DEVELOPMENT OF HEAD AND NECK

PHARYNGEAL APPARATUS

PHARYNGEAL APPARATUS

• CONSISTS OF---• 1 PHARYNGEAL/BRANCHIAL ARCHES• 2 PHARYNGEAL/BRANCHIAL POUCHES• 3 PHARYNGEAL/BRANCHIAL GROOVES• 4 PHARYNGEAL/BRANCHIAL MEMBRANES• THESE PRIMITIVE EMBRYONIC STRUCTURES

CONTRIBUTE GREATLY TO THE FORMATION OF HEAD & NECK

PHARYNGEAL APPARATUS

• PHARYNGEAL ANOMALIES RESULT FROM PERSISTENCE OF PARTS OF PHARYNGEAL APPARATUS THAT NORMALLY DISAPPEAR

• OROPHARYNGEAL MEMBRANE ,FORMED DURING THE THIRD WEEK,SEPARATES THE STOMODEUM FROM PRIMITIVE PHARYNX

• OROPHARYNGEAL MEMBRANE RUPTURES ON ABOUT DAY 26

PHARYNGEAL ARCHES

• BEGIN TO DEVELOP EARLY IN THE 4th WEEK WHEN NEURAL CREST CELLS MIGRATE INTO FUTURE HEAD & NECK REGION

• INITIALLY EACH ARCH CONSISTS OF A CORE OF MESENCHYME COVERED EXTERNALLY BY ECTODERM AND INTERNALLY BY ENDODERM

• THE MESENCHYME IS DERIVED FROM---• 1 PARAXIAL MESODERM• 2 LATERAL MESODERM• 3 NEURAL CREST CELLS

PHARYNGEAL ARCHES

• THE ARCHES SUPPORT THE LATERAL WALLS OF THE CRANIAL PART OF THE FOREGUT [ THE PRIMITIVE PHAYRYNX ]

• STOMODEUM [PRIMTIVE MOUTH ] APPEARS AS A SLIGHT DEPRESSION OF SURFACE ECTODERM

• STOMODEUM COVERED BY OROPHARNGEAL MEMBRANE

• PHARYNX COMMUNICATES WITH THE AMNIOTIC CAVITY WHEN OROPHARYNGEAL MEMBRANE RUPTURES

PHARYNGEAL ARCHES

• FIRST PAIR APPEARS LATERAL TO THE DEVELOPING PHARYNX

• OTHER ARCHES APPEAR AS ROUNDED ELEVATIONS ON EACH SIDE OF THE PHARYNX

• BY THE END OF THE 4th WEEK 4 WELL DEFINED PAIRS OF ARCHES ARE VISIBLE EXTERNALLY

• 5th & 6th PAIR OF ARCHES ARE RUDIMENTARY AND NOT VISIBLE EXTERNALLY

PHARYNGEAL ARCHES

• ARCHES ARE SEPARATED FROM EACH OTHER BY GROOVES

• ARCHES AND GROOVES ARE NUMBERED CRANIOCAUDALLY

• PHARYNGEAL ARCH COMPONENTS• 1 SKELETAL COMPONENT• 2 MUSCULAR COMPONENT• 3 ARTERIAL COMPONENT• 4 NERVE COMPONENT

PHARYNGEAL POUCHES

• PRIMITIVE PHARYNX WIDENS CRANIALLY WHERE IT JOINS THE MOUTH

• NARROWS CAUDALLY AS IT JOINS THE OESOPHAGUS

• ENDODERM OF PHARYNX LINES THE INTERNAL ASPECT OF ARCHES

• THE ENDODERM PASSES INTO BALLOON LIKE DIVERTICULA ---THE POUCHES

PHARYNGEAL POUCHES

• PAIRS OF ARCHES DEVELOP IN A CRANIOCAUDAL SEQUENCE • THE 1st PAIR OF POUCHES LIES B/W 1st & 2nd ARCHES• FATE OF PHARYNGEAL POUCHES• FIRST POUCH• EXPANDS INTO TUBOTYMPANIC RECESS WHICH GIVES RISE

TO---• 1 TYMPANIC CAVITY• 2 MASTOID ANTRUM• 3 AUDITORY TUBE WHICH CONNECTS THE TYMPANIC

CAVITY WITH THE PHARYNX

PHARYNGEAL POUCHES

• FATE OF POUCHES• SECOND POUCH• LARGELY OBLITERATES AS PALATINE TONSIL

DEVELOPS• PART OF THE CAVITY REMAINS AS

INTRATONSILLAR CLEFT• ENDODERM PROLIFERATES AND GROWS INTO

THE SURROUNDING MESENCHYME WHICH LATER DIFFERENTIATES INTO LYMPHOID TISSUE

PHARYNGEAL POUCHES

• FATE OF POUCHES• THIRD POUCH• EXPANDS AND FORMS---• 1 SOLID DORSAL BULBAR PORTION---FORMS

INFERIOR PARATHYROID GLAND• 2 HOLLOW ELOGATE VENTRAL PORTION---

FORMS THYMUS

PHARYNGEAL POUCHES

• FATE OF POUCHES• FOURTH POUCH• EXPANDS AND FORMS---• 1 DORSAL BULBAR PORTION---FORMS SUPERIOR

PARATHYROID• 2 VENTRAL ELONGATE PORTION---FORMS

ULTIMOBRANCHIAL BODY WHICH FUSES WITH THYROID GLAND AND GIVES RISE TO PARAFOLLICULAR CELLS

• FIFTH POUCH• RUDIMENTARY AND BECOMES PART OF FOURTH POUCH

PHARYNGEAL GROOVES

• FOUR GROOVES OR CLEFTS ARE PRESENT IN THE NECK REGION OF THE EMBRYO FROM 4th to 6th WEEK

• ONLY 1st GROOVE EXISTS AS EXTERNAL ACOUSTIC MEATUS

• OTHER GROOVES COME TO LIE IN A SLIT LIKE DEPRESSION ---THE CERVICAL SINUS

• THESE GROOVES NORMALLY OBLITERATE AS THE NECK DEVELOPS

PHARYNGEAL MEMBRANES

• TEMPORARY STRUCTURES• APPEAR IN THE BOTTOM OF PHARYNGEAL

GROOVES ON EACH SIDE OF THE NECK DURING THE 4th WEEK

• FORMED WHEN EPITHELIA OF A GROOVE [ECTODERM] AND A POUCH [ENDODERM ] APPROACH EACH OTHER SEPARATED BY MESENCHYME

• ONLY 1st MEMBRANE GIVES RISE TO THE TYMPANIC MEMBRANE