Development Of The Head And Neck Flashcards
When does development of the head and neck start?
Day 22
Describe the head and neck at day 22 of development
No defined facial features
Head + neck take up half of length of embryo
What are the pharyngeal arches?
Five pairs of mesenchymal proliferations
Why are there only 5 pharyngeal arches but they are named 1,2,3,4+6?
The 5th pharyngeal arch is present for a few days before it breaks down
Describe the pharyngeal arches
- outer ectoderm covering
- inner endoderm lining
- mesenchyme centre
- each arch has an associated cranial nerve, vessels + cartilage bar
What are the associated cranial nerves to the pharyngeal arches?
- 1: trigeminal V
- 2: facial VII
- 3: glossopharyngeal IX
- 4+6: vagus X
What are the associated aortic arches of the pharyngeal arches?
Same as their number
What are the associated muscles of the pharyngeal arches?
1 - muscles of mastication
2 - muscles of facial expression
3- stylopharngeus muscle
4+6 - pharyngeal + laryngeal muscles
What are the associated skeletal elements of the pharyngeal arches
1 - mandible, malleus + incus
2 - stapes + superior part of hyoid
3 - inferior part of hyoid
4+6 - laryngeal cartilages
List the associated structures with pharyngeal arch 1:
- nerve
- aoritc arch
- muscles
- skeletal elements
- trigeminal nerve V
- 1st aortic arch
- muscles of mastication
- mandible, malleus + incus
List the associated structures with pharyngeal arch 2:
- nerve
- aoritc arch
- muscles
- skeletal elements
- facial VII
- 2nd aortic arch
- muscles of facial expression
- stapes + superior part of hyoid
List the associated structures with pharyngeal arch 3:
- nerve
- aoritc arch
- muscles
- skeletal elements
- glossopharyngeal nerve IX
- 3rd aoritc arch
- stylopharyngeus
- inferior part of hyoid
List the associated structures with pharyngeal arches 4+6:
- nerve
- aoritc arch
- muscles
- skeletal elements
- vagus nerve X
- 4th+6th aortic arch
- pharyngeal + laryneal muscles
- laryngeal cartilages
What are the aortic derivatives from the aortic arches?
1+2 - none
3 - common, internal + external carotid arteries
4 - aorta L + brachiocephalic R
6- pulmonary arteries
What are pharyngeal clefts?
Invaginations of ectoderm (outside)
Cleft - eCtoderm
What are pharyngeal pouches?
Inner spaces between the pharyngeal arches that form pockets of endoderm
What are the derivates of the pharyngeal pouches?
1 - tubotympanic recess > eustachian tube
2 - palatine tonsil
3+4 - parathyroid glands + thymus
What are the derivates of the pharyngeal clefts?
- only the first cleft remains > external acoustic meatus
- remaining clefts are obliterated by second cleft moving down over them
What can form due to misobliteration of the pharyngeal clefts?
Branchial cysts, sinuses + fistulas
What are the key components of development of the face?
Frontonasal process
Maxillary process
Mandibular process
What does the frontonasal process become?
Forehead
Bridge of nose
Eyelids
Philtrum
What does the maxillary process become?
Cheeks
Lateral upper lip
Lateral upper jaw
Sides of nose
What does the mandibular process become?
Lower lip
Lower jaw
Outline the development of the mouth
- buccopharyngeal membrane disappears via apoptosis
- stomodeum forms (end of foregut that forms the mouth)
Outline the development of the nose
- nasal placodes on either side of frontonasal process invaginate to form olfactory/nasal pits
- these will become the nostrils
- nasal processes + maxillary processes move medially + fuse to form the nose + philtrum in the midline
What is a placode?
Ectodermal thickening in the cranial region of the embryo
Outline the development of the mandible
Mandibular processes move medially + fuse
Outline development of the palate
- two palatal shelves grow from the internal side of the maxillary processes
- fuse with the primary palate at the midline
- this forms the secondary palate which separates the oral and nasal cavities
What is cleft palate?
Failure of fusion of the palatal shelves in the midline
What is a cleft lip?
Failure of fusion of the medial nasal process + maxillary process
Outline the development of the ears
- arise in association with 1st pharyngeal cleft (external acoustic meatus)
- auricular hillocks (3 above-1st pharyngeal arch | 3 below-2nd pharyngeal arch) surround first pharyngeal cleft
- these structures ascend to become external ear
What is fetal alcohol syndrome?
- condition that results from alcohol exposure during mother’s pregnancy
- causes brain damage, growth problems + facial abnormalities
What impact does fetal alcohol syndrome have on the development of ears?
Low set ears due to interference of ascent
Outline the development of the tongue in regards to the pharyngeal arches
- 1st: anterior 2/3 of tongue
- 2nd+3rd posterior 1/3 of tongue
- 4th+6th: epiglottis + glottis of larynx
What is the sulcus terminalis of the tongue?
Demarcation between the anterior 2/3 and posterior 1/3 of the tongue
Innervation of the tongue
- anterior 2/3: sensation from trigeminal nerve V | taste from facial VII
- posterior 1/3: sensation + taste from glossopharyngeal IX
What is foramen caecum?
The point where the thyroid gland develops from
Where do the muscles of the tongue arise from?
Occipital somites
At level of hypoglossal nerve
What is the motor supply of the tongue?
Hypoglossal nerve
Outline the development of the thyroid gland
- originates from foramen caecum
- thyroid diverticulum grows down > thyroglossal duct
- as thyroid descends the thyroglossal duct breaks down
What are thyroglossal cysts due to?
Failure of the thyroglossal duct to break down
Abnormalities of the development of the thyroid gland
- thyroglossal cysts: failure of the thyroglossal duct to breakdown
- ectopic thyroid gland tissue can be left anywhere along the path of descent
Investigation + diagnosis of thyroglossal cysts
- fibrous band connects cyst to tongue
- ask patient to stick their tongue out > cyst will elevate
