PRE-NATAL GROWTH & PRE-NATAL GROWTH & DEVELOPMENT.DEVELOPMENT.

Dr. M. Sadegh BirjandiDr. M. Sadegh Birjandi

ContentsContents

IntroductionIntroduction DefinitionDefinition Pre-natal Growth & Pre-natal Growth &

DevelopmntDevelopmnt

Period of OvumPeriod of Ovum

Period of EmbryoPeriod of Embryo

Period of Fetus Period of Fetus Pharyngeal arches Pharyngeal arches Pharyngeal pouchesPharyngeal pouches

Development of skullDevelopment of skull Development of faceDevelopment of face Development of Development of

maxillamaxilla Development of Development of

mandiblemandible Development of Development of

tonguetongue ConclusionConclusion ReferencesReferences

INTRODUCTIONINTRODUCTION

Every individuals spends first nine months Every individuals spends first nine months of its life within the uterus of its mother.of its life within the uterus of its mother.

During this period it develops from a small During this period it develops from a small one celled structure to an organism having one celled structure to an organism having billions of cells.billions of cells.

Numerous tissues and organs are formed Numerous tissues and organs are formed and come to function in perfect harmony. and come to function in perfect harmony.

DEFINITIONDEFINITION

GrowthGrowth Growth may be defined as the normal Growth may be defined as the normal

changes in the amount of living substance. changes in the amount of living substance. (MOYERS)(MOYERS)

DevelopmentDevelopment Development refers to all naturally occuring Development refers to all naturally occuring

unidirectional changes in the life of an unidirectional changes in the life of an individual from its existance as a single cell individual from its existance as a single cell to its elaboration as a multifunctional unit to its elaboration as a multifunctional unit terminating in deathterminating in death

(MOYERS)(MOYERS)

Development = growth + differentiation + translocationDevelopment = growth + differentiation + translocation

DIFFERENTIATIONDIFFERENTIATION Change from general cells or tissue to a Change from general cells or tissue to a

more specialized kinds during development more specialized kinds during development

TRANSLOCATIONTRANSLOCATION Is change in positionIs change in position

EMBRYOLOGYEMBRYOLOGY It is the study of the formation and It is the study of the formation and

development of embryo (fetus) from the development of embryo (fetus) from the moment of its inception up to the time when moment of its inception up to the time when it is born as an infant.it is born as an infant.

Growth & development of an individual can be divided in to

Pre-natalPost-natal

Period of Ovum1-14th day

Period of embryo14th – 56th day

Period of Fetus56th – 270th day

Pre-Natal Growth & DevelopmentPre-Natal Growth & Development

It is a dynamic phase in the human It is a dynamic phase in the human development.development.

During this phase Height increases by During this phase Height increases by almost 5000 times as compared to only 3 almost 5000 times as compared to only 3 fold increase during post-natal period.fold increase during post-natal period.

Weight increases by 6.5 billion fold from Weight increases by 6.5 billion fold from Ovum to Birth & Post-natally there is only Ovum to Birth & Post-natally there is only 20 fold increase from birth to adulthood.20 fold increase from birth to adulthood.

PERIOD OF OVUM (1PERIOD OF OVUM (1stst 2 2 Weeks)Weeks)

FERTILIZATIONFERTILIZATIONFertilization is the process by which male and Fertilization is the process by which male and female gamates fuse occurs in the ampullary female gamates fuse occurs in the ampullary region of uterine tube. region of uterine tube. As soon as the spermatozoan has entered As soon as the spermatozoan has entered into the oocyte, the egg responds in three into the oocyte, the egg responds in three different ways.different ways.

Cortical and zona reactions: As a result of release Cortical and zona reactions: As a result of release of cortical occyte granules containing lysosomal of cortical occyte granules containing lysosomal enzymes.enzymes.

Oocyte membrane becomes impermeable to other Oocyte membrane becomes impermeable to other spermatozoaspermatozoaZono pellucida alters its structure and composition to Zono pellucida alters its structure and composition to prevent sperm bindingprevent sperm binding

Resumption of second meotic divisionResumption of second meotic divisionMetabolic activation of egg.Metabolic activation of egg.

The main results of fertilization areThe main results of fertilization are Restoration of diploid number of Restoration of diploid number of

chromosomeschromosomes Determination of sex of new individualDetermination of sex of new individual Initiation of cleavageInitiation of cleavage It fosters genetic variationIt fosters genetic variation Division of the Ovum in to several cells for Division of the Ovum in to several cells for

e.g., 2 celled stage, 3 celled stage, 4 e.g., 2 celled stage, 3 celled stage, 4 celled stage, 8 celled stage, morula (16 celled stage, 8 celled stage, morula (16 celled stage)celled stage)

Formation of morulaFormation of morula

MorulaMorula

Embryo by process of cleavage Embryo by process of cleavage reaches 16 celled stagereaches 16 celled stage

Looks like a mulberry that’s why Looks like a mulberry that’s why called socalled so

Zonapellucida still presentsZonapellucida still presents

Contains outer rim of cells called Contains outer rim of cells called trophoblasttrophoblast

Inner cell mass called embryoblast Inner cell mass called embryoblast

Function of ZonapellucidaFunction of Zonapellucida

Trophoblast has the property to stick to Trophoblast has the property to stick to any epithelium and eat up the cellsany epithelium and eat up the cells

Zonapellucida helps in preventing Zonapellucida helps in preventing implantation of embryo in abnormal implantation of embryo in abnormal locationlocation

Zonapellucida disappears as soon as the Zonapellucida disappears as soon as the morula reaches the uterine lumenmorula reaches the uterine lumen

Thus embryo gets implanted in lateral wall Thus embryo gets implanted in lateral wall of uterusof uterus

Formation of BlastocystFormation of Blastocyst

Some fluid passes into morula from uterine wall Some fluid passes into morula from uterine wall seperating the inner cell mass (embryoblast) seperating the inner cell mass (embryoblast) and outer cell mass (trophoblast)and outer cell mass (trophoblast)As the fluid quantity increases it acquires the As the fluid quantity increases it acquires the shape of cyst shape of cyst Trophoblast cells become flattened and Trophoblast cells become flattened and embryoblast cells get attached to one side embryoblast cells get attached to one side Now it is called blastocyst and cavity is called Now it is called blastocyst and cavity is called blastocoeleblastocoeleThe site of attachment of inner cell mass is The site of attachment of inner cell mass is called embryonic or animal pole and opposite called embryonic or animal pole and opposite site abembryonic polesite abembryonic pole

Formation of germ layersFormation of germ layers

Some cells of inner cell mass differentiate Some cells of inner cell mass differentiate into flattened cells that come to line its into flattened cells that come to line its free surface, these constitute Endodermfree surface, these constitute Endoderm

Endoderm is the first of the three germ Endoderm is the first of the three germ layers to be formedlayers to be formed

Remaining cells of inner cell mass become Remaining cells of inner cell mass become columnar. These cells form the second columnar. These cells form the second germ layer the ectoderm. The embryo is germ layer the ectoderm. The embryo is now in the form of disc having 2 layersnow in the form of disc having 2 layers

A space appears b/w the ectoderm (below) & A space appears b/w the ectoderm (below) & trophoblast (above) called amniotic cavity which trophoblast (above) called amniotic cavity which

is filled by amniotic fluid or liquor amniis filled by amniotic fluid or liquor amni

Primary yolk sacPrimary yolk sac

Extra embryonic mesoderm (primary Extra embryonic mesoderm (primary mesoderm)mesoderm)

Extra embryonic coelom (Chorinic cavity)Extra embryonic coelom (Chorinic cavity)

Parietal/Somatopluric extra emryonic Parietal/Somatopluric extra emryonic mesoderm (Chorionic plate)mesoderm (Chorionic plate)

Visceral/splanchnopleuric extra-emryonic Visceral/splanchnopleuric extra-emryonic mesodermmesoderm

Connecting stalkConnecting stalk

HUMAN BLASTOCYST OF 12 DAYS

Formation of chorion & AmnionFormation of chorion & Amnion

Secondary yolk sacSecondary yolk sac

Prochordal plate: Divides embryo into right Prochordal plate: Divides embryo into right & left& left

Primitive streakPrimitive streak

Intraembryonic mesoderm (Gastrulation)Intraembryonic mesoderm (Gastrulation)

Cloacal membraneCloacal membrane

Alternative view of formation of germ Alternative view of formation of germ layerslayers

GERM DISC AT THE END OF SECOND WEEK

GERM DISC AT THE 16 TH DAY

Time table of events in period of Time table of events in period of ovumovum

Fertilization to formation of bilaminar disc Fertilization to formation of bilaminar disc is called pre-organogenesis period( 1 – 14 is called pre-organogenesis period( 1 – 14 days)days)2 days after fertilization the embryo is in 2 2 days after fertilization the embryo is in 2 cell stage.cell stage.3 days after fertilization the embryo has 3 days after fertilization the embryo has become morulabecome morulaOn the 4On the 4thth day, the blastocyst has formed. day, the blastocyst has formed.By the 8By the 8thth day, the bilaminar disc has day, the bilaminar disc has been established. been established.

Around the 14Around the 14thth day, the prochordal day, the prochordal plate and primitive streak are seen.plate and primitive streak are seen.

On the 16On the 16thth day, we see the day, we see the formation of the intra-embryonic formation of the intra-embryonic mesoderm, i.e., the embryonic disc is mesoderm, i.e., the embryonic disc is now 3 layered.now 3 layered.

Period of EmbryoPeriod of Embryo

Formation of notochordFormation of notochord

It’s a midline structureIt’s a midline structureDevelops from cranial end of primitive streak to Develops from cranial end of primitive streak to caudal end of prochordal platecaudal end of prochordal platePrimitive Knot/primitive node/Henson’s nodePrimitive Knot/primitive node/Henson’s nodeBlastoporeBlastoporeNotochordal process/head processNotochordal process/head processDoes not give rise to vertebral column but lies in Does not give rise to vertebral column but lies in its future positionits future positionMost of it disappears but parts of it persist in the Most of it disappears but parts of it persist in the region of each intervertibral disc as the region of each intervertibral disc as the nucleus nucleus pulposuspulposus

Process of formation of notochordProcess of formation of notochord

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Neural tubeNeural tube

Formed from ectoderm over Formed from ectoderm over notochordnotochord

Extends from prochordal plate to Extends from prochordal plate to primitive knotprimitive knot

Divisible into cranial enlarged part Divisible into cranial enlarged part which forms brain and caudal tubular which forms brain and caudal tubular part which forms spinal cordpart which forms spinal cord

The process of formation is called The process of formation is called neurulationneurulation

Sub-divisions of intra embryonic Sub-divisions of intra embryonic mesodermmesoderm

Paraxial mesodermParaxial mesoderm

Lateral plate mesodermLateral plate mesoderm

Intermediate mesodermIntermediate mesoderm

Formation of the intra-embryonic coelomFormation of the intra-embryonic coelom

Forms by appearance of cavities in lateral plate Forms by appearance of cavities in lateral plate mesodermmesodermWith the formation of intra-embryonic coelom With the formation of intra-embryonic coelom lateral plate mesoderm splits in tolateral plate mesoderm splits in to

1.1. Somatopleuric/parietal, intra embryonic Somatopleuric/parietal, intra embryonic mesoderm (contact with ectoderm) mesoderm (contact with ectoderm)

2.2. Splanchnopleuric/visceral intra Splanchnopleuric/visceral intra embryonic embryonic mesoderm (contact with endoderm) mesoderm (contact with endoderm)Intra embryonic coelom gives rise to pericardial, Intra embryonic coelom gives rise to pericardial, pleural & peritoneal cavitiespleural & peritoneal cavitiesHeart forms from splanchanopleuric mesoderm Heart forms from splanchanopleuric mesoderm forming floor of this part of the coelomforming floor of this part of the coelom

The Neural crestThe Neural crestForms from neuro ectodermForms from neuro ectodermMigrate & differentiate extensively within the Migrate & differentiate extensively within the developing embryodeveloping embryoSpinal & cranial sensory ganglia, Sympathetic Spinal & cranial sensory ganglia, Sympathetic neurons, Schwann cells, pigment cells & neurons, Schwann cells, pigment cells & meningesmeningesMost of the connective tissue of the head is Most of the connective tissue of the head is formedformedMigration is essential for development of teeth & Migration is essential for development of teeth & facefaceAll the tissues of teeth (except enamel) & its All the tissues of teeth (except enamel) & its supporting apparatus are derived directly from supporting apparatus are derived directly from these cellsthese cellsTreacher collins syndrome Treacher collins syndrome

FETAL PERIODFETAL PERIOD It is characterized by maturation of tissues and It is characterized by maturation of tissues and

organs and rapid growth of the body.organs and rapid growth of the body.

The length of the featus usually indicated as crown The length of the featus usually indicated as crown Rump length (Sitting height) or crown Heal length Rump length (Sitting height) or crown Heal length (CHL) (CHL) measurement from vertex of the skull to measurement from vertex of the skull to the heel (Standing length).the heel (Standing length).

Growth in length is particularly striking, during 3Growth in length is particularly striking, during 3rdrd, , 44th, th, 55th th months, while increasing weight is most months, while increasing weight is most striking during last 2 months of gestation.striking during last 2 months of gestation.

During 3During 3rdrd month face become more human looking month face become more human looking

Primary ossification centres are present in the long bones Primary ossification centres are present in the long bones and skull by 12and skull by 12thth week. week.

During 5During 5thth month, movements of fetus are clearly month, movements of fetus are clearly recognized.recognized.

During 6During 6thth month, skin of the fetus is reddish and has month, skin of the fetus is reddish and has wrinkled appearance due to lack of underlying connective wrinkled appearance due to lack of underlying connective tissue. tissue.

During last two months, the featus obtains well rounded During last two months, the featus obtains well rounded contours as a result of deposition of subcutaneous fat.contours as a result of deposition of subcutaneous fat.

At the time of birth, weight of the featus is 3000-3400gm.At the time of birth, weight of the featus is 3000-3400gm.

CRL about 36cmCRL about 36cm

CHL about 50cmCHL about 50cm

Pharyngeal (Branchial) ArchesPharyngeal (Branchial) ArchesFormed by proliferating Formed by proliferating lateral plate mesodermlateral plate mesoderm sandwiched b/w ectoderm & endoderm bilaterallysandwiched b/w ectoderm & endoderm bilaterallyLater reinforced by neural crest cellsLater reinforced by neural crest cells6 cylindrical thickenings thus form, but 56 cylindrical thickenings thus form, but 5thth disappears disappears as soon as it is formedas soon as it is formedSeparated externally by small clefts called Separated externally by small clefts called branchial branchial grooves (Ectodermal clefts)grooves (Ectodermal clefts)On the inner aspect of pharyngeal wall are On the inner aspect of pharyngeal wall are corresponding small depressions called corresponding small depressions called pharyngeal pharyngeal pouchespouchesIn aquatic vertebrates both branchial grooves & In aquatic vertebrates both branchial grooves & pharyngeal pouches fuse to form gill slitspharyngeal pouches fuse to form gill slits

FormationFormation

Nerves & muscles of the archesNerves & muscles of the arches

ArchArch Nerve of the Nerve of the archarch

Muscles of the archMuscles of the arch

FirstFirst

(Mandibul(Mandibular arch)ar arch)

MandibularMandibular

(Trigeminal)(Trigeminal)

V th nerveV th nerve

Medial & lateral pterygoids, Masseter, Medial & lateral pterygoids, Masseter, Temporalis, Mylohyoid, ant belly of Temporalis, Mylohyoid, ant belly of digastric,tensor tympani, tensor palatidigastric,tensor tympani, tensor palati

SecondSecond

(Hyoid (Hyoid arch)arch)

FacialFacial

VII th nerveVII th nerveMuscles of face, Occipito-frontalis, Muscles of face, Occipito-frontalis, platysma, Stylohyoid, Posterior belly of platysma, Stylohyoid, Posterior belly of digastric, Stapedius, Aurticular digastric, Stapedius, Aurticular muscelsmuscels

ThirdThird GlossopharyngeaGlossopharyngeal,l,

IX th nerveIX th nerve

StylopharyngeusStylopharyngeus

FourthFourth Superior LarngealSuperior Larngeal Muscles of Pharynx & larynxMuscles of Pharynx & larynx

SixthSixth Recurrent Recurrent laryngeallaryngeal

Muscles of Pharynx & larynxMuscles of Pharynx & larynx

Derivatives of arch cartilagesDerivatives of arch cartilages

Arch Arch CartilageCartilage

DerivativesDerivatives

11stst arch arch (Meckel’s (Meckel’s cartilage)cartilage)

Mallus, Incus, Anterior ligament for mallus, Mallus, Incus, Anterior ligament for mallus, sphenomandibular ligament & lays down the sphenomandibular ligament & lays down the meshwork for formation of mandible & some meshwork for formation of mandible & some part of it may be included in mandiblepart of it may be included in mandible

22ndnd arch arch (Reichert’s (Reichert’s cartilage)cartilage)

Stapes, Styloid process, stylohyoid ligament, Stapes, Styloid process, stylohyoid ligament, smaller (lesser) cornu of hyoid bone, superior smaller (lesser) cornu of hyoid bone, superior part of body of hyoid bonepart of body of hyoid bone

33rdrd arch arch Greater cornu of hyoid bone, lower part of the Greater cornu of hyoid bone, lower part of the body of hyoid bonebody of hyoid bone

44thth & 6 & 6thth arch arch Cartilages of larynx, controversial, may have Cartilages of larynx, controversial, may have contribution from 5contribution from 5thth arch arch

Fate of grooves & pouchesFate of grooves & pouches

First groove & pouch form First groove & pouch form external auditory meatus, tympanic external auditory meatus, tympanic membrane, tympanic antrum, mastoid antrum & membrane, tympanic antrum, mastoid antrum & pharyngotympanic/eustachian tubepharyngotympanic/eustachian tube

22ndnd arch cleft grows much faster than the succeeding arches & arch cleft grows much faster than the succeeding arches & comes to over hang them. The space b/w the overhanging 2comes to over hang them. The space b/w the overhanging 2ndnd arch arch & 3& 3rdrd, 4, 4thth & 6 & 6thth is called is called cervical sinuscervical sinus

Cavity of the cervical sinus is normally obliterated but part of it Cavity of the cervical sinus is normally obliterated but part of it may persist and give rise to swelling in the neck along the anterior may persist and give rise to swelling in the neck along the anterior border of the sternocleidomastoid these are called border of the sternocleidomastoid these are called branchial cystsbranchial cysts & most commonly they are located below the angle of mandible& most commonly they are located below the angle of mandible

If the cyst opens on to the surface it is called If the cyst opens on to the surface it is called branchial sinusbranchial sinus

Rarely cervical sinus may open in to the lumen of the pharynx in Rarely cervical sinus may open in to the lumen of the pharynx in the region of tonsilthe region of tonsil

Endodermal pouchesEndodermal pouches11stst pouch: pouch:

Its ventral part is obliterated by the formation of tongueIts ventral part is obliterated by the formation of tongueDorsal part along with the dorsal part of 2Dorsal part along with the dorsal part of 2ndnd pouch form pouch form tubotympanic recess, auditory (pharyngotympanic) tube, middle tubotympanic recess, auditory (pharyngotympanic) tube, middle ear cavity including tympanic antrumear cavity including tympanic antrum

22ndnd pouch: pouch:Epithelium of ventral part gives palatine tonsilEpithelium of ventral part gives palatine tonsilDorsal part takes part in the formation of tubotympanic recessDorsal part takes part in the formation of tubotympanic recess

33rdrd pouch: pouch:Inferior parathyroid glandsInferior parathyroid glandsThymusThymus

44thth pouch: pouch:Superior parathyroid glandsSuperior parathyroid glandsContributes to thyroid glandContributes to thyroid gland

55thth pouch: pouch:Forms ultimobranchial body in some speciesForms ultimobranchial body in some speciesIn humans believed to be incorporated in 4In humans believed to be incorporated in 4thth pouch giving rise to pouch giving rise to caudal pharyngeal complex, which gives rise to superior caudal pharyngeal complex, which gives rise to superior parathyroid glands and parafollicular cells of thyroidparathyroid glands and parafollicular cells of thyroid

DEVELOPMENT OF SKULLDEVELOPMENT OF SKULL

• Neurocranium Neurocranium which forms protective which forms protective case around the braincase around the brain

• Viscerocranium Viscerocranium forms the skeleton of forms the skeleton of the facethe face

Approximately 110 ossification centres Approximately 110 ossification centres appear in embryonic human skull gives rise appear in embryonic human skull gives rise to 45 separate bones.to 45 separate bones.

Neurocranium:Neurocranium:Divided into two portions.Divided into two portions. Membranous part consisting of flat bones Membranous part consisting of flat bones

which surrounded the brain as a vaultwhich surrounded the brain as a vault Cartilagenous part / chondrocranium which Cartilagenous part / chondrocranium which

form the bones of the base of the skullform the bones of the base of the skull

Membranous neurocraniumMembranous neurocranium Roof and most of the sides develops from Roof and most of the sides develops from

neural crest cells, with only occipital region neural crest cells, with only occipital region and posterior part of the otic capsule arising and posterior part of the otic capsule arising from para-axial mesoderm. from para-axial mesoderm.

Mesenchyme from neural crest cells and Mesenchyme from neural crest cells and para-axial mesoderm invests the brain and para-axial mesoderm invests the brain and undergoes membraneous ossification. undergoes membraneous ossification.

Membraneous bone are formed that are Membraneous bone are formed that are characterized by the presence of needle characterized by the presence of needle like bone spicules.like bone spicules.

These spicules radiate to form primary These spicules radiate to form primary ossification centres towards the periphery.ossification centres towards the periphery.

Further growth during fetal postnatal life, Further growth during fetal postnatal life, membraneous bones enlarge by membraneous bones enlarge by apposition of new layers, on outer surface apposition of new layers, on outer surface and simultaenous osteoclastic resorption and simultaenous osteoclastic resorption from the inside.from the inside.

ChondrocraniumChondrocranium Chondrocranium initially consists of number Chondrocranium initially consists of number

of separate cartilages.of separate cartilages. Pituitary in the sella turcia derived from Pituitary in the sella turcia derived from

neural crest cells and from prechondral neural crest cells and from prechondral chondrocranium. chondrocranium.

The base of the occipital bone is formed by The base of the occipital bone is formed by parachondrial cartilage and bodies of three parachondrial cartilage and bodies of three occipital sclerotome. occipital sclerotome.

Hypophyseal cartilage and trabeculae carnii Hypophyseal cartilage and trabeculae carnii fuse to form the body of the sphenoid and fuse to form the body of the sphenoid and ehtmoid respectively. ehtmoid respectively.

33rdrd component, the periotic capsule gives component, the periotic capsule gives rise to the petrous and mastoid parts of rise to the petrous and mastoid parts of temporal bone. temporal bone.

Viscerocranium (Facial skeleton)Viscerocranium (Facial skeleton)

Formed from first two pharyngeal archesFormed from first two pharyngeal arches 11stst arch gives rise to two portions arch gives rise to two portions

• DorsalDorsal• VentralVentral• Dorsal portion: Maxillary process Dorsal portion: Maxillary process which which

gives rise to maxilla, the zygomatic bone gives rise to maxilla, the zygomatic bone and part of temporal bone. and part of temporal bone.

• Ventral portion: Mandibular process and contains Ventral portion: Mandibular process and contains Meckle’s cartilage.Meckle’s cartilage.

Mesenchyma around the Meckle’s cartilage Mesenchyma around the Meckle’s cartilage disappears except in sphenomandibular disappears except in sphenomandibular ligament.ligament.

Formation of faceFormation of face

Maxillary prominences can be Maxillary prominences can be distinguished lateral to the distinguished lateral to the stomodeum.stomodeum.

Mandibular prominences can be Mandibular prominences can be distinguished caudal to this distinguished caudal to this structure. structure.

The frontonasal prominence formed by The frontonasal prominence formed by proliferation of mesenchyme ventral to proliferation of mesenchyme ventral to brain vescicles constitute upper border of brain vescicles constitute upper border of the stomodeum.the stomodeum.

STRUCTURES CONTRIBUTING STRUCTURES CONTRIBUTING TO FORMATION OF FACETO FORMATION OF FACE

PROMINENCEPROMINENCE Structures formedStructures formed

FrontonasalFrontonasal

MaxillaryMaxillary

Medial nasalMedial nasal

Lateral nasalLateral nasal

MandibularMandibular

Forehead,bridge of Forehead,bridge of nose,medial and lateral nose,medial and lateral nasal prominence.nasal prominence.

Cheeks,lateral portion of Cheeks,lateral portion of upper lipupper lip

Philtrum of upper Philtrum of upper lip,crest and tip of noselip,crest and tip of nose

Alae of noseAlae of nose

Lower lipLower lip

Formation of palateFormation of palate

Primary palate (pre maxilla) develops Primary palate (pre maxilla) develops from frontonasal & median nasal from frontonasal & median nasal processprocess

Common oronasal cavity is bounded Common oronasal cavity is bounded by primary palate & occupied mainly by primary palate & occupied mainly by developing tongueby developing tongue

Palate proper develops from primary Palate proper develops from primary & secondary components& secondary components

Secondary palate:Secondary palate:Formation starts b/w 7 & 8 weeks & Formation starts b/w 7 & 8 weeks & completes by 3completes by 3rdrd month month

Only after its formation there is Only after its formation there is distinction b/w oral & nasal cavitiesdistinction b/w oral & nasal cavities

3 outgrowths appear in oral cavity, the 3 outgrowths appear in oral cavity, the nasal septum grows downward in the nasal septum grows downward in the midline from frontonasal process & 2 midline from frontonasal process & 2 palatine shelves from each side, extend palatine shelves from each side, extend from maxillary process towards midlinefrom maxillary process towards midline

The shelves are 1The shelves are 1stst directed directed downward on each side of the tonguedownward on each side of the tongue

After 7 weeks of development the After 7 weeks of development the tongue is withdrawn from b/w the tongue is withdrawn from b/w the shelves, which now elevate & fuse shelves, which now elevate & fuse with each other above the tongue & with each other above the tongue & with the primary palatewith the primary palate

The nasal septum & 2 shelves converge & fuse The nasal septum & 2 shelves converge & fuse along the midlinealong the midline

The closure of the secondary palate involves an The closure of the secondary palate involves an intrinsic force in palatine shelves the nature of intrinsic force in palatine shelves the nature of which has not been determined yet. The high which has not been determined yet. The high concentration of glycosaminoglycans which concentration of glycosaminoglycans which attract water & make the shelves turgid has been attract water & make the shelves turgid has been suggested as has the presence of contractile suggested as has the presence of contractile fibroblasts in palatine shelves, another factor in fibroblasts in palatine shelves, another factor in the closure of secondary palate is the the closure of secondary palate is the displacement of tongue from b/w the palatine displacement of tongue from b/w the palatine shelves by the growth pattern of the headshelves by the growth pattern of the head

Fusion:Fusion:

For the fusion of the shelves to occur elimination of the For the fusion of the shelves to occur elimination of the epithelial covering is necessaryepithelial covering is necessary

DNA synthesis ceases some 24-36 hrs before the DNA synthesis ceases some 24-36 hrs before the epithelial contactepithelial contact

Surface epithelial cells are sloughed off leading to the Surface epithelial cells are sloughed off leading to the exposure of basal epithelial cellsexposure of basal epithelial cells

These cells are carbohydrate rich that permits ready These cells are carbohydrate rich that permits ready adhesion & formation of junctions to achieve fusion of adhesion & formation of junctions to achieve fusion of process leading to formation of midline seamprocess leading to formation of midline seam

To achieve ectomesenchymal continuity this seam must To achieve ectomesenchymal continuity this seam must be removed this is achieved by growth of palatal be removed this is achieved by growth of palatal shelves with which it fails to keep pace with, it is shelves with which it fails to keep pace with, it is reduced to islands, later looses basal lamina & they reduced to islands, later looses basal lamina & they transform into fibroblaststransform into fibroblasts

Development of tongueDevelopment of tongueStarts to develop at about 4 weeks IUStarts to develop at about 4 weeks IUTuberculum impar in center & 2 lateral lingual Tuberculum impar in center & 2 lateral lingual swellings are derive in the floor of the swellings are derive in the floor of the pirimitive pharynx from proliferation of first pirimitive pharynx from proliferation of first branchial arch mesenchyme unite to form branchial arch mesenchyme unite to form mucous membrane of anterior mucous membrane of anterior 22//33 of tongue of tongueMucosa on root (posterior Mucosa on root (posterior 11//33) of the tongue is ) of the tongue is formed by formed by hypobranchial eminencehypobranchial eminence which is which is derived from 3derived from 3rdrd arch which overgrows second arch which overgrows second archarchMucosa on posterior most part of the tongue Mucosa on posterior most part of the tongue (epiglottis) is derived from 4(epiglottis) is derived from 4thth arch arch The muscles of the tongue arise from occipital The muscles of the tongue arise from occipital myotomes which have nerve supply from myotomes which have nerve supply from hypoglossal nerve (XII cranial nerve)hypoglossal nerve (XII cranial nerve)

Nerve Supply of tongueNerve Supply of tongueSensory:Sensory:

Anterior Anterior 22//33 Chorda tympani (through Chorda tympani (through lingual branch of mandibular nerve)lingual branch of mandibular nerve)( nerve of the first arch)( nerve of the first arch)

Posterior Posterior 11//3 3 glossopharyngeal nerve glossopharyngeal nerve (from nerve of the 3(from nerve of the 3rd rd arch). arch). Posterior superior laryngeal (branch Posterior superior laryngeal (branch of vagus)of vagus)

Motor:Motor:Hypoglossal nerveHypoglossal nerve

Anomalies of TongueAnomalies of TongueMicroglossia,macroglossia, aglossiaMicroglossia,macroglossia, aglossiaBifid tongue (non fusion of lingual swellings)Bifid tongue (non fusion of lingual swellings)Ankyloglossia/tongue tie, Ankyloglossia Ankyloglossia/tongue tie, Ankyloglossia superiorsuperiorMedian rhomboid glossitis (persistance of Median rhomboid glossitis (persistance of tuberculum impar in front of foramen tuberculum impar in front of foramen caecum)caecum)Lingual thyroid (faulty migration of normal Lingual thyroid (faulty migration of normal thyroid gland (sub-mucosal, intra-muscular)thyroid gland (sub-mucosal, intra-muscular)Remnants of thyroglossal duct may form Remnants of thyroglossal duct may form cysts at the base of tonguecysts at the base of tongueFissured/scrotal tongue Fissured/scrotal tongue

Development of mandibleDevelopment of mandibleDevelops from the mandibular process of 1Develops from the mandibular process of 1stst branchial archbranchial archThe cartilage of the 1The cartilage of the 1stst arch (Meckle’s arch (Meckle’s cartilage) forms lower jaw in the primitive cartilage) forms lower jaw in the primitive vertebratesvertebratesIn human beings Meckle’s cartilage has In human beings Meckle’s cartilage has close positional relationship to the close positional relationship to the developing mandible but makes no developing mandible but makes no contribution to itcontribution to itThe mandibular nerve has close relationship The mandibular nerve has close relationship to the Meckel’s cartilage, beginning to the Meckel’s cartilage, beginning 22//33 of of the way along the length of cartilage At this the way along the length of cartilage At this point mandibular nerve divides in to lingual point mandibular nerve divides in to lingual and inferior alveolar branchesand inferior alveolar branches

These nerves run in medial & lateral to These nerves run in medial & lateral to the meckel’s cartilagethe meckel’s cartilage

Inferior alveolar nerve further divides Inferior alveolar nerve further divides into incisive & mental branchesinto incisive & mental branches

On the lateral aspect of Meckel’s On the lateral aspect of Meckel’s cartilage, during the 6cartilage, during the 6thth week of the week of the embryonic development a condensation embryonic development a condensation of mesenchyme occurs in the angle of mesenchyme occurs in the angle formed by the division of inferior formed by the division of inferior alveolar nerve & its incisive & mental alveolar nerve & its incisive & mental branches.branches.

At 7 weeks intramembranous ossification At 7 weeks intramembranous ossification begins in its condensation forming the 1begins in its condensation forming the 1stst bone of the mandiblebone of the mandible

Bone formation spreads anteriorly Bone formation spreads anteriorly towards midline & posteriorly towards the towards midline & posteriorly towards the point where mandiular nerve divides into point where mandiular nerve divides into lingual & inferior alveolarlingual & inferior alveolar

This spread of new bone formation occurs This spread of new bone formation occurs anteriorly along the lateral aspect of the anteriorly along the lateral aspect of the meckel’s cartilage forming a trough that meckel’s cartilage forming a trough that consists of lateral & medial plates that consists of lateral & medial plates that unite beneath the incisor nerveunite beneath the incisor nerve

The trough of bone extends anteriorly The trough of bone extends anteriorly to meet adjoining one, the 2 separate to meet adjoining one, the 2 separate ossification centers remain separated ossification centers remain separated at the mandibular symphysis until at the mandibular symphysis until shortly after birthshortly after birthThe trough is soon converted into a The trough is soon converted into a canal as bone forms over the nerve, canal as bone forms over the nerve, joining the lateral & medial platesjoining the lateral & medial platesBackward extension of ossification Backward extension of ossification along the lateral aspect of the Meckel’s along the lateral aspect of the Meckel’s cartilage forms a gutter later cartilage forms a gutter later converted into a canal that contains converted into a canal that contains the inferior alveolar nervethe inferior alveolar nerve

The ramus of the mandible develops by a The ramus of the mandible develops by a rapid spread of ossification posteriorly into rapid spread of ossification posteriorly into the mesenchyme of the 1the mesenchyme of the 1stst arch, turning arch, turning away from Meckel’s cartilage. This point of away from Meckel’s cartilage. This point of divergence is marked by the lingula in the divergence is marked by the lingula in the adult mandible, the point at which the adult mandible, the point at which the inferior alveolar nerve enters the body of inferior alveolar nerve enters the body of mandiblemandible

Thus by 10 weeks rudimentary mandible is Thus by 10 weeks rudimentary mandible is formed almost entirely by membranous formed almost entirely by membranous ossification with little direct involvement of ossification with little direct involvement of Meckel’s cartilageMeckel’s cartilage

Fate of Meckel’s cartilageFate of Meckel’s cartilage

Posterior extremity forms malleus, Posterior extremity forms malleus, incus & sphenomandibular ligamentincus & sphenomandibular ligament

Most of the cartilage is absorbed Most of the cartilage is absorbed except for some portion in midline except for some portion in midline which may cause endochondrial which may cause endochondrial ossification ossification

Further growth of the mandible until birth is Further growth of the mandible until birth is influenced by the appearnce of 3 secondary influenced by the appearnce of 3 secondary cartilages (condylar, coronoid, symphyseal cartilages (condylar, coronoid, symphyseal cartilages) & development of muscular cartilages) & development of muscular attachmentsattachments

Condylar cartilage appears at 12Condylar cartilage appears at 12thth week of week of development development

Coronoid process appears at about 4 Coronoid process appears at about 4 months IUmonths IU

The symphyseal cartilages 2 in number The symphyseal cartilages 2 in number appear in connective tissue b/w the two appear in connective tissue b/w the two ends of Meckel’s cartilage but are entirely ends of Meckel’s cartilage but are entirely independent of it, they are obliterated independent of it, they are obliterated within the 1within the 1stst year of the birth. year of the birth.

Thus mandible is membrane bone developed in relation to Thus mandible is membrane bone developed in relation to the nerve of the 1the nerve of the 1stst arch & almost independent of Meckel’s arch & almost independent of Meckel’s

cartilage. The madible has neural,cartilage. The madible has neural, articular, alveolar & articular, alveolar & muscular elements & its growth is assisted by the muscular elements & its growth is assisted by the

development of secondary cartilagesdevelopment of secondary cartilages

Development of maxillaDevelopment of maxilla

Maxilla develops from a center of ossification in Maxilla develops from a center of ossification in mesenchyme of maxillary process of 1mesenchyme of maxillary process of 1stst arch which is arch which is associated closely with cartilage of associated closely with cartilage of nasalnasal capsulecapsule..

As in the mandible the center of ossification appears As in the mandible the center of ossification appears in the angle b/w the divisions of the nerve (i.e., where in the angle b/w the divisions of the nerve (i.e., where the anterior superior dental nerve is given off from the anterior superior dental nerve is given off from the inferior orbital nerve)the inferior orbital nerve)

From this center bone formation spreads posteriorly From this center bone formation spreads posteriorly below the orbit toward the developing zygoma & below the orbit toward the developing zygoma & anteriorly toward the future incisor region ossification anteriorly toward the future incisor region ossification also spreads toward the frontal processalso spreads toward the frontal process

As a result of this pattern of bone deposition a As a result of this pattern of bone deposition a bony trough forms for the infra orbital nervebony trough forms for the infra orbital nerve

From this trough a bony downward extension of From this trough a bony downward extension of bone forms the lateral alveolar plate for the bone forms the lateral alveolar plate for the maxillary tooth germsmaxillary tooth germs

Ossification also spreads in to the palatine Ossification also spreads in to the palatine process to form the hard palateprocess to form the hard palate

The medial alveolar plate develops from the The medial alveolar plate develops from the junction of the palatal process & main body of junction of the palatal process & main body of the forming maxillathe forming maxilla

This plate together with its lateral counterpart This plate together with its lateral counterpart forms a trough of bone around the maxillary forms a trough of bone around the maxillary tooth germs, which eventually become tooth germs, which eventually become enclosed in bony crypts.enclosed in bony crypts.

A secondary cartilage also contributes to A secondary cartilage also contributes to the development of maxilla, the development of maxilla, zygomaticzygomatic /malar/malar cartilage cartilage

At birth the frontal process of maxilla is At birth the frontal process of maxilla is well marked and body consists of alveolar well marked and body consists of alveolar process containing tooth germs & small process containing tooth germs & small zygomatic & palatal processzygomatic & palatal process

Maxillary sinus develops around 16Maxillary sinus develops around 16thth week of IUL. At birth the sinus is still week of IUL. At birth the sinus is still rudimentary in the size of small pearudimentary in the size of small pea

Common Features of Jaw Common Features of Jaw DevelopmentDevelopment

Both begin from a single center of Both begin from a single center of ossification related to the nerve & to a ossification related to the nerve & to a primary cartilageprimary cartilage

Both form a neural element related to the Both form a neural element related to the nervenerve

Both develop an alveolar element related Both develop an alveolar element related to the developing teethto the developing teeth

Both develop secondary cartilages to Both develop secondary cartilages to assist in their growthassist in their growth

Development of TMJDevelopment of TMJ

Before the condylar cartilage forms, a broad band Before the condylar cartilage forms, a broad band of undifferentiated mesenchyme exists b/w the of undifferentiated mesenchyme exists b/w the developing ramus of the mandible and developing ramus of the mandible and developing squamous tympanic bone.developing squamous tympanic bone.

With formation of condylar cartilage, this band is With formation of condylar cartilage, this band is reduced rapidly in width & converted into a reduced rapidly in width & converted into a dense strip of mesenchymedense strip of mesenchyme

The mesenchyme adjacent to this strip breaks The mesenchyme adjacent to this strip breaks down to form the joint cavity & the strip becomes down to form the joint cavity & the strip becomes the articular disc of the jointthe articular disc of the joint

Salivary gland developmentSalivary gland developmentParotid & submandublar appear in connective tissue Parotid & submandublar appear in connective tissue around 6around 6thth week week

Sublingual in 8Sublingual in 8thth week week

Development of major & minor salivary glands is same Development of major & minor salivary glands is same as any other gland in the bodyas any other gland in the body

Organization is completed by 3Organization is completed by 3rdrd month & month & differentiation of terminally located acinar cells & differentiation of terminally located acinar cells & canalization of ducts by 6canalization of ducts by 6thth prenatal month prenatal month

The acini of the mucous glands become functional The acini of the mucous glands become functional during the 6during the 6thth month, where as serous glands become month, where as serous glands become functional by birthfunctional by birth

ConclusionConclusion

ReferencesReferences Cranio Facial Embryology – G.H. SperberCranio Facial Embryology – G.H. Sperber Essentials of Facial Growth – Enlow and HansEssentials of Facial Growth – Enlow and Hans Human Embryology – Indrabir SinghHuman Embryology – Indrabir Singh Langman’s – EmbryologyLangman’s – Embryology Gray’s AnatomyGray’s Anatomy Oral Histology – A.R. TencateOral Histology – A.R. Tencate Handbook of Orthodontic – Robert MoyersHandbook of Orthodontic – Robert Moyers Orthodontics – Principles and Practice – T.M. Orthodontics – Principles and Practice – T.M.

GraberGraber Contemporary Orthodontics – Willium R. Proffit.Contemporary Orthodontics – Willium R. Proffit. Orthodontics principles and practice - BasavarajOrthodontics principles and practice - Basavaraj

BY: M. S. BIRJANDI BY: M. S. BIRJANDI

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