Embryology of face, tmj, tongue, paranasal sinuses, pharynx, larynx, trachea, oesophagus & salivary gland

Embryologic development of face, tmj, tongue, paranasal sinuses, pharynx, larynx, trachea, oesophagus & salivary glands-57

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EMBRYOLOGIC DEVELOPMENT OF FACE, TMJ,

TONGUE, PARANASAL SINUSES, PHARYNX, LARYNX, TRACHEA,

OESOPHAGUS & SALIVARY GLANDS

Presented by:Dr.Kanika Manral


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CONTENTSIntroductionEmbryologic Development of:FaceTemporomandibular JointTongueParanasal SinusesPharynxLarynxTrachea & OesophagusSalivary GlandsConclusionReferences


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INTRODUCTION

EMBRYOLOGY: “the branch of biology and medicine concerned with the study of embryos and their development”

EMBRYO: “the young of a viviparous animal, especially of a mammal, within the stages of intra-uterine development, in humans uptil the completion of gestation”

Webster-Merriam’s Medical Dictionary. 12th ed. Baltimore:Williams;2011. “Embryology”, “Embryo”;p.129


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DEVELOPMENT OF FACE


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•The primary development of the face occurs mainly between the 4th to 8th week in utero.

•Secondary development-post natal, accompanying supplementing structures.

INTRODUCTION..


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•Following implantation, progressive increase in size of embryo.

•Leads to folding of the cephalic(head) end and caudal(tail) end.

•Results in formation of cavity between cephalic end and cardiac bulge--the stomodaeum.


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In the 4th week in-utero, around this stomodaeum, five primordial swellings or prominences begin to appear:

•One Frontonasal Prominence•Two Maxillary Prominences &•Two Mandibular Prominences

Stomodaeum


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•By the end of the 4th week, bilateral oblong invaginations --nasal placodes(np)

•Bilateral horseshoe shaped swellings around placodes– medial nasal prominences(mnp) & lateral nasal prominences(lnp).

lnpnp mn

p

nasolacrimal groove


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The maxillary prominences grow and:•Laterally, merge with the mandibular prominences to form cheeks.

•Medially, compress the medial and lateral nasal prominences towards midline and fuse with them to form upper lip.

•Dorsiventrally, grow downwards and laterally, forming maxillae, zygomas and secondary palate.


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The mandibular prominences fuse with each other to form:•Chin•Lower lip & lower cheek regions•Mandible

The frontonasal prominence narrows & grows downwards to form:•Forehead•Bridge of the nose•Frontal and Nasal bones


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•The medial and lateral nasal prominences contribute to the formation of upper lip with the maxillary prominences.

•Individually:The lateral nasal prominences form the alae of the noseThe medial nasal prominences fuse and form the intermaxillary segment.


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The intermaxillary segment gives rise to:•Philtrum of the lip.

•Premaxillary part of the maxilla that bears the upper 4 incisors and the associated gingivae.

•Primary palate (region of hard palate just posterior to the upper incisors)


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•At the 5th intra-uterine week, surface bulgings appear between the maxillary and frontonasal processes on the lateral sides of the face--lens placodes-primordia of the eyes.

•The developing eyeballs within placodes then move towards the front of the face as the frontonasal process narrows medially.


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DEVELOPMENT OF TMJ

(Temporomandibular Joint)


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•Development of the TMJ, begins with condensation of the developing mesenchymal matrix around the embryonic meckel’s cartilage-VIth to VIIth wk I.U.

•Organisation occurs primarily around 2 centres:TEMPORAL/GLENOID BLASTEMA-ossifies and becomes the glenoid fossa.CONDYLAR BLASTEMA-becomes the condylar cartilage.


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•By the 10th wk I.U., ossification begins in the temporal blastema along with the resorption of the meckel’s cartilage.

•Ossification is followed in the 12th wk I.U. by formation of a ventral and dorsal intra-cartilage cleft which shall later differentiate into the upper and lower joint cavities.

•The intervening cartilage left between the developing clefts results in the primitive articular disc being formed.


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1.Glenoid Fossa2. Upper Joint Cavity3.Intra-Articular Disk4. Lower Joint Cavity5. Condyle

Further mesenchymal condensation and organisation by the 20th wk I.U. results in differentiation of the complex into the individual components.


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DEVELOPMENT OF TONGUE


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•The part of the embryo primarily responsible for the development of the tongue in the 5th week in-utero is the pharyngeal arches.

•These pharyngeal arches develop as outpouchings of the mesoderm in the wall of the foregut on the ventral side of the developing embryo.


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ARCH NERVE MUSCLE SKELETAL ELEMENTS

I Mandibular Muscles of mastication,

ant.digastric,mylohyoid, tensor tympani and

palati

Meckel’s cartilage,incus malleus, spheno mandibular,

anterior ligament of malleus,maxilla, mandible,

zygomatic, palatine, temporal

II Facial Muscles of face, occipito- frontalis, post

digastric, platysma, stylohyoid, stapedius,

auricular

Reicherts cartilage, Stapes, styloid process, styloid

ligament, lesser cornu of hyoid, sup part of body of

hyoidIII Glosso-

pharyngealStylopharyngeus Greater cornu of hyoid, lower

part of body of hyoid

IV Sup laryngeal

Muscles of pharynx Cartilage of larynx

VI Recurrent laryngeal

Muscles of larynx Cartilage of larynx

PHARYNGEAL ARCH DERIVATIVES


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•The development of the tongue can be divided into its epithelium and its musculature.

•The epithelium of:Ant. 2/3rd-from 2 lingual swellings & tuberculum impar of Ist arch.Post. 1/3rd-from cranial part of hypobranchial eminence of IIIrd archPost. most part- from IVth arch.


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•The tongue musculature and connective tissue develops from the occipital myotomes.

•These are derived from the local mesenchyme of the pharyngeal arches.

•The tongue separates from the floor of the mouth by a downgrowth of epithelium.

•It subsequently degenerates forming the lingual sulcus and giving the tongue its mobility.


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DEVELOPMENT OF PARANASAL

SINUSUS


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•4 pairs-Maxillary, Sphenoidal, Frontal, Ethmoidal•Development begins at the 3rd month in-utero•As outpouchings of mucous membranes of superior and middle nasal meatus.•Two primary processes: Primary Pneumatisation & Secondary Pneumatisation


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Sinus Development Primary Pneumatisatio

n

Secondary Pneumatisatio

n

Remarks

Maxillary From the middle meatus of the

nose invaginating into maxilla.

10 weeks I.U. 5th Month I.U. Large enough at birth to be clinically significant and

radiographically identifiable.

Sphenoidal As a recess between chonchae

of sphenoidal bone and

sphenoidal body.

4th Month I.U. 6-7 Yrs Responsible for lightening of the skull

superomedially.

Ethmoidal From the middle and superior meatus into ectethmoidal nasal capsule.

4th Month I.U. 2 Yrs Some ethmoidal air cells grow laterally into lacrimal bone

forming extramural sinus.

Frontal Frontal recess of middle meatus.

4th Month I.U. 6 Months Forms frontonasal duct via ethmoidal

bullae.


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•Growth and enlargement of the sinuses occurs via resorption of cancellous bone and entrapment of air cells.

•Formed primarily as an adaptive mechanism to lighten the skull and provide shock absorbance.

•Secondarily adding resonance to speech and conditioning & humidifying the inspired air.


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DEVELOPMENT OF

PHARYNX


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•The primitive pharynx forms in the early embryonic period as a dilation of the cranial end of the foregut in the IIIrd wk I.U.

•It lies between the developing heart ventrally and the neororium dorsally.

•The lateral aspects of the primitive pharynx project bilaterally as pharyngeal arches interjected by pharyngeal pouches.


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•These arches & pouches, as also mentioned earlier, form their respective ecto-, endo- and meso-dermal structures and then anteriorly fuse to form the walls of the primitive pharynx.


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DEVELOPMENT OF LARYNX


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•Development of larynx occurs during the 4th week of intra uterine life

•The larynx begins as a slit like diverticulum (laryngotracheal groove ) in the ventral wall of the primitive pharynx .

•The groove gradually deepens and its edges fuse to form a septum.

•This septum separates the laryngo-tracheal tube from the pharynx and oesophagus.


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•Between 5th & 6th weeks —3 swellings appear at the laryngeal aditus.

•An anterior swelling , a derivative of the hypo-branchial eminence from 4th arch—forms epiglottis.

•Two lateral arytenoid swellings, derived from the 6th branchial arch, move medially and form a T-shaped aperture.

•Laryngeal lumen— temporarily occluded at 8 weeks gestational age as a result of epithelial proliferation.


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•By the 10th week of gestation, recanalization occurs and consequently, a pair of laryngeal ventricles are formed.

•The laryngeal ventricles are bound by mesenchymal tissue that condenses and progresses into false and true vocal cords.

•Laryngeal cartilages develop from the mesenchyme of the branchial arches(Thyroid-IVth, All others-VIth)


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DEVELOPMENT OF TRACHEA & OESOPHAGUS


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•The laryngotracheal groove which gives rise to the larynx is also the primordium of the tracheobronchial tree.

•The endodermal lining of this groove forms the pulmonary ciliated columnar epithelium lining the trachea.

•By the 5th wk I.U., upon differentiation from the larynx, this groove evaginates forming the respiratory diverticulum or the lung bud.

•This diverticulum then elongates and invests with the foregut mesenchyme at its distal end giving rise to a globular tracheal bud.


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•This tracheal bud then eventually grows and gives rise to the bronchial buds that grow, enlarge and divide to form the tracheobronchial tree.

•The part of the distal end of the laryngotracheal groove that does not differentiate with the respiratory diverticulum, continues its association with the pharyngeal wall.

•This terminal part separates from the trachea through a tracheo-oesophageal fold and grows downwards and distally to form the oesophagus.


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DEVELOPMENT OF

SALIVARY GLANDS


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STAGES IN DEVELOPMENT

•Bud formation

•Cord formation

•Branching of cords

•Lobule formation

•Canalisation of cords

•Cytodifferentiation


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•BUD FORMATION

•Mesenchyme underlying buccal mucosa induces proliferation in the epithelium.

•Leads to formation of a growing bud, separated from mesenchyme by basal lamina


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•CORD FORMATION

•This epithelial bud then further proliferates to develop into a cord.

•It is accompanied by condensation of the mesenchyme around the developing cord.


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•BRANCHING OF CORDS

•Initiation of branching occurs in terminal parts of epithelial cord.

•These branches grow into terminal berry like bulbs.


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•LOBULE FORMATION

•As branching continues, connective tissue differentiates around them, eventually producing extensive lobulation.

•The glandular tissue forms from mesenchyme and surrounds the entire structure(presumptive acini).


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•CANALISATION OF CORDS

•Occurs due to: Differential rates of cell proliferation

Increased hydrostatic pressure due to fluid secretion by marginal (presumptive ductal) cells.


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•CYTODIFFERENTIATION

•Individual cells begin to differentiate into proacinar, ductal and tubular cells.

•Stem cells in the terminal bulb portions give rise to myoepithelial cells.


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•Parotid gland originates near the corner of stomodaeum by 6th wk I.U.

•Submandibular from floor of mouth by end of 6th wk I.U.

•Sublingual forms lateral to the submandibular gland at about 8th wk I.U.

•Minor glands develop by 12th wk I.U. in respective areas.


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TO SUMMARISE..

•FACE-4th to 8th wk I.U.-1st arch•TMJ-6th to 7th wk I.U.-1st arch•TONGUE-5th wk I.U.-1st, 3rd & 4th arch•PNS-10th wk to 4th month I.U.-1st arch•PHARYNX-3rd wk I.U.-All arches•LARYNX-4th wk I.U.-4th & 6th arch•TRACHEA & OESOPHAGUS-5th wk I.U.-6th arch•SALIVARY GLANDS-6th to 12th wk I.U.-mesenchyme of 1st arch


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CONCLUSION

Thorough, comprehensive knowledge of the in utero growth and development is of prime importance, as it not only allows for timely detection and diagnosis of anomalies, if any, at the right preliminary stage, but, retrospectively, also gives us an insight into the fundamentals of foetogenesis for prevention of the same.


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REFERENCES

•Avery JK. Essentials of Oral Histology and Embryology. 3rd ed. St.Louis: Elsevier; 2006

•Bath-Balogh M. Dental Embryology, Histology and Anatomy. 2nd ed. Seattle:Elsevier; 2006

•Sadler TW. Langman’s Medical Embryology. 11th ed. Baltimore: Lippincott Williams & Wilkins;2010


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•Singh I. Human Embryology. 9th ed. New Delhi: Macmillan Inc;2012

•Sperber GH. Craniofacial Development. 5th ed. London:BC Decker Inc;2001


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Education

Embryology of face, tmj, tongue, paranasal sinuses, pharynx, larynx, trachea, oesophagus & salivary gland