ENT Embryology Flashcards
what are pharyngeal (branchial) arches formed from?
developed from gill arches (remnants of fish gills)
When are pharyngeal (branchial) arches formed?
Develop cranial to caudal
Arch 1 – Day 22
Arch 2 + 3 – Day 24
Arch 4 + 6 – Day 29
(5 is missing because it doesn’t form in humans)
Pharyngeal apparatus? (3)
Function of clefts and pouches?
* Core pharyngeal arch (mesenchymal tissue)
* external pharyngeal cleft (ectoderm)
* internal pharyngeal pouch (endoderm)
Clefts and pouches seperate arches (external layer is cleft, internal layer is pouch)
What is each pharyngeal arch made up of? (4)
* Core of mesenchyme derived from paraxial and lateral plate mesoderm (musculature of the face)
* neural crest cells (skeletal components of face)
* cranial nerve
* Artery (aortic arch arteries)
…
What skeletal elements is first arch split into?
Maxillary process (cranial)
* maxilla
* zygomatic bone
* squamous portion of temporal bone
Mandibular process (caudal)
* formes meckel’s cartilage
* incus and malleous (ear)
* mandible
Muscles and nerves of 1st arch?
All muscles supplies by CN V3
* muscles of mastication
* anterior belly of digastric
* mylohyoid
* tensor tympani
* tensor veli palatini
Sensory supply to skin of the face
* V1 (opthalmic)
* V2 (maxillary)
* V3 (mandibular)
Skeletal elements of 2nd arch? (5)
* stapes (ear)
* styloid process of temporal bone
* stylohyoid ligament
* lesser horn of hyoid
* upper part of hyoid body
What is the cartilage of the 1st arch known as?
2nd arch?
1st arch = Meckel’s cartilage
2nd arch = Reichert’s cartilage
2nd arch muscles and nerves?
All musculature supplied by CNVII
* muscles of facial expression
* posterior belly of digastric
* stylohyoid (elevates tongue)
* strapedius
* auricular muscles
Skeletal components of 3rd arch?
* greater horn o fhyoid
* lower part of hyoid bone
Muscles and nerves of arch 3?
Supplied by glossopharyngeal (CN IX) nerve
* stylopharyngeus
* longitudinal pharyngeal muscle
Muscles of arch 4? (3)
Supplied by?
Cricothyroid
levator veli palatini
pharyngeal constrictors
* vagus (CN x) = same as arch 6
Muscles of arch 6?
Suppplied by?
Intrinsic laryngeal - moves inner vocal cords
Supplied by vagus (CN X) = same as arch 4
What do the pharyngeal clefts become?
1st cleft = external acoustic meatus
2 - 4th cleft = form cervical sinus (eventually disappears)
What happens if cervical sinus does not disappear during development?
Branchial fistulas + cervical cyst
What do pharyngeal pouches become?
1st pouch = middle ear, tympanic membrane, eustachian tube
2nd pouch = palatine tonsil
3rd pouch = inferior parathyroid gland, thymus
* the reason it is inferior is because it buds off
4th pouch = superior parathyroid gland, ultimobranchial body
…
Development of the ear?
Inner ear
* balance (semicircular canals)
* hearing (organ of Corti)
Middle Ear
* tympanic cavity
* ossicles
External Ear
* External auditory meatus - 1st cleft
* auricle
What do otic vesicles give rise to?
What are they formed from?
Otic vesicles give rise to inner ear
* otic placode -> otic pit -> otic vesicle
What does utricular portion of inner ear give rise to?
Saccular portion?
Utricular = semicircular canals (balance)
Saccular = cochlear (hearing)
Development of cochlear duct?
Cochlear duct grows in spiral between 6-8 weeks
* surrounding mesnechyme becomes cartilaginous
* coil becomes origin of Corti (hearing)
Development of external ear?
* External auditory meatus -> dorsal part of first pharyngeal cleft
* Month 3 - epithelial cells proliferate to form Meatal Plug
* Plug dissolves in month 7 and contributes to ear drum
* 6 auricular Hillocks fuse to form auricle
(plug can lead to congenital deafness, can be surgically removed)
Origins of facial features? (2)
Ventral facial features
* pharyngeal arch 1 = maxilla, mandible, zygomatic, temporal bones + muscles of mastication
* pharyngeal arch 2 = muscles of facial expression
Facial swellings?
5 swellings present from week 4
* frontonasal prminence (frontal bone + nasal bone)
* maxillary prominence (x2)
* mandibular prominence (x2)
where are facial swellings present at week 4 located?
surround primitive oral cavity = stromodeum
what facial swellings develop at week 5?
4 additional nasal swellings develop on the frontonasal prominence in week 5:
- Medial nasal swellings (x2)
- Lateral nasal swellings (x2)
what happens to nasal swellings at week 6?
Medionasal prominences come towards each other medially.
Nasolacrimal groove?
What does it eventually form?
Lies between the maxillary prominence and the lateral nasal prominence
* forms nasolacrimal duct
Components of the face at 10 weeks?
Upper lip
* medial nasal priminences (x2)
* maxillary prominences (x2)
Lower lip
* mandibular prominences
Nose
* frontonasal prominence (bridge and nasal septum)
* medial nasal prominences (crest and tip)
* lateral nasal prominences (alae)
Primary palate?
What is this?
Fusion of medial nasal prominences give Intermaxillary segment
Intermaxillary segment
* labial portion - philtrum
* palatal component - primary palate
* upper jaw component - carries 4 incisors
at week 10, septum descends and conchae sprout
How do nasal cavities communicate with oral cavity before definite conchae develop?
primitive conchae
what does development of secondary palate give rise to?
Definitive conchae between nasal cavity and oral cavity
