Embryology-Pharyngeal Arches Flashcards
What are these?
These are the first two pharyngeal arches that appear around week 4. Note that the arches develop in a rostral to caudal direction and you will not see all pharyngeal arches at the same time?
What are the different structures of the 5 pharyngeal arches seen below?
1) Pharyngeal clefts (ectoderm lining) 2) Pharyngeal pouches (endoderm) 3) Muscle 4) Skeletal 5) Cranial nerve 6) Aortic arch
What two processes extend from the first pharyngeal arch?
Maxillary and mandibular
What aortic arches are largely associated with the pharyngeal arches?
III, IV and VI aortic arches. I and II digress.
What becomes of the different aortic arches seen below?
III) Gives off common carotids. IV) Gives off right subclavian and aortic arch VI) Gives off pulmonary arteries
What nerve is associated with the 6th aortic arch?
Recurrent laryngeal nerve. The connection between the VI aortic arch and the dorsal aorta disappears on the right side but not on the left (ductus arteriosus). This causes the right recurrent laryngeal to loop around the right subclavian artery (IV arch) and the left recurrent laryngeal to loop around the ductus arteriosus (VI arch).
What do the pharyngeal arch cartilages indicated below go on to become?
Note that there is a rostral to caudal development of these structures. Arch I) Part of temporal bone, maxilla, mandible, malleus, incus and spenomandibular ligament. Arch II) Stapes, styloid, stylohyoid ligament, upper hyoid. Arch III) Hyoid. ArchesIV and VI) Laryngeal cartilages
What pharyngeal arches do bones in the inner ear develop from?
Malleus and incus come from arch I. Stapes comes from arch II.
What embryological layer do the pharyngeal arch muscles develop from?
Paraxial mesoderm forms somitomeres and somites that migrate to the pharyngeal arch region
What muscles do the pharyngeal arch regions indicated below go on to become?
Arch I) “M M MATT” Mastication muscles, Mylohyoid, Ant. belly of digastric, Tensor tympani (ear), Tensor veli palatini (palate) Arch II) “FESS P” Facial expression muscles, occipital, frontalis, platysma, stapedius, stylohyoid, posterior belly of digastric. Arch III) Stylopharyngeus Arch IV) All but 1 pharyngeal muscle (stylopharyngeus), all but 1 palatal muscle (tensor veli palatini) and 1 laryngeal muscle Arch VI) All laryngeal muscles except cricothyroid
What cranial nerves do the pharyngeal arch regions indicated below go on to be innervated by?
I) CN V3 mandibular branch. II) CN VII facial. III) CN IX glossopharyngeal. IV and VI) CN X vagus.
What adult structures develop from the region indicated below?
This shows pharyngeal arches I and II with the pharyngeal cleft between the two. The pharyngeal cleft will become the external auditory meatus and the pharyngeal arches I and II will form the external ear.
What embryonic layers does the eardrum have in it?
Endoderm from the pharyngeal pouch, ectoderm from the pharyngeal cleft and mesoderm from where the two met.
What happens to the tissue from pharyngeal arch II after it forms the external ear?
It grows down and obliterates arches III and IV. And forms a cervical sinus which should eventually close.
What causes a cervical cyst to form during development?
Failure of complete closure of the second pharyngeal arch after it extends down over arches III and IV.
What adult structure is formed from the second pharyngeal pouch? The third?
Second = Palatine tonsils. Third = inferior parathyroid & thymus. Fourth = Superior parathyroid and thyroid C-cells
Where do the developing structures from the pharyngeal pouches migrate to?
They start up in the region of the head. Auditory tube & tonsillar crypts stay where they are. The inferior parathyroid, thymus, superior parathyroid and c-cells of the thyroid all migrate inferiorly
What pharyngeal arches is the tongue derived from?
Anterior 2/3 (lateral lingual swellings & tuberculum impar) come from pharyngeal arch I. The copula comes from arches II, III and IV, but III overgrows II. Arch III develops into the sulcus terminals. Arch IV gives rise to the epiglottis and the root of the tongue.
How is the tongue innervated for sensation, taste and motor?
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Where does the thyroid begin development?
At the junction of the first and second pharyngeal arches. Then it migrates down to its normal adult position.
What is your diagnosis?
Thyroglossal cyst. Note that it is just above the hyoid bone along the path of migration the thyroid takes.
What are the five prominences of the face during development?
1) Frontonasal prominence 2) Maxillary prominence 3) Mandibular prominence 4) Nasomedial prominence 5) Nasolateral prominence
What causes formation of a midline cleft palate?
Failure of left and right mandibular prominences to fuse.
What causes formation of a cleft face?
Failure of the maxillary prominences to fuse with the nasomedial & nasolateral prominences.
What causes your classic cleft lip?
Failure of the maxillary prominence to fuse with the nasomedial prominence.
Underdeveloped jaw, underdeveloped zygomatic arch and hearing problems. What syndrome is this?
Treacher Collins Syndrome. This is a 1st arch syndrome. The 1st arch also helps to form the external ear which would contribute to hearing problems.
Small lower jaw, cleft palate, posteriorly placed tongue, macrostomia and underdeveloped zygomatic arch. What syndrome is this?
Pierre Robin Syndrome. This is a 1st arch syndrome.
How does the nasal cavity form in the developing embryo?
Nasal placodes continue to sink further in to from nasal pits above the primary palate. The nasal septum continues to develop from the frontonasal prominence and medionasal prominences. The mandible grows down to take the tongue out of the way. The maxillary prominence of the 1st arch then forms the soft palate. Finally the palatine shells and the nasal septum fuse to form the soft palate.
How are cleft palates classified?
Anterior clefts and posterior clefts.
