Pharyngeal Pouches by Dr. Rabia Inam Gandapore.pptx

Pharyngeal Pouches
Dr. Rabia Inam Gandapore
Assistant Professor
Head of Department Anatomy
(Dentistry-BKCD)
B.D.S (SBDC), M.Phil. Anatomy (KMU),
Dip. Implant (Sharjah, Bangkok, ACHERS) , CHPE
(KMU),CHR (KMU), Dip. Arts (Florence, Italy)

Pharyngeal pouches are outpocketings of developing
Pharyngeal endothelium

Pharyngeal Pouches
Endoderm of pharynx lines the internal aspects of
pharyngeal arches & passes into balloon like diverticula –
pharyngeal pouches.
 Pair of pouches develops in a craniocaudal sequence
between the arches.
There are 4 well-defined pairs of pharyngeal pouches;
the fifth pair is absent or rudimentary.

First Pharyngeal Pouch
The 1st pharyngeal pouch forms a stalk – like diverticulum, the
tubotympanic recess, that comes in contact with the epithelial
lining of the 1st pharyngeal cleft, the future external auditory
meatus.
The distal portion of the diverticulum widens into a sac-like
structure, the primitive tympanic or middle ear cavity,
whereas the proximal part remains narrow, forming the
auditory (eustachian) tube.
The lining of the tympanic cavity later forms the tympanic
membrane or ear drum.

Development of Pharyngeal Pouches
• First pouch
gives rise to:
• middle ear cavity
• auditory tube
First Arch
Second Arch

Second Pharyngeal Pouch
 Epithelial lining of the 2nd
pharyngeal pouch proliferates &
forms buds that penetrate into
surrounding mesenchyme.
 The buds are secondarily invaded
by mesodermal tissue, forming
primordium of palatine tonsil.
 During 3rd and 5th months, the
tonsil is infiltrated by lymphatic
tissue.
 Part of pouch remains & is found in
adult as tonsillar fossa.

Third Pharyngeal Pouch
3rd & 4th pouches are
characterized at their distal
extremity by a dorsal &
ventral wing.
In 5th week, epithelium of
dorsal wing of 3rd pouch
differentiates into inferior
parathyroid gland & ventral
wing forms thymus.
Parathyroid tissue of 3rd
pouch finally comes to rest
on dorsal surface of thyroid
gland & forms inferior
parathyroid gland.

Tongue
 Largest single muscular organ inside oral cavity
 Originates from muscles of occipital myotomes
 Innervated by 5th
(Trigeminal), 7th
(Facial), 9th
(Glosspharyngeal), 10th
( Vagus) Cranial Nerves

Development of Tongue
 Organ of Oral Cavity
 Develops in relation to pharyngeal
arches in floor of mouth
 Pharyngeal arches arises as a
mesodermal thickenings in lateral
wall of foregut & grows to meet
corresponding arch on other side
Medial part of mandibular arch
proliferates to form 2 lingual
swellings, on either side of midline
 Median swelling also appears
between 2 lingual swelling Called
Tuberculum Impar

Parts of Tongue
 1st
Pharyngeal arch tissue forms anterior (movable) body of
tongue
 2nd
& 3rd
Arches forms posterior (immovable) body & base.

Tissues of tongue has 3 parts
1. Central tuberculum
2. 2-lateral lingual swellings

Formation of Tongue
 Tongue begins to develop at 4th
weeks’
 Local proliferation of mesenchyme
then gives rise to a number of
swellings in floor of mouth.
1. First Swelling: Tuberculum Impar,
arises in midline in mandibular process
2. Second Swelling: Tuberculum
impar is flanked by 2 other bulges i.e.
lingual swelling
 Lateral Lingual swellings enlarge &
merge with each other & tuberculum
impar to form a large mass from
which mucous membrane of anterior
2/3rd
of tongue is formed.

 2. Third Swelling: Root of tongue arises from
hypobranchial eminence-large midline swelling
developed from mesenchyme of 3rd
arch.
 Hypobranchial eminence is primordial of epiglottis (thin
plate of cartilage infront of glottis that protects it) during
swallowing.
 Mesenchyme of 3rd
arch rapidly overgrows that of 2nd
arch
, which is excluded from further involvement in
development of tongue.
 Hypobranchial eminence gives rise to mucous covering
root or posterior 3rd
of tongue.

 Some authorities divide hypobranchial eminence into:
1. Anterior copula: Which gives origin to mucosa covering
the root of tongue)
2. Hypobranchial eminence (Which give rise to epiglottis)

 Muscles of tongue have a different origin:
 Arise from occipital somites which have migrated
forward into tongue area, carrying with them their nerve
supply the 12th
cranial (Hypoglossal nerve)
 This unusual development of tongue explains its
innervation
 Since the mucosa of anterior 2/3rd
of tongue is derived
from 1st
arch, it is supplied by 5th
cranial nerve
*Trigeminal nerve.
 While, mucosa of posterior 1/3rd
of tongue is derived
from 3rd
arch so supplied by 9th
Cranial nerve
( Glossopharyngeal nerve )

 Body & Base of tongue
differ in structure of mucous
membrane:
1. Anterior (body): Papillary
in nature
2. Posterior (base):
Lymphatic in nature
 This are separated by V-
shaped sulcus known as
sulcus terminalis

 Anterior 2/3rd
is divided into
2 lateral halves by a lingual
septum w/c is manifested
externally as median sulcus
Dorsal mucosa covering
anterior part is velvet like in
appearance because of
presence of invagination &
evaginations known as lingual
papilla

Ankyloglossia (Tongue Tie)
 Tongue is not free from floor
of mouth & extends to tip of
tongue
 Normally extensive cell
degeneration occurs
 Frenulum is only tissue that
anchors tongue to floor of
mouth

Development of Thymus
 Endoderm of third pouch
proliferates & gives rise to
thymus during week 4.
 First start as endodermal tubes.
 This tissue envades mesoderm.
3rd Pouch
Thymus

 Thymic tissue then loses connection with pharynx.
 Thymus descends during weeks 4 - 7.

Thyroid
Thymus
 Thymus migrates into superior
mediastinum

 Thymus cortical epithelium is derived from ectoderm.
 Thymus medullary epithelium is derived from endoderm.
 Lymphoid tissue infiltrates later.

Fourth Pharyngeal Pouch
Epithelium of dorsal wing of
this pouch forms superior
parathyroid gland.
When parathyroid gland loses
contact with wall of pharynx, it
attaches itself to the caudally
migrating thyroid & finally is
located on dorsal surface of
thyroid as superior
parathyroid gland.

Development of Parathyroids
 Inferior parathyroids develop from third pouch at week 5.
 Detach from pharynx and descend.

 End up at inferior pole of
dorsum of thyroid by week 7.
Inferior
parathyroids

 Superior parathyroids develop from the fourth pouch at week 5.
 Detach from pharynx and descend.

 End up at the superior
pole of the dorsum of
the thyroid by week 7.
Superior parathyroids
Inferior parathyroids

Parathyroid
 Chief cells
• Parathyroid hormone:
• Increase Calcium
concentration in blood
• Decrease Phosphate
concentration in blood
 Oxyphil cells Parathyroid
glands become hyperplastic
when cannot produce
sufficient PTH to correct
external stimuli (i.e. low
blood calcium, high blood
phosphate, or low calcitriol
levels)

Fifth Pharyngeal Pouch
It gives rise to ultimobranchial body, which is later
incorporated into thyroid gland as parafollicular or C
cells of thyroid gland.
These cells secrete calcitonin, a hormone involved in
regulation of calcium level in the blood.

Development Of Thyroid Gland
 First body's endocrine glands to
develop,
⚫approx. 24th day of development.
 Sources of origin:
median part -Primitive pharynx
(endoderm)
Lateral part –Neural crest cells
 The rudimentary lateral thyroid
develops from neural crest cells (to
form Parafollicular C cells
ultimately),
 while the median thyroid, which
forms the bulk of gland, arises from
primitive pharynx.

Development of Thyroid
 Develops as a diverticulum from foramen cecum.
 Foramen cecum is located between tuberculum impar &
hypobranchial eminence.
lingual
swelling
1st arch
2nd arch
3rd arch 4th
arch
hypobranchial
eminence
Foramen
Cecum
epiglottal
swelling
tuberculum
impar
1st cleft

 Develops as a diverticulum from foramen cecum.
 Foramen cecum is located between tuberculum impar &
hypobranchial eminence.
tuberculum impar
1st cleft
hypobranchial eminence
Foramen Cecum
lingual swelling
1st arch
2nd arch
3rd arch 4th arch
epiglottal
swelling

 Thyroid descends in front of pharynx.
Thryoglossal Duct

 Thyroid gland remains in
contact with tongue
(pharynx) for a period of
time by a narrow duct
called thyroglossal duct.
Thryoglossal Duct

 Thyroid gland descends to region of
junction of trachea & larynx.
Tongue
Thryoglossal

• Path of
migration of
thyroid.
• From base of
tongue
• In front of hyoid
• In front of
thyroid cartilage
Thyroid gland

Development of parafollicular cells of
thyroid
 Parafollicular cells of
thyroid are C cells that
produce calcitonin.
 They develop from 4th
(5th) Pouch
(Ultimobranchial
body)

Migration Of Ultimobranchial Body

 Thyroid
 Follicles filled with thyroglobulin
 Follicle secretes:
 Thyroxine (T4) and Triiodothyronine (T3)
 Parafollicular cells of thyroid
 Calcitonin – protection against excess bone resorption
Follicle
Follicle
Follicle
Parafollicular
cells
Follicular cells

Pharyngeal Clefts Or Grooves
 5-week embryo is characterized by presence of four
pharyngeal clefts, of which only one contributes to the
definitive structure of embryo.
 Dorsal part of 1st cleft penetrates underlying
mesenchyme & gives rise to external auditory meatus.
 Epithelial lining at the bottom of meatus participates in
formation of eardrum.

 Active proliferation of
mesenchymal tissue in 2nd
arch causes it to overlap
3rd and 4th arches.
Finally it merges with the
epicardial ridge in the
lower part of neck, & 2nd,
3rd, and 4th clefts lose
contact with the outside.
Temporarily, the clefts form
a cavity lined with
ectodermal epithelium, the
cervical sinus, but with
further development this
sinus disappears.

Development of External Auditory
Meatus
3rd arch
4th arch
■First Pharyngeal Cleft gives rise to external auditory meatus.
■1st & 2nd arches give rise to external ear
1st pouch
1st arch
2nd arch
external
auditory
meatus
auditory
tube

1st arch
2nd arch
3rd arch
4th arch
1st pouch
external
auditory
meatus
auditory
tube
cervical
sinus
 The region between the 2nd arch and the 3rd,
4th and 6th arches is called the cervical sinus.

Thyroglossal Cyst
 Its a cystic remnant of
thyroglossal duct
 Thyroglossal cyst may lie at any
point along the migratory
pathway of thyroid gland & is
always near or in midline of
neck.
 Approx. 50% are close to or just
inferior to body of hyoid bone
 Base of tongue
 Close to thyroid cartilage.

Branchial Cleft
Cysts/Fistulas
Sometimes, a thyroglossal cyst is
connected to outside by a fistulous
canal, a thyroglossal fistula.

Congenital Hypothyroidism
 Thyroid dysgenesis,
 Thyroid agenesis (congenital absence of a thyroid)
 Hypoplasia (congenitally small thyroid)

Craniofascial Defects
 Treacher Collin’s syndrome
 Digeorge anomaly

Treacher Collin’s syndrome
 Underdevelopment of
zygomatic bone
 Down slanting palpebral
fissures
 Malformed external ears
 Autosomal dominat trait

Treacher Collins Syndrome
The skull is generally
normal, but the ridges over
the eyes may be
underdeveloped.
The cheek bones are
underdeveloped or missing
completely.
Eyelids slope downwards
and ears are often
abnormal in shape with
impaired hearing present.
The lower jaw is small and
angles down, contributing
to an open bite.
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Digeorge Anomaly
 Deletion on the long arm
of chromosome 22.
 Abnormal development
of neural crest cells
 Hypoplasia or absence
of the thymus
 Parathyroid glands with
or without cardiovascular
defect,microganthia,hype
rtelorism
 Having immunological
deficiencies
 Hypocalcemia

First Pharyngeal Arch
• First arch develops
into 4 prominences:
• Two maxillary
prominences
• Two mandibular
prominences
• First Cleft

Fate of Ectoderm
 1st Arch
 skin over maxilla, mandible, some around the ear
and external auditory meatus
 salivary glands
 enamel of teeth
 epithelium of buccal cavity
 epithelium over anterior body of tongue

Ectoderm
 Second Arch
 epithelium over part of external auditory
meatus
 some epithelium behind the ear

Ectoderm
 Third Arch
 epithelium around ear
 Fourth Arch
 epithelium around ear

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