Development of Pharyngeal Apparatus Flashcards
1
Q
- consists of sets of pharyngeal arches, pouches, grooves (clefts), and membranes
- contributes to the formation of nasal cavities, oral cavity, tongue, larynx, pharynx, ear, and neck
A
pharyngeal apparatus
2
Q
Describe the development of the pharyngeal arches:
A
- develop early in the 4th week as neural crest cells (ectoderm) migrate into future head and neck
- 1st arch: primordial jaws, appear lateral to developing pharynx
- 2-4 arches: appear shortly after 1st as ridges on each side of future head and neck regions
- 5-6 arches: rudimentary and not visible on surface of embryo
3
Q
What structures of the face do the neural crest cells migrating from forebrain, midbrain, and hindbrain develop into?
A
- forebrain: frontal nasal prominence (forehead)
- midbrain and hindbrain: midfacial regions (cheekbones and upper jaw)
- hindbrain (some midbrain): lower part of face (lower jaw)
- hindbrain: neck
4
Q
What are the germ layer components of the pharyngeal arches and what do these layers give rise to?
A
- each arch has a mixed core of mesoderm and mesenchyme
- mesoderm
- arises from paraxial mesoderm
- populates each arch to form PA musculature
- mesenchyme
- embryonic CT derived from migratory NCC
- forms all CT in head, including dermis and smooth muscle
- mesoderm
-
lateral plate mesoderm
- angioblasts differentiate into endothelium
-
prechordal plate mesoderm
- extraocular musculature
- externally covered by ectoderm
- internally covered by endoderm
- plays essential role in regulating development of the arches
5
Q
What do the pharyngeal arches do shortly after they are formed?
A
- support lateral walls of the primitive pharynx
- give rise to facial prominences that contribute to craniofacial development
6
Q
What are the derivatives of PA1?
A
Meckel’s cartilage
- dorsal portion forms malleus and incus
- perichondrium > anterior L. of malleus and sphenomandibular L.
- ventral parts > primordium of the mandible
- bone forms laterally to Meckel’s, which disintegrates
7
Q
What are the derivatives of PA2?
A
Riechert’s cartilage
- dorsal region contributes to stapes and styloid process of temporal bone, remained disintegrates
- perichondrium > stylohyoid L.
- ventral end ossifies > forms lesser cornu/horn of hyoid bone
8
Q
What are the derivatives of PA3?
A
- ossifies > forms greater cornu of hyoid bone
- body of hyoid bone is formed by hypopharyngeal eminence (prominence in floor of embryonic pharynx (from PA3 and PA4)
9
Q
What are the derivatives of PA4 and PA6?
A
- 4th arch > laryngeal cartilages including epiglottis (NCC derived)
- 6th arch > laryngeal cartilages, but origin is uncertain
10
Q
What muscular structures do the arches give rise to?
A
most muscular components arise from paraxial mesoderm
- 1st arch
- muscles of mastication (CN V)
- also: mylohyoid M., tensor Ms., anterior belly of digastric M.
- # chewonthat
- 2nd arch
- stapedius and muscles of facial expression (CN VII)
- # smileandsaycheese
- 3rd arch
- stylopharyngeus (CN IX)
- # elevateanddilate
- 4th arch
- cricothyroid, pharyngeal constrictors (CN X)
- pushitpushitrealgood
- 6th arch
- intrinsic muscles of the larynx (CN X)
- # soundoff
- extraocular muscles from prechordal plate
- tongue musculature from occipital myotomes
11
Q
What is the motor innervation of the pharyngeal arches?
A
-
trigeminal N. (CN V): 1st arch
- principal sensory nerve of the head and neck
- motor nerve for muscles of mastication
-
facial N. (CN VII): 2nd arch
- muscles of facial expression
-
glossopharyngeal N. (CN IX): 3rd arch
- stylopharyngeus M.
-
vagus N. (CN X): 4-6th arches
- 4th arch > superior laryngeal and recurrent laryngeal branches of CN X
- constrictors of pharynx (4th) and intrinstic muscles of larynx (6th)
12
Q
- abnormal development of the components of the first arch
- malformation of eyes, ears, mandible, and palate, which together constitute this syndrome
- results from insufficient migration of NCC into the first arch during 4th week
- most common types: Treacher-Collins syndrome and Pierre Robin sequence
A
first arch syndrome
13
Q
- malar hypoplasia w/ down-slanting palpebral fissures, defects of lower eyelids, deformed external ears, and sometimes middle and internal ears
- autosomal dominant disorder: mutations in _______-_______-Franceschetti syndrome 1 gene (TCOF1)
- gene encodes for protein TREACLE, involved in ribosome biogenesis
- truncated proteins in this syndrome lead to increase in apoptosis of cranial NCC
A
Treacher-Collins syndrome (mandibulofacial dysotosis)
14
Q
- typically occurs de novo in most patients
- a/w hypoplasia of mandible, cleft palate, and defects of eyes and ears
- initiating defect in small mandible (micrognathia) results in posterior displacement of tongue > obstruction of full closure of palate > results in bilateral cleft palate
A
Pierre Robin sequence
15
Q
What are the nearby structures a/w pharyngeal arches?
A
- pharyngeal grooves: located externally between pharyngeal arches, covered w/ ectoderm
- pharyngeal pouches: located internally as part of the pharynx, covered w/ endoderm (1st pair lies between 1st and 2nd arches)
- pharyngeal membranes: located in between
16
Q
What are the derivatives of the 1st groove, 1st pouch, and 1st membrane?
A
-
1st groove: forms the external acoustic meatus
- grooves 2-4 lies in cervical sinus, eventually obliterated
- birth defects of 2nd groove are common
-
1st pouch
- expands into tubotympanic recess > tympanic cavity and mastoid antrum
- elongates to form pharyngotympanic tube
- endoderm contacts 1st pharyngeal groove > contributes to tympanic membrane
- 1st membrane + intervening mesenchyme > tympanic membrane
*all “1st” structures contribute to ear formation*
17
Q
What are the derivatives of the 2nd pouch?
A
- portion forms tonsillar sinus
- endoderm forms tonsillar epithelium
- mesenchyme forms lymphoid nodules of palatine tonsil
18
Q
What are the derivatives of the 3rd pouch?
A
- dorsal portion differentiates into inferior parathyroid gland
- ventral portions form thymus
- both migrate caudally due to growth of brain and cardiac regions
19
Q
What are the derivatives of the 4th pouch?
A
- dorsal portion differentiates into superior parathyroid glands
- ultimobranchial body > fuses w/ thyroid gland and gives rise to parafollicular cells
20
Q
- failure of 2nd groove and cervical sinus to obliterate
- typically external, internal is rare
- detected due to discharge of mucus
- commonly a/w auricular sinuses
A
external cervical sinus branchial anomaly
21
Q
- persistence of 2nd pouch
- rare
- open into tonsillar sinus or near palatopharyngeal arch
A
internal cervical sinus branchial anomaly
22
Q
- remnants of cervical sinus and/or 2nd groove
- slowly enlarging, painless, free-lying cyst in the neck, inferior to angle of the mandible
- accumulation of fluid and cellular debris
A
cervical cysts
23
Q
- canal that opens into tonsillar sinus and external side of the neck
- persistence of parts of 2nd groove and pouch
- ascends through subcutaneous tissue and platysma to reach carotid sheath; passes between carotids and opens into tonsillar sinus
A
cervical fistula
24
Q
Describe the process of thyroid gland development:
A
- first endocrine gland to develop (~24 dpf) > thyroid primordium
- forms from an endodermal thickening in floor of primordial pharynx
- descends in the neck as tongue grows > ventral to hyoid bone and laryngeal cartilages
- connected to the tongue by a narrow tube, thyroglossal duct
- primordium is hollow, but will become solid, cellular mass
- divides into right/left lobes connected by the isthmus
- definitive shape by 7 weeks and thyroglossal duct will degenerate
25
Q
What are the 3 most common thyroid gland development anomalies?
A
- ectopic thyroid tissue (accessory, lingual, cervical): can form along the course of the duct
- sublingual thyroid gland: forms but does not descend in the neck
- thyroglossal duct cyst: form in tongue or anterior neck, critical to distinguish from ectopic thyroid prior to surgical removal
26
Q
What are congenital anomalies related to the thyroid development?
A
- agenesis of thyroid gland: absence of a thyroid gland or one of its lobes (rare)
- thyroid hemiagenesis: (unilateral failure of formation) left lobe is more commonly absent, mutations in the receptor for TSH are likely involved
- DiGeorge Syndrome: breakdown of signaling from PA ectoderm to NCC; agenesis of thymus and parathyroid glands; congenital hypoparathyroidism; congenital hypoparathyroidism; shortened philtrum of upper lip, low set and notched ears; nasal clefts, thyroid hypoplasia; cardiac abnormalities (defects of the aortic arch and heart)
