Embryology

Question 1

Branchial cleft

Answer 1

derived from ectoderm

Question 2

Branchial arch

Answer 2

derived from mesoderm (muscles, arteries) and neural crest (bones, cartilage)

Question 3

Branchial pouches

Answer 3

derived from endoderm

Question 4

1st cleft

Answer 4

external auditory meatus

Question 5

2nd- 4th cleft

Answer 5

temporary cervical sinuses, obliterated by proliferation of 2nd arch

Question 6

What is the derivative of a branchial cleft cyst?

Answer 6

Persistent cervical sinus (2-4 branchial cleft)

appears in the lateral neck

Question 7

1st arch

Answer 7

• Meckel cartilage: Mandible, Malleus, incus, sphenomandibular ligament
• CN V2,V3
• muscles of mastication, mylohyoid, belly of digastric, tensor tympani, tensor veil palatini

Question 8

Treacher Collins syndrome

Answer 8

1st arch neural crest fails to migrate –> mandibular hypoplasia, fail abnormalities

Question 9

2nd arch

Answer 9

• Reichert cartilage: stapes, styloid process, lesser horn of hyoid, stylohyoid ligament
• Muscles of facial expression, stapedius, stylohyoid, belly of digastric
• CN VII

Question 10

Congenital pharyngocutaneous fistula

Answer 10

persistence of 2nd cleft and pouch –> fistula between internal tonsillar area and external neck
found along anterior border of sternocleidomastoid

Question 11

3rd arch

Answer 11

• greater horn of hyoid cartilage
• stylopharyngeous m.
• CN XII

Question 12

4th-6th arch

Answer 12

-cartilage: thyroid, cricoid, arytennoids, corniculate, cuneiform
-4th: muscle of pharyngeal constriction, cricothyroid, legato veil palatine
-6th: all intrinsic muscles of larynx except cricothyroid
4th arch: CN X (superior laryngeal branch)
6th arch: CN X (recurrent laryngeal branch)

Question 13

1st pouch

Answer 13

“auditory tube”

: middle ear eustachian tube, mastoid cells

Question 14

2nd pouch

Answer 14

“tonsillar fossa”

: epithelial lining of palatine tonsil

Question 15

3rd pouch

Answer 15

“thymus and inferior parathyroid”
: dorsal wing = inferrior parathyroid; ventral wing = thymus
note 3rd pouch structures end up below 4th pouch

Question 16

4th pouch

Answer 16

“superior parathyroids”

:Dorsal wings= superior parathyroid

Question 17

Cleft lip

Answer 17

failure of fusion of maxillary and medial nasal processes (primary palate)

Question 18

Cleft Palate

Answer 18

1. failure of fusion of two lateral palatine processes
2. failure of fusion of lateral palatine process with nasal septum and/or medial palatine process
   (formation of secondary palate)

Question 19

Genital tubercle–> M/F homolog

Answer 19

Male: glans penis, corpus cavernosum and spongiosum
Female: Gans clitoris, vestibular bulbs

Question 20

Urogenital sinus–> M/F homolog

Answer 20

Male: bulbourethral glands of cowper, prostate gland
Female: greater vestibular glands of bartholin, urethral and pararurethral glands of skene

Question 21

Urogenital folds –> M/F homolog

Answer 21

Male: ventral shaft of penis (penile urethra)
Female: labia minora

Question 22

Labiosacral swelling –> M/F homolog

Answer 22

Male: scrotum
Female: labia majora