ENT Embryology

Question 1

what are pharyngeal (branchial) arches formed from?

Answer 1

developed from gill arches (remnants of fish gills)

Question 2

When are pharyngeal (branchial) arches formed?

Answer 2

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)

Question 3

Pharyngeal apparatus? (3)

Function of clefts and pouches?

Answer 3

* 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)

Question 4

What is each pharyngeal arch made up of? (4)

Answer 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)

Question 5

Answer 5

…

Question 6

What skeletal elements is first arch split into?

Answer 6

Maxillary process (cranial)

* maxilla

* zygomatic bone

* squamous portion of temporal bone

Mandibular process (caudal)

* formes meckel’s cartilage

* incus and malleous (ear)

* mandible

Question 7

Muscles and nerves of 1st arch?

Answer 7

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)

Question 8

Skeletal elements of 2nd arch? (5)

Answer 8

* stapes (ear)

* styloid process of temporal bone

* stylohyoid ligament

* lesser horn of hyoid

* upper part of hyoid body

Question 9

What is the cartilage of the 1st arch known as?

2nd arch?

Answer 9

1st arch = Meckel’s cartilage

2nd arch = Reichert’s cartilage

Question 10

2nd arch muscles and nerves?

Answer 10

All musculature supplied by CNVII

* muscles of facial expression

* posterior belly of digastric

* stylohyoid (elevates tongue)

* strapedius

* auricular muscles

Question 11

Skeletal components of 3rd arch?

Answer 11

* greater horn o fhyoid

* lower part of hyoid bone

Question 12

Muscles and nerves of arch 3?

Answer 12

Supplied by glossopharyngeal (CN IX) nerve

* stylopharyngeus

* longitudinal pharyngeal muscle

Question 13

Muscles of arch 4? (3)

Supplied by?

Answer 13

Cricothyroid

levator veli palatini

pharyngeal constrictors

* vagus (CN x) = same as arch 6

Question 14

Muscles of arch 6?

Suppplied by?

Answer 14

Intrinsic laryngeal - moves inner vocal cords

Supplied by vagus (CN X) = same as arch 4

Question 15

What do the pharyngeal clefts become?

Answer 15

1st cleft = external acoustic meatus

2 - 4th cleft = form cervical sinus (eventually disappears)

Question 16

What happens if cervical sinus does not disappear during development?

Answer 16

Branchial fistulas + cervical cyst

Question 17

What do pharyngeal pouches become?

Answer 17

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

Question 18

Question 19

Answer 19

…

Question 20

Development of the ear?

Answer 20

Inner ear

* balance (semicircular canals)

* hearing (organ of Corti)

Middle Ear

* tympanic cavity

* ossicles

External Ear

* External auditory meatus - 1st cleft

* auricle

Question 21

What do otic vesicles give rise to?

What are they formed from?

Answer 21

Otic vesicles give rise to inner ear

* otic placode -> otic pit -> otic vesicle

Question 22

What does utricular portion of inner ear give rise to?
Saccular portion?

Answer 22

Utricular = semicircular canals (balance)

Saccular = cochlear (hearing)

Question 23

Development of cochlear duct?

Answer 23

Cochlear duct grows in spiral between 6-8 weeks

* surrounding mesnechyme becomes cartilaginous

* coil becomes origin of Corti (hearing)

Question 24

Development of external ear?

Answer 24

* 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)

Question 25

Origins of facial features? (2)

Answer 25

Ventral facial features

* pharyngeal arch 1 = maxilla, mandible, zygomatic, temporal bones + muscles of mastication

* pharyngeal arch 2 = muscles of facial expression

Question 26

Facial swellings?

Answer 26

5 swellings present from week 4

* frontonasal prminence (frontal bone + nasal bone)

* maxillary prominence (x2)

* mandibular prominence (x2)

Question 27

where are facial swellings present at week 4 located?

Answer 27

surround primitive oral cavity = stromodeum

Question 28

what facial swellings develop at week 5?

Answer 28

4 additional nasal swellings develop on the frontonasal prominence in week 5:

• Medial nasal swellings (x2)
• Lateral nasal swellings (x2)

Question 29

what happens to nasal swellings at week 6?

Answer 29

Medionasal prominences come towards each other medially.

Question 30

Nasolacrimal groove?

What does it eventually form?

Answer 30

Lies between the maxillary prominence and the lateral nasal prominence

* forms nasolacrimal duct

Question 31

Components of the face at 10 weeks?

Answer 31

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)

Question 32

Primary palate?

What is this?

Answer 32

Fusion of medial nasal prominences give Intermaxillary segment

Intermaxillary segment

* labial portion - philtrum

* palatal component - primary palate

* upper jaw component - carries 4 incisors

Question 33

Answer 33

at week 10, septum descends and conchae sprout

Question 34

How do nasal cavities communicate with oral cavity before definite conchae develop?

Answer 34

primitive conchae

Question 35

what does development of secondary palate give rise to?

Answer 35

Definitive conchae between nasal cavity and oral cavity