11 - Embryology of the Head and Neck I Flashcards
What is the embryological origin of the head and neck?
- In week 4 there are pharyngeal (branchial) arches in the lateral walls of the embryonic pharynx
- Mesenchyme core covered by ectoderm externally forming clefts between each arch
- Endoderm on inside but forms pouches not grooves
- Pharyngeal arches and FNP are head and neck
What organs develop in the cranial end of the embryo?
- CVS
- Brain
- Special sensory organs
What can we say about the derivative of each arch?
Each arch has its own associated artery, cranial nerve and cartilage bar
How many pharyngeal arches are there and what are the cranial nerves associated with each arch?
XI and XII also have special relationship with pharyngeal system
What are the muscular derivatives of each pharyngeal arch?
What are the cartilage derivatives of each pharyngeal arch?
4-6 remain cartilaginous
What are each of the arteries associated with each pharyngeal arch?
This is why the vagus nerve gets hooked on arteries
What do the pharyngeal pouches go on to become?
Endoderm pockets go on to become tympanic cavity and glandular structures
What is the pharyngeal apparatus?
- Pharyngeal arches
- Pharyngeal clefts
- Pouches
What do the pharyngeal clefts go on to become?
- 1st and 2nd become the external auditory meatus
- External ear forms from swellings around the meatus
- 2nd cleft covers all of the others
- Initially creates cervical sinus with its inner edges formed by ectoderm.
- Sinus fuses
Where would a branchial cyst present in the neck and how do these cysts and fistulas form?
- Smooth non tender mass along anterior border SCM so lateral neck
- Persistence of cervical sinus due to incomplete fusion of 2nd cleft
- If part fo the sinus closes off this will form a cyst not a fistula
What drives the development of the face?
- Expansion of cranial neural tube
- Appearence of complex tissue systems like cranial gut tube and CVS
- Development of sense organs
What is the embryological origin of each of the adult facial feaurs?
- Eyes start on the lateral side as outgrowths of the brain
- Nasal placodes on FNP
How does the nose form embryonically?
- Nasal placodes sink to become nasal pits
- Medial and lateral prominences either side of the pit
- Maxillary prominences fuse with medial nasal prominence and force it midline so nasal prominences have to fuse
- Oronasal membrane disappears so oral and nasal cavity one big space
What is a placode?
Thickening of ectoderm that will then differentiate to give rise to a sensory structure
How does the nasal and oral cavity separate?
- Median nasal prominence forms philtrum to separate nostrils from mouth
- Palatal shelf grows from each maxillary prominence towards midline and fuse to form primary pallate
- Mandible grows large enough to allow tongue to drop
- Shelves can fuse in midline and forms the secondary pallate
- Separation of nose and oral cavity
What does the fusion of the medial nasal prominences form?
Intermaxillary segment consisting of:
- Philtrum
- Upper 4 incisors
- Primary palate
How does a cleft lip and palate form?
Lip: failure of fusion of the median nasal prominence and the maxillary prominence
Palate: failure of palatal shelves to meet in the midline
Why do cleft lips and palates occur and how are they managed?
- Genetic and environmental factors
- Picked up in antenatal scan or by sticking gloved finger in hard palate before discharge of baby
- Difficulty with speech and feeding so given specialist feeding techniques until 3 months when surgical repair for lip and 9-12 month repair for palate
How do the ears get to their final position on the face?
- Start in the neck
- As the mandible grows the ears ascend and get in line with eyes
- Common chromosomal abnormalities have external ear anomolies so low set ears can be a sign
Why does a trisomy 13 lead to low set ears and cleft palates a lot of the time?
Issue with mandible development which is needed for development of both of these structures
What is fetal alcohol syndrome?
- Babies exposed to alcohol in the womb can develop disorders
- Facial skeleton derived from neural crest cells in pharyngeal arches and these are sensitive to alcohol
- 1 in 100 births
Summarise the nerve, muscular and skeletal origin of each of the pharyngeal arches.
What is the fate of the following facial prominences?
What is the 4th and 6th arch branch of the vagus nerve?
4th: superior laryngeal nerve to cricothyroid and constrictors of the pharynx
6th: recurrent laryngeal to intrinsic muscles of the larynx
What do the nerves associated with a pharyngeal arch innervate?
The mucosa and muscular derivatives of the arch
