Introductory Embryology, Oral-Facial Development And Associated Developmental Anomalies

Question 1

Stages of human development:

Answer 1

Proliferation Period (0-3 weeks)
 Embryonic Period (3-8 weeks)
 Fetal Development Period
(9 weeks to term)

Question 2

Fertilization of

ovum yields?

Answer 2

zygote

Question 3

Mitotic cleavage

of zygote forms?

Answer 3

blastomere

Question 4

≥ 32 Blastomeres

is called a?

Answer 4

morula

Question 5

The 64 cell stage

morula develops? referred to as?

Answer 5

internal blastocystic
cavity and thereafter
is referred to as a
blastocyst

Question 6

embryoblast

Answer 6

The blastocyst also develops an inner cell mass at days 6-7

and thereafter is referred to as the embryoblast.

Question 7

implantation, structure that accomplsihes it? occurs when?

Answer 7

Implantation of the embryoblast in the uterine wall begins
at day 4 and is complete at day 10. accomplished with syncytiotrophoblasts projections of blastocyst. will slowly move deeper into uterine wall.

Question 8

inner cell mass of the embryoblast becomes?

Answer 8

bilaminar embryonic disc

two layers

Question 9

outer cell mass of the embryoblast becomes?

Answer 9

Outer cell mass 
becomes the
cytotrophoblast 
& syntrophoblast
layers which are 
precursor to the
placenta

Question 10

layers of bilaminar embryotic disc

Answer 10

epiblast: meso/ectoderm
hypoblast: endoderm

Question 11

structures associated with the bilaminar embryotic disc

Answer 11

Epiblast Layer 
• Hypoblast Layer 
• Amniotic Cavity 
• Blastocyst Cavity (yolk sac)
• Syntrophoblasts
• Cytotrophobasts

Question 12

Heuser’s membrane-formation and purpose (new term?)

Answer 12

formed by enlargement of the amniotic cavity and migration
of cells out of the hypoblast
Heuser’s membrane will form the
internal lining of the blastocyst cavity – now called the yolk sac

Question 13

cell layers and embryotic cavities of the embryoblast

Answer 13

cell layers: 
Epiblast
 Embryonic mesoderm
 Hypoblast
embryonic cavities: 
 Amniotic
 Yolk sac
 Chorionic

Question 14

During the 3rd week of development, the bilaminar

embryonic disc is characterized by formation of what structures?

Answer 14

Primitive Streak
Notochord
Neural tube
AND the 3 germ layers (ecto formerly the epiblast and endo formerly the hypoblast)

Question 15

portions of primitive streak (gives rise to? order?)

Answer 15

Primitive Streak>
Notochord>
>Neural Tube
(in this order)

Question 16

the primitive node will give rise to?

Answer 16

notochord

Question 17

notochord formation, when it occurs

Answer 17

Primitive node → Notochordal Process → Notochord
• Pre-notochordal cells invaginate within the primitive
node and migrate towards the cephalad until the
reach the prechordal plate. They detach themselves
from the ectodermal layer to line within the
mesoderm forming the notochord.
completed by week 3: proliferation period

Question 18

notochrod functions

Answer 18

• The notochord functions as a primitive skeletal support of the
embryo around which the axial skeleton later forms. establishes symmetry and polarity of development
• The notochord also induces formation of somites, the precursors
of the vertebral column, ribs, associated back muscles and
overlying dermis.

Question 19

notochord formed by?

Answer 19

ectodermal cells derived from the primitive node. The cells then migrate
within the mesodermal layer
to their appropriate midline
position.

Question 20

different mesoderms formed in development

Answer 20

• Paraxial 
Mesoderm (central) 
• Intermediate 
Mesoderm (between) 
• Lateral Plate 
Mesoderm (more lateral) 
 Parietal 
 Visceral

Question 21

derivatives of the different mesoderms

Answer 21

• Paraxial mesoderm → somites (stimulated by notochord)
• Intermediate mesoderm →urogenital system
• Lateral plate mesoderm:
Parietal mesoderm → mesothelial (serous)
membranes that cover the peritoneal, pleural
and pericardial cavities.
Visceral mesoderm → forms the thin serous
membranes that cover individual organs,
e.g., stomach, pancreas, spleen, etc.

Question 22

derivatives of ectoderm

Answer 22

• Epidermis, hair and nails
• Epithelium of the oral and nasal cavities 
and paranasal sinuses 
• Salivary and endocrine glands
• Nervous system
• Tooth enamel

Question 23

derivatives of endoderm

Answer 23

• GI tract epithelium and associated glands

Question 24

development of neural tube with diagram

Answer 24

epiblast layer above notochord will fold to from the neural groove, tips of the waves=neural crest cells. neural crest cells join with continued folding and migrate towards the sides and form various structures (dorsal root ganglia, etc.). joining of the fold also produces the neural tube.

Question 25

Neural Tube Related Developmental Defects

Answer 25

Spina Bifida, Meningocele, Meningomyelocele, Meningoencephalocele, Anencephaly

Question 26

Spina Bifida cause (deficiency in?)

Answer 26

folic acid deficiency

Question 27

Meningocele cause

Answer 27

extrusion of dura and arachnoid mater

Question 28

Meningomyelocele cause

Answer 28

extrusion of neural tissue plus all three meninges

Question 29

Meningoencephalocele cause

Answer 29

extrustion of a ventricular cistern plus neural tissue

Question 30

Anencephaly

Answer 30

fatal defect characterized by lack of development of | the cranium and brain

Question 31

The clinical consequences of a defect in neural tube closure (range)

Answer 31

mild to fatal mild: Spina bifida and meningocele severe: meningomyelocele and meningohydroencephalocele fatal: Anencephaly

Question 32

cavities developed along with the bilaminar cell layer

Answer 32

amniotic cavity: above epiblast | yolk sac: below hypoblast

Question 33

what cavity forms once the embryoblast embeds in the uterine wall?

Answer 33

Chorionic cavity, envelopes entire blastocyst

Question 34

which cell layer does the primitive streak give rise to?

Answer 34

mesoderm, will give rise to notochord and eventually somites

Question 35

what stimulates the neural tube formation?

Answer 35

notochord

Question 36

neural crest cells form? depends on?

Answer 36

form various structures based on where they form in relation to the neural tube.

Question 37

additional name for neural crest cells

Answer 37

Ectomesenchyme | Neuroectoderm

Question 38

pharyngeal arches formed when? purpose?

Answer 38

formed around day 28, will give rise to all structures above the shoulders

Question 39

content of pharyngeal arch

Answer 39

blood vessel, cranial nerve "each can innervate its own body structure) and sometimes its own cartilage

Question 40

pharyngeal pouch (cleft)

Answer 40

where two arches meet, pouch is inside cleft is outside

Question 41

1st branchial groove becomes?

Answer 41

ext auditory canal

Question 42

1st brachchial pouch become?

Answer 42

eustachian tube

Question 43

2nd branchial pouch becomes?

Answer 43

⇒ palatine tonsils

Question 44

3rd branchial pouch becomes?

Answer 44

⇒ inferior parathyroids/thymus

Question 45

4th branchial pouch becomes?

Answer 45

⇒ superior parathyroids/ultimobranchial body

Question 46

head size between month 3-9

Answer 46

remains relatively same size but body will grow

Question 47

processes making the face (diagram)

Answer 47

will all mash together to form face

Question 48

facial clefts

Answer 48

result of the failure of processes to join in facial development (various kinds)

Question 49

cleft palate

Answer 49

failure of the palate to join in the development, the tongue may fail to descend/ nassal septum doesn't get out of way for the palatal shelves to join.

Question 50

primary palate, failure to form?

Answer 50

palate from lateral incisor to other lateral incisors, failure to join can lead to cleft lip.

Question 51

Defective fusion of the medial nasal process with the maxillary process results in? fusion usually occurs when?

Answer 51

cleft lip, fusion typically at 5-6 weeks

Question 52

Defective fusion of the palatine shelves results in? typical fusion time?

Answer 52

cleft palate, Fusion of the palatine shelves normally begins during the 8th week of gestation and is completed by the 12th week.

Question 53

cleft palate, lip and both cases prevalence.

Answer 53

* 45% of all clefts are combined cleft lip/cleft palate. * 30% of cases are isolated cleft palate. * 25% of cases are isolated cleft lip.

Question 54

The incidence of cleft lip/cleft palate demographics

Answer 54

• 1 in 500 births in Chinese, Japanese and Native American populations • 1 in 700 births in Caucasian populations • 1 in 500 births in Afro-American populations

Question 55

incidence of cleft overall and genetics (siblings)?

Answer 55

• The incidence of cleft palate alone is 1 in 2,500 births. • If one child is born with cleft lip, there is a 40% chance of a second child exhibiting the same defect.

Question 56

teratogens associated with congenital malformations

Answer 56

Drugs: Ethanol, Tetracycline, Dilantin, Lithium, Methotrexate, Warfarin, Thalidomide, Androgens, Progesterone, Retinoic Acid Chemicals: Methylmercury, polychlorinated biphenyls Radiation: High levels of ionizing radiation

Question 57

cyst of anterior oral cavity

Answer 57

usually develops at fusion point between the primary palate and palatine shelves= nasopalatine duct cyst

Question 58

2nd branchial arch unique action

Answer 58

will grow downwards to cover the 3rd/4th arch, seals them off

Question 59

foramen cecum

Answer 59

depression on the back of the tongue that will form thyroid gland, tissue invaginates to make a small ball that descends and dif into the thyroid gland

Question 60

cervical sinus

Answer 60

formed by downgrowth of the 2nd branchial arch, usually reabsorbed by week 7

Question 61

persistance of cervical sinus

Answer 61

forms a lateral cervical cyst, forms along the sternomastoid muscle

Question 62

development of the tongue from?

Answer 62

back portions of the branchial arches

Question 63

Branchial Arch #1 contributuoin to toingue

Answer 63

Median Tongue Bud, Foramen Cecum, Lateral Lingual Swellings>Overgrown by lateral lingual swellings, Origin of the thyroid ectoderms, Anterior 2/3 of the tongue

Question 64

Branchial Arch #2 contribution to tongue

Answer 64

Copula/Tuberculum Impar>Overgrown by the hypobranchial eminence

Question 65

Branchial Arch #3 contribution to tongue

Answer 65

Hypobranchial Eminence>posterior third of tongue

Question 66

Branchial Arch #4 contributiuion to tongue

Answer 66

Minor contributions to the | hypobranchial eminence>no adult structure

Question 67

brachial arches inn and associated structutres

Answer 67

Question 68

thyroglossal duct cyst

Answer 68

``` Failure of thyroglossal duct to involute (failure of thyroid precursor to migrate/ gets hung up on something) , Located in midline of neck ```

Question 69

ectopic lingual thyroid

Answer 69

occurs if thyroid precursor cells fail to migrate (some or all), results in thyroid tissue on tongue

Question 70

branchial arches cartilages

Answer 70

Question 71

development of ear

Answer 71

made of six processes, swirl around to form the ear shape

Question 72

neural tube becomes?

Answer 72

brain and spinal cord

Question 73

events of proliferation period 0-3 weeks

Answer 73

implantation bilaminar embryotic disc neural tube and notochord formation mesoderm formation

Question 74

events of embryotic development 3-8weeks

Answer 74

neural crest cells | pharyngeal arches

Question 75

events of fetal development 9 weeks-term

Answer 75

facial/oral cavity development | body growth