1. Pharyngeal Arches
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2. That’s why they called it branchial apparatus
Because branchial mean gill , which is a Greek word
The head and the neck region of four week human embryo look like the same region in a fish embryo at the same time ( the 4th week )
خيشوم

3. Pharyngeal apparatus consists of :
Pharyngeal membran
Pharyngeal groove
Pharyngeal pouch
Pharyngeal arch

4. Pharyngeal arches begin to develop early in the fourth week as neural crest cells migrate into the head and neck region

5. The first pair of pharyngeal arches ( primordium of jaws) appears as an elevation on the surface , lateral to the developing pharynx
soon other arches appear on each side of the future head and neck region

6. By the end oh 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 from each other by a depression called pharyngeal groove or cleft externally , and pharyngeal pouch internally
They are numbered in craniocaudal sequence

7. Maxillary
process
Mandibular process
The first pharyngeal arch ( mandibular arch ) gives a rise to maxillary and mandibular process
the first pair of pharyngeal arches plays a major role in facial development

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

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

10. Mesenchyme is derived from mesoderm in the third week
during the fourth week most of the mesenchyme is derived from neural crest cells
that migrate into the pharyngeal arches

11. The pharyngeal arches contribute exclusively in the formation of the :
face
Nasal cavities
mouth
larynx
pharynx
neck

12. forming an ectodermal depression called cervical sinus
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

13. A typical pharyngeal arch contains:
1- An aortic arch , an artery that arises from the truncus arteriosus of the primordial heart
2- A cartilaginous rod that forms the skeleton of the arch
3- A muscular component that differentiates into muscles in the head and neck
4- A nerve that supplies the mucosa and muscles derived from the arch

14. Derivatives of The First Pharyngeal Arch Cartilage
The dorsal end of first arch cartilage ( Meckel 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 [

16. Derivatives of The second Pharyngeal Arch Cartilage
The dorsal end of second arch cartilage (Reichert cartilage) ossifies to form the stapes and styloid process of the temporal bone
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 ( fibrous around the cartilage ) forms the stylohyoid ligament

18. 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

19. Derivatives of The Pharyngeal Arch Cartilages
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

20. Derivatives of Pharyngeal Arch Muscles
The muscles of the first pharyngeal arch forms the muscles of mastication

21. Derivatives of 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

22. Derivatives of Pharyngeal Arch Muscles
The third arch forms the :
stylopharyngeus

23. Derivatives of Pharyngeal Arch Muscles
The fourth arch forms :
1 - cricothyroid muscle
2 - levator veli palatini
3 - constrictors of pharynx

24. Derivatives of Pharyngeal Arch Muscles
The sixth pharyngeal arch forms the intrinsic muscles of the larynx

25. 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

26. Derivatives of Pharyngeal Arch Nerves
The facial nerv ( 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

27. 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

28. Pharyngeal Pouches
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

29. Pharyngeal Pouches
The connection between the endoderm of the pharyngeal pouches and the ectoderm of the pharyngeal grooves form a double layered membrane called the pharyngeal membrane
that separate the pharyngeal pouches from the pharyngeal grooves

30. Derivatives of First Pharyngeal Pouch
The first pharyngeal pouch expands into an elongate tubotympanic recess

31. 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

32. 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

33. Derivatives of Second Pharyngeal Pouch
The endoderm of the pouch proliferates and grows into the underlying mesenchyme
the central parts of these buds form crypts

34. Derivatives of Second Pharyngeal Pouch
The endoderm of the pouch forms the surface epithelium and the lining of the tonsillar crypts
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

35. Derivatives of Third Pharyngeal Pouch
These bilateral primordia of thymus come together in the median plane to form thymus
It descends into the superior mediastenum
The bilobed form of thymus remains throughout life
The third pharyngeal pouch expands and develops a :
1- solid dorsal bulbar part
2- hollow elongate 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 bulbar part begins to differentiate into inferior parathyroid gland
2 - each elongate ventral parts begins to differentiate into primordia of thymus
Separately encapsulated and each lobe has its own blood supply, lymphatic drainage and nerve supply

36. 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

37. Derivatives of Fourth Pharyngeal Pouch
The fourth pharyngeal pouch also expands into
1- dorsal bulbar part
2- elongate ventral parts
By the sixth week, each dorsal part develops into a superior parathyroid gland
Its connection with the pharynx is reduced to a narrow duct that soon degenerates
It lies on the dorsal surface of the thyroid gland

38. 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

39. The Fifth Pharyngeal Pouch
When this develops , this rudimentary pouch becomes part of the fourth pharyngeal pouch and helps to form the ultimopharyngeal body

40. Histogenesis of Parathyroid Gland
The epithelium of the ]bulbar dorsal parts[ of the third and fourth pouches proliferates during the fifth week
Forming small nodules on the dorsal aspect of each pouch
soon the Vascular mesenchyme grows into (enter ) these nodules, forming capillary network
The chief or principal cells differentiate during the embryonic period and regulate fetal calcium metabolism
The oxiphil cells differentiate 5 to 7 years after birth

41. Histogenesis of Parathyroid Gland
The elongated ventral part of each fourth pouch develops into ultimopharyngeal body
Its cells disseminate ( spread ) within the thyroid gland , giving rise to parafollicular cells
They are also called “C” cells because they produce calcitonin that regulate normal calcium level in body fluids
“C” cells differentiate from neural crest cells

42. 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

43. 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 )

44.
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