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Medicine > Development of the pharyngeal arches > Flashcards

Development of the pharyngeal arches Flashcards

1
Q

how many pharyngeal arches are there

A

6, but number 5 disappears
1,2,3,4,6

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2
Q

what does the 1st arch divide into

A

maxillary prominence (upper)-smaller
mandibular prominence (lower)- larger

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3
Q

what does the 1st arch divide into

A

maxillary prominence (up
mandibular prominence

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4
Q

what separates the arches

A

clefts

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5
Q

what does each arch have

A

a mesenchyme core (from mesoderm and neural crest)
contains elements that will develop into
-muscle
-cartilage element
-artery
-cranial nerve

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6
Q

what is the difference between pharyngeal clefts and pouches

A

clefts- external (ectoderm)
pouches- internal (endoderm)

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7
Q

what are somitomeres
and what do they do

A

pseudo segments
condensations of paraxial mesoderm in the head region rostral to somites

migrate towards arches and make muscles and blood vessels

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8
Q

what do muscle and blood vessels originate from

A

come from PARAXIAL medsoderm

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9
Q

where is paraxial mesoderm found

A

near the notochord (centre)

-intermediate
-lateral

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10
Q

what does lateral plate mesoderm give rise to

A

trapezius
SCM
some cartilages
laryngeal cartilages
regional connective tissue

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11
Q

what do neural crest cells form

A

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

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12
Q

what are ectodermal placodes

A

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

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13
Q

what do each arch

A

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

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14
Q

describe muscles and their arch derivatives

A

mastication- arch 1
facial expression- arch 2
stylopharyngeus- arch 3
constrictors, soft palate, lev v palatini, cricothyroid, larynx musculature- arch 4 and 6

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15
Q

what happens to the blood supply during development

A

have dorsal and ventral arteries
arch arteries go under differential loss

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16
Q

discuss the aortic arches and what derives from them

A

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

17
Q

cartilaginous elements of pharyngeal arches

A

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

18
Q

what replaces meckels cartilage as skeletal structure

A

membrane bones
zygomatic bones
mandible
temporal
maxilla

still neural crest derived

19
Q

what is the viscerocranium derived from

A

NEURAL CREST

20
Q

what is the neurocranium derived from

A

PARAXIAL MESODERM

21
Q

what are the laryngeals derived from

A

LATERAL PLATE MESODERM

22
Q

what originates from paraxial mesoderm

A

all voluntary muscles
arteries
neurocranium
meningies
dorsal dermis

23
Q

how do pouches form

A

invaginations of endoderm in the lateral walls of the pharynx

24
Q

what do the different pouches form

A

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)

25
Q

what is ectopic parathyroid

A

inferior parathyroids can be variable in position
from aberrant migration

26
Q

what is ectopic thymus

A

thymus tissue in an abnormal location
it can remain in the neck

27
Q

what are the cleft derivatives

A

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

28
Q

what is the cervical sinus

A

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

29
Q

discuss the neural crest migration from rhombomeres

A

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

30
Q

-is treacher collins syndrome AD or ar
-what protein is affected
-what fails to happen

A

AD
Defective protein called Treacle (TCOF1 gene)
– failure of formation/apoptosis of neural crest cells and migration into first and second pharyngeal arches

31
Q

what are some effects of treacher collins syndrome

A

abnormal eye shape
micrognathia
conductive hearing loss
underdeveloped zygoma
malformed ears

CRANIOFACIAL NERUAL CREST PROBLEM

32
Q

What are the symptoms of DiGeorge syndrome

A

CATH-22 disorder

Cardiac abnormality- (tetralogy of Fallot)
Abnormal cafs
Thymic aplasia
Cleft palate
Hypocalcaemia

33
Q

what happens in DiGeorge syndrome/ what is it also known as

A

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

34
Q

what does inadequate SHH function cause

A

narrowing and fusing of eyes and midstructure

35
Q

what happens if there is xs SHH

A

duplication and widening structures
-diprosopus

36
Q

what is craniosynostosis syndrome
- eg. APERT syndrome
-eg. CROUZON syndrome

A

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

Medicine (54 decks)

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