Embryology I

Question 1

What system are helped to develop by the pharyngeal arteries?

Answer 1

Brian
CVS - heart and great vessels
Special sensory organs (eye, nose ear)

Question 2

What are pharyngeal arches?

Answer 2

• They are compromised of a system of mesenchymal proliferation’s in the neck region of the embryo.
• 5 in total, numbers 1-6 (5 not formed in humans)
• Together with FNP (frontonasal prominence) they constitute the building blocks for the head and neck region.

Question 3

Which cranial nerve is associated with which of the brachial arteries?

Answer 3

All the mixed sensory and motor ones.

1 = CN V
2 = CN VII
3 = CN IX 
4-6 = CN X 
CN XII

These nerves supply the derivatives of the pharyngeal system.

Question 4

What arch derives the muscles of mastication?

Answer 4

Pharyngeal arch 1

Question 5

What arch derives the muscles of facial expression?

Answer 5

Pharyngeal Arch 2

Question 6

What muscles are derived from pharyngeal arch 3?

Answer 6

Stylopharyngeus

Question 7

What muscles are derived from pharyngeal arch 4?

Answer 7

Crycothyroid
Levator palantini
Constrictors of the pharynx

Question 8

Wha muscles are derived from pharyngeal arch arch 6?

Answer 8

Intrinsic muscles of the larynx

Question 9

What cartilage is formed from each of the pharyngeal arches?

Answer 9

Ph A 1 = Meckel’s cartilage: malleus and incus and a template for formation of the mandible.

Ph A 2 = Reichert’s: stapes plus upper part of the hyoid bone.

Ph A 3 = remainder of hyoid bone

Ph A 4 & 6 = Cartilages of the larynx

Question 10

What happens to aortic arches?

Answer 10

1 and 2 - disappear
3 - internal carotid
4 - left arch of aorta and right brachiocephalic artery
6 - pulmonary arch

Question 11

Where are the recurrent laryngeal nerves positioned?

Answer 11

Right - under right subclavian

Left - under aortic arch

Question 12

What are the pharyngeal pouches? And what is made form them?

Answer 12

Endoderm lined pockets in the pharynx.

First pouch is the largest and becomes the tympanic cavity (ear stuff).

Development results in formation of palatine tonsils and parathyroid glands and the thymus.

Question 13

What happens to the pharyngeal clefts?

Answer 13

Only the first one is left. This becomes the external acoustic meatus.

2nd arch grows down to cover others, obliterating all other clefts.

Branchial cysts (hard mass) or fistula (opening to surface of the neck) can occur if there are remnants.

Branchial cyst would sit anterior to SCM

Question 14

What drives development of the face?

Answer 14

Expansion of the cranial neural tube

Appearance of a complex tissue system associated with cranial gut give and outflow of the developing heart.

Development of the sense organs also occurs and they need to separate the respiratory tract from the GI tract.

Question 15

What are the embryological components of the face?

Answer 15

Stomatodeum - buccopharyngeal membrane

Frontonasal prominence

1st pharyngeal arch - maxillary prominence and madibular prominance

Question 16

What parts of the face are made from the FNP?

Answer 16

Forehead
Bridge of nose.
Nose
Philtrum (upper lip dip)

Question 17

WHat parts of the phase are made from the maxillary prominence?

Answer 17

Cheeks
Lateral upper lip
Lateral upper jaw

Question 18

What parts of the face are made form mandibular prominence?

Answer 18

Lower lip and jaw

Question 19

How does the nose begin to develop?

Answer 19

Nasal placoderms appear on frontonasal prominence

Then sink to become the nasal pits

Medial and lateraled nasal prominence form on either side of the pits.

Maxillary prominences grow medically, pushing the nasal prominences close together in the midline.

Maxillary prominences fuse with medial nasal prominences.

Medial nasal prominences then fuse in the midline.

Question 20

How do the nasal and oral cavities separate?

Answer 20

Mandible grows large enough to allow the tongue drops

Palatial shelves grow towards each other and fuse in the midline.

Nasal septum develops as a midline down-growth and ultimately fuses with palatial shelves.

Question 21

How does cleft lip / palate occur?

Answer 21

Lateral cleft lip - failure of fusion of medial nasal prominence and maxillary prominence.

Cleft lip and palate - combined with failure of palatial shelves to meet in the midline.

Question 22

Where does the external acoustic meatus develop from?

Answer 22

1st Pharyngeal cleft

Question 23

Where do the middle ear cavity and ossicles develop from?

Answer 23

1st pharyngeal pouch and cartilages of 1st and 2nd arches respectively.

Question 24

How do the auricle develop?

Answer 24

Auricles develop from proliferation within the 1st and 2nd pharyngeal arches surrounding the meatus.

Question 25

How do the ears end up on the side of the head?

Answer 25

External ears develop initially in the neck

As mandible grows, the ears ascend to the side of the head to lie in line with the eyes.

All common chromosomal abnormalities have associated external ear abnormalities.

Question 26

Why can pregnancy people not drink alcohol?

Answer 26

Embryo and foetus sensitive to small concentrations of alcohol.

Most effects of alcohol seen in the head and neck region as the facial skeleton is derived from neural crest cells and the migration of these cells and development of the brain is extremely sensitive to alcohol.

Question 27

What is foetal alcohol syndrome?

Answer 27

Facial skeleton is developed from neural crest cells - make cartilaginous bars.

Neural crests are extremely sensitive to alcohol.

Seen is significant high conc. of alcohol during pregnancy

Occur 1 in 100 births.

Facial features - small head, flat mid face, thin upper lip, small eye opening, short nose, low nasal bridge, underdeveloped jaw ect.