Embryology of Branchial Embryology of Branchial Arches & Nerve SupplyArches & Nerve Supply

((Applied AnatomyApplied Anatomy))

By: Osama ElhamzawyBy: Osama Elhamzawy

Faculty of Medicine Faculty of Medicine Alexandria University - EgyptAlexandria University - Egypt

During the pre –Embryonic period, the cells differentiate into three germ layers:

Ectoderm (outside layer)

Mesoderm (middle layer)

Endoderm (inside layer)

Introduction:

Ectoderm gives rise to the CNS, peripheral nervous system; sensory epithelia of the eye, ear, and nose; epidermis and its appendages (hair and nails).

Neural crest cells derived from neuroectoderm, give rise to the cells of the spinal, cranial (cranial nerves V, VII, IX, and X), and autonomic ganglia; ensheathing cells of the peripheral nervous system; pigment cells of the dermis; muscle, connective tissues, and bone of pharyngeal arch origin and meninges (coverings) of the brain and spinal cord.

Introduction:

Mesoderm gives rise to connective tissue; cartilage; bone; striated and smooth muscles; blood, and lymphatic vessels; heart, kidneys; ovaries; testes; genital ducts; serous membranes lining the body cavities (pericardial, pleural, and peritoneal); spleen; and cortex of suprarenal glands.

Endoderm gives rise to the epithelial lining of the gastrointestinal and respiratory tracts, urinary bladder , tympanic cavity, tympanic antrum, and auditory tube parenchyma of the tonsils, thyroid and parathyroid glands, thymus, liver, and pancreas.

Introduction:

The pharyngeal arches begin to develop early in the fourth week as neural crest cells migrate into the future head and neck regions.

The first pair of pharyngeal arches, the primordium of

the jaws, appears as surface elevations lateral to the developing pharynx.

Soon other arches appear as obliquely disposed, rounded ridges on each side of the future head and neck regions.

Pharyngeal Arches

Pharyngeal Arches By the end of the fourth week, four pairs of pharyngeal

arches are visible externally.

The fifth and sixth arches are rudimentary and are not visible on the surface of the embryo.

The pharyngeal arches are separated from each other by the pharyngeal grooves. Like the pharyngeal arches, the grooves are numbered in a craniocaudal sequence.

Pharyngeal ApparatusPharyngeal Apparatus

Pharyngeal apparatus consists of:Pharyngeal apparatus consists of:

Pharyngeal archesPharyngeal arches Pharyngeal pouchesPharyngeal pouches Pharyngeal groovesPharyngeal grooves Pharyngeal membranePharyngeal membrane

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

But during the fourth week most of the But during the fourth week most of the mesenchyme is derived from neural crest cells mesenchyme is derived from neural crest cells that migrate into the pharyngeal archesthat migrate into the pharyngeal arches

Fate of Pharyngeal ArchesFate of Pharyngeal Arches 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 An aortic archaortic arch, an artery that arises from the truncus , an artery that arises from the truncus arteriosus of the primordial heartarteriosus of the primordial heart

A A cartilaginous rod cartilaginous rod that forms the skeleton of the archthat forms the skeleton of the arch

A A muscular component muscular component that differentiates into muscles that differentiates into muscles in the head and neckin the head and neck

A A nervenerve that supplies the mucosa and muscles derived that supplies the mucosa and muscles derived from the archfrom the arch

The dorsal end (Meckel cartilage) ossifies to The dorsal end (Meckel cartilage) ossifies to form malleus and incusform malleus and incus

The middle part forms anterior ligament of The middle part forms anterior ligament of malleus (sphenomandibular ligament)malleus (sphenomandibular ligament)

Ventral part forms primordium of the mandibleVentral part forms primordium of the mandible

The cartilage disappears as mandible develops The cartilage disappears as mandible develops around it around it

First Pharyngeal Arch cartilageFirst Pharyngeal Arch cartilage

The dorsal end (Reichert cartilage) ossifies to The dorsal end (Reichert cartilage) ossifies to form the stapes and styloid process of the form the stapes and styloid process of the temporal bonetemporal bone

The ventral end ossifies to form the lesser cornu The ventral end ossifies to form the lesser cornu and superior part of the body of the hyoid bone and superior part of the body of the hyoid bone

Its perichondrium forms the stylohyoid ligament Its perichondrium forms the stylohyoid ligament

Second Pharyngeal Arch Second Pharyngeal Arch cartilagecartilage

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 the laryngeal cartilages except epiglottisepiglottis which which develops from develops from hypopharyngealhypopharyngeal eminence eminence

The fifth pharyngeal arch is rudimentary and has The fifth pharyngeal arch is rudimentary and has no derivativesno derivatives

Third, Fourth, Fifth and Sixth Third, Fourth, Fifth and Sixth Pharyngeal Arches cartilagesPharyngeal Arches cartilages

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 and constrictors of The fourth arch forms cricothyroid and constrictors of pharynxpharynx

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

The first pharyngeal arch supplied by the caudal two The first pharyngeal arch supplied by the caudal two branches of Trigeminal nerve (maxillary and mandibular) branches of Trigeminal nerve (maxillary and mandibular)

The second pharyngeal arch supplied by facial nerves The second pharyngeal arch supplied by facial nerves supply, and caudal (fourth to sixth) arches respectivelysupply, and caudal (fourth to sixth) arches respectively

The third pharyngeal arch supplied by glossopharyngeal The third pharyngeal arch supplied by glossopharyngeal nervenerve

Fourth to sixth supplied by vagus Fourth to sixth supplied by vagus 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

There are four well defined pairs of pharyngeal There are four well defined pairs of pharyngeal pouchespouches

The pairs of pouches develop in a craniocaudal The pairs of pouches develop in a craniocaudal sequence between the archessequence between the arches

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

First Pharyngeal PouchFirst Pharyngeal Pouch

The first pharyngeal pouch expands into an The first pharyngeal pouch expands into an elongate tubotympanic recesselongate tubotympanic recess

And forms the endoderm lines the future And forms the endoderm lines the future Eustachian tube , middle ear, mastoid antrum.Eustachian tube , middle ear, mastoid antrum.

And inner layer of the tympanic membraneAnd inner layer of the tympanic membrane

Second Pharyngeal PouchSecond Pharyngeal Pouch

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

Second Pharyngeal PouchSecond Pharyngeal Pouch

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

Third Pharyngeal PouchThird Pharyngeal Pouch

The third pharyngeal pouch expands and The third pharyngeal pouch expands and develops a solid, develops a solid, dorsal bulbar dorsal bulbar part and a part and a hollow hollow elongate ventral elongate ventral partpart

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

Third Pharyngeal PouchThird Pharyngeal Pouch The epithelium of the The epithelium of the elongate ventral elongate ventral parts of third parts of third

pharyngeal pouch (primordia of thymus) proliferates and pharyngeal pouch (primordia of thymus) proliferates and their cavities obliteratetheir cavities obliterate

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

Each lobe has its capsule own blood supply, lymphatic Each lobe has its capsule own blood supply, lymphatic drainage and nerve supplydrainage and nerve supply

Third Pharyngeal PouchThird Pharyngeal Pouch

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

Fourth Pharyngeal PouchFourth Pharyngeal Pouch

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

Fourth Pharyngeal PouchFourth Pharyngeal Pouch

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

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 body that gives the ultimopharyngeal body that gives the calcitonin producing cells (parafollicular calcitonin producing cells (parafollicular cells or C cells of the thyroid gland)cells or C cells of the thyroid gland)

Pharyngeal GroovesPharyngeal Grooves

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

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

Only first pharyngeal membrane becomes the Only first pharyngeal membrane becomes the tympanic membrane, others obliteratetympanic membrane, others obliterate

Birth Defects Involving the

Pharyngeal Region

Birth Defects Involving the Pharyngeal Region

1. Ectopic Thymic and Parathyroid Tissue2. Branchial Fistulas 3. Neural Crest Cells and Craniofacial Defects

• Treacher Collins syndrome (mandibulofacial dysostosis)

• Robin sequence• DiGeorge anomaly• Velocardiofacial syndrome (VCFS) and conotruncal

anomalies face syndrome• Oculoauriculovertebral spectrum (Goldenhar

syndrome) 4. Thyroglossal Duct and Thyroid Abnormalities5. Face anomalies6. Palate anomalies

Birth Defects Involving the Pharyngeal Region

1. Ectopic Thymic and Parathyroid Tissue:

Since glandular tissue derived from the pouches undergoes migration ; accessory glands or remnants of tissue may persist along the pathway particularly for thymic tissue, which may remain in the neck, and for the parathyroid glands.

The inferior parathyroids are more variable in position than the superior ones and are sometimes found at the bifurcation of the common carotid artery.

Birth Defects Involving the Pharyngeal Region

2. Branchial Fistulas

• When the second pharyngeal arch fails to grow caudally over the third and fourth arches, leaving remnants of the second, third, and fourth clefts in contact with the surface by a narrow canal.

• These cysts are always on the lateral side of the neck in front of the sternocleidomastoid muscle.

• They commonly lie under the angle of the mandible and do not enlarge until later in life.

• Internal branchial fistulas are rare and occur when the cervical sinus is connected to the lumen of the pharynx by a small canal, which usually opens in the tonsillar region.

Birth Defects Involving the Pharyngeal Region

3. Neural Crest Cells and Craniofacial Defects

Crest cells also contribute to the conotruncal endocardial cushions which septate the outflow tract of the heart into pulmonary and aortic channelsSo many infants with craniofacial defects may also have cardiac abnormalities such as:•Persistent truncus arteriosus•Tetralogy of Fallot•Transposition of the great vessels

Birth Defects Involving the Pharyngeal Region

Examples of craniofacial defects involving crest cells:

1. Treacher Collins syndrome (mandibulofacial dysostosis)

inherited as an autosomal dominant trait60% of cases arising as new mutations

Characterizaed by : •Malar hypoplasia due to underdevelopment of the zygomatic bones•Mandibular hypoplasia•Down-slanting palpebral fissures•Lower eyelid colobomas•Malformed external ears

Birth Defects Involving the Pharyngeal Region

2. DiGeorge anomaly:

Characterizaed by:•Microstomia•Partial or complete absence of the thymus•immunological deficiencies•Hypocalcemia

Prognosis:Poor

3. Oculoauriculovertebral spectrum (Goldenhar syndrome)

Birth Defects Involving the Pharyngeal Region

Characterized by:•Number of craniofacial abnormalities that usually involve the maxillary, temporal, and zygomatic bones, which are small and flat. •Ear (anotia, microtia)•Eye (tumors and dermoids in the eyeball)•Vertebral (fused hemivertebrae spina bifida)•Cardiac abnormalities (Tetralogy of Fallot and ventricular septal defects)

Birth Defects Involving the Pharyngeal Region

4. Thyroglossal Duct and Thyroid Abnormalities

lie at any point along the migratory pathway of the thyroid gland but is always near or in the midline of the neck

Thyroglossal fistula

Usually arises secondarily after rupture of a cyst but may be present at birth.

5- Face anomalies

Birth Defects Involving the Pharyngeal Region

5- Face anomalies

Birth Defects Involving the Pharyngeal Region

5- Face anomalies

Birth Defects Involving the Pharyngeal Region

1-cleft upper lip:•May be uni/bilateral•There is a defect between the philtrum and the lateral part of the lip•It is due to failure of fusion between the maxillary process and intermaxillary process•Common in males 2-oblique facial cleft:•It is a defect in the face from the medial angle of the eye crossing the side of the nose to the upper lip•It is due to failure of fusion between Maxillary process and the lateral and medial nasal processes•Nasolacrimal duct is exposed to ant. 3-median cleft lower lip:•It is due to failure of fusion between the mandibular processes (rare) 

5- Face anomalies

Birth Defects Involving the Pharyngeal Region

4-macrostomia:It is due to arrest of fusion between Maxillary and mandibular processes to shift the angles medially 5-microstomia: It is due to excessive fusion bet. The maxillary and mandibular processes 

Birth Defects Involving the Pharyngeal Region

5- Face anomalies

5- Face anomalies

Birth Defects Involving the Pharyngeal Region

Birth Defects Involving the Pharyngeal Region

6- Palate anomalies1-cleft palate:Fomes:•Bifid uvula•Cleft soft palate•Cleft hard palate and soft palateIt is due to failure of fusion between the two palatine processes posterior or with the primary palate anterior

2-perforated palate:•It is due to failure of fusion between The 2 palatine processes at certain point at midline.

Birth Defects Involving the Pharyngeal Region

6- Palate anomalies