Flashcards in H&N Deck (409)
Structurally, what do the arches do?
Separate stomodeum from developing heart
Describe the structure of the branchial arches
Ectoderm - lines outside
Endoderm - lines inside
Mesenchymal tissue - core
Each has own nerve, blood, muscle and cartilage
Nerve and blood supply structures formed
Describe branchial grooves and pouches
Groove: ectodermal cleft between adjacent arches
Pouch: endodermal outpocketing from rostral foregut
What is the branchial membrane?
Site of contact between groove and pouch
Describe the mandibular arch
Forms the face
Has mandible and maxillary processes
What is the stomodeum?
Depression between brain and pericardium in embryo which is primitive oral and nasal cavity
Formed by ectoderm, contacts endoderm at oropharyngeal membrane
What is the palatoglossal arch?
Physical remnant of branchial arches
Site of the oropharyngeal membrane separating oral cavity and pharynx
What are the cartilages of the mandibular arch?
Ant. ligament of malleus
The stapes, styloid process, stylohyoid ligament and lesser horn and upper 1/2 body of hyoid bone are the cartilages of which arch?
2nd - hyoid arch
The 3rd arch has what cartilages,
Greater horn and lower 1/2 body of hyoid bone
The 4 and 6 arches have what cartilage?
Cartilages of pharynx
What are the derivatives of the pouch of each arch?
1. Tubotympanic recess - auditory tube, tympanic cavity
2. Lining (crypts of palatine tonsils)
3. Inf. parathyroid glands and thymus
4. Sup. parathyroid glands and C-cells (calcitonin)
The groove of which arch is the only one to form structures in adults and what does it form?
Groove - external auditory meatus
Membrane - tympanic membrane
Pouch - auditory tube
What does the face develop from? Name them
Frontonasal prominence - forehead, bridge of nose
2 maxillary prominences - cheeks, upper jaw
2 mandibular prominences - chin, lower jaw
What are nasal placodes?
Ectodermal thickenings on frontonasal prominence
How and when do the maxillary prominences grow?
Medically (toward midline)
How and when do nasal pits form?
Ectoderm in centre of each nasal placode invaginates
What does the formation of nasal pits do?
Divides frontonasal prominence into lateral and medial nasal processes on each side of embryonic face
Describe the growth of the face in week 6
Medial nasal processes grow medially, fuse in middle forming intermaxillary process
Maxillary prominences grow, fuse with intermaxillary process forming philtrum and primary palate
What can happen if the medial nasal prominences don't fuse?
Lead to formation of bifid nose
How is the primary palate formed?
From internal swelling of intermaxillary process
How does the 2ndary palate form?
From 2 lateral palatine shelves
Develop as internal projection of maxillary prominences
Shelves grow down on either side of tongue from maxillary prominences while nasal septum grows down from base of skull
When tongue descends into throat palatine shelves rotate upward
Where do the palatine shelves fuse and with what?
At midline with nasal septum
How does a cleft lip occur?
Failure of maxillary prominences to fuse with intermaxillary process
How can a cleft lip be restored?
Using nasal retainer
Maintains shape of nasal passage after surgery, helps mound and approximate parts of cleft before surgery
What is a X-bite?
Abnormal occlusion in which mandibular teeth enclose the maxillary
How does a cleft palate occur?
Failure of palatine shelves to fuse OR
tongue too large or oral cavity too small for palatine shelves to rotate up and fuse
What is Meckel's cartilage?
Cartilage of 1st branchial arch associated with formation of mandible
Describe the growth of the mandible in week 6
Meckel's cartilage develops rod surrounded by fibrocellular capsule
2 cartilages don't meet, separated by symphysis
On lateral aspect of symphysis condensation of mesenchymal forms