Pharyngeal App Flashcards
Facial development occurs
simultaneously with mouth.
Week 4
Pharyngeal arches appear
Pharyngeal arches appear as pairs of
bulges overlying the head & neck regions due to migration of neural crest cells.
The pharyngeal apparatus is made of 4 components
arches and grooves/clefts externally, membranes and pouches internally
Components of pharyngeal apparatus give rise to structures of the
face, mouth, pharynx, larynx, and neck
Origin of the mesenchyme of the face and pharynx:
neural crest cells (for the skeletal elements)
•paraxial mesoderm (for striated muscle, dermis, endothelium of blood vessels, vertebrae)
• specifically, the paraxial mesoderm of the occipital somites to the tongue
Cranial region is the 1st part of the
neural plate to differentiate in the trilaminar embryo – beginning at 18 days – prior to 1st somite.
Mesenchyme
tissue made up of non-epithelial cells, no obvious polarity separated by extracellular matrix
What is the significance of the fact that neural crest cells provide the mesenchyme for the skeletal elements of the face?
Neural crest cells migrate and differentiate. Through such differentiation they make a major contribution to the development of the face and ear, and abnormalities are associated with abnormal neural crest cell migration.
Neural crest cells also provide the
mesenchymal components of the salivary, thyroid, parathyroid and thymus glands and type 1 cells of the carotid body, corneal epithelium of the eye and contributions to the developing heart (mesenchyme of the truncus arteriosus, cons cordis and endocardial cushions. May explain why congenital abnormalities of the face are sometimes associated with congenital heart defects.)
Pharyngeal app
Pharyngeal arches
Branchial arches
Exterior is
ectoderm. All groves and clefts – ectoderm.
Arch 5
does not give rise to any structures and regress rapidly
Arch 6
associated with aortic arch, proximal segments of pulmonary arteries and ductus arteriosus, intrinsic laryngeal muscles, skeletal m. of the esophagus, and laryngeal cartilages (this is together with arch 4 components.)
Consider 4 and 6 together
same innervation.
Frontonasal process
main process for facial development
Pharyngeal arches
also called branchial or visceral arches)
•condensations of mesenchyme in the anterior pharynx
Pharyngeal arches are comprised of a
layer of mesenchyme between 2 epithelia: surface ectoderm & pharyngeal endoderm
2 epithelia
surface ectoderm & pharyngeal endoderm
Pharyngeal clefts
depressions between the arches lined with ectoderm
•on the exterior of the pharynx
pharyngeal cleft – not = to clinical clefts which are actually a result of the failure of developing prominences to close or fuse properly
Pharyngeal pouches
outpouchings between the arches lined with endoderm
•on the interior of the pharynx
Pharynx derived structures include: face, palate, tongue, thyroid gland, pharynx, larynx, and external & middle ear components
mesoderm
derived from neural crest
Pouch and clefts come together with little to no tissue between them
membranes
The pharyngeal apparatus is made of 4 components
arches and grooves/clefts externally, membranes and pouches internally.
Each arch has an artery, nerve, cartilage, and muscle component.
Two distinct prominence of first arch
Maxillary prominance is top one.
Pouch lined with
endoderm
Each arch is lined externally by
ectoderm, internally by endoderm, and has a core of mesenchyme.
Within each arch:
Artery
- Cranial n.
- Muscle
- Cartilage
1 CN to each
arch
Cartilage from 1st arch forms a
maxillary process and a mandibular process
Maxillary process:
Maxillary bones (including inferior nasal conchae)
- Zygomatic bones
- Vomer
Mandibular process:
- Mandible
- Squamous portion of temporal bone
These are the cartilagenous components of first arch (and prior slide)
Mandibular process contains “
Meckel’s cartilage”. Dorsal portions of cartilage break off to form:
-Malleus
-Incus
(arch 1 is close to ear)
Perichondrium from middle portion of Meckel’s cartilage persists as:
Anterior ligament of malleus
-Sphenomandibular ligament
Meckel’s cartilage degenerates except for the
dorsal portion, which forms the malleus, incus, and two ligaments.
Meckel cartilage
correlates to rough location of mandibular canal. Inner ear, sphenomandibular lig also associated with first arch (maleus and incus).
Portion of 2nd arch cartilage
Reichert’s cartilage”, is close to developing ear.
Reichert’s cartilage Forms
Stapes 3rd ossicle
Styloid process
Perichondrium from middle portion of Reichert’s cartilage persists as:
Stylohyoid ligament
Ventral portion of 2nd arch cartilage becomes
Lesser cornu (horn) of hyoid bone + upper body of hyoid bone
3rd arch
cartilage
The rest of the hyoid bone (greater cornu (horn) + lower body)
4th & 6th arch
cartilage
The cartilage of the epiglottis is derived from mesenchyme within the hypopharyngeal eminence (an elevation that develops on the floor of the pharynx of arch 3 + 4 levels).
1st Arch Muscle
Muscles of mastication
(temporalis, masseter, lateral & medial pterygoid mm.)
Mylohyoid m.
Anterior belly of digastric m.
“Two tiny tensors”: tensor tympani & tensor veli palatini mm.
All innervated by CN5
2nd Arch Muscle
Muscles of facial expression
Stapedius m.
Posterior belly of digastric m.
Stylohyoid m.
CN7
Stapedius
middle ear muscle.
3rd Arch Muscle
Stylopharyngeus m.
CN IX
4th Arch Muscle
Pharyngeal constrictor mm.
Levator veli palatini m.
Cricothyroid m.
CNX
Pharyngeal constrictor mm.
Levator veli palatini m.
soft pallet muscles
Cricothyroid associated with
larynx
6th Arch Muscle
Intrinsic mm. of the larynx
Arch 1: CN V: Trigeminal n.
(V2 + V3 divisions = max and mandibular divisions)
superior laryngeal branch of vagus
nerve to 4th arch
recurrent laryngeal branch of vagus
nerve to 6th arch
Pharyngeal Pouches
4 pairs of pouches, lined by endoderm
Where endoderm of pouches meets
ectoderm invagination of grooves/clefts we form a two-layered pharyngeal membrane (red arrows)
A 5th pair of pharyngeal pouches will be
rudimentary if present
Pouch 1 Derivatives - middle portion
becomes tympanic cavity (middle ear cavity) + mastoid antrum (opening into mastoid air cells
Connection between the tubotympanic recess & pharynx will elongate to form - Pouch 1
the pharyngotympanic tube (Eustachian tube (connects pharynx and middle ear))
pharyngotympanic tube (Eustachian tube)
a connection between the middle ear cavity and the pharynx
Extends as the tubotympanic recess
Middle portion of tubotympanic recess
becomes tympanic cavity (middle ear cavity) + mastoid antrum (opening into mastoid air cels)
The connection between the tubotympanic recess & pharynx will elongate to form the
pharyngotympanic tube (Eustachian tube)
Pouch 3 Derivatives - Dorsal buds
Inferior parathyroid glands
Ventral buds - pouch 3
fuse together at midline, forming thymus
The thymus and parathyroid glands will separate
caudally from the pharynx. Move quite a bit
The third pouch develops into a
dorsal and a ventral portion.
The dorsal portion of the third pharyngeal pouch differentiates into the
inferior parathyroid glands.
The ventral portion of the third pharyngeal pouch differentiates into the
thymus gland
Pouch 4 DerivativesDorsal buds
Superior parathyroid glands
Ventral buds - pouch 4
Ultimopharyngeal body = elongated portion of each ventral bud that will fuse with thyroid gland. Cells w/in bodies will become parafollicular cells (“C cells”) that produce calcitonin to regulate levels of calcium in the blood.
Ultimopharyngeal body
elongated portion of each ventral bud that will fuse with thyroid gland. Cells w/in bodies will become parafollicular cells (“C cells”) that produce calcitonin to regulate levels of calcium in the blood.
1st pouch
1st: middle ear, pharyngotympanic tube, tympanic membrane (endoderm)
2nd pouch
2nd: palatine tonsils
3rd pouch
3rd: inferior parathyroid glands, thymus
4th pouch
4th: superior parathyroid glands, ultimopharyngeal body, parafollicular “C cells” of thryoid galnd that produce calcitonin. These cells interdigitate throughout thyroid
The first pharyngeal groove/cleft is the only groove to contribute to a
postnatal structure, the external acoustic meatus. As well as contribue to external surface of tympanic membrane.
2nd-4th Pharyngeal Grooves/Clefts
During week 5, arch 2 begins to overgrow arches 3 + 4
Grooves 2-4 unite to form a depression or small pocket: the cervical sinus
2nd arch overgrows, creates
cervical sinus. This will be absorbed. Abnormality = it stays (cervical cyst).
Fistula can also form
Cervical (Branchial) Cyst
Remnants of a cervical sinus/vesicle or 2nd groove can form a fluid-filled cyst in the neck
Often develops just below the angle of the mandible
Cervical vesicle normally
resorbed
thyroid gland
The first endocrine gland to develop in the embryo
Develops as a ventral thickening & outpocketing of endoderm between arches 1 & 2 and descends below the hyoid bone + laryngeal cartilages as embryo grows
For a short time, the thyroid gland and tongue are connected by a narrow tube, the thyroglossal duct
The thyroglossal duct will obliterate, but a small depression in the tongue remains as the
foramen cecum where the connection was
3rd pouch
Dorsal buds
Inferior parathyroid glands
Ventral buds
fuse together at midline, forming thymus
4th pouch
Dorsal buds: Superior parathyroid glands
Develops from foramen secum in tongue
foramen cecum
This will invaginate through tongue to form thyroglossal duct. Gland will continue to migrate to a position anterior to hyoid bone.This duct is normally resorbed.
If no resorption, you can have cysts along pathway.
Thyroglossal Duct Cyst
result from imperfect closure of the thyroglossal duct
midline
may move with the tongue during swallowing
Without pouch or cleft, likelihood of cysts decreases.
Tongue
A median lingual swelling and 2 lateral lingual swellings develop at level of 1st arch- CN5
Lateral lingual swellings grow, approach midline
& fuse, overgrowing median lingual swelling and forming anterior 2/3 of tongue
The tongue begins to develop towards the end of the
4th week
Tongue develops from…
Ddevelops from floor of pharyngeal apparatus with contributions from all arches. Thus, innervation of tongue is complicated
Posterior 1/3 of tongue forms from
elevations in the floor of the pharynx:
-Copula (2nd arch level)
-Hypopharyngeal eminence
(3rd + 4th arch level)
Hypopharyngeal eminence overgrows
the copula, forming the posterior 1/3 of tongue
Terminal sulcus
V-shaped line separating anterior 2/3 from posterior 1/3. Foramen cecum = midline for this.
Copula
Copula disappears in bottom right, as it gets incorporated. CN7
Anterior 2/3: from 1st arch –
CN V3 (general sensory) CN VII (chorda tympani) (taste)
Posterior 1/3: mostly from 3rd arch -
CN IX (general sensory + taste)
Epiglottis: 4th arch -
CN X (general sensory + taste)
Motor innervation to tongue mm
supplied by CN XII