Embryology of head and neck

Question 1

in week 1, what are the developmental stages after fertilisation? (6)

Answer 1

egg –> zygote –> 2 cell stage –> 4 cell stage –> morula –> blastocyst

Question 2

in week 2 after fertilisation, cells would arrange into 2 layers
what are their names?

Answer 2

• epiblast

- hypoblast

Question 3

the trilaminar germ disc is froming in week number …..

Answer 3

3

Question 4

pharyngeal arches would appear during which weeks?

Answer 4

4-5th

Question 5

what is the faith of the 5th arch in humans?

Answer 5

never form or quickly regress

Question 6

arch apparatus consists of … (4)

Answer 6

• pharyngeal arches
• pharyngeal clefts
• pharyngeal pouches
• pharyngeal membranes

Question 7

the pharyngeal arch is externally lined with…….. and internally lined with……
while the core consists of……. and ……..

Answer 7

ectoderm
endoderm
mesoderm and neural crest cells

Question 8

each arch would give rise to four components
1- what are they? (4)
2- are they nearer to endoderm or ectoderm?

Answer 8

1- 
cartilagenues skeletal element 
skeletal muscle 
the cranial nerve associate to the particular arch 
aortic arch artery 

2- cartilagenues skeletal element and skeletal muscle are nearer to endoderm
the cranial nerve associate to the particular arch and aortic arch artery are nearer to ectoderm

Question 9

the skeletal element derivatives from 1 -4 pharyngeal arches are….

Answer 9

1- incus + malleus
2- stapes + upper rim of hyoid
3- lower rim of hyoid
4- laryngeal cartilages

Question 10

the skeletal muscle derivatives from 1 -4 pharyngeal arches are….

Answer 10

1- muscles of mastication. ex: anterior digastric
2- muscles of facial expression. ex: posterior digastric
3- stylopharyngeus
4- pharyngeal muscles

Question 11

cranial nerves directed into arches by….

Answer 11

neural crest cells

Question 12

the cranial nerve associate to each arch from 1 -6 (except 5) are….

Answer 12

1- trigeminal nerve (mandibular branch)
2- facial nerve 
3- glossopharyngeal nerve 
4- vagus nerve 
6- recurrent laryngeal nerve (a branch of vagus)

Question 13

aortic arch arteries are arising from the…

Answer 13

dorsal aortae

Question 14

the first pharyngeal cleft is forming the…

Answer 14

external acoustic meatus

Question 15

how the smooth neck contour is formed…

Answer 15

the 2nd arch overgrows the 3rd and 4th arches. then, the clefts in between will disappear

Question 16

what causes the lateral cervical cyst to appear?

Answer 16

failure of the 2nd arch overgrowing the 3rd and 4th arches. so, remnant clefts are showing like a cyst

Question 17

the internal branchial fistula opens into the pharynx at the level of the….

Answer 17

palatine tonsil

Question 18

the first pharyngeal membrane is forming the…

Answer 18

eardrum/ tympanic membrane

Question 19

the first pharyngeal pouch is forming the…

Answer 19

middle ear and auditory tube

Question 20

the second pharyngeal pouch is forming the…

Answer 20

palatine tonsils

Question 21

the ventral wing of the third pharyngeal pouch is forming the…
and the dorsal wing is forming the…

Answer 21

ventral: thymic lobules
dorsal: inferior parathyroids

Question 22

the ventral wing of the fourth pharyngeal pouch is forming the…
and the dorsal wing is forming the…

Answer 22

ventral: the parafollicular cells of the thyroid glands
dorsal: the superior parathyroid glands

Question 23

1- what is the defect causing DiGeorge syndrome?
2- what is the result?
3- what is the chromosomal defect?

Answer 23

1- failure of the third and fourth pouches to differentiate

2- hypoplasia or absence of the or/ and parathyroid gland affecting the immunity and calcium control

3- small deletion in chromosome 22