embryology

Question 1

how are the definitive endoderm and mesoderm formed?

Answer 1

Invagination of the epiblast cells through the primitive streak

Question 2

what are the 3 main groups of the mesoderm?

Answer 2

Paraxial, Intermediate and Lateral plate

Question 3

when do the pharyngeal arched develop?

Answer 3

Arch 1 – Day 22
Arch 2 + 3 – Day 24
Arch 4 + 6 – Day 29
(no arch 5 in mammals)

Question 4

what are the components of the pharyngeal apparatus?

Answer 4

Core pharyngeal arch (Mesenchymal tissue)
External pharyngeal cleft (Ectoderm)
Internal pharyngeal pouch (Endoderm

Question 5

what does each pahryngeal arch consist of?

Answer 5

• core of mesenchyme (derived from paraxial and lateral plate mesoderm)
• neural crest cells
• cranial nerve component
• artery (aortic arch arteries)

Question 6

what does the 1st pharyngeal arch from?

Answer 6

maxillary process
- maxilla and zygomatic bone

& mandibular process
- Forms Meckel’s cartilage
- incus and Malleus (ear ossicles)
- Mandible
- Squamous portion of temporal bone

Question 7

what does the 2nd cranial arch form?

Answer 7

reichet’s cartilage
skeletal derivatives-
- Stapes
- Styloid process of temporal bone
- Stylohyoid ligament
- Lesser horn of Hyoid
- upper part of Hyoid body

Question 8

what does the 3rd pharyngeal arch form?

Answer 8

greater horn & lower part of hyoid bone

Question 9

what do the 4th-6th pharyngeal arches form?

Answer 9

laryngeal cartilages

Question 10

what nerve is the 1st pharyngeal arch related to?

Answer 10

CN V2 and CN V3

Question 11

what nerve is the 2nd pharyngeal arch related to?

Answer 11

CN VII (facial)

Question 12

what nerve is the 3rd pharyngeal arch related to?

Answer 12

CN IX (glossopharyngeal)

Question 13

what nerve are the 4th-6th pharyngeal arches related to?

Answer 13

CN X (vagus)
arch 4 - superior laryngeal branch
arch 6 - recurrent laryngeal branch

Question 14

what muscular derivatives are formed by each of the pharyngeal arches?

Answer 14

the muscles supplied by their associated nerves

Question 15

where are cervical cysts and fistulas usually found?

Answer 15

along the anterior border or the sternocleidomastoid

Question 16

what does the 1st pharyngeal pouch form?

Answer 16

Tympanic membrane
Middle ear
Eustachian tube

Question 17

what does the 2nd pharyngeal pouch form?

Answer 17

palatine tonsil

Question 18

what does the 3rd pharyngeal pouch form?

Answer 18

inferior parathyroid gland
thymus

Question 19

what does the 4th pharyngeal pouch form?

Answer 19

superior thyroid gland
ultimobranchial body

Question 20

describe the nasolacrimal groove

Answer 20

Lies between the maxillary prominence and the lateral nasal prominence
Solid epithelial cord in floor of groove
Cord detaches from the ectoderm
Canalization forms the nasolacrimal duct

Question 21

what are the embryological origins of the upper and lower lip?

Answer 21

Upper lip
2 medial nasal prominences
2 maxillary prominences

Lower lip
Mandibular prominences

Question 22

what are the embryological origins of the nose?

Answer 22

Frontonasal prominence = Bridge and nasal septum
Medial nasal prominences = Crest and tip
Lateral nasal prominences = Alae (sides)

Question 23

how does the primary palate develop?

Answer 23

fusion of medial nasal prominences to give intermaxillary segment:
Labial portion -> Philtrum of upper lip
Upper jaw component -> Carries 4 incisors
Palatal component -> form primary palate

Question 24

describe development of the nasal cavities

Answer 24

Nasal pits deepen and penetrate into the underlying mesenchyme with forward growth of frontonasal prominence

As the intermaxillary segment forms it is connected by a nasal fin.

Nasal fin vacuolizes and thins, this opens the developing nasal sac.

Nasal cavities communicate with oral cavity via Primitive choanae behind primary palate

Definitive choanae open at junction of nasal cavity with pharynx due to formation of secondary palate

Question 25

describe the formation of the secondary palate

Answer 25

Right and left palatal shelves develop parallel to the tongue.
Fused in the central region initially then expands anteriorly and posteriorly.
Mandibular development facilitates clearance of the tongue

Question 26

what can happen if there is an error in fusion of the secondary palate?

Answer 26

cleft palate