Mid Oral Histo

7/31/2019 Mid Oral Histo

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MID SUBJECT REVISION for oral histology

The emryogenesis stages :

Pre -emryonic stage (starts from fertilization until 2 weeks ): Fertilization , imlantation of zygote, formation of bilaminar

emriyonic disc .

Embryonic stage ( 2weeks until 8 weeks) :

Tissue development , formation of organ system.

Fetal stage ( 8 weeks until birth): Increace in body weight and size .

Fertilization = oocyte + sperm = Zygote

Zygote is 1 cell then its state to divide to 2 cells , then 4,then ( 12-16) when they reach ( 16) we call it morula .

Wall of zygote CALLED zona pellucida . Cells inside the zona pellucida CALLED blastomeres ( so when its

contain 16 balstomere we call it morula )

Morula enters the uterine cavity 3-4 days after fertilization , thecells flatten and compact on the inside of the cavity .

Blastocoel : blastocysts cavity which contain fluid between thecells . this fluid seperates the cells into 2 layes :


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Embryobalst inner Trophoblast ( tropho-nourishment) outer : responsible for

the attachment and forms the PLACENTA.

HOW ?

** During the implantation the trophoblast cells prolifrate forming 2 kind of cells (

cytotrophobalsts inner and syncytiotrophoblast outer )

** once the implantation is comleted the trophoblast cells engulf and destroy cells of

the uterine linig creation blood pools so the syncytiotrophoblast starts to engulf and eat

the cells of the endometrium to implant it self inside . THATS stimulate new capillaries

to grow and foretelling the growth of placenta and starts placental circulation .

Blastocysts is completely embedded in the endometrium & bloodclot is formed at day 10 .

Which cells secrete HCG ? the syncytiotrophoblast cells . Embryobalst inner cell mass divides into :

amniotic cavity ( starts to form by 8th day ) Primitive Yolk sac or exocoelomic cavity ( enclosed by the

exocoelomic membrane ) (then it become yolk sac ).

amniotic cavity is filled with amnioticfluid , its functions: shock absorber prevent dry out of the fetus adhesion with surrounding tissue

Amniotic rupture just before the birth & flow out .


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What are the structure we can identify at ( Emryonic stage )?

Prochordal ( cephalic )plate : the head end of the embryo and itwill become in the future the buccopharyngeal membrane.

Caudal ( cloacal ) membrane : the tail of the embryo Intra emryonic mesoderm : appeared from ectoderm at 15th or

16th

day.

Notochordal process

The formation ofmesoderm leaves behind it : Primitive streak Primitive ( hensens) node

Notochordal process is a blind-ended tube that forms from the

End of primitive streak at day 17 .

Mesoderm seperates the ectoderm form endoderm in all areasEXCEPT : the procordal plate , the notochordal process, the

cloacal membrane .

Primitive streak is a thickening of the embryonic epiblast ectoat the caudal end , it grows toward the head end , it gives :

The primitive knot The primitive pit


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The primitive groove

Different stuctures formed from germ layers

Ectodrem Mesoderm Endoderm

- skin and

appendages.

- oral and anal

mucosa.

- lining of nose &

paranasal sinuses.

- enamel.

- nevous system.

Pituitary and

mammary glands.

-lens of the eyes

-inner ear.

-adrenal medulla.

-all bones

-muscles

-dermis of the skin

-all the connective tissue.

-all the dental tissue

EXCEPT enamel.

-lymphatic tissue & spleen.

- blood cells&lymphatic

cells

-heart, lungs

- reproductive & excretory

systems(kidneys,gonads)

- adrenal cortex.

- GIT system

- lining

epithelium of :

the tonsils, lungs,

excretory system,

- liver , pancreas

The mesoderm (day 17) develop into 3 groups of cells ( we canIdentify them on either side of notochord ), these groups are :

Paraxial mesoderm.(closest to the midline) Intermediate mesoderm.(lateral to the paraxial) Lateral plate mesoderm.( at periphery)

Paraxial mesoderm : 2 rodes starts at cephalic end (week 3),segmented into somites which are cuboidal masses.


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Somites cells = somatomeres Number of somites : 42-45 pairs (end of week 5)

Intermediate mesoderm:

Cranially : 2 segmentally arranged group of cells Caudally : 2 un-segmented rodes of tissue called the

nephrogenic cords which gives most of urinary system.

Somites divided into :

Dermatome : forms the dermis of the skin. Myotome : forms the vertebral , intercostal & some limb

musculature.

Sclerorome: forms the ribs & starnum .

Head somites : Preotic somites : gives the muscle of the eyes. Metotic somites : gives the muscle of the tounge.

The emryogenesis heart forms in a region that is more cephalicthan the mouth .


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So according to the embryological location before the longitudinalfolding : more cephalic is the liver , then the heart , then the

mouth , then the brain .

NOTE : these organs names in the embryo are :

buccopharyngeal membrane for the mouth

primitive heart for the heart

developing brain for the brain

septum transversum for the liver

Neural plate: located caudal to procoerdal plate ant its the earlydevelopment of CNS , and its thichening of the ectoderm over the

notochord.

Neural crest cells : located originally at the periphery of the neuralplate ( ecto) .

Then we will have neural groove and folds which arch and fusewith each other until forming a tube will moved down thats

called neural tube

Neural crest cells will pinched off from the ectoderms too , andthey will spread in the mesoderm . NOW the called

ectomesnchymal cells

Note : when that happened the size of the emryo is ( 1.5-4 mm)only .

Ectomesnchymal tissue forms :


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Dermis of head region Dental tissue EXCEPT enamel.

Branchial arches : transient or temporary structures thatappear in the lower jaw & neck region .

Neural crest cells give : Ectomesenchyme tissue in head rigon:

( dermis,lamina propria,dental tissue except

enamel,branchial arches,skeleton,part ofmusculatuer,pigment cellsmelanocytes

Meninges. Spinal & cranial nerve ganglia. Symp. & parasymp. System. Adrenal medulla. Schwann cells.

Development of epithelial structures

Epidemis : from surface ectodermal cells

Dermis: from underlying mesoderm of somited BUT in headregion its from ectomesenchyme tissue.

Before thw 11th week , the ectodermal layer in only 1 single layer,but after that ( 11-12 weeks) it give 4 layers :


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Basal layer : which forms all the epithelial & epidermis, andsecrete melanin pigmentation ( the melanocyes are from

neural crest cells

2 middle layers Superfacial layer epithelium

Some structures develop from a combination ofdermal &epidermal tissues such as : (mammary,sebaceuos,salivary glands )

& ( teeth) &(nails) & ( hair ) .

Development of connective tissue (CT)

CT develop from somites as migrating from either side of neuraltube.

Development of cartilage & bone

the 1st skeletal stucture in the embryo is : cartilage. Its function : supporting the soft embryo, make rigidity,support

the 3D shape of the embryo.

Cartilage migrates to surround notochord forming spinal coloum. 2 types of cartilage growth : appositional (layer by layer) &

interstitial (cell grow in size & tissue get bgger ) .


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Types of cartilage ( hyaline , elastic , fibrous ) Bone replaces the cartilage as a 2nd stage.

2 types of bone formation : intramembranous ossification &endochondral ossification .

intramembranous ossification:

mesenchymal tissue is condensed

to form bone.

endochondral ossification :Where

ever we have complexity in the

shape of the bone . ( 1st

cartilage)

Examples :

-Cranial vault

-some bones of the face

Examples :

-base of the skull

-nasal area, nasal capsule.- long bones( ulna,radius,

humerus)

-ramus of mandible.

Achondroplasia : a problem in the endochondral ossification insome people like dwarfs , the intramembranous isnt affected,

so they have normal growth in the trunk but have short limbs .

Epiphyseal growth = endochondral ossification in the long bone Epiphyseal plate is between the epiphysis & diaphysis , and its

the actie area for bone growth.

Development of muscles

By 10th week


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Myoblasts migrate from myotomes of somites.

Development of CVS

By 3rd week Originates from angiogenic clusters : 2 groups :

Outer cells (peripheral) : forming blood vessles , heart,endothelial walls of blood vessels.

Inner cells ( central) : forming the RBCs.

Nutrition of embryo: vatelline vascular system in post.wall ofyolc sac untill 8

thweek . Then umbilical or placental vascular

system.

When the heart starts to beat ? at 4th week . The heart starts as a tube , then internal partitioning to form 4

chambers , an opening between atria remains until bitrh .

Development of oro-facial & branchial arches

At 21st day ( 3rd week). Branchial arched located within the neck and lower jaw region. The buccopharyngeal membrane ruptures at the age of 21 day, so

will be communication between the outside atmosphere & inside

or early GIT.


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The junctions between 1st and 2nd branchial arches : From outside called ( branchial clefts )

From inside called ( branchial pounch)

They are 5~6 pairs of branchial arches apear on day 22 . The early GIT in the embryo divided into: forgut,midgut,endgut. We can recognize the fronto-nasal process at day 21 , which is

developing forebrain .

Skeletal elements of the branchial arches :

1st

branchial arch : (meckels cartilage) which divides into :

Anterior :guides the formation of the body of mandible.( notreplaced.. only guides )

Middle part : the perichondrium becomes the anti.malleolarligament and sphenomandibular ligament.

Posterior or dorsal: this part is ossifies to become the malleus.

Also an other cartilage from 1st branchial arch which is : ( pterygo-quadrate bar cartilage) that ossifies to become the incus.


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2nd

branchial arch: ( Reicherts cartilage)

the dorsal end of this becomes stapes , and the remainder of thiscartilage becomes styloid process & stylohyoid ligament & hyoid

bone ( body&lesser horn EXCEPT greater horn )

3rd

branchial arch : gives the greater horn of hyoid.

4th_

6th

branchial arch : ( thyroid , cricoid, arytenoid cartilages of

the larynx) .

Nervous & Muscular elements of the branchial arches :

1st branchial arch : trigeminal nerve (5)Muscles innervated ( mastication M & anti.belly of digastric &

mylohyoid & tensor tympani & tensor veli palatini )

2nd branchial arch : facial nerve (7)Muscles innervated ( facial expression M .& post.belly of

digastric & stylohyoid M.)

3rd branchial arch : glossopharyngeal (9)Muscles innervated ( stylopharyngeus M.)


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4th -6th branchial arch : vagus nerve ( 10-laryngeal branches)Muscles innervated ( pharyngeal M.EXCEPT stylopharyngeus ,,

Muscles of the soft palate EXCEPT tensor veli palatine, intrinsic

& extrinsic laryngeal Ms )

vascular elements of the branchial arches :

1st

or (mandibular )aortic arch artery: max. artery of the upper

jaw.

2nd

or ( hyoid ) aortic arch artery : small stapedial& thyroid

arteries.

3rd

aortic arch artery: the common carotid artery & the internal

carotid artery & external carotid artery 1st

& 2nd

arches too .

4th

aortic arch : on the right if forms the brachiocephalic artery

leading to the right subclavian & right common carotid . On the

left it becomes the arch of aorta .

5th

aortic arch : transitory & leaves no memorial.

6th

or (pulmonary) aortic arch : pulmonary artery

The pharyngeal pouches & clefts ( we have 6 arches so 5 pouches)


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1st

pouch or tubotympanic recess gives : the auditory tube &

the middle ear cavity .

1st

pharyngeal cleft : form the external acoustic or auditory

meatus.

2nd

pouch gives: palatine tonsils

3rd

pouch gives : inferior parathyroid & thymus .

4th

pouch gives : superior parathyroid

5th

pouch gives: ultimobranchial body

2nd

,3rd

,4th

clefts :are over grown by the 2nd

branchial arch to form

the transient ectodermally lined cervical sinus.

Development of the tongue


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At 4th week ( 32nd day) Swellings from 1st,3rd ,4th arches fuse to form the tongue. (Lateral lingual swelling + tubeculum impar) from the 1st arch fuse

to form the anterior 3/2 + ( copula) from the 3rd

arch gives the

posterior 3/1 = the tounge

The 3rd arch is over grow the 2nd arch , but the 2nd arch is onlycontributes to the taste buds

The swellings of the 4th archbecome the epiglottis Sulcus terminalis: is the junction between the anterior 2-3 &

posterior 1-3 .

Foramen cecum : is a depression in the center of sulcus terminalis,and its the starting point for formation of thyroid gland.


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Innervation of the tongue :

Anterior 2/3 :

Sensory: trigeminal nerve ( lingual nerve branch)

The taste: facial nerve ( chorda tympani branch)

Motor: hypoglossal nerve

Posterior 1/3 :

Sensory & taste : glossopharyngeal nerve.

Extreme posterior:

Sensory & taste : vagus nerve ( superior laryngeal nerve branch )

NOTE: we have group of papillae called circumvallates papillae

these are located anterior to sulcus terminalis BUT they are not from 1st

arch , the r from 3rd

arch , so the innervations for them is from

glossopharyngeal nerve

The thyroid gland starts do develop : 17

th

day.

Where ? from the foramen cecum region as a thyroglossal ductwhich disappear later after the development of thyroid .

It passed down in front the developing hyoid by : 7th week .


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Development of the face

The face is formed by growth of3 processes :

Maxillary process Mandibular process Frontonasal process

Then they fuse in an organize pattern to form the face. Stomodeum: is the primitive mouth area which was

buccopharyngeal membrane and rupture at 21st

day.

In Frontonasal process : we have to nasal pits called ( placodes)that forms nostrils of the nasal cavity .

Arround each nasal pits there r 2 swellings : medial nasal swellings& lateral nasal swellings .

The medial nasal swellings: fuse and form intermaxillarysegment which is between the 2 maxillary processes , ant it

forms :

Mid portion of the nose & colamella of the nose . Philtrum of the upper lip The primary palate ( premaxilla) : which is the alveolar bone

that carry the upper central & lateral incisors.

The lateral nasal swellings: form the alae of the nose .


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The Nasolacrimal duct ( tears duct ) : it reaches from the lacrimalsac to the area on lateral side if nasal cavity.

Maxillary processes form: Much of maxilla EXCEPT 3 parts that arises from intermaxillary

segment.

Lateral parts of upper lips. Mandibular processes form :

Mandible , lower lip, alveolar bone that carries all the teeth.Development of palate

The palate is formed from 3 processes : The primary palate premaxilla: from the frontonasal process. The secondary palate: 2 shelves called lateral palatine

processes each one come from the maxillary processes .


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Notethat failed in fusion of palate forming a condition called cleft palate ( 1:700 births)

We have : cleft lips , cleft palate , cleft lip & palate ( unilateral orbilateral cleft palate )

Development of the Maxilla

Maxilla developed by the process of( intramembranousassification )bcuz we dont have any cartilage in the maxilla.

2 ossification centers : Maxilla proper : ossifies at 40 day. Premaxilla ( primary palate)

The maxilla sinus : a space inside the maxilla , later on it starts togrow in size and increace the vertical length of maxilla .

Processes of maxilla : Frontal Zygomatic Palatine Medial & lateral alveolar plates : which forms the alveolar

process that carries the teeth.


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Development of mandible

Development of body :

Intra-membranous ossification.

Close associated with meckels cartilage . Ossification starts at 7th week. At the site where mental nerve branch off. Continues around IAN inferior alveolar nerve Alveolar process has 2 plates : 1 medial , 1 lateral . Symphisis menti : junction between 2 mandible which fuse at

1st

postnatal year.

Development of ramus : Endochondral ossification .

That happens by ossification of 2 cartilages : Condylar cartilage: 2ndary cartilage bcuz its not among the

primary cartilage that form parts of skull of the embryo ,

appears at 11th

week and grow until 21st

years.

Coronoid cartilage: starts at 14

th

week

Replaced by bone before birth.Development of the Teeth


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Bud stage Cap stage Bell stage

-Rounded or ovoid

enamel organ

- poorly

morphological&

histologicaldifferentiation.

- no shape for the

crown.

Early:

-distinguished cells (

central & peripheral)

.

Late:

-Diffrentiation of SR

- EEE remain

cuboidal.

-IEE become more

columnar.

- We can see the

Dental papilla &dental follicle.

Early:

-differential cell division along the

IEE.

-mapping out the occlusal shape ofthe crown.

- dental lamina breaks down.

-histological differentiation ,

appearance of 4 layers (

EEE,IEE,SR,SI)

Late :

-hard tissue formation.

-appearance of lingual down growthof EEE in primary teeth its called

successor lamina

-reciprocal interaction between EO &

ectomesenchyme .

-development of ameloblasts ( pre-

ameloblasts)

Note: the remain of dental lamina after breaking down calledepithelial rests of serres

What are the early sings of tooth development?

Condensation of ectomesenchymal tissue. Capillary network beneath epithelium at specific sites.


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We find a structure that starts to appear called primaryepithelium band PEB at week 6.

PEB divides into : vestibular lamina & dental lamina .

Transient structures in tooth development :

Enamel knot : localized mass of cells in the center of IEE.

Enamel cord: extending from SI to SR , and if its reach the EEE wecall it enamel septum.

Enamel naval Enamel niche: area enclosed by double attachment of EO to

dental lamina .

Good Luck

Done by : Duaa Alfardan

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Mid Oral Histo