Oral Embryology

Question 1

Where does fertilisation occur?

Answer 1

Within the oviduct

Question 2

How long is tubal transport of the fertilised ova?

Answer 2

7-10 days

Question 3

At what stage does the embryo enter the uterus?

Answer 3

The morula or early blastocyst

Question 4

When does the blastocyst implant?

Answer 4

By day 17

Question 5

What is the internal cavity of the blastocyst called?

Answer 5

A blastocoele

Question 6

In what direction does general embryologic development occur?

Answer 6

Cephal-caudal direction

Question 7

What is the sequence of embryological development?

Answer 7

1. Head folds
2. Neural tube closure
3. Somite formation
4. Development of the brachial clefts
5. Development of the lens placode
6. Development of the otic placode
7. Development of the cardiac bulg
8. Development of the limb buds

Question 8

Define gastrulation?

Answer 8

The formation of the embryo’s germ layers

Question 9

What is the Rauber’s layer?

Answer 9

The area that gives rise to the proliferation of the inner cell mass during gastrulation

Question 10

What develops from the inner cell mass?

Answer 10

The endodermal layer, then the embryonic disc

Question 11

How are mesodermal tissues and the notochord formed?

Answer 11

From infolding of the embroynic disc in a cephalon-caudal direction

Question 12

How are pharyngeal clefts formed?

Answer 12

By invaginations of the surface ectoderm

Question 13

What do the pharyngeal clefts define?

Answer 13

Pharyngeal arches

Question 14

What are the pharyngeal arches composed of?

Answer 14

Mesenchyme and neural crest cells; aortic arch artery and an associated cranial nerve

Question 15

What does facial formation depend on?

Answer 15

The correct formation, development and fusion of five primordial structures:

1. Single fronto-nasal prominence
2. Paired maxillary prominences
3. Paired mandibular prominences

Question 16

How are the nasal cavities formed?

Answer 16

An ectodermal thickening forms the nasal placodes; then mesenchymal thickenings alongside this form the medial and lateral nasal prominences

Question 17

How is the primary palate formed?

Answer 17

A thin membrane separates the nasal pits from the oral cavity. The caudal portion of this later atrophies to form a common oro-nasal opening (the choana); and the remaining rostral portion of the membrane forms the incisive process and the primary palate

Question 18

How does the tongue develop?

Answer 18

From the proliferation of mesenchymal tissues on the floor of the primordial pharynx.

Question 19

What part of the tongue develops from the first pharyngeal arch?

Answer 19

Two lateral lingual swellings and one medial lingual swelling

Question 20

What part of the tongue develops from the second and third pharyngeal arch?

Answer 20

A midline swelling known as the Copula

Question 21

What part of the tongue develops from the third and fourth pharyngeal arch?

Answer 21

The hypopharyngeal eminence

Question 22

How does the rostral 2/3 of the tongue form?

Answer 22

The fusion of the two lateral lingual swellings and the medial lingual swelling

Question 23

How does the caudal 1/3 of the tongue form?

Answer 23

From the expansion of the Copula with some contribution from the hypopharyngeal eminence

Question 24

What forms the lung bud?

Answer 24

The laryngo-tracheal groove at the caudal portion of the pharyngeal arches forms the primordial trachea

Question 25

How is the secondary palate formed?

Answer 25

The fused palatine processes separate the nasal and oral cavities, forming the secondary palate.

Question 26

How is a cleft palate formed?

Answer 26

The failure to develop the primary palate correctly, leading to the malpositioning of the secondary palate

Question 27

What can cause a cleft palate to develop?

Answer 27

1. Failure of the processes to develop
2. Failure of fusion
3. Failure of the central mesenchyme to merge properly
4. Rupture of the shelf after fusion

Question 28

By what mechanism do most of the facial bones form?

Answer 28

Intramembranous ossification (appositional growth)

Question 29

What is Meckel’s cartilage?

Answer 29

The cartilage structure within the mandible