Pharyngeal Arches Flashcards
How and when do pharyngeal arches begin to form?
Via what molecular signals?
4th week
- neural crest cells migrate into future head/neck regions
- sonic hedgehog signals influence formation of the first arches
What spaces separate the pharyngeal arches externally?
What embryological cell type lines them?
Pharyngeal Grooves
- lined with ectoderm
What are the two important parts of the 1st pharyngeal arch?
What do they become?
Maxillary Prominence - maxilla, zygomatic, part of vomer
Mandibular Prominence - mandible and squamous part of temporal
What are the nerve, cartilage and muscles associated with the first pharyngeal arch?
What does its cartilage become?
- Nerve - Trigeminal (Mandibular + Maxillary) (N V)
- Cartilage - Meckel’s
- malleus
- incus
- ant. ligament of malleus (perichondrium)
- sphenomandibular lig.
- Muscles:
- Muscles of mastication (masseter, temporalis, pterygoids)
- Mylohyoid
- Ant. Belly Digastric
- Tensor Tympani
- Tensor Veli Palatini
Remember MMATT (Mastication, Mylohoid, Ant. belly, Tensor Tympani)
What are the nerve, cartilage and muscles associated with pharyngeal arch 2?
What does the cartilage become?
- Nerve - Facial (N VII)
- Cartilage - Reichert’s
- stapes
- styloid process
- stylohyoid ligament (perichondrium)
- lesser horn of hyoid
- upper part hyoid body
remember … St St St Hy
- Muscles
- Posterior Belly of Digastric
- Mimetic Muscles
- Stapedius
- Stylohyoid
(Remember PMSS)
What are the nerve, cartilages and muscles associated with the 3rd pharyngeal arch?
- Nerve
- Glossopharyngeal (N IX)
- Cartilages
- Greater Horn of Hyoid
- Lower Part of Body of Hyoid
- Muscles
- Stylopharyngeus
(Remember “Gosh” … GSHH … glossophar, stylophar, 2 parts of hyoid)
What is special about the 4th arch?
What are the nerve, cartilages and muscles associated with pharyngeal arch 4?
The fourth arch cartilage fuses with the sixth arch cartilage to form the structures listed below.
(The fifth regresses.)
- Nerve - Vagus (N X) (Superior + Recurrent Laryngeals)
- Cartilages
- Laryngeal Cartilages (except epiglottis!)
- Muscles
- Pharyngeal Constrictors
- Intrinsic Laryngeal Muscles
- Cricothyroid
- Levator Veli Palatini
- Striated Esophageal Muscles
(Remember … PICLS!!!)
What is the name of the thin “pinched” areas between the arches where the grooves and pouches are close together?
What is the one important derivative of these pouches?
Branchial/Pharyngeal Membranes
- similar to oropharyngeal and cloacal membranes… just where endo-/ectoderm layers are closer together
- tympanic membrane forms from the 1st pharyngeal membrane (and intervening mesenchyme)
What is the name of the areas between the arches on the inside?
What embryonic cell type lines them?
Pharyngeal Pouches
- endoderm
What are the derivatives of the 1st pharyngeal pouch?
Auditory/Pharyngotympanic Tube
Inner Lining of Tympanic Cavity
- pouch expands outward towards groove to form tubotympanic recess which gives these structures
What are the derivatives of the 2nd pharyngeal pouch?
Palatine Tonsil
(inside the tonsillar fossa)
- endoderm proliferates into underlying mesenchyme
- endoderm forms the tonsillar crypts + surface epithelium over the mesenchyme
- mesenchyme differentiates into lymph tissue
What are the derivatives of the 3rd pharyngeal pouch?
Inferior Parathyroid Gland
- from a dorsal bulbar expansion of the pouch
Thymus
- via hollow, elongated ventral expansion of pouch
(both via FGF signaling)
What are the derivative(s) of the 4th pharyngeal pouch?
Why is does this seem paradoxical and how does this apparent paradox correct itself during development?
Superior Parathyroid Glands
- via dorsal bulbar expansions of the pouch
Ultimopharyngeal Body
- fuses with thyroid, giving Parafollicular or C Cells (calcitonin producers) from neural crest cells
- via elongated ventral expansion of pouch
- the superior parathyroids start to develop below the inferior, but all parathyroids descend with the thymus and switch relative positions via further descent of the inferiors
What is the fate of the 5th pharyngeal pouch?
becomes part of the 4th pouch
- contributes to ultimopharyngeal body
What are the derivatives of the first pharyngeal groove?
external acoustic meatus
