Embryology of the Pharyngeal apparatus Flashcards
What does the Pharyngeal Apparatus give rise to
consists of pharyngeal arches (PA), pouches, grooves (clefts) and membranes
Contribute to the formation of nasal cavities, mouth, larynx, pharynx, and neck
When do the Pharyngeal arches develop and where?
4th week as neural crest cells migrate into the future head and neck
1st pair of arches (primodial jaws) appear lateral to developing larynx
Arches 2-4 appear as ridges on each side of future neck and head regions
5/6 arches are rudimentary and not visible
What does each pharyngeal arch consists of embrylogically?
core of mesoderm and mesenchyme
covered externally by Ectoderm
and covered internally by endoderm
(mesenchyme is derived from migratory NCC)
(head mesoderm forms from paraxial mesoderm)
What do the Pharyngeal arches give rise to and function?
Support the lateral walls of the primordial pharynx
give rise to the prominences of tissue that contribute to craniofacial development
What are the 4 embryological Pharyngeal arch components and what do they give rise to
NCC derived Mesenchyme: forms all the connective tissue in the head including the dermis and smooth muscle
Paraxial Mesoderm: Populates each arch to form Pharyngeal arch musculature
Lateral Plate Mesoderm: Angioblasts that differentiate into the endothelium
Prechordal Plate Mesoderm: Extraocular musculature
Pharyngeal endoderm plays an essential role inregulating the development of the arches
The pharyngeal arch contains 4 st ructures
Cartilaginous rod: forms the skeletal element
Muscular component: differentiates into the muscles in the head and neck
Cranial Nerves: sensory and or motor components
Arch Artery: arising from the truncus arteriosus of primodial heart, it passes around the primordial pharynx to enter the dorsal aorta
Pharyngeal Arch 1: Cartilage
Meckels cartilage
Dorsal portion forms the malleus and incus
Perichondrium: makes anterior ligament of malleus and sphenomandibular ligament
Ventral parts: primordium (model) of the mandible the bone will form laterally to meckels
Pharyngeal Arch 2: Cartilage
Riecherts Cartilage
Dorsal region contributes to the stapes and styloid process of the temporal bone
Perichondrium: stylohyoid ligament
ventral end ossifies and forms the lesser cornu/horn of hyoid bone
Pharyngeal Arch 3: cartilage
Ossifies and forms the greater cornu of hyoid bone
Body of the Hyoid bone is formed by the hypopharyngeal eminence via PA3 and PA4
Pharyngeal Arch 4 cartilages
laryngeal cartilages including the epiglottis (NCC derived
Pharyngeal Arch 6 cartilages
Laryngeal cartilages, but orgin is uncertain
Pharyngeal Arch 1 Muscles
Muscles of Mastication (CN V)
Pharyngeal Arch 2 Muscles
Stapedius and muscles of facial expression (CN VII))
Pharyngeal Arch 3 Muscles
Stylopharyngeus Muscle (CN IX)
Pharyngeal Arch 4 Muscles
Cricothyroid, levator veli palatini, constrictors of pharynx (CN X)
Pharyngeal Arch 6 muscles
Intrinsic muscles of the larynx (CN X)
What nerve supplies the 1st PA
Trigeminal Nerve: supplies the first arch
principle sensory to the head and neck
Motor nerve for the muscles of mastication
What nerve supplies the 2nd PA
Facial Nerve which will supply the muscles of facial expression
What nerve supplies the 3rd PA
Glossopharyngeal nerve (CN IX)
also supplies the stylopharyngeus m
What nerve supplies the 4th-6th Arch
Vagus Nerve (CN X)
4th arch supplied by the superior laryngeal branch of CN X and its recurrent laryngeal branch
also supplies the constrictors of pharynx and intrinsic muscles of the larynx
what do the arch arteries arise from?
5 pairs of arteries arise from the Aortic sac
it is a basket like structure arising from the dorsal aorta that gets remodeled into the great arteries of the thorax and head/neck
arteries arising from the 1st -3rd aortic arch are bilateral and 4th and 6th are asymmetrical
come from mesoderm
What are Pharyngeal Grooves and what do they give rise to
Located between the pharyngeal arches
covered with ectoderm
first groove gives rise to the external acoustic meatus
grooves 2-4 lie in the cervical sinus and these will eventually go away
What are Pharyngeal pouches
Pharyngeal endoderm lines the pharynx internally and create pharyngeal pouches
5 pairs of pouches that develop between the craniocaudal sequence between the arches
Cervical Cysts branchial anomaly
Remnants of cervical sinus and or the 2nd groove
persist to form a slowly enlarging painless free lying cyst in the neck inferior to the angle of the mandible
Accumulation of fluid and cellular debris derived from desquamation of their epithelial linings
Cervical sinus branchial anomaly
failure of the 2nd PA groove and cervical sinus to obliterate
detected due to discharge of mucus
typically bilateral and commonly associated with auricular sinuses
Cervical Fistula branchial anomaly
Abnormal canal that opens into the tonsillar sinus and externally in the side of the neck
persistence of parts of 2nd groove and pouch
What is the pharyngeal membrane, and what gives rise from the pharyngeal membrane
form where the pouch endoderm contacts ectoderm of the pharyngeal
quickly infiltrated by mesenchyme
1st pharyngeal membrane plus the intervening mesenchyme forms the tympanic membrane
What does the first pouch form
expands into the tubotympanic recess creating the tympanic cavity and the mastoid antrum
elongates to form pharyngotympanic tube
What does the 2nd pouch form
Portion of the tonsillar sinus
Endoderm proliferates to form the tonsillar epithelium
mesenchyme differentiates to form the lymphoid nodules of palatine tonsil
What does the 3rd pouch form
Dorsal portion forms the inferior parathyroid gland
ventral portion forms the thymus (this will caudally migrate due to growth of brain and cardiac regions
What does the 4th pouch form
Dorsal portion differentiates into the superior parathyroid glands
Ultimobranchial body fuses with the thyroid gland to give rise to the para follicular cells
(this will stay put as the contents of the third pouch will migrate inferiorly past)
Thymus development, and the function of the three epithelial cords
Thymic primordium develops from PA3 endoderm composed of epithelial cords
these function:
grow into surrounding mesenchyme- thymic lobules
Become arranged around a central point- forming thymic corpscule
Form an epithelial reticulum for housing lymphocytes
growth is still very active during childhood
Thyroid Gland Development
First endocrine gland to develop - thyroid primordium
Forms from a median endodermal thickening in floor of primordial pharynx
descends in the neck with tongue growth and passes ventral to developing hyoid bone and laryngeal cartilages
connected to tongue by a narrow tube- thyroglossal duct but this will then disintegrate
First Arch Syndromes
abnormal development of the first arch
malformation of the eyes, ears, mandible, and palate
results from insufficient migration of NCC into the 1st arch during 4th week
Treacher-Collins Syndrome (mandibulofacial dysostosis
Malar hypoplasia with down slanting palpebral fissures, defects of lower eyelids, deformed external ears, and sometimes middle and internal ears
Autosomal dominant disorder due to mutations in Treacher Collins Franceschetti syndrome 1 gene (TCOF 1)
encodes for the protein TREACLE involved in ribosome biogenesis
truncated in TCS leading to increased apoptosis of Cranial NCC
Pierre Robin sequence
hypoplasia of the mandible, cleft palate, and defects of the eyes and ears
initiating defect is a small mandible (micrognathia) which results in posterior displacement of the tongue and obstruction of full closure of the palate resulting in bilateral cleft palate
Agenesis of thyroid gland
absence of a thyroid gland or one of its lobes
Thyroid hemigenesis
unilateral failure of formation usually the left lobe
mutations in the receptor for the thyroid stimulating hormone are likely involved
DiGeorge Syndrome
Breakdown of signaling from the PA endoderm to NCC
agenesis of the thymus and the parathyroid glands
congenital hypothyroidism
shortened philitrum of upper lip, low set and notched ears
nasal clefts, thyroid hypoplasia
cardiac abnormalities due to defects of the aortic arch
