special embryo tibb tanta

7/31/2019 Special Embryo Tibb Tanta

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During 4 th week intrauterine life of embryo : Neck not yet formed. Head swelling followed by cardiac swelling & bothe separated by depression of stomodeum

(future mouth). During 5 th week : middle mesodermal layer on each side show anteroposterior segmentation into 6 segments of pharyngeal @ branchial arches. Each arch have :

a core of mesenchymal tissue (derived from neural crest cells) covered on outside by ectoderm & inside byendoderm.

its own blood & nerve supply. 1st arch (mandibular arch) divides maxillary & mandibular processes 2nd arch known as hyoid arch Succeeding arches are 3 rd , 4 th , 5 th & 6 th 5 th arch is rudimentary & disappear d/t early degeneration of its blood supply Externally , arches separated by ectodermal grooves called pharyngeal clefts . this clefts is enumerated 1 st to4 th in craniocaudal direction

Internally , arches separated by endodermal groove pharyngeal pouches (4)

BRANCHIAL APPARATUS (PHARYNGEAL ARCHES)

SEQUENCE OF EVENTS


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1st Divides into : maxillary & mandibular processes Its cartilage forms malleus, incus & Meckels cartilage Mesenchyme of maxillary process give rises to premaxilla, maxilla, zygomatic bone & part of temporalbone through membranous ossification Membranous ossification of mesodermal condensation around Meckels cartilage mandible Meckels cartilage regresses & disappears except small part which change to fibrous band forming sphenomandibular ligament

Skeletal derivatives :i. Malleus, incus

ii. Sphenomandibular ligamentiii. Mandible by mesodermal condensation around Meckels cartilage

Muscle derivatives (muscles supply by mandibular n. ): i. Muscles of mastication (4)

ii. Anterior belly of digastriciii. Mylohyoidiv. Tensor palativ. Tensor tympani

Nerve : mandibular n. Artery : 1 st aortic arch disappears except small portion persists forming maxillary a.

2nd Its cartilage called :Reicherts cartilage Skeletal derivatives :

i. Stapesii. Styloid process temporal bone

iii. Stylohyoid ligamentiv. Lesser cornu & upper part body of hyoid bone

Muscle derivatives : i. Muscles of facial expression, occipitofrontalis, muscles of auricle & platysma

ii. Posterior belly of digastriciii. Stylohyoidiv. Stapedius of middle ear

Nerve : facial n. Artery : 2nd aortic arch disappears except small portion persists forming stapedial & hyoid a.

3 rd Its cartilage forming lower part of the body & greater horn of hyoid bone Muscle : stylopharyngeus (the only muscle) Nerve : glossopharyngeal n. Artery : 3 rd aortic arch persists forming common carotid a. & stem of ICA on both sides

4 th Its cartilage forms thyroid cartilage Muscle : cricothyroid Nerve : superior laryngeal n. (its external laryngeal br. supplies cricothyroid Artery :

i. Left 4 th aortic arch persist forming main part arch of aortaii. Right 4 th aortic arch persist forming stem of right subclavian artery

6 th its cartilage forming : cricoid, arytenoid, corniculate & cuneiform cartilages Muscle : intrinsic muscle of larynx Nerve : recurrent laryngeal br. of vagus.

MESODERMAL DERIVATIVES OF PHARYNGEAL ARCHES


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Summary Of Mesodermal Derivatives, Artery & Their Innervation

PharyngealArch

Nerve Artery Muscles Skeleton

1

(mandibular)

Mandibular n. Maxillary a. Muscles of mastication Mylohyoid Anterior belly of digastric Tensor palatine Tensor tympani

Malleus, incus &

Meckels cartilage Sphenomandibularligament

2(hyoid)

Facial (cr. iii) Stapedial & hyoida.

Muscles of facialexpression Buccinator Auricularis frontalis Platysma Orbicularis oris & oculi Stylohyoid Stapedius

Stapes Styloid process Lesser horn & upperportion body of hyoidbone

3 Glossopharyngeal n.(cr ix)

CCA & stem of ICAon both sides

Stylopharyngeus Greater horn & lowerportion body of hyoidbone

4 Superior laryngeal br.(vagus)

Main part arch of aorta (left arch) Stem of rightsubclavian a. (rightarch)

Cricothyroid Levator palati Constrictor of pharynx

Laryngeal cartilages(thyroid, cricoid,arytenoid, corniculate& cuneiform )

6 Recurrent laryngeal br(vagus)

Intrinsic muscles of larynx


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Endodermal grooves separating pharyngeal arches 4 pouchs. The last one is atypical & divided into 2 parts Epithelial endodermal lining of the pouch gives rise to important organ

Pouch Explanation

1 It forms a stalk like diverticulum, the tubotympanic recess which comes in contact with epitheliallining the first branchial cleft Distal portion of the recess widens forming primitive tympanic (middle ear) cavity Proximal part remains narrow forming auditory (Eustachian) tube Middle ear cavity come into relation with external acoustic meatus, the separating membraneforming tympanic membrane

2 Forms palatine tonsils Endodermal lining forms solid epithelial outgrowth into surrounding mesenchyme Its central cella degenarated forming tonsillar crypts During 3 rd to 5 th months, tonsil gradually infiltrated by lymphatic tissue

Capsule of tonsils formed from condensation of mesenchyme In adult : part of pouch remains is known as tonsillar fossa

3 Each 3 rd & 4th pouchs is divided into dorsal & ventral wings. In 5 th week , endodermal lining of dorsal wing forms inferior parathyroid gland (parathyroid III)while the ventral partforms thymus As thymus enlarges, it migrates in a caudal & medial direction, pull the P III with it Both glands loose their connection with pharyngeal wall The 2 lobes of thymus come in contact with each other in front pericardium &grat vessels P III adheres to posterior surface of thyroid gland

4 Epithelium dorsal wing forms superior parathyroid gland (parathyroid IV) Epithelium of ventral wing forms ultimo-branchial body & a small amount of thymus tissue(rudimentary thymus) P IV looses connection with pharyngeal wall & migrate caudally with thyroid gland. It becomesadherent to posterior surface thyroid gland at higher level than P III ultimo-branchial body separates from wall of pharynx & becomes incorporated into developingthyroid gland forming parafollicular cells. Other views : ultimobranchial body degenerates &disappears

Fate Of Pharyngeal Pouches

Pouch Derivatives1 middle ear cavity

Eustachian tube of middle ear Tympanic membrane

2 Palatine tonsillar fossa

3 Dorsal : inferior parathyroid Ventral : primordium of thymus

4 Dorsal : superior parathyroid Ventral : ultimo-branchial body incorporated into thyroid then degenerates

: rumdimentary thymus soon disappears

PHARYNGEAL POUCHES


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In 5th week , 4 ectodermal grooves are seen between arches called pharyngeal clefts Dorsal part 1 st cleft penetrates underlying mesenchyme forming external auditory meatus .

Ectodermal lining the meatus forming tympanic membrane Around developing meatus, pinna is formed d/t growth & fusion 6small surface elevations,

3 derived from first arch & 3 from second archRemaining cleft buried by second pharyngeal arch which enlarges & grows inferiorly in neckTherefore : 2nd , 3 rd & 4th clefts formf floor of cavity lined by ectoderm called cervical sinus sinus then obliterated by fusion of its walls

1.Branchial cysts Remnants of cervical sinus located below the angle of the jaw

2.External branchialfistula

Occur when 2 nd arch fails to graow caudally over the 3 rd & 4 th arches. Thus, cervical sinus remains in contact with surface by a narrow canal It usually lies along anterior border of sternomastoid

3.Internal branchialfistula

Cervical sinus connected to lumen of pharynx by small canal which opens intonsillar region.

PHARYNGEAL CLEFTS

CONGENITAL ANOMALIES


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Tongue : mass of muscles covered by mucous membrane Mucous membrane dorsum of tongue divided by sulcus terminalis (V-shaped) into : ant 2/3, post 1/3 because

they develop from 2 differents origin & have different nerve supply. At 4 th week swelling (from 1 st pharyngeal arches) :

2 lateral lingual swelling 1 median swelling (tuberculum impar)

2nd mesodermal swelling : copula (hypobranchial eminence) develop in floor of pharynx atpharyngeal arches 2,3,4.

3 rd median swelling from posterior part 4 th arch : development of epiglottis . Laryngeal orrifice lies behind thisswelling & surrounded by arytenoid swelling .

d/t growth of lateral swelling, they overgrow the tuberculum impar & fuse with each other anterior 2/3 @body of tongue. The hypobranchial eminence overgrows & eliminate contribution 2 nd pharyngeal arch definitive adult tongue. This part enlarges & spreads cranially in V-shaped fromed fuses with anterior 2/3along sulcus terminalis to form posterior 1/3

muscle of tongue : develop bilaterally from occipital myotomes migrate in ventrally around side wall of pharynx to be under mucosa of tongue together with hypoglossal n.

First, tongue is immobile because it adherent to mouth floor a groove appears at ventral & lateral sides &extends deeply tip & anterior part freely mobile.

Innervations confirmed their development : Ant 2/3 : lingual br. Mandibular n. (n. 1 st arch)

Post 1/3 : glossopharyngeal br. (n. 3 rd arch) Most post. & epiglottis : superior laryngeal n. Of vagus (n. 4 th arch)

DEVELOPMENT OF TONGUE

DEVELOPMENT


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Aglossia Complete/partial absence of tongueMacroglossia Abnormal large oftongueMicroglossia Abnormal smallBifid Tongue Split involve ant 2/3 d/t failure lateral lingual swellings 1 st arch to fuses in midlineAnkyloglossia Tongue tie to floor of mouth (not free)

Held by short frenulumExcessive lengthof frenulum

Excssive mobile of tongue & may fall back & occlude the pharynx suffocation


DEVELOPMENT OF FACE, LIPS, CHEEK & NOSE


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Frontonasal process : start as proliferation mesenchyme on ventral surfac developing brain & grows towardstomodeum.

2 maxillary process : grow out from upper end of each 1 st pharyngeal arch , pass medially forming inferiorborder developing orbit

2 mandibular process of 1st

arch : approach each other in mid line, inferior to stomodeum & fuse to form lower jaw & lower lip.

Local thickening surface of ectoderm, nasal (olfactory) placodes appear on both sides frontonasal process underinductive influence ventral portion forebrain.

At 5 th week : nasal placodes invaginate nasal pits. Each pits surrounded by : Lateral nasal process : on outer edge pit Medial nasal process : on inner edge pit

During following 2 weeks : maxillary process increase in size, grow in medial direction , compressed medial nasalprocess toward midline.

Then medial nasal & maxillary process fuses. Upper lip formed by : 2 medial nasal process (form philtrum) & 2 maxillary process (form lateral part). Lower lip & jaw formed from mandibular process ( which fuses across midline ). Iniatially, maxillary & lateral nasal pocesses separated by nasolacrimal groove . Ectoderm floor of the groove

form solid epithelial cord, which detaches from overlying ectoderm maxillary & lateral nasal processes fuseswith each other.

Then, this cord is canalized nasolacrimal duct, its upper end widen lacrimal sac Maxillary process enlarge cheek & maxilla. Nose formed from 5 facial processes :

Frontonasal bridge

Fused medial nasal crest & tip Lateral nasal side (Alae)


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STRUCTURES CONTRIBUTES TO FACE FORMATION

PROCESS STRUCTURES FORMED

Frontonasal Forehead Bridge of nose

Maxillary Cheeks Lateral portion upper lip

Medial nasal Incissive fossa & primary palate Philtrum upper lip Crest & tip of nose

Lateral nasal Alae of noseMandibular Lower lip

A. INTERMAXILLARYSEGMENT

d/t medial growth maxillary processes, 2 medial nasal processes fuse at surface &deeper level.

Structure formed by these process known as intermaxillary segment, composed of : Labial component : form philtrum uppe rlip Upper jaw component : carries 4 incissor teeth Palatal component : form triangular primary palate

B. SECONDARYPLATE

In 6 th week, main part definitive plate appear in the form of 2 palatine shelves frommaxillary process & directed obliquely downward on either side of tongue.

In 7

th

week, palatine shelves attain horizontal position above tongue & fuses witheach other 2o palate. Anteriorly : the shelves fuse with 1 o palate & incissive foramen in adults considered asmidline landmark between 1 o & 2o palates.

Fusion takes place from ant to post uvula is last structure to be formed

DEVELOPMENT OF PALATE


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Cleft lip Unilateral : most common, d/t failure maxillary process to fuse with medial nasal proce Bilateral : d/t failure both maxillary process to fuse with medial ansla process

Oblique facial

cleft

Cleft lip on one side to medial margin orbit

d/t failure maxilarry process to fuse with lateral ansal process.Median cleft lip d/t failure fusion both medial nasal processesCleft lower lip d/t incomplete fusion mandibular processesMacrostomia large mouth d/t incomplete fusion maxillary with mandible processesMicrostomia small mouth d/t excessive fusion of these processesCleft palate all degrees of cleft palate d/t failure of palatine shelves of maxilla to fuse with each oth

midline @ to fuse with primary palateAtresianasolacrimalduct

failure of canalization developing duct



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It develop from 2 different parts ; Rathkes pouch : small ectodermal diverticulum, grow upwards from roof of stomodeum immediately

anterior to buccopharyngeal Infundibulum : small ectodermal diverticulum , grows inferiorly from floor of diencephalon

During 2 nd month development : Rathkes pouch comes in contact with anterior surface infundibulum then losesconnection with stomodeum (mouth cavity)

Furtherly, cells in anterior wall of teh pouch increase rapidly in number pars distalis Upward extension pars distalis around stalk of infundibulum pars intermedia Cavity of the pouch disappeared .

Infundibulum : differentiated stalk & pars nervosa pituitary gland, composed of neuroglia cells & nerve fibersfrom hypothalamus.

During 3 rd to 4 th month, pars distalis cells differentiated chromophobe cells, acidophil cells & basophil cells.

Craniopharyngioma From remnants Rat hkes pouch pituitary dysfunction

Pharyngealhypophysis

Small portion Rathkes pouch persist in small portion

DEVELOPMENT OF PITUITARY GLAND

SEQUENCE OF EVENTS



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3rd week : median endodermal thickening in middle floor of pharynx at V-shaped junction ant 2/3 & post 1/3 of tongue between tuberculum impar & copula.

Thickening diverticulum that grows inferiorly into underlying mesenchme Thyroglossal duct . Duct elongates becomes solid cord of cells & bilobed terminal swelling expands thyroid gland. Furtherly, thyroid gland descnd in front hyoid bone & laryngeal cartilages until reaches infront trachea at 7 th

week. Solid cord connect the thyroid gland to tongue degenerates. Site origin thyroglossal duct on tongue remains as pit called foramen coecum. Thyroid gland may divided into small median isthmus & 2 large lateral lobes.

HISTOLOGICAL DIFFERENTIATION Early stage, thyroid gland consist of a solid mass of cells mass broken d/t invasion surrounding vascular

mesenchymal tissue become small clusters of cells

3rd

month : colloid accumulate in center of each cluster folicles Fibrous capsule & CT develop from surrounding mesenchyme. Ultimobronchial bodies incorporated into thyroid glands forming parafollicular cells (produce calcitonin). Other

views report it degenarate & disappear.

DEVELOPMENT OF THYROID GLAND

SEQUENCE OF EVENTS


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Agenesis of thyroid gland cretinismIncomplete dscend of thyroid gland

Descend arrested at any point between base of tongue & trachea Type :

Lingual thyroid (common) Cervical thyroid

Etopic thyroid tissues Found in : thorax, bronchi & oesophagusThyroglossal cyst Part of thyroglossal duct persist cyst along @ close to midline.

Commonly occur in hyoid bone region.Thyroglssal fistula Thyroglossal cyst rupture sinusCretinism Deficiency Thyroid hormone production during intrauterine life.



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Develop from 2 components : Cortex is mesodermal : from coelomic epithelium Medulla is ectodermal : from sympathetic ganglion

During 5 th week development : mesothelial clls of coelomic epithelium (between root of mesentery & developinggonad) begin to proliferate & form foetal (primitive) cortex.

Then, cells from neural crest & differentiating into sympathetic ganglion migrate & invade medial aspect fetalcortex to form suprarenal medulla . These cells differentiate chromaffin cells.

Then, second series of cells arise from coelomic epithelium & enclose foetal cortex. These cells gives definitive(permanent) cortex.

Differentiation characteristic adrenal cortical zones start during late fetal period. Zona glomerulosa & zonafasciculata present at birth, but zona reticularis not recognizable till the end of 3 rd year.. some auuthor said zonareticularis is remnant foetal cortex.

CONGENITAL ANOMALY Phiochromocytoma : chromafin cells tumour in suprarenal gland region

DEVELOPMENT OF SUPRARENAL GLAND

special embryo tibb tanta

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