Development of the pharyngeal arches Flashcards
how many pharyngeal arches are there
6, but number 5 disappears
1,2,3,4,6
what does the 1st arch divide into
maxillary prominence (upper)-smaller
mandibular prominence (lower)- larger
what does the 1st arch divide into
maxillary prominence (up
mandibular prominence
what separates the arches
clefts
what does each arch have
a mesenchyme core (from mesoderm and neural crest)
contains elements that will develop into
-muscle
-cartilage element
-artery
-cranial nerve
what is the difference between pharyngeal clefts and pouches
clefts- external (ectoderm)
pouches- internal (endoderm)
what are somitomeres
and what do they do
pseudo segments
condensations of paraxial mesoderm in the head region rostral to somites
migrate towards arches and make muscles and blood vessels
what do muscle and blood vessels originate from
come from PARAXIAL medsoderm
where is paraxial mesoderm found
near the notochord (centre)
-intermediate
-lateral
what does lateral plate mesoderm give rise to
trapezius
SCM
some cartilages
laryngeal cartilages
regional connective tissue
what do neural crest cells form
neural crest migrate around forming nervous system
bone, most cartilage, nerves
pharyngeal arch skeleton
viscerocranium
glandular connect tissue
collaboration with placodes– gives rise to sensory neurones/ganglia
what are ectodermal placodes
thickening of ectoderm that give rise to sensory neurons/ ganglia
they join with neural crest to form neurons of sensory ganglia (V, VII, IX, X)
also sensory apparatus
what do each arch
1st- supplied by trigeminal nerve V
2nd- supplied by facial nerve VII
3rd- supplied by glossopharyngeal IX
4 and 6- supplied by vagus V
4 supply superior laryngeal branch
6 supply recurrent laryngeal nerve
describe muscles and their arch derivatives
mastication- arch 1
facial expression- arch 2
stylopharyngeus- arch 3
constrictors, soft palate, lev v palatini, cricothyroid, larynx musculature- arch 4 and 6
what happens to the blood supply during development
have dorsal and ventral arteries
arch arteries go under differential loss
discuss the aortic arches and what derives from them
arch 1
-external carotid artery
arch 2 goes
arch 3
-internal and common carotid artery
arch 4
LEFT
-develops majorly into aortic arch
RIGHT
-right subclavian artery
arch 5 disappears
arch 6
LEFT
-left pulmonary artery
-ductus arteriosus
RIGHT
-right pulmonary artery
cartilaginous elements of pharyngeal arches
arch 1
-meckel’s cartilage- soon disappears, replaced by membrane bone
-top end = malleus and most of incus form within this cartilage
-sphenomandibular ligament (remnant of this system) joins forming membrane bone of the mandible
arch 2
-stapes
-little incus
-styloid process
disappears and make stylohyoid ligament and join lesser of hyoid bone
arch 3
-greater horn of hyoid bone
arch 4 and 6
-laryngeals
COME FROM LATERAL PLATE MESODERM
most others are neural crest derivatives
what replaces meckels cartilage as skeletal structure
membrane bones
zygomatic bones
mandible
temporal
maxilla
still neural crest derived
what is the viscerocranium derived from
NEURAL CREST
what is the neurocranium derived from
PARAXIAL MESODERM
what are the laryngeals derived from
LATERAL PLATE MESODERM
what originates from paraxial mesoderm
all voluntary muscles
arteries
neurocranium
meningies
dorsal dermis
how do pouches form
invaginations of endoderm in the lateral walls of the pharynx
what do the different pouches form
pouch 1 - makes eustachian tube, primitive tympanic cavity
pouch 2 - palatine tonsil/tonsillar fissure
pouch 3 - parathyroid (inferior) and thymus
pouch 4 - parathyroid (superior) so does not migrate as far, ultimobranchial body– give rise parafollicular cells of thyroid)
what is ectopic parathyroid
inferior parathyroids can be variable in position
from aberrant migration
what is ectopic thymus
thymus tissue in an abnormal location
it can remain in the neck
what are the cleft derivatives
1- external auditory meatus and external part of tympanic membrane
2- proliferates and overgrows 3 and 4 arches creating a CERVICAL SINUS
2, 3, 4 lose contact with exterior forming cervical sinus
-after losing connection with exterior the cervical sinus disappears
what is the cervical sinus
it is formed by the 2nd arch proliferating and overgrowing the 3rd and 4th arch.
usually disappears after losing connection with exterior
CLINICAL
SCM bump- tumour/ cervical sinus remnant?
presume cancerous until proven otherwise
discuss the neural crest migration from rhombomeres
there are 3 streams of neural crest cells that migrate from segments of hindbrain called rhombomeres
carry expression of homeodomain containing transcription factor OTX and HOX genes into pharyngeal arches
provide guidance cues for cranial nerves growing back from ganglia
neural crest cells respond to pouch endoderm signals
-specifies mesenchymal expression pattern and arch characteristics– skeletal muscle
-is treacher collins syndrome AD or ar
-what protein is affected
-what fails to happen
AD
Defective protein called Treacle (TCOF1 gene)
– failure of formation/apoptosis of neural crest cells and migration into first and second pharyngeal arches
what are some effects of treacher collins syndrome
abnormal eye shape
micrognathia
conductive hearing loss
underdeveloped zygoma
malformed ears
CRANIOFACIAL NERUAL CREST PROBLEM
What are the symptoms of DiGeorge syndrome
CATH-22 disorder
Cardiac abnormality- (tetralogy of Fallot)
Abnormal cafs
Thymic aplasia
Cleft palate
Hypocalcaemia
what happens in DiGeorge syndrome/ what is it also known as
22q11 deletion syndrome
congenital thymic hypoplasia
3rd and 4th pharyngeal pouch syndrome
3rd and 4th pouches fail to develop and thymus and parathyroids are defective
what does inadequate SHH function cause
narrowing and fusing of eyes and midstructure
what happens if there is xs SHH
duplication and widening structures
-diprosopus
what is craniosynostosis syndrome
- eg. APERT syndrome
-eg. CROUZON syndrome
due to genetic causes (FGFR, TWIST transcription factor, EPHRIN-B1)
eg. FGFR2 and FGFR3 mutation
gain of function– activation of receptors
generate early calcification and reduces cell proliferation in mesenchyme at suture– PREMATURE FUSIONS OF SUTURES
mutations spontaneous in the paternal line increase with age
