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Pharyngeal Arches, Pharyngeal Arches, Pouches and CleftsPouches and Clefts
By: Dr. Mujahid KhanBy: Dr. Mujahid Khan
Pharyngeal ApparatusPharyngeal Apparatus
The head and neck region of four week The head and neck region of four week human embryo somewhat resemble these human embryo somewhat resemble these regions of a fish embryo of comparable regions of a fish embryo of comparable stagestage
This explains the former use of This explains the former use of designation branchial apparatusdesignation branchial apparatus
Branchial is derived from the Greek word Branchial is derived from the Greek word branchia or gill branchia or gill
Pharyngeal ApparatusPharyngeal Apparatus
Pharyngeal apparatus consists of:Pharyngeal apparatus consists of:
Pharyngeal archesPharyngeal arches Pharyngeal pouchesPharyngeal pouches Pharyngeal groovesPharyngeal grooves Pharyngeal membranePharyngeal membrane
Pharyngeal ArchesPharyngeal Arches
Pharyngeal arches begin to develop early in the Pharyngeal arches begin to develop early in the fourth week as neural crest cells migrate into the fourth week as neural crest cells migrate into the head and neck regionhead and neck region
The first pair of pharyngeal arches (primordium The first pair of pharyngeal arches (primordium of jaws) appears as a surface elevations lateral of jaws) appears as a surface elevations lateral to the developing pharynxto the developing pharynx
Soon other arches appear as obliquely Soon other arches appear as obliquely disposed, rounded ridges on each side of the disposed, rounded ridges on each side of the future head and neck regionsfuture head and neck regions
Pharyngeal ArchesPharyngeal Arches
By the end of the fourth week, four pairs of By the end of the fourth week, four pairs of pharyngeal arches are visible externallypharyngeal arches are visible externally
The fifth and sixth arches are rudimentary and The fifth and sixth arches are rudimentary and are not visible on the surface of the embryoare not visible on the surface of the embryo
The pharyngeal arches are separated from each The pharyngeal arches are separated from each other by fissures called pharyngeal groovesother by fissures called pharyngeal grooves
They are numbered in craniocaudal sequenceThey are numbered in craniocaudal sequence
Pharyngeal Arch ComponentsPharyngeal Arch Components
Each pharyngeal arch consists of a core of Each pharyngeal arch consists of a core of mesenchymemesenchyme
Is covered externally by ectoderm and internally Is covered externally by ectoderm and internally by endodermby endoderm
In the third week the original mesenchyme is In the third week the original mesenchyme is derived from mesodermderived from mesoderm
During the fourth week most of the mesenchyme During the fourth week most of the mesenchyme is derived from neural crest cells that migrate is derived from neural crest cells that migrate into the pharyngeal archesinto the pharyngeal arches
Fate of Pharyngeal ArchesFate of Pharyngeal Arches
The pharyngeal arches contribute exclusively to The pharyngeal arches contribute exclusively to the formation the face, nasal cavities, mouth, the formation the face, nasal cavities, mouth, larynx, pharynx and necklarynx, pharynx and neck
During the fifth week, the second pharyngeal During the fifth week, the second pharyngeal arch enlarges and overgrows the third and fourth arch enlarges and overgrows the third and fourth arches, forming the ectodermal depression arches, forming the ectodermal depression called cervical sinuscalled cervical sinus
By the end of seventh week the second to fourth By the end of seventh week the second to fourth pharyngeal grooves and the cervical sinus have pharyngeal grooves and the cervical sinus have disappeared, giving the neck a smooth contourdisappeared, giving the neck a smooth contour
Fate of Pharyngeal ArchesFate of Pharyngeal Arches
A typical pharyngeal arch contains:A typical pharyngeal arch contains:
An aortic arch, an artery that arises from the truncus An aortic arch, an artery that arises from the truncus arteriosus of the primordial heartarteriosus of the primordial heart
A cartilaginous rod that forms the skeleton of the archA cartilaginous rod that forms the skeleton of the arch
A muscular component that differentiates into muscles in A muscular component that differentiates into muscles in the head and neckthe head and neck
A nerve that supplies the mucosa and muscles derived A nerve that supplies the mucosa and muscles derived from the archfrom the arch
Pharyngeal ArchesPharyngeal Arches
The first pharyngeal arch (mandibular The first pharyngeal arch (mandibular arch) develops maxillary and mandibular arch) develops maxillary and mandibular prominencesprominences
The first pair of pharyngeal arches plays a The first pair of pharyngeal arches plays a major role in facial developmentmajor role in facial development
The second pharyngeal arch (hyoid arch) The second pharyngeal arch (hyoid arch) contributes to the formation of hyoid bone contributes to the formation of hyoid bone
Derivatives of Pharyngeal Arch Derivatives of Pharyngeal Arch CartilagesCartilages
The dorsal end of first arch cartilage (Meckel The dorsal end of first arch cartilage (Meckel cartilage) ossifies to form malleus and incuscartilage) ossifies to form malleus and incus
The middle part of cartilage forms anterior The middle part of cartilage forms anterior ligament of malleus sphenomandibular ligamentligament of malleus sphenomandibular ligament
Ventral part of the first arch cartilages form Ventral part of the first arch cartilages form primordium of the mandibleprimordium of the mandible
The cartilage disappears as mandible develops The cartilage disappears as mandible develops around it around it
Derivatives of Pharyngeal Arch Derivatives of Pharyngeal Arch CartilagesCartilages
The dorsal end of second arch cartilage The dorsal end of second arch cartilage (Reichert cartilage) ossifies to form the stapes (Reichert cartilage) ossifies to form the stapes and styloid process of the temporal boneand styloid process of the temporal bone
The ventral end of second arch cartilage ossifies The ventral end of second arch cartilage ossifies to form the lesser cornu and superior part of the to form the lesser cornu and superior part of the body of the hyoid bone body of the hyoid bone
Its perichondrium forms the stylohyoid ligament Its perichondrium forms the stylohyoid ligament
Derivatives of Pharyngeal Arch Derivatives of Pharyngeal Arch CartilagesCartilages
The third arch cartilage ossifies to form the The third arch cartilage ossifies to form the greater cornu and the inferior part of the body of greater cornu and the inferior part of the body of the hyoid bonethe hyoid bone
The fourth and sixth arch cartilages fuse to form The fourth and sixth arch cartilages fuse to form the laryngeal cartilages except epiglottis which the laryngeal cartilages except epiglottis which develops from hypopharyngeal eminencedevelops from hypopharyngeal eminence
The fifth pharyngeal arch is rudimentary and has The fifth pharyngeal arch is rudimentary and has no derivativesno derivatives
Derivatives of Pharyngeal Arch Derivatives of Pharyngeal Arch MusclesMuscles
The musculature of the first pharyngeal arch forms the The musculature of the first pharyngeal arch forms the muscles of masticationmuscles of mastication
The second pharyngeal arch forms the stapedius, The second pharyngeal arch forms the stapedius, stylohyoid, posterior belly of digastric, auricular and stylohyoid, posterior belly of digastric, auricular and muscles of facial expressionmuscles of facial expression
The third arch forms the stylopharyngeusThe third arch forms the stylopharyngeus
The fourth arch forms cricothyroid, levator veli palatini The fourth arch forms cricothyroid, levator veli palatini and constrictors of pharynxand constrictors of pharynx
Sixth pharyngeal arch forms the intrinsic muscles of the Sixth pharyngeal arch forms the intrinsic muscles of the larynxlarynx
Derivatives of Pharyngeal Arch Derivatives of Pharyngeal Arch NervesNerves
Caudal two branches of Trigeminal nerve (maxillary and Caudal two branches of Trigeminal nerve (maxillary and mandibular) supply derivatives of the first pharyngeal mandibular) supply derivatives of the first pharyngeal archarch
The facial, glossopharyngeal and vagus nerves supply The facial, glossopharyngeal and vagus nerves supply the second, third and caudal (fourth to sixth) arches the second, third and caudal (fourth to sixth) arches respectivelyrespectively
The fourth arch is supplied by superior laryngeal branch The fourth arch is supplied by superior laryngeal branch of vagus nerveof vagus nerve
The sixth arch is supplied by its recurrent laryngeal The sixth arch is supplied by its recurrent laryngeal branchbranch
Pharyngeal PouchesPharyngeal Pouches
The primordial pharynx, derived from the The primordial pharynx, derived from the foregut, widens cranially where it joins the foregut, widens cranially where it joins the primordial mouth or stomodeumprimordial mouth or stomodeum
It narrows caudally where it joins the esophagusIt narrows caudally where it joins the esophagus
The endoderm of the pharynx lines the internal The endoderm of the pharynx lines the internal aspects of pharyngeal arches and passes into aspects of pharyngeal arches and passes into balloonlike diverticula called pharyngeal balloonlike diverticula called pharyngeal pouchespouches
Pharyngeal PouchesPharyngeal Pouches
The pairs of pouches develop in a craniocaudal The pairs of pouches develop in a craniocaudal sequence between the archessequence between the arches
The first pair of pouches lies between the first The first pair of pouches lies between the first and second pharyngeal archesand second pharyngeal arches
There are four well defined pairs of pharyngeal There are four well defined pairs of pharyngeal pouchespouches
The fifth pair is absent or rudimentaryThe fifth pair is absent or rudimentary
Pharyngeal PouchesPharyngeal Pouches
The endoderm of the pouches contacts The endoderm of the pouches contacts the ectoderm of the pharyngeal grooves the ectoderm of the pharyngeal grooves and together they form the double layered and together they form the double layered pharyngeal membranes that separate the pharyngeal membranes that separate the pharyngeal pouches from the pharyngeal pharyngeal pouches from the pharyngeal groovesgrooves
Derivatives of First Pharyngeal Derivatives of First Pharyngeal PouchPouch
The first pharyngeal pouch expands into an The first pharyngeal pouch expands into an elongate tubotympanic recesselongate tubotympanic recess
The expanded distal part of this recess contacts The expanded distal part of this recess contacts
the first pharyngeal groove, where it contributes the first pharyngeal groove, where it contributes to the formation of the tympanic membrane to the formation of the tympanic membrane (eardrum)(eardrum)
The cavity of the tubotympanic recess gives rise The cavity of the tubotympanic recess gives rise to the tympanic cavity and mastoid antrumto the tympanic cavity and mastoid antrum
Derivatives of Second Pharyngeal Derivatives of Second Pharyngeal PouchPouch
The second pharyngeal pouch is largely The second pharyngeal pouch is largely obliterated as the palatine tonsils developobliterated as the palatine tonsils develop
Part of the cavity of this pouch remains as the Part of the cavity of this pouch remains as the tonsillar sinus or fossatonsillar sinus or fossa
The endoderm of the pouch proliferates and The endoderm of the pouch proliferates and grows into the underlying mesenchymegrows into the underlying mesenchyme
The central parts of these buds form crypts The central parts of these buds form crypts
Derivatives of Second Pharyngeal Derivatives of Second Pharyngeal PouchPouch
The pouch endoderm forms the surface The pouch endoderm forms the surface epithelium and the lining of the tonsillar epithelium and the lining of the tonsillar cryptscrypts
At about 20 weeks the mesenchyme At about 20 weeks the mesenchyme around the crypts differentiates into around the crypts differentiates into lymphoid tissuelymphoid tissue
These tissues soon organizes into the These tissues soon organizes into the lymphatic nodules of the palatine tonsillymphatic nodules of the palatine tonsil
Derivatives of Third Pharyngeal Derivatives of Third Pharyngeal PouchPouch
The third pharyngeal pouch expands and The third pharyngeal pouch expands and develops a solid, dorsal bulbar part and a hollow develops a solid, dorsal bulbar part and a hollow elongate ventral partelongate ventral part
Its connection with the pharynx is reduced to a Its connection with the pharynx is reduced to a narrow duct that soon degeneratesnarrow duct that soon degenerates
By the sixth week the epithelium of each dorsal By the sixth week the epithelium of each dorsal bulbar part begins to differentiate into inferior bulbar part begins to differentiate into inferior parathyroid glandparathyroid gland
Derivatives of Third Pharyngeal Derivatives of Third Pharyngeal PouchPouch
The epithelium of the elongate ventral parts of third The epithelium of the elongate ventral parts of third pharyngeal pouch proliferates and their cavities pharyngeal pouch proliferates and their cavities obliterateobliterate
These bilateral primordia of thymus come together in the These bilateral primordia of thymus come together in the median plane to form thymus median plane to form thymus
It descends into the superior mediastenumIt descends into the superior mediastenum
The bilobed form of thymus remains throughout lifeThe bilobed form of thymus remains throughout life
Discretely encapsulated and each lobe has its own blood Discretely encapsulated and each lobe has its own blood supply, lymphatic drainage and nerve supplysupply, lymphatic drainage and nerve supply
Derivatives of Third Pharyngeal Derivatives of Third Pharyngeal PouchPouch
The primordia of thymus and parathyroid The primordia of thymus and parathyroid glands lose their connections with the glands lose their connections with the pharynx and migrate into the neckpharynx and migrate into the neck
Later the parathyroid glands separate from Later the parathyroid glands separate from the thymus and lie on the dorsal surface of the thymus and lie on the dorsal surface of the thyroid glandthe thyroid gland
Derivatives of Fourth Pharyngeal Derivatives of Fourth Pharyngeal PouchPouch
The fourth pharyngeal pouch also expands into The fourth pharyngeal pouch also expands into dorsal bulbar and elongate ventral partsdorsal bulbar and elongate ventral parts
Its connection with the pharynx is reduced to a Its connection with the pharynx is reduced to a narrow duct that soon degeneratesnarrow duct that soon degenerates
By the sixth week, each dorsal part develops By the sixth week, each dorsal part develops into a superior parathyroid glandinto a superior parathyroid gland
It lies on the dorsal surface of the thyroid glandIt lies on the dorsal surface of the thyroid gland
Derivatives of Fourth Pharyngeal Derivatives of Fourth Pharyngeal PouchPouch
The parathyroid glands derived from the The parathyroid glands derived from the third pouches descend with the thymus third pouches descend with the thymus and are carried to a more inferior position and are carried to a more inferior position than the parathyroid derived from the than the parathyroid derived from the fourth pouchesfourth pouches
This explains why the parathyroid glands This explains why the parathyroid glands derived from the third pair of pouches are derived from the third pair of pouches are located inferior to those from the fourth located inferior to those from the fourth pouchespouches
Histogenesis of Parathyroid GlandHistogenesis of Parathyroid Gland
The epithelium of the dorsal parts of the third and fourth The epithelium of the dorsal parts of the third and fourth pouches proliferates during the fifth weekpouches proliferates during the fifth week
Forms small nodules on the dorsal aspect of each pouchForms small nodules on the dorsal aspect of each pouch
Vascular mesenchyme soon grows into these nodules, Vascular mesenchyme soon grows into these nodules, forming capillary networkforming capillary network
The chief or principal cells differentiate during the The chief or principal cells differentiate during the embryonic period and regulate fetal calcium metabolismembryonic period and regulate fetal calcium metabolism
The oxiphil cells differentiate 5 to 7 years after birthThe oxiphil cells differentiate 5 to 7 years after birth
Histogenesis of Parathyroid GlandHistogenesis of Parathyroid Gland
The elongated ventral part of each fourth pouch The elongated ventral part of each fourth pouch develops into ultimopharyngeal bodydevelops into ultimopharyngeal body
Its cells disseminate within the thyroid gland, Its cells disseminate within the thyroid gland, giving rise to parafollicular cellsgiving rise to parafollicular cells
They are also called “C” cells because they They are also called “C” cells because they produce calcitonin that regulate normal calcium produce calcitonin that regulate normal calcium level in body fluidslevel in body fluids
““C” cells differentiate from neural crest cellsC” cells differentiate from neural crest cells
The Fifth Pharyngeal PouchThe Fifth Pharyngeal Pouch
When this develops, this rudimentary When this develops, this rudimentary pouch becomes part of the fourth pouch becomes part of the fourth pharyngeal pouch and helps to form the pharyngeal pouch and helps to form the ultimopharyngeal bodyultimopharyngeal body
Pharyngeal GroovesPharyngeal Grooves
During the fourth and fifth weeks, head and neck During the fourth and fifth weeks, head and neck region of the human embryo exhibit four region of the human embryo exhibit four pharyngeal grooves or clefts on each side pharyngeal grooves or clefts on each side
These grooves separate the pharyngeal arches These grooves separate the pharyngeal arches externallyexternally
Only first pair persists as the external acoustic Only first pair persists as the external acoustic meatusmeatus
The other grooves normally obliterated with the The other grooves normally obliterated with the cervical sinus as the neck developscervical sinus as the neck develops
Pharyngeal MembranesPharyngeal Membranes
Pharyngeal membranes appear in the floor of Pharyngeal membranes appear in the floor of the pharyngeal groovesthe pharyngeal grooves
These membranes form where the epithelia of These membranes form where the epithelia of the grooves and pouches approach each otherthe grooves and pouches approach each other
The endoderm of the pouches and ectoderm of The endoderm of the pouches and ectoderm of the grooves are soon separated by the grooves are soon separated by mesenchymemesenchyme
Only first pharyngeal membrane becomes the Only first pharyngeal membrane becomes the tympanic membrane, others obliteratetympanic membrane, others obliterate