Empirical Embryology

Question 1

At what AOG do the hillocks of His form?

Answer 1

4-6 weeks AOG

Question 2

From what structure do the hillocks of His form?

Answer 2

First to second arch

Question 3

At what AOG do the hillocks of His fuse?

Answer 3

7 weeks AOG

Question 4

At what AOG is the auricle recognizable?

Answer 4

15-20 weeks AOG

Question 5

At what AOG is the tympanic ring formed? When do the ossification centers appear?

Answer 5

Mesenchyme condenses around the tympanic membrane to form a c-shaped ring and by the 9th week four centers of ossification appear in the ring and fuse by the 10th week giving rise to the primitive tympanic bone.

Question 6

At what AOG does the EAC epithelial core begin to reabsorb?

Answer 6

21 weeks AOG

Question 7

At what AOG does the EAC epithelial core completely reabsorb?

Answer 7

28 weeks AOG

Question 8

At what age does the external ear stop growing?

Answer 8

9 years old

Question 9

Anatomic changes in the tube with growth and development include what? (4)

Answer 9

“LACE”
L - increased length and diameter
A - increasing tubal angle
C - change in cellular composition of tubal cartilage
E - increased efficiency of tubal opening.

Question 10

Tubal length in infants vs. adult

Answer 10

Tubal length progresses from 17.5 mm in infants to reach an adult length of 37.5 mm.

Question 11

What are the changes in cellular composition of tubal cartilage during growth and development?

Answer 11

• decrease in cartilage cell density (midcartilaginous portion)
• increase in intercellular elastin (hinge region between the medial and lateral laminae)
• medial lamina develops more than the lateral lamina
• lateral lamina and lateral wall of the tube develop more of an S shape (allow for more efficient tubal recoil)

Question 12

What are the changes in efficiency of tubal opening during growth and development?

Answer 12

• surface area of the tensor veli palatini

- more perpendicular angle of insertion of the dilatory muscles (dilator tubae) to the cartilaginous tube,

Question 13

At what AOG do the pharyngeal arches form?

Answer 13

Day 28-32

Question 14

At what AOG do the malleus and incus begin to form?

Answer 14

At the 4th week a condensed mesenchymal interbranchial bridge is formed. This connects the upper end of the mandibular visceral bar to the central region of the hyoid visceral bar. It is thought that the head of the malleus and the body of the incus originate from the interbranchial bridge while the manubrium of the malleus, the long process of the incus, the stapedial crura and the lateral (tympanic) surface of the footplate arise from the hyoid visceral bar.

Question 15

At what AOG does the otic placode appear?

Answer 15

Day 25-28 or 3rd week

Question 16

At what AOG does the optic & nasal placode appear?

Answer 16

Day 31-35

Question 17

At what AOG are the ossicles are clearly formed and are fully formed?

Answer 17

Week 15

Question 18

At what AOG is the stapes clearly seen to be separated from the otic capsule?

Answer 18

At the 16th week

Question 19

At what AOG do the ossicles get ossified?

Answer 19

The malleus and incus gets ossified by the 16th week and the stapes gets ossified by the 18th week.

Question 20

At what AOG are the ossicles are fully developed?

Answer 20

At the 25th week

Question 21

At what age does the TM reach its vertical position?

Answer 21

At the time of birth the tympanic membrane makes an angle of approximately 30 degrees with the horizontal plane. Its vertical position is only reached by the age of 4 months.

Question 22

At what age does the organ of Corti develop form the epithelium of the cochlear duct?

Answer 22

5th week AOG

Question 23

At what age does the organ of Corti reach adult size?

Answer 23

25th week AOG

Question 24

At what age does the otic capsule begin to ossify?

Answer 24

Ossification of the otic capsule begins in the 15th week. It has 14 distinct centers of ossification.

Question 25

At what age does the otic capsule completely form its bony shell?

Answer 25

By the 23rd week these centers are fused without any suture line to form a complete bony shell, the otic capsule.

Question 26

Precursor of Organ of Corti

Answer 26

Organ of Kolliker

Question 27

At what week do the ethmoturbinals fuse and regress?

Answer 27

8th week

Question 28

Enumerate the structures that the ethmoturbinals (1-5) gives rise to

Answer 28

1st ET: ascending portion (agger nasi), descending portion (lateral extension of uncinate) 2nd ET: middle turb 3rd ET: superior turb 4th & 5th ET: supreme turb (when present)

Question 29

What embryological structure gives rise to the inferior turbinate?

Answer 29

maxilloturbinal

Question 30

enumerate the embryological structures (5) that contribute to the nose and which part it gives rise to

Answer 30

frontonasal prominence (nasal bridge) 2x medial nasal prominence (crest and tip) 2x lateral nasal prominence (alae)

Question 31

At what age does the frontal sinus reach adult size?

Answer 31

21 years old

Question 32

At what age does the ethmoid sinus reach adult size?

Answer 32

12 years old

Question 33

At what age does the maxillary sinus reach adult size?

Answer 33

18 years old

Question 34

At what age does the sphenoid sinus reach adult size?

Answer 34

15 years old

Question 35

What is the purpose of the vomeronasal organ?

Answer 35

pheromone detection (vestigial remnant)

Question 36

Where is the vomeronasal organ located?

Answer 36

pit on the anteroinferior nasal septum

Question 37

Embryologic origin of suprglottis + name the arch

Answer 37

bucoopharyngeal primordium from the 3rd and 4th branchial arch

Question 38

Embryologic origin of glottis and subglottis + name the arch

Answer 38

tracheobronchial primodium from the 6th branchial arch

Question 39

At what week do the salivary glands begin their development?

Answer 39

during the 6th week of life as a solid, ridge-like ingrowths of the oral epithelium

Question 40

Which salivary gland is the first to begin its development? order of the subsequent glands?

Answer 40

Parotid anlage is the 1st to develop at 6wk AOG followed by SMG then SL

Question 41

At what week does the parotid gland begin secretion?

Answer 41

Secretion by the parotid via parotid duct begins at about 18 weeks of gestation

Question 42

At what week do the cords in the parotid anlage canalize and form ducts?

Answer 42

At 10 weeks, these cords are canalized and form ducts with the largest becoming the parotid duct