Transcript 02-Pharyngeal Arches..

Pharyngeal Arches
Stay with us
• That’s why they called • The head and the
it branchial apparatus
neck region of four
week human embryo
‫خيشوم‬
look
like
the
same
• Because branchial
region in a fish
mean gill , which is a
embryo at the same
Greek word
time ( the 4th week )
Pharyngeal apparatus consists of :
Pharyngeal
membran
Pharyngeal groove
Pharyngeal arch
Pharyngeal pouch
• Pharyngeal arches begin to
develop early in the fourth week as
neural crest cells migrate into the
head and neck region
• 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
• 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
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
• The second pharyngeal arch ( hyoid arch ) contributes to the formation of hyoid
bone
• Each pharyngeal arch consist of a core of mesenchyme
• That is covered externally by ectoderm and internally by endoderm
mesenchyme
• 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
•The pharyngeal arches
contribute exclusively in
the formation of the :
• face
• Nasal cavities
• mouth
• larynx
• pharynx
• neck
• 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 , 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
Derivatives of The First Pharyngeal Arch Cartilage
• Ventral part of the first
arch cartilages form
primordium of the
mandible
• The middle part of
cartilage forms anterior
ligament of malleus
and sphenomandibular
ligament
• The dorsal end of
first arch cartilage
( Meckel cartilage )
ossifies to form
malleus and incus
] The cartilage disappears as mandible develops around it [
Derivatives of The second Pharyngeal Arch Cartilage
• The ventral end of second
arch cartilage ossifies to form
the lesser cornu and superior
part of the body of the hyoid
bone
• The dorsal end of second
arch cartilage (Reichert
cartilage) ossifies to form
the stapes and styloid
process of the temporal
bone
Its perichondrium ( fibrous around the cartilage ) forms the stylohyoid ligament
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
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
Derivatives of Pharyngeal Arch Muscles
• The muscles of
the first
pharyngeal arch
forms the
muscles of
mastication
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
Derivatives of Pharyngeal Arch Muscles
• The third arch
forms the :
stylopharyngeus
Derivatives of Pharyngeal Arch Muscles
• The fourth arch
forms :
1 - cricothyroid
muscle
2 - levator veli
palatini
3 - constrictors of
pharynx
Derivatives of 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 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
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
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
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
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
The cavity
thepharyngeal
tubotympanic
recess
contacts
theoffirst
groove
, gives
rise toitthe
tympanicto
cavity
and mastoid
where
contributes
the formation
of the
antrum membrane (eardrum)
tympanic
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
proliferates and grows into the
underlying mesenchyme
the central parts of these buds
form crypts
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
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
• 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
• 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
Separately encapsulated and each lobe has its own blood supply, lymphatic drainage
and nerve supply
Derivatives of Third Pharyngeal Pouch
• The primordia of thymus and
inferior parathyroid glands lose
their connections with the pharynx
and migrate into the neck
superior
inferior
• Later the inferior parathyroid
glands separate from the thymus
and lie on the dorsal surface of
the thyroid gland
Derivatives of Fourth Pharyngeal Pouch
• By the sixth week,
each dorsal part
develops into a
superior parathyroid
gland
• The fourth pharyngeal
pouch also expands into
1- dorsal bulbar part
2- elongate ventral parts
It lies on the dorsal surface of the thyroid gland
• Its connection
with the pharynx is
reduced to a
narrow duct that
soon degenerates
Derivatives of Fourth Pharyngeal Pouch
•The
parathyroid
derived from
the derived
third pouches
descend
withofthe
This explains
whyglands
the parathyroid
glands
from the
third pair
pouches
thymus
are located inferior to those from the fourth pouches
and are carried to a more inferior position than the parathyroid derived 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
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
• The chief or principal cells differentiate during
the embryonic period and regulate fetal calcium
metabolism
• soon the Vascular
mesenchyme grows into (enter
) these nodules, forming
capillary network
•The oxiphil cells differentiate 5
to 7 years after birth
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
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
• Only first pharyngeal
pharyngeal grooves
membrane becomes the
•tympanic
These membranes
membrane,
formed
where the epithelia
others obliterate
of
the grooves
( disappear
) and
pouches approach each
other
• The endoderm of the
pouches and ectoderm of
the grooves are soon
separated by
mesenchyme
-----------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------