary bone deposited over

calcified cartilagecalcified cartilage

Calicified cartilage resorbed by giantCalicified cartilage resorbed by giantmutinucleated cellsmutinucleated cells

Primary ossification centerPrimary ossification center

Secondary ossification centers at theSecondary ossification centers at the

epiphyses in a similar patternepiphyses in a similar pattern In secondary ossification centersIn secondary ossification centers

cartilage remains in 2 regionscartilage remains in 2 regions TheThe articular cartilagearticular cartilage

Protection and mobilityProtection and mobility

TheThe epiphyseal plateepiphyseal plate Growth until closure at 20 ysGrowth until closure at 20 ys


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Development of muscleDevelopment of muscle

By 10By 10thth week, myoblasts migrate fromweek, myoblasts migrate from

myotomesmyotomes

MuscleMuscle SkeletalSkeletal

SmoothSmooth

CardiacCardiac


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Development of CVSDevelopment of CVS

Originate from angioblastsOriginate from angioblasts

Angioblasts are from angiogenic clusters in the walls ofAngioblasts are from angiogenic clusters in the walls ofthe yolk sacthe yolk sac

Angiogenic clustersAngiogenic clusters Outer cellsOuter cells elongating tubeselongating tubes

Inner cellsInner cells blood cellsblood cells

Nutrition of embryoNutrition of embryo At firstAt first -- vatelline vascular systemvatelline vascular system

ThenThen umbilical vascular systemumbilical vascular system Hearts beats by 4Hearts beats by 4thth weekweek

Starts as a tubeStarts as a tube internal partitioninginternal partitioning

An opening between atria remain until birthAn opening between atria remain until birth

oral histo ,, first lec

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