PHARYNGEAL APPARATUS

Branchial apparatus

• “GILL” , (Greek)

Pharyngeal apparatus consists of :

Pharyngeal arch

Pharyngeal pouch

Pharyngeal membrane

Pharyngeal groove

PHARYNGEAL APPARATUS

PHARYNGEAL ARCHES

• The pharyngeal arches contribute exclusively in the formation of the :

• Face• Nasal cavities• Mouth• Larynx• Pharynx• Neck

• The first pair of pharyngeal arches appears as an elevation on the surface , lateral to the developing pharynx

• By the end of the fourth week 4 pairs of pharyngeal arches are visible externally

• The fifth and sixth arches are not visible externally

• The pharyngeal arches are separated by a depression called pharyngeal groove or cleft externally , and pharyngeal pouch internally

• Numbered in craniocaudal sequence

• Each pharyngeal arch consist of a core of mesenchyme • That is covered externally by ectoderm and internally by endoderm

mesenchyme

• 3rd week mesenchyme - derived from mesoderm

• 4th week mesenchyme - derived from neural crest cells that migrate into the pharyngeal arches

• During the 5th week , the second pharyngeal arch enlarges and overgrows the 4th and the 3rd

arches forming an ectodermal depression called cervical sinus

• by the end of 7th week , the 2nd to the 4th pharyngeal grooves and the cervical sinus are disappeared , giving the neck a smooth surface

2nd arch

A typical pharyngeal arch contains:

1- An aortic arch

2- A cartilaginous rod

3- A muscular component

4- A nerve

PHARYNGEAL APPARATUS

PHARYNGEAL ARCH DERIVATIVES

Derivatives of The First Pharyngeal Arch Cartilage

• The dorsal end of first arch cartilage ( Meckel’s cartilage ) ossifies to form malleus and incus

• The middle part of cartilage forms anterior ligament of malleus and sphenomandibular ligament

• Ventral part of the first arch cartilages form primordium of the mandible

] The cartilage disappears as mandible develops around it [

• The first pharyngeal arch gives a rise to maxillary and mandibular process

• Major role in facial development

Mandibular processMaxillaryprocess

Derivatives of second pharyngeal arch

• The dorsal end of second arch cartilage (Reichert cartilage) ossifies to form

• the stapes and

• styloid process

• The ventral end of second arch cartilage ossifies to form

• the lesser cornu and

• superior part of the body of the hyoid bone

Its perichondrium forms the stylohyoid ligament

• The second pharyngeal arch ( hyoid arch ) contributes to the formation of hyoid bone

Derivatives of The Third Pharyngeal Arch Cartilage

• The third arch cartilage ossifies to form the greater cornu and the inferior part of the body of the hyoid bone

• The fourth and sixth arch cartilages fuse to form the laryngeal cartilages except epiglottis which develops from hypopharyngeal eminence

• The fifth pharyngeal arch is rudimentary ( disappear later) and has no derivatives

Derivatives of fourth pharyngeal arch cartilages

Derivatives of Pharyngeal Arch Muscles

• The muscles of the first pharyngeal arch forms the muscles of mastication

Derivatives of 2nd Pharyngeal arch muscles

• The second pharyngeal arch forms the :

1 - stapedius

2 - stylohyoid

3 - posterior belly of digastric

4 - auricular

5 - muscles of facial expression

Derivatives of 3rd pharyngeal arch muscles

• The third arch forms the :

stylopharyngeus

Derivatives of 4th pharyngeal arch muscles

• The fourth arch forms :

1 - cricothyroid muscle

2 - levator veli palatini

3 - constrictors of pharynx

Derivatives of 6th pharyngeal arch muscles

• The sixth pharyngeal arch forms the intrinsic muscles of the larynx

Derivatives of Pharyngeal Arch Nerves

• The trigeminal nerve ( the fifth cranial nerve ) supply derivatives of the first pharyngeal arch by it’s caudal two branches

1 - maxillary branch

2- mandibular branch

Derivatives of Pharyngeal Arch Nerves

• The facial nerve ( VII ( supply the second arch

• The glossopharyngeal nerve (IX) supply the third arch

• The vagus nerve (X) supply the fourth and sixth arches by :

1 - superior laryngeal branch supply the 4th

2 - recurrent laryngeal branch supply the 6th

PHARYNGEAL APPARATUS

PHARYNGEAL POUCHES

• The primordial pharynx , derived from the foregut

widens cranially where it joins the primordial mouth or stomodeum• It narrows caudally where it joins the esophagus

• The pharyngeal pouches are balloonlike diverticula that formed on the endodermal side between the pharyngeal arches

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

• The first pair of pouches lies between the first and second pharyngeal arches

• There are four well defined pairs of pharyngeal pouches

• The fifth pair is absent or rudimentary

Derivatives of First Pharyngeal Pouch

• The first pharyngeal pouch expands into an elongate tubotympanic recess

Derivatives of First Pharyngeal Pouch

The expanded distal part of this recess contacts the first pharyngeal groove , where it contributes to the formation of the tympanic membrane (eardrum)

The cavity of the tubotympanic recess gives rise to the tympanic cavity and mastoid antrum

Derivatives of Second Pharyngeal Pouch

• The second pharyngeal pouch is largely obliterated (disappear) as the palatine tonsils develop

• Part of the cavity of this pouch remains as the tonsillar sinus or fossa

Derivatives of Second Pharyngeal Pouch

The endoderm of the pouch grows into the underlying mesenchyme.

the central parts of these buds form crypts

Derivatives of Second Pharyngeal Pouch

• At about 20 weeks the mesenchyme around the crypts differentiates into lymphoid tissue

• These tissues soon organize into the lymphatic nodules of the palatine tonsil

Derivatives of Third Pharyngeal Pouch

• The third pharyngeal pouch expands and develops a :

1- solid dorsal part

2- hollow ventral part• Its connection with the

pharynx is reduced to a narrow duct that soon degenerates

• By the sixth week the epithelium of :

1- each dorsal part begins to differentiate into inferior parathyroid gland

2 – each ventral parts begins to differentiate into primordia of thymus

• These bilateral primordia of thymus come together in the median plane to form thymus

• It descends into the superior mediastenum

Derivatives of Third Pharyngeal Pouch

• The primordia of thymus and inferior parathyroid glands lose their connections with the pharynx and migrate into the neck

• Later the inferior parathyroid glands separate from the thymus and lie on the dorsal surface of the thyroid gland

superior

inferior

Derivatives of Fourth Pharyngeal Pouch

• The fourth pharyngeal pouch also expands into

1- dorsal part

2- ventral parts

• Its connection with the pharynx is reduced to a narrow duct that soon degenerates

• By the sixth week, each dorsal part develops into a superior parathyroid gland

Derivatives of Fourth Pharyngeal Pouch

• The parathyroid glands derived from the third pouches descend with the thymus

and are carried to a more inferior position than the parathyroid derived from the fourth pouches

This explains why the parathyroid glands derived from the third pair of pouches are located inferior to those from the fourth pouches

The Fifth Pharyngeal Pouch

• When this develops , this rudimentary pouch becomes part of the fourth pharyngeal pouch and helps to form the ultimopharyngeal body

PHARYNGEAL APPARATUS

PHARYNGEAL GROOVES

• During the fourth and fifth weeks, head and neck region of the human embryo exhibit four pharyngeal grooves or clefts on each side

• These grooves separate the pharyngeal arches externally

• Only first pair persists as the external acoustic meatus ( external auditory canal )

• The other grooves normally obliterated ( disappear ) with the cervical sinus as the neck develops

Pharyngeal Membranes

• Pharyngeal membranes appear in the floor of the pharyngeal grooves

• These membranes formed where the epithelia of the grooves and pouches approach each other

• The endoderm of the pouches and ectoderm of the grooves are soon separated by mesenchyme

• Only first pharyngeal membrane becomes the tympanic membrane, others obliterate ( disappear )

RECOMMENDED READING

• LANGMAN’S MEDICAL EMBRYOLOGY – 11th edition

• CHAPTER 16 – Head and Neck Pgs. 265 – 278