Introductory Embryology, Oral-Facial Development And Associated Developmental Anomalies Flashcards
Stages of human development:
Proliferation Period (0-3 weeks)
Embryonic Period (3-8 weeks)
Fetal Development Period
(9 weeks to term)
Fertilization of
ovum yields?
zygote
Mitotic cleavage
of zygote forms?
blastomere
≥ 32 Blastomeres
is called a?
morula
The 64 cell stage
morula develops? referred to as?
internal blastocystic
cavity and thereafter
is referred to as a
blastocyst
embryoblast
The blastocyst also develops an inner cell mass at days 6-7
and thereafter is referred to as the embryoblast.
implantation, structure that accomplsihes it? occurs when?
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.
inner cell mass of the embryoblast becomes?
bilaminar embryonic disc
two layers
outer cell mass of the embryoblast becomes?
Outer cell mass becomes the cytotrophoblast & syntrophoblast layers which are precursor to the placenta
layers of bilaminar embryotic disc
epiblast: meso/ectoderm
hypoblast: endoderm
structures associated with the bilaminar embryotic disc
Epiblast Layer • Hypoblast Layer • Amniotic Cavity • Blastocyst Cavity (yolk sac) • Syntrophoblasts • Cytotrophobasts
Heuser’s membrane-formation and purpose (new term?)
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
cell layers and embryotic cavities of the embryoblast
cell layers: Epiblast Embryonic mesoderm Hypoblast embryonic cavities: Amniotic Yolk sac Chorionic
During the 3rd week of development, the bilaminar
embryonic disc is characterized by formation of what structures?
Primitive Streak
Notochord
Neural tube
AND the 3 germ layers (ecto formerly the epiblast and endo formerly the hypoblast)
portions of primitive streak (gives rise to? order?)
Primitive Streak>
Notochord>
>Neural Tube
(in this order)
the primitive node will give rise to?
notochord
notochord formation, when it occurs
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
notochrod functions
• 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.
notochord formed by?
ectodermal cells derived from the primitive node. The cells then migrate
within the mesodermal layer
to their appropriate midline
position.
different mesoderms formed in development
• Paraxial Mesoderm (central) • Intermediate Mesoderm (between) • Lateral Plate Mesoderm (more lateral) Parietal Visceral
derivatives of the different mesoderms
• 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.
derivatives of ectoderm
• Epidermis, hair and nails • Epithelium of the oral and nasal cavities and paranasal sinuses • Salivary and endocrine glands • Nervous system • Tooth enamel
derivatives of endoderm
• GI tract epithelium and associated glands
development of neural tube with diagram
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.
Neural Tube Related Developmental Defects
Spina Bifida, Meningocele, Meningomyelocele, Meningoencephalocele, Anencephaly
Spina Bifida cause (deficiency in?)
folic acid deficiency
Meningocele cause
extrusion of dura and arachnoid mater
Meningomyelocele cause
extrusion of neural tissue plus all three meninges
Meningoencephalocele cause
extrustion of a ventricular cistern plus neural tissue
Anencephaly
fatal defect characterized by lack of development of
the cranium and brain
The clinical consequences of a defect in neural tube closure (range)
mild to fatal
mild: Spina bifida and meningocele
severe: meningomyelocele and meningohydroencephalocele
fatal: Anencephaly
cavities developed along with the bilaminar cell layer
amniotic cavity: above epiblast
yolk sac: below hypoblast
what cavity forms once the embryoblast embeds in the uterine wall?
Chorionic cavity, envelopes entire blastocyst
which cell layer does the primitive streak give rise to?
mesoderm, will give rise to notochord and eventually somites
what stimulates the neural tube formation?
notochord
neural crest cells form? depends on?
form various structures based on where they form in relation to the neural tube.
additional name for neural crest cells
Ectomesenchyme
Neuroectoderm
pharyngeal arches formed when? purpose?
formed around day 28, will give rise to all structures above the shoulders
content of pharyngeal arch
blood vessel, cranial nerve “each can innervate its own body structure) and sometimes its own cartilage
pharyngeal pouch (cleft)
where two arches meet, pouch is inside cleft is outside
1st branchial groove becomes?
ext auditory canal
1st brachchial pouch become?
eustachian tube
2nd branchial pouch becomes?
⇒ palatine tonsils
3rd branchial pouch becomes?
⇒ inferior parathyroids/thymus
4th branchial pouch becomes?
⇒ superior parathyroids/ultimobranchial body
head size between month 3-9
remains relatively same size but body will grow
processes making the face (diagram)
will all mash together to form face
facial clefts
result of the failure of processes to join in facial development (various kinds)
cleft palate
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.
primary palate, failure to form?
palate from lateral incisor to other lateral incisors, failure to join can lead to cleft lip.
Defective fusion of the medial nasal process with the maxillary
process results in? fusion usually occurs when?
cleft lip, fusion typically at 5-6 weeks
Defective fusion of the palatine shelves results in? typical fusion time?
cleft palate, Fusion of the palatine shelves normally begins during the 8th
week of gestation and is completed by the 12th week.
cleft palate, lip and both cases prevalence.
- 45% of all clefts are combined cleft lip/cleft palate.
- 30% of cases are isolated cleft palate.
- 25% of cases are isolated cleft lip.
The incidence of cleft lip/cleft palate demographics
• 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
incidence of cleft overall and genetics (siblings)?
• 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.
teratogens associated with congenital malformations
Drugs: Ethanol, Tetracycline, Dilantin, Lithium,
Methotrexate, Warfarin, Thalidomide,
Androgens, Progesterone, Retinoic Acid
Chemicals: Methylmercury, polychlorinated biphenyls
Radiation: High levels of ionizing radiation
cyst of anterior oral cavity
usually develops at fusion point between the primary palate and palatine shelves= nasopalatine duct cyst
2nd branchial arch unique action
will grow downwards to cover the 3rd/4th arch, seals them off
foramen cecum
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
cervical sinus
formed by downgrowth of the 2nd branchial arch, usually reabsorbed by week 7
persistance of cervical sinus
forms a lateral cervical cyst, forms along the sternomastoid muscle
development of the tongue from?
back portions of the branchial arches
Branchial Arch #1 contributuoin to toingue
Median Tongue Bud, Foramen Cecum, Lateral Lingual Swellings>Overgrown by lateral lingual swellings, Origin of the thyroid ectoderms, Anterior 2/3 of the tongue
Branchial Arch #2 contribution to tongue
Copula/Tuberculum Impar>Overgrown by the hypobranchial eminence
Branchial Arch #3 contribution to tongue
Hypobranchial Eminence>posterior third of tongue
Branchial Arch #4 contributiuion to tongue
Minor contributions to the
hypobranchial eminence>no adult structure
brachial arches inn and associated structutres
thyroglossal duct cyst
Failure of thyroglossal duct to involute (failure of thyroid precursor to migrate/ gets hung up on something) , Located in midline of neck
ectopic lingual thyroid
occurs if thyroid precursor cells fail to migrate (some or all), results in thyroid tissue on tongue
branchial arches cartilages
development of ear
made of six processes, swirl around to form the ear shape
neural tube becomes?
brain and spinal cord
events of proliferation period 0-3 weeks
implantation
bilaminar embryotic disc
neural tube and notochord formation
mesoderm formation
events of embryotic development 3-8weeks
neural crest cells
pharyngeal arches
events of fetal development 9 weeks-term
facial/oral cavity development
body growth
