H&N Embryology

Question 1

How many pharyngeal arches?

Answer 1

5, numbered one to six (5th doesn’t form)

Question 2

What is the structure of the pharyngeal arches?

Answer 2

A core of proliferating mesenchyme covered by ectoderm on the outside surface, and endoderm on the inside surface

(Derived by paraxial and lateral plate mesoderm with some neural crest contribution)

Question 3

Where are the pharyngeal pouches and clefts?

Answer 3

Clefts are outside ectoderm surface

Pouches are on the inside endoderm surface

Question 4

What are the nerves of the pharyngeal arches?

Answer 4

CN V, VII, IX, X

Question 5

What is derived from the cartilage of 1st pharyngeal arch?

Answer 5

Known as Meckel’s cartilage

Becomes the mandible, malleus and incus

Question 6

What artery and nerve is associated with the 1st pharyngeal arch?

Answer 6

No associated artery

Nerve is trigeminal nerve

Question 7

What is derived from the 2nd pharyngeal arch cartilage?

Answer 7

Known as Reichert’s cartilage

Forms the stapes of the middle ear and the styloid process and part of the hyoid bone

Question 8

What nerve and artery is associated with the 2nd pharyngeal arch?

Answer 8

Facial nerve

No associated artery

Question 9

What does the cartilage of the 3rd pharyngeal arch contribute to?

Answer 9

Remainder of the hyoid bone

Question 10

What nerve and artery is associated with the 3rd pharyngeal arch?

Answer 10

Glossopharyngeal nerve

Internal carotid artery

Question 11

Which nerve is associated with the 4th pharyngeal arch?

Answer 11

Vagus nerve, superior laryngeal branch (innervates cricothyroid)

Question 12

Which nerve is associated with the 6th pharyngeal arch?

Answer 12

Vagus nerve, recurrent laryngeal branch (innervates intrinsic muscles of larynx except cricothyroid)

Question 13

Which artery is associated with the 4th pharyngeal arch?

Answer 13

Right contribute to subclavian

Left contribute to arch of aorta

Question 14

Which artery is associated with the 6th pharyngeal arch?

Answer 14

Right and left pulmonary arteries

Question 15

What does the 1st pharyngeal pouch form?

Answer 15

Eustachian tube and tympanic cavity

Question 16

What does the 2nd pharyngeal pouch form?

Answer 16

Palatine tonsils

Question 17

What does the 3rd pharyngeal pouch form?

Answer 17

Inferior parathyroid gland and thymus

Question 18

What does the 4th pharyngeal pouch form?

Answer 18

Superior parathyroid gland

Question 19

What happens to the pharyngeal clefts?

Answer 19

1st is all that remains

The 2nd cleft grows down to cover the 3rd and 4th cleft and obliterate them

Question 20

How and where can branchial cysts form?

Answer 20

Along the anterior border of the SCM

due to failure of the cervical sinus to be obliterated

Question 21

How does the nose form?

Answer 21

Nasal placoderms appear on FNP
These deepens to form nasal pits
Medial and lateral nasal prominences form on either side of both nasal pits

Maxillary prominences fuse towards each other, pushing the medial nasal prominences closer to the midline
Medial nasal prominences fuse to each other, and to the maxillary prominence
This forms the philtrum and primary palate

Question 22

How do the primary and secondary palates form?

Answer 22

Primary palate forms by fusion of medial nasal prominences with maxillary prominence
Secondary palate forms when the palatal shelves from the maxillary prominences fuses together

Question 23

How do cleft lips and cleft palates differ?

Answer 23

Cleft lip is due to failure of medial nasal prominences to fuse to maxillary prominence

Cleft palate is due to failure of palatal shelves to fuse in the midline

Question 24

How do the eyes form?

Answer 24

From optic placodes (out pocketing of forebrain that grow to make contact with overlying ectoderm)
These are positioned on the outside of the head, but move to the front of the face as the facial prominences grow

Question 25

How does the ear form?

Answer 25

Auricle from 1st and 2nd pharyngeal arch surrounding meatus External auditory meatus from the 1st pharyngeal cleft Inner ear forms from Otic placodes Ear initially develops in the neck but ascends to be in line with the eyes

Question 26

What is foetal alcohol syndrome?

Answer 26

Alcohol consumed by mother can easily cross the placenta, and affect sensitive neural crest cells Causes abnormal appearance eg thin lip, small head, underdeveloped jaw, low intelligence

Question 27

How does the neuroectoderm portion of the pituitary gland form?

Answer 27

Outgrowth of the forebrain towards the pharynx known as ten infundibulum

Question 28

How does the ectodermal portion of the pituitary gland form?

Answer 28

Invagination of the roof of the pharynx towards the forebrain known as Rathke's pouch

Question 29

What does Rathke's pouch form?

Answer 29

The anterior lobe of the pituitary

Question 30

What does the infundibulum go on to form?

Answer 30

The posterior pituitary and the stalk

Question 31

What is the V-shaped division on the tongue?

Answer 31

The sulcus terminalis, divides the anterior 2/3rds of the tongue from the posterior 1/3rd

Question 32

What are the emrbyological components of the tongue?

Answer 32

2 lateral lingual swellings | 3 medial lingual swellings (tuberculum impar, cupola, epiglottis swellings)

Question 33

What pharyngeal arches do the derivatives the the tongue form from?

Answer 33

Lateral lingual swellings from Ph. Arch 1 Tuberculum impar from arch 1 Cupola from arches 2 and 3 Epiglottis swellings from arch 4

Question 34

How does the tongue form?

Answer 34

The lateral lingual swellings overgrow the tuberculum impar 3rd arch component of the cupola overgrows the 2nd arch component Extensive apoptosis degeneration to free the tongue from the floor of the oral cavity, apart from the lingual frenulum

Question 35

Where does the primordial thyroid gland appear?

Answer 35

In the floor of the pharynx between the tuberculum impar and cupola (marked by the foramen caecum)

Question 36

How does the primitive thyroid gland end up in the neck?

Answer 36

Descends down, but remains connect to the tongue by the thyroglossal duct

Question 37

What can occur if the thyroglossal duct doesn't resolve?

Answer 37

Thyroglossal cysts | Ectopic thyroid tissue can remain anywhere along the path of the thyroid descent

Question 38

What is Treacher-Collins syndrome?

Answer 38

Failure of neural crest cells to migrate into the 1st Ph. arch resulting in defects in development Autosomal dominant Hypoplasia of mandible and facial bones