Head and Neck Embryology Flashcards
pharyngeal arch vs cleft vs pouch
pharyngeal arch = mounds of mesoderm/mesenchyme
ectoderm covers outer surface of arches, endoderm lines inner surface
clefts = ectoderm wedged between each pair of arches
pouches = endoderm wedged between arches
what is the only pharyngeal cleft that goes on to become something relevant?
FIRST pharyngeal cleft (outer ectoderm wedged between pharyngeal arches) forms epithelial lining of external ear canal and external ear drum surface
remaining clefts disappear or persist as cysts
what is the embryonic origin of head/neck skeletal muscle vs mesenchyme?
paraxial mesoderm-derived somites —> head/neck skeletal muscles
neural crest and mesoderm —> mesenchyme (forms connective tissue)
when during prenatal development do the pharyngeal arches appear?
week four
1, 2, 3, 4, 6 (5th arch quickly disappears)
which cranial nerve is associated with each of the pharyngeal arches?
CN V (trigeminal) - 1st arch
CN VII (facial) - 2nd arch
CN IX (glossopharyngeal) - 3rd arch
CN X (vagus) - 4th and 6th arches
[recall 5th arch quickly disappears. also recall that CN extend from developing brain stem into the arches, hence are not created by the aches]
from which pharyngeal arch are the following arteries derived?
a. carotid
b. pulmonary
c. arch of aorta
d. subclavian
e. maxillary
f. staoedial
1st arch - maxillary
2nd arch - staoedial
3rd arch - carotid
4th arch - subclavian, arch of aorta
6th arch - pulmonary
[recall no 5th arch]
what head/neck structures originate from each of the pharyngeal pouches?
pouches = endoderm on internal surface of pharyngeal arches
1st pouch —> tympanic membrane, auditory tube
2nd pouch —> palatine tonsils
3rd pouch —> inferior parathyroid gland, thymus
4th pouch —> superior parathyroid gland (note parafollicular cells of thyroid are migratory neural crest cells)
[foramen cecum —> thyroid gland]
